26 files changed, 4428 insertions, 0 deletions

diff --git a/server/src/api.cpp b/server/src/api.cpp
new file mode 100644
index 0000000..b3c8e31
--- /dev/null
+++ b/server/src/api.cpp
@@ -0,0 +1,206 @@
+module;
+
+#include <boost/geometry.hpp>
+#include <boost/json.hpp>
+
+module routemon:api$impl;
+
+import std;
+import :api;
+import :datex2;
+import :geo;
+import :gpx;
+import :log;
+import :req_ctx;
+import :time;
+import :trace;
+
+namespace {
+
+  namespace chrono = std::chrono;
+  namespace json = boost::json;
+  namespace views = std::views;
+
+} // namespace <anonymous>
+
+namespace routemon::api {
+
+  auto json_value_from_point(geo::point const& p) -> json::value {
+    return json::array{bgeo::get<1>(p), bgeo::get<0>(p)};
+  }
+  auto json_value_from_linestring(geo::linestring const& ls) -> json::value {
+    json::array a;
+    for (auto const& p : ls)
+      a.push_back(json_value_from_point(p));
+    return a;
+  }
+  auto json_value_from_linestrings(std::vector<geo::linestring> const& lss) -> json::value {
+    json::array a;
+    for (auto const& ls : lss)
+      a.push_back(json_value_from_linestring(ls));
+    return a;
+  }
+
+  auto tag_invoke(json::value_from_tag, json::value& jv, relevant_road_closure const& clo) -> void {
+    jv = json::object{
+      {"relevant_lss", json_value_from_linestrings(clo.relevant_lss)},
+    };
+  }
+  auto tag_invoke(json::value_from_tag, json::value& jv, relevant_situation const& sit) -> void {
+    jv = json::object{
+      {"id",                     json::value_from(sit.id)},
+      {"location",               sit.location ? json_value_from_point(*sit.location) : nullptr},
+      {"comments",               json::value_from(sit.comments)},
+      {"relevant_road_closures", json::value_from(sit.relevant_road_closures)},
+    };
+  }
+  auto tag_invoke(json::value_from_tag, json::value& jv, track_segment const& seg) -> void {
+    jv = json::object{
+      {"points", json_value_from_linestring(seg.points)},
+    };
+  }
+  auto tag_invoke(json::value_from_tag, json::value& jv, track const& track) -> void {
+    jv = json::object{
+      {"segments", json::value_from(track.segments)},
+    };
+  }
+  auto tag_invoke(json::value_from_tag, json::value& jv, process_gpx_result const& res) -> void {
+    jv = json::object{
+      {"tracks",              json::value_from(res.tracks)},
+      {"relevant_situations", json::value_from(res.relevant_situations)},
+    };
+  }
+  auto tag_invoke(json::value_from_tag, json::value& jv, sysinfo const& info) -> void {
+    jv = json::object{
+      {"using_publication_of", std::format("{:%FT%TZ}", info.using_publication_of)},
+    };
+  }
+
+  handler::handler(log::logger const& l, datex2::situation_publication pub)
+    : l_{l.sub("handler")}, pub_{std::move(pub)}
+  {
+    l_.info("Building indices");
+    auto const before_build = chrono::steady_clock::now();
+    for (auto const& sit : pub_.situations) {
+      for (auto const& rc : sit->road_closures) {
+        for (auto const& ls : rc->relevant_line_strings) {
+          auto box = geo::box{};
+          bgeo::envelope(*ls, box);
+          lse_index_.insert(std::make_tuple(box, ls, rc));
+        }
+        for (auto p : rc->relevant_points) {
+          p_index_.insert(std::make_pair(p, rc));
+        }
+      }
+    }
+    auto const after_build = chrono::steady_clock::now();
+    auto const dur_build = chrono::duration_cast<chrono::milliseconds>(after_build - before_build);
+    l_.info("Indices built in {}", dur_build);
+    l_.info("LSE index size: {}", lse_index_.size());
+    l_.info("Point index size: {}", p_index_.size());
+  }
+
+  auto handler::process_gpx(gpx::file&& gpx_file) -> std::optional<process_gpx_result> {
+    auto const now = chrono::utc_clock::now();
+    auto const relevant = std::initializer_list<time::period>{time::period{now - chrono::days(7), now + chrono::days(7)}};
+    auto const check_periods = time::period_seq{relevant.begin(), relevant.end()};
+
+    auto splits_with_overlap_segments = std::vector<geo::linestring>{};
+    for (auto const& track : gpx_file.tracks)
+      for (auto const& seg : track.segments)
+        geo::split_linestring_with_overlap_segments(seg.waypoints, 5000 /* meters max total dist until a new split is forced */,
+                                                    splits_with_overlap_segments);
+    auto const before_query = chrono::steady_clock::now();
+
+    l_.debug("Querying for relevant situations");
+    auto relevant_road_closures = std::unordered_set<std::shared_ptr<datex2::road_closure>>{};
+    auto ls_checked = 0uz;
+    auto p_checked = 0uz;
+    auto i = 0;
+    for (geo::linestring const& part : splits_with_overlap_segments) {
+      l_.debug("Checking part [{}/{}]", ++i, splits_with_overlap_segments.size());
+
+      auto part_box = geo::box{};
+      bgeo::envelope(part, part_box);
+
+      for (auto it = lse_index_.qbegin(bgeo::index::intersects(part_box)); it != lse_index_.qend(); it++) {
+        // Cannot use structured bindings here, as boost::geometry::get interferes with ADL.
+        // It is a candidate as the namespace boost::geometry is part of the associated namespace set,
+        // which happens because geo::linestring ≡ boost::geometry::model::linestring<geo::point> is part
+        // of the whole tuple type (lse_index_value) that is the value_type of the iterator.
+        std::shared_ptr<geo::linestring> const& ls = std::get<1>(*it);
+        std::shared_ptr<datex2::road_closure> const& rc = std::get<2>(*it);
+        if (rc->validity && rc->validity->intersect(check_periods).periods().empty())
+          continue;
+        if (bgeo::distance(*ls, part, geo::vincenty_strategy{}) < 5.0)
+          relevant_road_closures.emplace(rc);
+        ls_checked++;
+      }
+      for (auto it = p_index_.qbegin(bgeo::index::intersects(part_box)); it != p_index_.qend(); it++) {
+        // Cannot use structured bindings here for the same reason as above.
+        geo::point const& p = std::get<0>(*it);
+        std::shared_ptr<datex2::road_closure> const& rc = std::get<1>(*it);
+        if (rc->validity && rc->validity->intersect(check_periods).periods().empty())
+          continue;
+        if (bgeo::distance(p, part, geo::vincenty_strategy{}) < 5.0)
+          relevant_road_closures.emplace(rc);
+        p_checked++;
+      }
+    }
+
+    auto const after_query = chrono::steady_clock::now();
+    l_.debug("Done (checked {} line string(s) and {} point(s)) in {}",
+              ls_checked, p_checked, chrono::duration_cast<chrono::milliseconds>(after_query - before_query));
+
+    auto relevant_situations = std::unordered_set<std::shared_ptr<datex2::situation>>{};
+    for (auto const& rc : relevant_road_closures)
+      relevant_situations.emplace(rc->parent);
+
+    l_.debug("Identified {} relevant road closure(s), part of {} unique situation(s)",
+              relevant_road_closures.size(), relevant_situations.size());
+    for (auto const& sit : relevant_situations)
+      l_.debug("Relevant situation: {}", sit->id);
+
+    return process_gpx_result{
+      .tracks = gpx_file.tracks
+      | views::transform([](auto const& trk) -> track {
+        return {
+          .segments = trk.segments
+          | views::transform([](auto const& seg) -> track_segment {
+            return {.points = seg.waypoints};
+          })
+          | std::ranges::to<std::vector<track_segment>>(),
+        };
+      })
+      | std::ranges::to<std::vector<track>>(),
+      .relevant_situations = relevant_situations
+      | views::transform([&](std::shared_ptr<datex2::situation> sit) -> relevant_situation {
+        return {
+          .id       = sit->id,
+          .location = sit->location,
+          .comments = sit->comments,
+          .relevant_road_closures = relevant_road_closures
+          | views::filter([&](std::shared_ptr<datex2::road_closure> const& rc) -> bool {
+            return std::shared_ptr{rc->parent} == sit;
+          })
+          | views::transform([](std::shared_ptr<datex2::road_closure> const& rc) -> relevant_road_closure {
+            return {
+              .relevant_lss = rc->relevant_line_strings
+              | views::transform([](auto const& lsp) -> geo::linestring {
+                return *lsp;
+              })
+              | std::ranges::to<std::vector<geo::linestring>>(),
+            };
+          })
+          | std::ranges::to<std::vector<relevant_road_closure>>(),
+        };
+      })
+      | std::ranges::to<std::vector<relevant_situation>>(),
+    };
+  }
+
+  auto handler::sysinfo() -> struct sysinfo {
+    return {.using_publication_of = pub_.publication_time};
+  }
+
+} // namespace routemon::api
diff --git a/server/src/api.cppm b/server/src/api.cppm
new file mode 100644
index 0000000..caeb44c
--- /dev/null
+++ b/server/src/api.cppm
@@ -0,0 +1,79 @@
+module;
+
+#include <boost/geometry.hpp>
+#include <boost/json.hpp>
+
+export module routemon:api;
+
+import std;
+import :datex2;
+import :geo;
+import :gpx;
+import :log;
+import :time;
+import :trace;
+
+namespace {
+
+  namespace chrono = std::chrono;
+  namespace json = boost::json;
+  namespace views = std::views;
+
+} // namespace <anonymous>
+
+export
+namespace routemon::api {
+
+  struct relevant_road_closure {
+    std::vector<geo::linestring> relevant_lss;
+  };
+  auto tag_invoke(json::value_from_tag, json::value& jv, relevant_road_closure const& clo) -> void;
+
+  struct relevant_situation {
+    std::string id;
+    std::optional<geo::point> location;
+    std::vector<std::string> comments;
+    std::vector<relevant_road_closure> relevant_road_closures;
+  };
+  auto tag_invoke(json::value_from_tag, json::value& jv, relevant_situation const& sit) -> void;
+
+  struct track_segment {
+    geo::linestring points;
+  };
+  auto tag_invoke(json::value_from_tag, json::value& jv, track_segment const& seg) -> void;
+
+  struct track {
+    std::vector<track_segment> segments;
+  };
+  auto tag_invoke(json::value_from_tag, json::value& jv, track const& track) -> void;
+
+  struct process_gpx_result {
+    std::vector<track> tracks;
+    std::vector<relevant_situation> relevant_situations;
+  };
+  auto tag_invoke(json::value_from_tag, json::value& jv, process_gpx_result const& res) -> void;
+
+  struct sysinfo {
+    time::timestamp using_publication_of;
+  };
+  auto tag_invoke(json::value_from_tag, json::value& jv, sysinfo const& info) -> void;
+
+  class handler {
+    using lse_index_value = std::tuple<geo::box, std::shared_ptr<geo::linestring>, std::shared_ptr<datex2::road_closure>>;
+    using p_index_value = std::pair<geo::point, std::shared_ptr<datex2::road_closure>>;
+    using lse_index = bgeo::index::rtree<lse_index_value, bgeo::index::quadratic<16>>;
+    using p_index = bgeo::index::rtree<p_index_value, bgeo::index::quadratic<16>>;
+
+    log::logger l_;
+    datex2::situation_publication pub_;
+    lse_index lse_index_;
+    p_index   p_index_;
+
+  public:
+    explicit handler(log::logger const& l, datex2::situation_publication pub);
+
+    auto process_gpx(gpx::file&& gpx_file) -> std::optional<process_gpx_result>;
+    auto sysinfo() -> sysinfo;
+  };
+
+} // namespace routemon::api
diff --git a/server/src/config.cpp b/server/src/config.cpp
new file mode 100644
index 0000000..3b17691
--- /dev/null
+++ b/server/src/config.cpp
@@ -0,0 +1,167 @@
+module;
+
+#include <boost/json.hpp>
+#include <boost/system/system_error.hpp>
+
+module routemon:config$impl;
+
+import std;
+import :config;
+import :log;
+import :util;
+
+namespace json = boost::json;
+
+namespace routemon::config {
+
+  class location {
+    std::optional<std::pair<std::string_view, util::not_null<location const*>>> next_;
+
+    auto append_to(std::string& s) const -> void {
+      if (next_) {
+        s += next_->first;
+        s += ".";
+        next_->second->append_to(s);
+      }
+    }
+
+  public:
+    location() = default;
+
+    explicit location(location const& next, std::string_view entry)
+      : next_{std::make_pair(entry, util::not_null{&next})}
+    {}
+
+    [[nodiscard]] auto to_string() const -> std::string {
+      if (!next_)
+        return "";
+      auto s = std::string{next_->first};
+      next_->second->append_to(s);
+      return s;
+    }
+
+    auto sub(std::string_view entry) const& -> location {
+      return location{*this, entry};
+    }
+  };
+
+  class object_reader {
+    location loc_;
+    json::object const& obj_;
+    std::unordered_set<std::string> visited_;
+
+  public:
+    object_reader(json::value const& jv, location loc)
+      try : loc_{std::move(loc)}, obj_{jv.as_object()}
+    {} catch (boost::system::system_error const&) {
+        throw std::runtime_error{std::format("expected an object at {}", loc.to_string())};
+      }
+
+    auto check_unused() const -> void {
+      for (auto const& kv : obj_) {
+        if (!visited_.contains(std::string{kv.key()})) {
+          throw std::runtime_error{std::format("unexpected key {}", loc_.sub(kv.key()).to_string())};
+        }
+      }
+    }
+
+    template<class T>
+    auto expect_at(std::string_view key) -> T {
+      visited_.emplace(key);
+      auto const loc = loc_.sub(key);
+      if (auto const jv = obj_.try_at(key)) {
+        try {
+          return json::value_to<T>(*jv, loc);
+        } catch (boost::system::system_error const& e) {
+          throw std::runtime_error{std::format("failed to read {}: {}", loc.to_string(), e.code().message())};
+        }
+      } else {
+        throw std::runtime_error{std::format("did not find expected key {}", loc.to_string())};
+      }
+    }
+  };
+
+  auto as_checked_object(json::value const& jv, location const& loc, std::invocable<object_reader&> auto const& f) -> decltype(f(std::declval<object_reader&>())) {
+    auto r = object_reader{jv, loc};
+    auto&& v = f(r);
+    r.check_unused();
+    return std::forward<decltype(f(r))>(v);
+  }
+
+  auto tag_invoke(json::value_to_tag<rwgps> const&, json::value const& jv, location const& loc) -> rwgps {
+    return as_checked_object(jv, loc, [](object_reader& r) -> rwgps {
+      return {
+        .api_key    = r.expect_at<std::string>("api_key"),
+        .auth_token = r.expect_at<std::string>("auth_token"),
+      };
+    });
+  }
+
+  auto tag_invoke(json::value_to_tag<situations> const&, json::value const& jv, location const& loc) -> situations {
+    return as_checked_object(jv, loc, [](object_reader& r) -> situations {
+      return {
+        .datex2_filename = r.expect_at<std::string>("datex2_filename"),
+      };
+    });
+  }
+
+  auto tag_invoke(json::value_to_tag<database> const&, json::value const& jv, location const& loc) -> database {
+    return as_checked_object(jv, loc, [](object_reader& r) -> database {
+      return {
+        .sqlite3_filename = r.expect_at<std::string>("sqlite3_filename"),
+      };
+    });
+  }
+
+  auto tag_invoke(json::value_to_tag<http_server> const&, json::value const& jv, location const& loc) -> http_server {
+    return as_checked_object(jv, loc, [](object_reader& r) -> http_server {
+      return {
+        .lax_cors = r.expect_at<bool>("lax_cors"),
+      };
+    });
+  }
+
+  auto tag_invoke(json::value_to_tag<logger> const&, json::value const& jv, location const& loc) -> logger {
+    return as_checked_object(jv, loc, [obj_loc = loc](object_reader& r) -> logger {
+      auto const level_str = r.expect_at<std::string>("level");
+      auto level = log::level{};
+      if (level_str == "debug")
+        level = log::level::debug;
+      else if (level_str == "info")
+        level = log::level::info;
+      else if (level_str == "warn")
+        level = log::level::warn;
+      else if (level_str == "error")
+        level = log::level::error;
+      else
+        throw std::runtime_error{std::format("unable to parse log level {:?} at {}: expected one of {{debug, info, warn, error}}", level_str, obj_loc.sub("level").to_string())};
+      return logger{level};
+    });
+  }
+
+  auto json_value_to_app(json::value const& jv) -> app {
+    return as_checked_object(jv, location{}, [](object_reader& r) -> app {
+      return {
+        .rwgps       = r.expect_at<rwgps>("rwgps"),
+        .situations  = r.expect_at<situations>("situations"),
+        .database    = r.expect_at<database>("database"),
+        .http_server = r.expect_at<http_server>("http_server"),
+        .logger      = r.expect_at<logger>("logger"),
+      };
+    });
+  }
+
+  auto load_file(std::string const& filename) -> app {
+    auto f = std::ifstream{filename}; // TODO: ensure that we are opening in binary mode?
+    if (!f.is_open())
+      throw std::runtime_error{std::format("failed to open {}", filename)};
+    auto jv = json::value{};
+    try {
+      jv = json::parse(f);
+    } catch (boost::system::system_error const& e) {
+      throw std::runtime_error{std::format("failed to parse: {}", e.code().message())};
+    }
+    return json_value_to_app(jv);
+  }
+
+} // namespace routemon::config
diff --git a/server/src/config.cppm b/server/src/config.cppm
new file mode 100644
index 0000000..ef827a6
--- /dev/null
+++ b/server/src/config.cppm
@@ -0,0 +1,39 @@
+export module routemon:config;
+
+import std;
+import :log;
+
+namespace routemon::config {
+
+  export struct rwgps {
+    std::string api_key;
+    std::string auth_token;
+  };
+
+  export struct situations {
+    std::string datex2_filename;
+  };
+
+  export struct database {
+    std::string sqlite3_filename;
+  };
+
+  export struct http_server {
+    bool lax_cors;
+  };
+
+  export struct logger {
+    log::level level;
+  };
+
+  export struct app {
+    rwgps       rwgps;
+    situations  situations;
+    database    database;
+    http_server http_server;
+    logger      logger;
+  };
+
+  export auto load_file(std::string const& filename) -> app;
+
+} // namespace routemon::config
diff --git a/server/src/database.cppm b/server/src/database.cppm
new file mode 100644
index 0000000..0312dda
--- /dev/null
+++ b/server/src/database.cppm
@@ -0,0 +1,37 @@
+export module routemon:database;
+
+import std;
+import :sqlite3;
+
+namespace routemon::database {
+
+  static constexpr std::int64_t expected_database_version = 1;
+
+  export class connection {
+    sqlite3::connection dbc_;
+
+    explicit connection(sqlite3::connection dbc) : dbc_{std::move(dbc)} {}
+
+    friend auto open(std::string const& filename) -> std::shared_ptr<connection>;
+
+  public:
+    // Nothing here yet
+  };
+
+  export auto open(std::string const& filename) -> std::shared_ptr<connection> {
+    auto dbc = sqlite3::open(filename);
+    try {
+      auto version = std::optional<std::int64_t>{};
+      dbc.query("SELECT version FROM migration;").scan_single(version);
+      if (!version)
+        throw std::runtime_error{"failed to fetch database migration version"};
+      if (version != expected_database_version) {
+        throw std::runtime_error{std::format("database migration version ({}) does not match expected version ({}), consider running migrations", *version, expected_database_version)};
+      }
+    } catch (std::exception const& e) {
+      throw std::runtime_error{std::format("failed to query database version: {}", e.what())};
+    }
+    return std::shared_ptr<connection>{new connection{std::move(dbc)}};
+  }
+
+} // namespace routemon::database
diff --git a/server/src/datex2.cppm b/server/src/datex2.cppm
new file mode 100644
index 0000000..b507e6f
--- /dev/null
+++ b/server/src/datex2.cppm
@@ -0,0 +1,296 @@
+module;
+
+#include <boost/geometry/algorithms/is_empty.hpp>
+#include <boost/geometry/srs/transformation.hpp>
+#include <boost/geometry/srs/epsg.hpp>
+
+#include <pugixml.hpp>
+
+export module routemon:datex2;
+
+import std;
+import :geo;
+import :time;
+import :util;
+
+using namespace std::literals::string_view_literals;
+
+namespace routemon::datex2 {
+
+  export struct situation;
+
+  export struct road_closure {
+    std::weak_ptr<situation> parent;
+    std::optional<time::period_seq> validity;
+    std::vector<geo::point> relevant_points = {};
+    std::vector<std::shared_ptr<geo::linestring>> relevant_line_strings = {};
+  };
+
+  export struct situation {
+    std::string id;
+    std::optional<geo::point> location = std::nullopt;  // as shown on the map, not used for querying
+    std::vector<std::string> comments = {};
+    std::vector<std::shared_ptr<road_closure>> road_closures = {};
+  };
+
+  export struct situation_publication {
+    time::timestamp publication_time;
+    std::vector<std::shared_ptr<situation>> situations;
+  };
+
+  auto parse_timestamp(char const* in) -> std::optional<time::timestamp> {
+    auto res = time::timestamp{};
+    auto is = std::istringstream{in};
+    is >> std::chrono::parse("%Y-%m-%dT%H:%M:%SZ", res);
+    return is.fail() ? std::nullopt : std::make_optional(res);
+  }
+
+  export class loader {
+    // ETRS 89 (EPSG:4258) -> WGS 84 (EPSG:4326)
+    bgeo::srs::transformation<bgeo::srs::static_epsg<4258>, bgeo::srs::static_epsg<4326>> etrs89_to_wgs84_{};
+
+    std::multiset<std::string> warnings_;
+
+    auto add_location_from_xml(road_closure& rc, pugi::xml_node const& loc_xml) -> void {
+      auto loc_xml_type = std::string_view{loc_xml.attribute("xsi:type").value()};
+      if (loc_xml_type == "loc:ItineraryByIndexedLocations") {
+        for (auto const loc_cont_xml : loc_xml.children("loc:locationContainedInItinerary")) {
+          add_location_from_xml(rc, loc_cont_xml.child("loc:location"));
+        }
+      } else if (loc_xml_type == "loc:LinearLocation" || loc_xml_type == "loc:SingleRoadLinearLocation") {
+        auto const& loc_gml_xml = loc_xml.child("loc:gmlLineString");
+        if (!loc_gml_xml)
+          return;
+
+        auto const srs_name = std::string_view{loc_gml_xml.attribute("srsName").value()};
+        if (srs_name != "WGS 84"sv) {
+          warnings_.insert(std::format("don't now how to handle the CRS {}", srs_name));
+          return;
+        }
+        auto const pos_list_str = std::string_view{loc_gml_xml.child_value("loc:posList")};
+        // lat1 long1 lat2 long2 ... lat(n-1) long(n-1) latn longn
+
+        auto ls = std::make_shared<geo::linestring>();
+
+        auto lat_set = false;
+        auto lat = 0.0;
+        for (auto const lat_or_long_str : std::views::split(pos_list_str, " "sv)) {
+          auto mlat_or_long = util::parse_double(std::string_view{lat_or_long_str});
+          if (!mlat_or_long) {
+            warnings_.insert(std::format("failed to parse coordinate {:?}", std::string_view{lat_or_long_str}));
+            return;
+          }
+
+          if (!lat_set) {
+            lat = *mlat_or_long;
+            lat_set = true;
+          } else {
+            bgeo::append(*ls, geo::point{*mlat_or_long, lat});
+            lat = 0;
+            lat_set = false;
+          }
+        }
+
+        if (bgeo::is_empty(*ls)) {
+          warnings_.emplace("empty line string in data set");
+          return;
+        }
+
+        rc.relevant_line_strings.push_back(ls);
+      } else if (loc_xml_type == "loc:PointLocation") {
+        auto const& coords_xml = loc_xml.child("loc:pointByCoordinates").child("loc:pointCoordinates");
+        if (!coords_xml)
+          return;
+
+        auto mlat = util::parse_double(coords_xml.child_value("loc:latitude"));
+        auto mlon = util::parse_double(coords_xml.child_value("loc:longitude"));
+        if (!mlat || !mlon) {
+          warnings_.emplace("failed to parse PointLocation coordinates");
+          return;
+        }
+
+        // Vaag genoeg zegt NDW dat het hier om WGS 84 gaat:
+        //   https://docs.ndw.nu/en/dataformaten/datex2-v3/elementen/locationreferencing/pointCoordinates/
+        // maar heeft het UML-model van DATEX II v3 het over ETRS 89:
+        //   https://docs.datex2.eu/_static/data/v3.7/umlmodel/html/EARoot/EA3/EA3/EA5/EA676.htm
+
+        auto const coords_etrs89 = geo::point{*mlon, *mlat};
+        auto coords_wgs84 = geo::point{};
+        etrs89_to_wgs84_.forward(coords_etrs89, coords_wgs84);
+
+        rc.relevant_points.push_back(coords_wgs84);
+      } else {
+        warnings_.insert(std::format("don't know how to hande location of type {}, ignoring", loc_xml.attribute("xsi:type").value()));
+        return;
+      }
+    }
+
+    auto handle_road_or_carriageway_or_lane_management(pugi::xml_node const& record_xml, std::weak_ptr<situation> parent) -> std::optional<std::shared_ptr<road_closure>> {
+      auto const type = std::string_view{record_xml.child("sit:roadOrCarriagewayOrLaneManagementType").child_value()};
+      if (type != "carriagewayClosures" && type != "roadClosed")
+        // TODO: checken of er nog andere types fietsers de doorgang zouden kunnen blokkeren?
+        return std::nullopt;
+
+      auto const& restricted_vehicle_types_xml = record_xml.child("sit:forVehiclesWithCharacteristicsOf");
+      bool likely_restriction_for_bikes = restricted_vehicle_types_xml.empty();
+      for (auto const vehicle_type_xml : restricted_vehicle_types_xml.children("com:vehicleType")) {
+        auto vehicle_type = std::string_view{vehicle_type_xml.child_value()};
+        if (vehicle_type == "anyVehicle" || vehicle_type == "bicycle" ||
+            vehicle_type == "unknown" || vehicle_type == "other") {
+          likely_restriction_for_bikes = true;
+        }
+      }
+      if (!likely_restriction_for_bikes)
+        return std::nullopt;
+
+      //---- Check if within the defined validity period
+
+      auto validity = std::optional<time::period_seq>{};
+      auto const& validity_xml = record_xml.child("sit:validity");
+      if (validity_xml && validity_xml.child_value("com:validityStatus") == "definedByValidityTimeSpec"sv) {
+        auto const& validity_spec_xml = validity_xml.child("com:validityTimeSpecification");
+
+        auto valid_periods = std::vector<time::period>{};
+        auto exception_periods = std::vector<time::period>{};
+
+        // TODO: com:overallEndTime may be missing (according to the DATEX II v3 data model)
+        auto const overall_start_time = parse_timestamp(validity_spec_xml.child_value("com:overallStartTime"));
+        auto const overall_end_time   = parse_timestamp(validity_spec_xml.child_value("com:overallEndTime"));
+        if (overall_start_time && overall_end_time && *overall_start_time < *overall_end_time) {
+          valid_periods.emplace_back(*overall_start_time, *overall_end_time);
+
+          for (auto const valid_period_xml : validity_xml.children("com:validPeriod")) {
+            auto const start_of_period = parse_timestamp(valid_period_xml.child_value("com:startOfPeriod"));
+            auto const end_of_period   = parse_timestamp(valid_period_xml.child_value("com:endOfPeriod"));
+            if (start_of_period && end_of_period && *start_of_period < *end_of_period) {
+              valid_periods.emplace_back(*start_of_period, *end_of_period);
+            }
+          }
+          for (auto const exception_period_xml : validity_xml.children("com:exceptionPeriod")) {
+            auto const start_of_period = parse_timestamp(exception_period_xml.child_value("com:startOfPeriod"));
+            auto const end_of_period   = parse_timestamp(exception_period_xml.child_value("com:endOfPeriod"));
+            if (start_of_period && end_of_period && *start_of_period < *end_of_period) {
+              exception_periods.emplace_back(*start_of_period, *end_of_period);
+            }
+          }
+
+          validity = time::period_seq{valid_periods.begin(), valid_periods.end()}
+            .except(time::period_seq{exception_periods.begin(), exception_periods.end()});
+        } else {
+          warnings_.insert(std::format("invalid overall start / end time (start time: {}, end time: {})",
+                                        validity_spec_xml.child_value("com:overallStartTime"),
+                                        validity_spec_xml.child_value("com:overallEndTime")));
+          return std::nullopt;
+        }
+      }
+
+      //---- Try to extract the location info
+
+      auto rc = std::make_shared<road_closure>(std::move(parent), validity);
+      add_location_from_xml(*rc, record_xml.child("sit:locationReference"));
+      return rc;
+    }
+
+  public:
+    [[nodiscard]] auto load_situation_publication(std::string const& filename) -> situation_publication {
+      auto doc = pugi::xml_document{};
+      if (auto result = doc.load_file(filename.c_str()); !result) {
+        throw std::runtime_error{result.description()};
+      }
+      auto payload_xml = doc.child("mc:messageContainer").child("mc:payload");
+      auto mpublication_time = parse_timestamp(payload_xml.child_value("com:publicationTime"));
+      if (!mpublication_time)
+        throw std::runtime_error{"provided publication does not name publication time"};
+
+      auto situations = std::vector<std::shared_ptr<situation>>{};
+      for (auto const sit_xml : payload_xml.children("sit:situation")) {
+        auto id = std::string_view{sit_xml.attribute("id").value()};
+
+        auto const sit = std::make_shared<situation>(std::string{id});
+        situations.push_back(sit);
+
+        auto const& header_info_xml = sit_xml.child("sit:headerInformation");
+        if (header_info_xml.child_value("com:informationStatus") != "real"sv)
+          continue;
+
+        for (auto const record_xml : sit_xml.children("sit:situationRecord")) {
+          auto const record_type = std::string_view{record_xml.attribute("xsi:type").value()};
+          auto const primary_record_types = std::unordered_set<std::string_view>{
+            "sit:Roadworks",
+            /* { */ "sit:MaintenanceWorks",
+            /* | */ "sit:ConstructionWorks",
+            /* } */
+            "sit:Obstruction",
+            /* { */ "sit:EnvironmentalObstruction",
+            /* | */ "sit:GeneralObstruction",
+            /* | */ "sit:InfrastructureDamageObstruction",
+            /* } */
+            "sit:Activity",
+            /* { */ "sit:PublicEvent",
+            /* } */
+          };
+
+          if (record_type == "sit:RoadOrCarriagewayOrLaneManagement") {
+            if (auto rc = handle_road_or_carriageway_or_lane_management(record_xml, sit)) {
+              sit->road_closures.push_back(*rc);
+            }
+          } else if (primary_record_types.contains(record_type)) {
+            for (auto const comment_xml : record_xml.children("sit:generalPublicComment")) {
+//            if (comment_xml.child_value("sit:commentType") == "internalNote"sv) {
+                auto candidate = std::optional<std::pair<std::string_view, std::string_view>>{}; // (text, language)
+                for (auto const comment_value_xml : comment_xml.child("sit:comment").child("com:values").children("com:value")) {
+                  if (!candidate ||
+                      comment_value_xml.attribute("lang").value() == "nl"sv ||
+                      (candidate->second != "nl"sv && comment_value_xml.attribute("lang").value() == "nl"sv)) {
+                    candidate = std::make_pair(comment_value_xml.child_value(), comment_value_xml.attribute("lang").value());
+                  }
+                }
+                if (candidate) {
+                  auto already_present = false;
+                  for (auto const& comment : sit->comments)
+                    already_present = already_present || comment == candidate->first;
+                  if (!already_present) {
+                    sit->comments.emplace_back(candidate->first);
+                  }
+                }
+//            }
+            }
+
+            if (auto const location_ref_xml = record_xml.child("sit:locationReference")) {
+              if (location_ref_xml.attribute("xsi:type").value() == "loc:PointLocation"sv) {
+                if (auto const coords_xml = location_ref_xml.child("loc:pointByCoordinates").child("loc:pointCoordinates")) {
+                  auto const mlat = util::parse_double(coords_xml.child_value("loc:latitude"));
+                  auto const mlon = util::parse_double(coords_xml.child_value("loc:longitude"));
+                  if (mlat && mlon) {
+                    // Vaag genoeg zegt NDW dat het hier om WGS 84 gaat:
+                    //   https://docs.ndw.nu/en/dataformaten/datex2-v3/elementen/locationreferencing/pointCoordinates/
+                    // maar heeft het UML-model van DATEX II v3 het over ETRS 89:
+                    //   https://docs.datex2.eu/_static/data/v3.7/umlmodel/html/EARoot/EA3/EA3/EA5/EA676.htm
+
+                    auto const coords_etrs89 = geo::point{*mlon, *mlat};
+                    auto coords_wgs84 = geo::point{};
+                    etrs89_to_wgs84_.forward(coords_etrs89, coords_wgs84);
+
+                    if (!sit->location) {
+                      sit->location = coords_wgs84;
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+
+      return {
+        .publication_time = *mpublication_time,
+        .situations       = situations,
+      };
+    }
+
+    [[nodiscard]] auto warnings() const -> std::multiset<std::string> const& {
+      return warnings_;
+    }
+  };
+
+} // namespace routemon::datex2
diff --git a/server/src/geo.cppm b/server/src/geo.cppm
new file mode 100644
index 0000000..5cdbdd9
--- /dev/null
+++ b/server/src/geo.cppm
@@ -0,0 +1,40 @@
+module;
+
+#include <boost/geometry.hpp>
+
+export module routemon:geo;
+
+export namespace bgeo = boost::geometry;
+
+export namespace routemon::geo {
+
+  using point = bgeo::model::point<double, 2, bgeo::cs::spherical_equatorial<bgeo::degree>>;
+  using linestring = bgeo::model::linestring<point>;
+  using box = bgeo::model::box<point>;
+  using stype = bgeo::srs::spheroid<double>;
+  using vincenty_strategy = bgeo::strategy::distance::vincenty<stype>;
+
+  auto split_linestring_with_overlap_segments(linestring const& ls, double max_split_distance_m, std::vector<linestring>& append_to) -> void {
+    if (bgeo::is_empty(ls))
+      return;
+
+    auto current_ls = linestring{};
+    auto current_ls_length = 0.0;
+    auto previous = std::optional<point>{};
+    bgeo::for_each_point(ls, [&](point p) -> void {
+      bgeo::append(current_ls, p);
+      if (previous) {
+        auto d = bgeo::distance(*previous, p, vincenty_strategy());
+        current_ls_length += d;
+        if (current_ls_length > max_split_distance_m) {
+          append_to.push_back(std::move(current_ls));
+          current_ls = linestring{*previous, p};
+          current_ls_length = d;
+        }
+      }
+      previous = p;
+    });
+    append_to.emplace_back(std::move(current_ls));
+  }
+
+} // namespace routemon::geo
diff --git a/server/src/gpx.cpp b/server/src/gpx.cpp
new file mode 100644
index 0000000..62dccff
--- /dev/null
+++ b/server/src/gpx.cpp
@@ -0,0 +1,189 @@
+module;
+
+#include <boost/geometry/algorithms/append.hpp>
+
+module routemon:gpx$impl;
+
+import std;
+import :gpx;
+import :util;
+import :xml;
+
+using namespace std::literals::string_view_literals;
+
+namespace routemon::gpx {
+
+  namespace v10 {
+
+    constexpr auto xmlns = "http://www.topografix.com/GPX/1/0"sv;
+    auto qname(std::string_view local) -> xml::qname_view {
+      return {.ns_uri = xmlns, .local = local};
+    }
+
+    auto parse_wpt(xml::executor_ref e, xml::attribute_view attrs) -> xml::parser<geo::point> {
+      auto parse_xml_double = [](std::string_view sv) -> std::optional<double> {
+        return util::parse_double(sv, std::chars_format::fixed);
+      };
+      auto mlat = std::optional<double>{};
+      auto mlon = std::optional<double>{};
+      for (auto const& [name, value] : attrs) {
+        if (name == qname("lat")) {
+          mlat = parse_xml_double(value);
+        } else if (name == qname("lon")) {
+          mlon = parse_xml_double(value);
+        }
+      }
+      if (!mlat || !mlon)
+        throw std::runtime_error{"expected valid latitude and longitude for waypoint"};
+      co_await xml::ignore_contents(e);
+      co_return geo::point{*mlon, *mlat};
+    }
+
+    auto parse_trkseg(xml::executor_ref e, xml::attribute_view) -> xml::parser<track_segment> {
+      auto s = track_segment{};
+      while (auto mwpt = co_await allow_element(e, qname("trkpt"), xml::hohalo<parse_wpt>()))
+        bgeo::append(s.waypoints, *mwpt);
+      co_return std::move(s);
+    }
+
+    auto parse_trk(xml::executor_ref e, xml::attribute_view) -> xml::parser<track> {
+      auto t = track{};
+      t.name = co_await allow_element(e, qname("name"), xml::hohalo<xml::read_string_contents>());
+      co_await allow_element(e, qname("cmt"), xml::hohalo<xml::ignore_element_contents>());
+      t.desc = co_await allow_element(e, qname("desc"), xml::hohalo<xml::read_string_contents>());
+      co_await xml::ignore_contents(e, /* until */ qname("trkseg"));
+      while (auto mseg = co_await allow_element(e, qname("trkseg"), xml::hohalo<parse_trkseg>()))
+        t.segments.push_back(std::move(*mseg));
+      co_return std::move(t);
+    }
+
+    auto parse_gpx(xml::executor_ref e, xml::attribute_view attrs) -> xml::parser<file> {
+      auto f = file{};
+      if (attrs.lookup(qname("version")) != "1.0"sv)
+        throw std::runtime_error{"expected GPX version to be 1.0"};
+      if (auto mcreator = attrs.lookup(qname("creator")))
+        f.creator = *mcreator;
+      else
+        throw std::runtime_error{"expected GPX file to have creator"};
+
+      f.meta.name = co_await allow_element(e, qname("name"), xml::hohalo<xml::read_string_contents>());
+      f.meta.desc = co_await allow_element(e, qname("desc"), xml::hohalo<xml::read_string_contents>());
+
+      co_await xml::ignore_contents(e, /* until */ qname("trk"));
+      while (auto mtrk = co_await allow_element(e, qname("trk"), xml::hohalo<parse_trk>()))
+        f.tracks.push_back(std::move(*mtrk));
+      co_await xml::ignore_contents(e);
+
+      co_return std::move(f);
+    }
+
+  } // namespace v10
+
+  namespace v11 {
+
+    constexpr auto xmlns = "http://www.topografix.com/GPX/1/1"sv;
+    auto qname(std::string_view local) -> xml::qname_view {
+      return {.ns_uri = xmlns, .local = local};
+    }
+
+    auto parse_metadata(xml::executor_ref e, xml::attribute_view) -> xml::parser<metadata> {
+      auto meta = metadata{};
+      meta.name = co_await allow_element(e, qname("name"), xml::hohalo<xml::read_string_contents>());
+      meta.desc = co_await allow_element(e, qname("desc"), xml::hohalo<xml::read_string_contents>());
+      co_await xml::ignore_contents(e);
+      co_return meta;
+    }
+
+    auto parse_wpt(xml::executor_ref e, xml::attribute_view attrs) -> xml::parser<geo::point> {
+      auto parse_xml_double = [](std::string_view sv) -> std::optional<double> {
+        return util::parse_double(sv, std::chars_format::fixed);
+      };
+      auto mlat = std::optional<double>{};
+      auto mlon = std::optional<double>{};
+      for (auto const& [name, value] : attrs) {
+        if (name == qname("lat")) {
+          mlat = parse_xml_double(value);
+        } else if (name == qname("lon")) {
+          mlon = parse_xml_double(value);
+        }
+      }
+      if (!mlat || !mlon)
+        throw std::runtime_error{"expected valid latitude and longitude for waypoint"};
+      co_await xml::ignore_contents(e);
+      co_return geo::point{*mlon, *mlat};
+    }
+
+    auto parse_trkseg(xml::executor_ref e, xml::attribute_view) -> xml::parser<track_segment> {
+      auto s = track_segment{};
+      while (auto mwpt = co_await allow_element(e, qname("trkpt"), xml::hohalo<parse_wpt>()))
+        bgeo::append(s.waypoints, *mwpt);
+      co_await allow_element(e, qname("extensions"), xml::hohalo<xml::ignore_element_contents>());
+      co_return std::move(s);
+    }
+
+    auto parse_trk(xml::executor_ref e, xml::attribute_view) -> xml::parser<track> {
+      auto t = track{};
+      t.name = co_await allow_element(e, qname("name"), xml::hohalo<xml::read_string_contents>());
+      co_await allow_element(e, qname("cmt"), xml::hohalo<xml::ignore_element_contents>());
+      t.desc = co_await allow_element(e, qname("desc"), xml::hohalo<xml::read_string_contents>());
+      co_await xml::ignore_contents(e, /* until */ qname("trkseg"));
+      while (auto mseg = co_await allow_element(e, qname("trkseg"), xml::hohalo<parse_trkseg>()))
+        t.segments.push_back(std::move(*mseg));
+      co_return std::move(t);
+    }
+
+    auto parse_gpx(xml::executor_ref e, xml::attribute_view attrs) -> xml::parser<file> {
+      auto f = file{};
+      if (attrs.lookup(qname("version")) != "1.1"sv)
+        throw std::runtime_error{"expected GPX version to be 1.1"};
+      if (auto mcreator = attrs.lookup(qname("creator")))
+        f.creator = *mcreator;
+      else
+        throw std::runtime_error{"expected GPX file to have creator"};
+
+      if (auto mmeta = co_await allow_element(e, qname("metadata"), xml::hohalo<parse_metadata>()))
+        f.meta = *mmeta;
+      co_await xml::ignore_contents(e, /* until */ qname("trk"));
+      while (auto mtrk = co_await allow_element(e, qname("trk"), xml::hohalo<parse_trk>()))
+        f.tracks.push_back(std::move(*mtrk));
+      co_await allow_element(e, qname("extensions"), xml::hohalo<xml::ignore_element_contents>());
+
+      co_return std::move(f);
+    }
+
+  } // namespace v11
+
+  auto parse_file(xml::executor_ref e) -> xml::parser<file> {
+    auto decl = co_await expect_event<xml::xml_decl_event>(e);
+    if (decl.version != "1.0"sv)
+      throw std::runtime_error{std::format("unsupported XML version, got {}", std::string_view{decl.version})};
+    if (decl.encoding != "UTF-8"sv)
+      throw std::runtime_error{"unsupported encoding"};
+    if (auto mf = co_await allow_element(e, v10::qname("gpx"), xml::hohalo<v10::parse_gpx>()))
+      co_return std::move(*mf);
+    if (auto mf = co_await allow_element(e, v11::qname("gpx"), xml::hohalo<v11::parse_gpx>()))
+      co_return std::move(*mf);
+    throw std::runtime_error{"no supported GPX document found"};
+  }
+
+  reader::reader()
+    : p_{parse_file(util::not_null{&e_})}
+  { e_.set_continuation(p_.promise().base_handle()); }
+
+  auto reader::init() -> void {
+    e_.start();
+  }
+
+  auto reader::put(std::string_view buf) -> void {
+    e_.read(buf, false);
+  }
+
+  auto reader::finish() -> gpx::file {
+    e_.read(std::string_view{}, true);
+    e_.end();
+    // Promise is still alive since the last coroutine performs a
+    // symmetric transfer to std::noop_coroutine() in final_suspend().
+    return std::move(p_.promise().returned_value());
+  }
+
+} // namespace routemon::gpx
diff --git a/server/src/gpx.cppm b/server/src/gpx.cppm
new file mode 100644
index 0000000..20e6242
--- /dev/null
+++ b/server/src/gpx.cppm
@@ -0,0 +1,43 @@
+export module routemon:gpx;
+
+import std;
+import :geo;
+import :util;
+import :xml;
+
+namespace routemon::gpx {
+
+  struct metadata {
+    std::optional<std::string> name;
+    std::optional<std::string> desc;
+  };
+
+  struct track_segment {
+    geo::linestring waypoints;
+  };
+
+  struct track {
+    std::optional<std::string> name;
+    std::optional<std::string> desc;
+    std::vector<track_segment> segments;
+  };
+
+  struct file {
+    std::string creator;
+    metadata meta;
+    std::vector<track> tracks;
+  };
+
+  class reader {
+    xml::executor e_;
+    xml::parser<file> p_;
+
+  public:
+    explicit reader();
+
+    auto init() -> void;
+    auto put(std::string_view buf) -> void;
+    [[nodiscard]] auto finish() -> gpx::file;
+  };
+
+} // namespace routemon::gpx
diff --git a/server/src/http_client.cppm b/server/src/http_client.cppm
new file mode 100644
index 0000000..d5316d6
--- /dev/null
+++ b/server/src/http_client.cppm
@@ -0,0 +1,62 @@
+module;
+
+#include <boost/asio/connect.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/ssl.hpp>
+#include <boost/beast/core.hpp>
+#include <boost/beast/http.hpp>
+
+export module routemon:http.client;
+
+export import :http.common;
+
+namespace net = boost::asio;
+namespace ssl = net::ssl;
+using tcp = net::ip::tcp;
+
+namespace routemon::http {
+
+  export class client {
+    net::io_context& ioc_;
+    ssl::context sslc_{ssl::context::tlsv12_client};
+    tcp::resolver resolver_;
+
+  public:
+    explicit client(net::io_context& ioc)
+      : ioc_{ioc}, resolver_{ioc}
+    {
+      sslc_.set_default_verify_paths();
+      sslc_.set_verify_mode(net::ssl::verify_peer | net::ssl::verify_fail_if_no_peer_cert);
+    }
+
+    template<class ReqBody>
+    auto do_request(bhttp::request<ReqBody>& req) -> bhttp::response<bhttp::dynamic_body> {
+      auto stream = ssl::stream<beast::tcp_stream>{ioc_, sslc_};
+
+      auto host = std::string{req.at(bhttp::field::host)};
+      if (!SSL_set_tlsext_host_name(stream.native_handle(), host.c_str())) {
+        throw beast::system_error(static_cast<int>(::ERR_get_error()),
+                                  net::error::get_ssl_category());
+      }
+      stream.set_verify_callback(ssl::host_name_verification(host));
+      auto const results = resolver_.resolve(host, "443");
+      beast::get_lowest_layer(stream).connect(results);
+      stream.handshake(ssl::stream_base::client);
+
+      req.set(bhttp::field::user_agent, "routemon/1.0");
+      bhttp::write(stream, req);
+
+      auto buffer = beast::flat_buffer{};
+      auto res = bhttp::response<bhttp::dynamic_body>{};
+      bhttp::read(stream, buffer, res);
+
+      auto ec = beast::error_code{};
+      stream.shutdown(ec);
+      if (ec != net::ssl::error::stream_truncated)
+        throw beast::system_error{ec};
+
+      return res;
+    }
+  };
+
+} // namespace routemon::http
diff --git a/server/src/http_common.cppm b/server/src/http_common.cppm
new file mode 100644
index 0000000..3c38da7
--- /dev/null
+++ b/server/src/http_common.cppm
@@ -0,0 +1,139 @@
+module;
+
+#include <boost/beast/core.hpp>
+#include <boost/beast/http.hpp>
+
+export module routemon:http.common;
+
+namespace beast = boost::beast;
+export namespace bhttp = beast::http;
+
+namespace boost::beast {
+
+  namespace concepts {
+
+    template<class T>
+    concept buffers_generator = beast::is_buffers_generator<T>::value;
+
+    template<class T>
+    concept const_buffer_sequence = beast::is_const_buffer_sequence<T>::value;
+
+  } // namespace concepts
+
+  namespace http::concepts {
+
+    template<class T>
+    concept fields = is_fields<T>::value;
+
+    template<class T>
+    concept body = is_body<T>::value;
+
+    template<class T>
+    concept body_reader = is_body_reader<T>::value;
+
+  } // namespace http::concepts
+
+} // namespace boost::beast
+
+namespace routemon::http {
+
+  struct supported_verb {
+    enum supported_verb_t : std::uint8_t {
+      options,
+      delete_,
+      get,
+      head,
+      post,
+      put,
+    };
+
+    supported_verb_t value;
+
+    supported_verb(supported_verb_t value) : value{value} {}
+
+    static auto from(bhttp::verb v) -> std::optional<supported_verb> {
+      switch (v) {
+      case bhttp::verb::options: return supported_verb::options;
+      case bhttp::verb::delete_: return supported_verb::delete_;
+      case bhttp::verb::get:     return supported_verb::get;
+      case bhttp::verb::head:    return supported_verb::head;
+      case bhttp::verb::post:    return supported_verb::post;
+      case bhttp::verb::put:     return supported_verb::put;
+      default:                   return std::nullopt;
+      }
+    }
+
+    operator bhttp::verb() const {
+      switch (value) {
+      case supported_verb::options: return bhttp::verb::options;
+      case supported_verb::delete_: return bhttp::verb::delete_;
+      case supported_verb::get:     return bhttp::verb::get;
+      case supported_verb::head:    return bhttp::verb::head;
+      case supported_verb::post:    return bhttp::verb::post;
+      case supported_verb::put:     return bhttp::verb::put;
+      }
+    }
+  };
+
+  export struct verb_set {
+    bool delete_ : 1 = false;
+    bool get     : 1 = false;
+    bool head    : 1 = false;
+    bool post    : 1 = false;
+    bool put     : 1 = false;
+    bool options : 1 = false;
+
+    auto enable(supported_verb v) -> void {
+      switch (v.value) {
+      case supported_verb::delete_:
+        delete_ = true;
+        break;
+      case supported_verb::get:
+        get = true;
+        break;
+      case supported_verb::head:
+        head = true;
+        break;
+      case supported_verb::post:
+        post = true;
+        break;
+      case supported_verb::put:
+        put = true;
+        break;
+      case supported_verb::options:
+        options = true;
+        break;
+      default:;
+      }
+    }
+
+    auto operator==(verb_set const& rhs) const noexcept -> bool = default;
+
+    auto empty() const -> bool {
+      return *this == verb_set{};
+    }
+
+    verb_set(std::initializer_list<supported_verb> vs) {
+      for (auto const v : vs) enable(v);
+    }
+
+    auto to_string() const -> std::string {
+      std::ostringstream ss;
+      bool wrote = false;
+      auto write = [&](bhttp::verb v) {
+        if (wrote)
+          ss << ", ";
+        ss << v;
+        wrote = true;
+      };
+      if (delete_) write(bhttp::verb::delete_);
+      if (get)     write(bhttp::verb::get);
+      if (head)    write(bhttp::verb::head);
+      if (post)    write(bhttp::verb::post);
+      if (put)     write(bhttp::verb::put);
+      if (options) write(bhttp::verb::options);
+      return ss.str();
+    }
+  };
+
+} // namespace routemon::http
diff --git a/server/src/http_server.cppm b/server/src/http_server.cppm
new file mode 100644
index 0000000..0770d97
--- /dev/null
+++ b/server/src/http_server.cppm
@@ -0,0 +1,661 @@
+module;
+
+#include <boost/config.hpp>
+#include <boost/asio/as_tuple.hpp>
+#include <boost/asio/awaitable.hpp>
+#include <boost/asio/co_spawn.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/beast/core.hpp>
+#include <boost/beast/http.hpp>
+#include <boost/json/serialize.hpp>
+#include <boost/url.hpp>
+
+export module routemon:http.server;
+
+import std;
+import :config;
+import :trace;
+export import :http.common;
+import :problem;
+
+namespace net = boost::asio;
+using tcp = net::ip::tcp;
+
+namespace routemon::http {
+
+  struct readable_request {
+    util::not_null<bhttp::request_parser<bhttp::empty_body>*> p;
+    util::not_null<beast::tcp_stream*> strm;
+    util::not_null<beast::flat_buffer*> buf;
+  };
+
+  class presponse {
+  public:
+    using const_buffers_type = beast::span<net::const_buffer>;
+
+  private:
+    struct impl_base {
+      virtual ~impl_base() = default;
+      virtual auto header() -> bhttp::response_header<bhttp::fields>& = 0;
+      virtual auto header() const -> bhttp::response_header<bhttp::fields> const& = 0;
+      virtual auto is_done() const -> bool = 0;
+      virtual auto prepare(beast::error_code&) -> const_buffers_type = 0;
+      virtual auto consume(std::size_t n) -> void = 0;
+      virtual auto keep_alive() const -> bool = 0;
+    };
+    std::unique_ptr<impl_base> impl_;
+
+    template<bhttp::concepts::body Body>
+    class impl : public impl_base {
+      // Initializes in the response state.
+      // At the first call to prepare, we switch to the message generator state.
+      // After that point, header may not be called anymore (it will throw).
+      std::variant<bhttp::response<Body>, bhttp::message_generator> state_;
+
+      auto ensure_message_generator() -> bhttp::message_generator& {
+        if (auto prsp = std::get_if<bhttp::response<Body>>(&state_)) {
+          auto rsp = bhttp::response<Body>{std::move(*prsp)};
+          state_.template emplace<bhttp::message_generator>(std::move(rsp));
+        }
+        return std::get<bhttp::message_generator>(state_);
+      }
+
+    public:
+      explicit impl(bhttp::response<Body>&& rsp) : state_{std::move(rsp)} {}
+
+      auto header() -> bhttp::response_header<bhttp::fields>& override {
+        if (auto prsp = std::get_if<bhttp::response<Body>>(&state_)) {
+          return prsp->base();
+        } else {
+          // TODO: define custom exception type presponse::bad_header_access
+          throw std::logic_error{"header() may not be called after prepare()"};
+        }
+      }
+      auto header() const -> bhttp::response_header<bhttp::fields> const& override {
+        if (auto prsp = std::get_if<bhttp::response<Body>>(&state_)) {
+          return prsp->base();
+        } else {
+          throw std::logic_error{"header() may not be called after prepare()"};
+        }
+      }
+
+      auto is_done() const -> bool override {
+        if (auto pgen = std::get_if<bhttp::message_generator>(&state_)) {
+          return pgen->is_done();
+        } else /* still in the response state */ {
+          return false;
+        }
+      }
+
+      auto prepare(beast::error_code& ec) -> const_buffers_type override {
+        return ensure_message_generator().prepare(ec);
+      }
+
+      auto consume(std::size_t n) -> void override {
+        ensure_message_generator().consume(n);
+      }
+
+      auto keep_alive() const noexcept -> bool override {
+        return state_.visit(util::overloaded{
+            [](bhttp::response<Body> const& rsp) -> bool {
+              return rsp.keep_alive();
+            },
+            [](bhttp::message_generator const& gen) -> bool {
+              return gen.keep_alive();
+            },
+          });
+      }
+    };
+
+  public:
+    template<bhttp::concepts::body Body>
+    explicit presponse(bhttp::response<Body>&& rsp)
+      : impl_{new impl{std::move(rsp)}}
+    {}
+
+    auto header() -> bhttp::response_header<bhttp::fields>& {
+      return impl_->header();
+    }
+    auto header() const -> bhttp::response_header<bhttp::fields> const& {
+      return impl_->header();
+    }
+
+    auto is_done() const -> bool {
+      return impl_->is_done();
+    }
+
+    auto prepare(beast::error_code& ec) -> const_buffers_type {
+      return impl_->prepare(ec);
+    }
+
+    auto consume(std::size_t n) -> void {
+      return impl_->consume(n);
+    }
+
+    auto keep_alive() const noexcept -> bool {
+      return impl_->keep_alive();
+    }
+  };
+  static_assert(beast::concepts::buffers_generator<presponse>);
+
+  template<class Ctx>
+  using next_handler_t = std::function<auto(Ctx) -> net::awaitable<presponse>>;
+
+  template<class OuterCtx, class InnerCtx>
+  using middleware_t = std::function<auto(OuterCtx, bhttp::request_header<bhttp::fields>&, next_handler_t<InnerCtx>) -> net::awaitable<presponse>>;
+
+  template<class Ctx>
+  auto lax_cors_middleware(Ctx ctx, bhttp::request_header<bhttp::fields>& req_hdr, next_handler_t<Ctx> next) -> net::awaitable<presponse> {
+    std::ignore = req_hdr;
+    auto prersp = co_await next(ctx);
+    prersp.header().set(bhttp::field::access_control_allow_origin, "*");
+    co_return std::move(prersp);
+  }
+
+  template<class InnerCtx>
+  struct trace_id_ctx : InnerCtx {
+    trace::id trace_id = {};
+  };
+
+  template<class OuterCtx>
+  auto trace_id_middleware(OuterCtx ctx0, bhttp::request_header<bhttp::fields>& req_hdr, next_handler_t<trace_id_ctx<OuterCtx>> next) -> net::awaitable<presponse> {
+    std::ignore = req_hdr;
+    auto ctx = trace_id_ctx{std::move(ctx0)};
+    auto prersp = co_await next(std::move(ctx));
+    prersp.header().set("X-Routemon-Trace-Id", std::string_view{ctx.trace_id.as_string()});
+    prersp.header().insert(bhttp::field::access_control_expose_headers, "X-Routemon-Trace-Id");
+    co_return std::move(prersp);
+  }
+
+  struct base_ctx {
+    std::locale locale;
+  };
+
+  template<class Ctx>
+  using basic_route_handler_fn_t = std::function<auto(Ctx, readable_request, std::vector<std::string> const& matches) -> net::awaitable<presponse>>;
+
+  struct keep_alive {
+    bool value;
+
+    explicit keep_alive(bool value) : value{value} {}
+  };
+
+  template<bhttp::concepts::body Body>
+  auto make_rsp(bhttp::status status, keep_alive ka) -> bhttp::response<Body> {
+    auto rsp = bhttp::response<Body>{}; // HTTP version gets set later
+    rsp.result(status);
+    rsp.keep_alive(ka.value);
+    return rsp;
+  }
+
+  auto problem_rsp(base_ctx const& ctx, problem::details const& problem, keep_alive ka) -> presponse {
+    auto rsp = make_rsp<bhttp::string_body>(problem.status, ka);
+    rsp.set(bhttp::field::content_type, "application/problem+json");
+    rsp.body() = json::serialize(json::value_from(problem, ctx.locale));
+    rsp.prepare_payload();
+    return presponse{std::move(rsp)};
+  }
+
+  struct preflight_response {
+    verb_set allow_methods;
+    std::vector<bhttp::field> allow_headers;
+  };
+  auto make_preflight_rsp(preflight_response res, keep_alive ka) -> bhttp::response<bhttp::empty_body> {
+    auto rsp = make_rsp<bhttp::empty_body>(bhttp::status::no_content, ka);
+    auto allow_headers_str = res.allow_headers
+      | std::views::transform([](auto const& field) -> std::string_view { return bhttp::to_string(field); })
+      | std::views::join_with(std::string_view{", "})
+      | std::ranges::to<std::string>();
+    rsp.set(bhttp::field::access_control_allow_methods, res.allow_methods.to_string());
+    rsp.set(bhttp::field::access_control_allow_headers, allow_headers_str);
+    rsp.prepare_payload();
+    return rsp;
+  }
+
+  // Using base_ctx instead of a template here since that saves you
+  // typing on invocation (and we do not care about the context type
+  // anyway, but all context types should derive from base_ctx).
+  template<bhttp::concepts::body_reader Body>
+  auto read_request(base_ctx const& ctx, readable_request&& r) -> net::awaitable<std::expected<bhttp::request<Body>, presponse>> {
+    std::ignore = ctx;
+    auto p = bhttp::request_parser<Body>{std::move(*r.p)};
+    co_await bhttp::async_read(*r.strm, *r.buf, p);
+    co_return std::move(p.release());
+  }
+
+  template<>
+  auto read_request<bhttp::empty_body>(base_ctx const& ctx, readable_request&& r) -> net::awaitable<std::expected<bhttp::request<bhttp::empty_body>, presponse>> {
+    auto [ec, _] = co_await bhttp::async_read(*r.strm, *r.buf, *r.p, net::as_tuple);
+    if (ec == bhttp::error::unexpected_body) {
+      auto tpl = problem::tpl{
+        .status   = bhttp::status::bad_request,
+        .title    = translate("No body expected for this request"),
+        .type_uri = "https://routemon.fautchen.eu/problems/unexpected-body",
+      };
+      co_return std::unexpected{problem_rsp(ctx, tpl.instantiate(), keep_alive{false})};
+    } else if (ec) {
+      throw boost::system::system_error{ec};
+    }
+    co_return r.p->release();
+  }
+
+  template<class InnerCtx>
+  struct routed_ctx : InnerCtx {
+    verb_set route_methods;
+  };
+
+  template<class Ctx>
+  requires requires(Ctx ctx) {
+    // Ctx must be derived from an instantiation of routed_ctx
+    []<class InnerCtx>(routed_ctx<InnerCtx> const&) {}(ctx);
+  }
+  auto default_options_handler(Ctx const& ctx, readable_request r, std::vector<std::string> const&) -> net::awaitable<presponse> {
+    auto mreq = co_await read_request<bhttp::empty_body>(ctx, std::move(r));
+    if (!mreq)
+      co_return std::move(mreq.error());
+
+    if (mreq->find(bhttp::field::access_control_request_method) != mreq->end()) {
+      // CORS preflight request
+      co_return make_preflight_rsp(preflight_response{
+          // TODO: should access-control-allow-methods contain OPTIONS?
+          .allow_methods = ctx.route_methods,
+          .allow_headers = {bhttp::field::content_type},
+        }, keep_alive{mreq->keep_alive()});
+    } else {
+      // Normal OPTIONS request
+      auto rsp = make_rsp<bhttp::empty_body>(bhttp::status::no_content, keep_alive{mreq->keep_alive()});
+      rsp.set(bhttp::field::allow, ctx.route_methods.to_string());
+      rsp.prepare_payload();
+      co_return std::move(rsp);
+    }
+  }
+
+  auto global_options_handler(base_ctx const& ctx, readable_request r) -> net::awaitable<presponse> {
+    // TODO: switch to "small (4KB) discarded" body type, similar to what Go does?
+    // Same goes for default_options_handler? Not sure.
+    if (auto res = co_await read_request<bhttp::empty_body>(ctx, std::move(r)); !res)
+      co_return std::move(res.error());
+    auto req = r.p->release();
+    auto rsp = make_rsp<bhttp::empty_body>(bhttp::status::no_content, keep_alive{req.keep_alive()});
+    rsp.prepare_payload();
+    co_return std::move(rsp);
+  }
+
+  template<class Ctx>
+  auto id_middleware(Ctx ctx, bhttp::request_header<bhttp::fields>&, next_handler_t<Ctx> next) -> net::awaitable<presponse> {
+    co_return co_await next(std::move(ctx));
+  }
+
+  template<class A, class B, class C>
+  auto middleware_compose(middleware_t<A, B> ab, middleware_t<B, C> bc) -> middleware_t<A, C> {
+    return [ab = std::move(ab), bc = std::move(bc)](A a, bhttp::request_header<bhttp::fields>& header, next_handler_t<C> next) -> net::awaitable<presponse> {
+      co_return co_await ab(std::move(a), header, [&](B b) -> net::awaitable<presponse> {
+          co_return co_await bc(std::move(b), header, next);
+        });
+    };
+  }
+
+  template<class A, class B>
+  auto middleware_wrap_fn(middleware_t<A, B> ab, basic_route_handler_fn_t<B> fn) -> basic_route_handler_fn_t<A> {
+    return [ab = std::move(ab), fn = std::move(fn)](A a_ctx, readable_request r, std::vector<std::string> const& matches) -> net::awaitable<presponse> {
+      co_return co_await ab(std::move(a_ctx), r.p->get().base(), [&](B b_ctx) -> net::awaitable<presponse> {
+          co_return co_await fn(std::move(b_ctx), r, matches);
+        });
+    };
+  }
+
+  template<std::default_initializable V>
+  requires requires(V v) {
+    { static_cast<bool>(v) };
+  }
+  struct handler_map {
+    V options = {};
+    V delete_ = {};
+    V get     = {};
+    V head    = {};
+    V post    = {};
+    V put     = {};
+
+    template<class Self>
+    auto lookup(this Self&& self, supported_verb v) -> auto&& {
+      switch (v.value) {
+      case supported_verb::options: return std::forward<Self>(self).options;
+      case supported_verb::delete_: return std::forward<Self>(self).delete_;
+      case supported_verb::get:     return std::forward<Self>(self).get;
+      case supported_verb::head:    return std::forward<Self>(self).head;
+      case supported_verb::post:    return std::forward<Self>(self).post;
+      case supported_verb::put:     return std::forward<Self>(self).put;
+      }
+    }
+
+    auto verbs() const -> verb_set {
+      auto set = verb_set{};
+      if (static_cast<bool>(options))
+        set.enable(supported_verb::options);
+      if (static_cast<bool>(delete_))
+        set.enable(supported_verb::delete_);
+      if (static_cast<bool>(get))
+        set.enable(supported_verb::get);
+      if (static_cast<bool>(head))
+        set.enable(supported_verb::head);
+      if (static_cast<bool>(post))
+        set.enable(supported_verb::post);
+      if (static_cast<bool>(put))
+        set.enable(supported_verb::put);
+      return set;
+    }
+
+    auto empty() const -> bool {
+      return verbs().empty();
+    }
+
+    template<std::default_initializable U>
+    auto map(std::invocable<V const&> auto f) const -> handler_map<U>
+      requires std::assignable_from<U&, std::invoke_result_t<decltype(f), V const&>>
+    {
+      return {
+        .options = static_cast<bool>(options) ? f(options) : U{},
+        .delete_ = static_cast<bool>(delete_) ? f(delete_) : U{},
+        .get     = static_cast<bool>(get)     ? f(get)     : U{},
+        .head    = static_cast<bool>(head)    ? f(head)    : U{},
+        .post    = static_cast<bool>(post)    ? f(post)    : U{},
+        .put     = static_cast<bool>(put)     ? f(put)     : U{},
+      };
+    }
+  };
+
+  template<class Ctx>
+  struct route_tree {
+    using leaves = handler_map<basic_route_handler_fn_t<Ctx>>;
+    using named_subtrees = std::unordered_map<std::string, route_tree>;
+    using wildcard_subtree = std::indirect<route_tree>;
+
+    leaves here;
+    // TODO: consider making the first alternative a radix tree
+    // Note: the map is the first variant here; the variant will be
+    // default-constructed with the default-constructed first
+    // alternative. The empty map denotes a lack of subtrees.
+    std::variant<named_subtrees, wildcard_subtree> sub;
+  };
+
+  template<class OuterCtx, class InnerCtx>
+  auto middleware_wrap_tree(middleware_t<OuterCtx, InnerCtx> mw, route_tree<InnerCtx> const& tree) -> route_tree<OuterCtx> {
+    auto new_leaves = tree.here.template map<basic_route_handler_fn_t<OuterCtx>>(std::bind_front(middleware_wrap_fn<OuterCtx, InnerCtx>, mw));
+    auto new_sub = tree.sub.visit(util::overloaded{
+        [&mw](route_tree<InnerCtx>::named_subtrees const& subtrees) -> decltype(route_tree<OuterCtx>::sub) {
+          auto new_subtrees = typename route_tree<OuterCtx>::named_subtrees{};
+          for (auto [seg, subtree] : subtrees)
+            new_subtrees[seg] = middleware_wrap_tree(mw, subtree);
+          return new_subtrees;
+        },
+        [&mw](route_tree<InnerCtx>::wildcard_subtree const& subtree) -> decltype(route_tree<OuterCtx>::sub) {
+          return typename route_tree<OuterCtx>::wildcard_subtree{middleware_wrap_tree(mw, *subtree)};
+        },
+      });
+    return {.here = new_leaves, .sub = new_sub};
+  }
+
+  template<class T>
+  concept match_arg = std::constructible_from<T, std::string const&>;
+
+  template<class Ctx, match_arg... MatchArgs>
+  using route_handler_fn_t = std::function<auto(Ctx, readable_request, MatchArgs...) -> net::awaitable<presponse>>;
+
+  template<class Ctx, match_arg... MatchArgs>
+  auto degen_route_handler(route_handler_fn_t<Ctx, MatchArgs...> fn) -> basic_route_handler_fn_t<Ctx> {
+    return [fn = std::move(fn)](Ctx ctx, readable_request r, std::vector<std::string> const& matches) -> net::awaitable<presponse> {
+      if (sizeof...(MatchArgs) != matches.size())
+        throw std::runtime_error{"got unexpected amount of matches"};
+      auto it = matches.begin();
+      co_return co_await fn(std::move(ctx), r, MatchArgs{static_cast<std::string const&>(*it++)}...);
+    };
+  }
+
+  template<class Ctx, match_arg... MatchArgs>
+  struct ctree : route_tree<Ctx> {
+    template<class OuterCtx>
+    auto wrap(middleware_t<OuterCtx, Ctx> mw) const -> ctree<OuterCtx, MatchArgs...> {
+      return {middleware_wrap_tree(std::move(mw), *this)};
+    }
+  };
+
+  template<class Ctx, match_arg... MatchArgs>
+  struct dtree : handler_map<route_handler_fn_t<Ctx, MatchArgs...>> {
+    [[nodiscard]] auto to_leaves() const -> typename route_tree<Ctx>::leaves {
+      auto here = this->template map<basic_route_handler_fn_t<Ctx>>(degen_route_handler<Ctx, MatchArgs...>);
+      if (!here.verbs().empty() && !static_cast<bool>(this->options))
+        here.options = default_options_handler<Ctx>;
+      return here;
+    }
+
+    [[nodiscard]] auto named_subtrees(std::initializer_list<std::pair<std::string, ctree<Ctx, MatchArgs...>>> subtrees) const -> ctree<Ctx, MatchArgs...> {
+      auto sub = typename route_tree<Ctx>::named_subtrees{
+        std::from_range,
+        subtrees | std::views::transform([](auto const& p) {
+          return std::make_pair(p.first, static_cast<route_tree<Ctx>>(p.second));
+        })
+      };
+      return {route_tree<Ctx>{.here = to_leaves(), .sub = sub}};
+    }
+
+    template<match_arg MatchArg>
+    [[nodiscard]] auto wildcard_subtree(ctree<Ctx, MatchArgs..., MatchArg> subtree) -> ctree<Ctx, MatchArgs...> {
+      return {route_tree<Ctx>{.here = to_leaves(), .sub = typename route_tree<Ctx>::wildcard_subtree{static_cast<route_tree<Ctx>>(subtree)}}};
+    }
+
+    [[nodiscard]] auto no_subtrees() const -> ctree<Ctx, MatchArgs...> {
+      return {route_tree<Ctx>{.here = to_leaves(), .sub = {}}};
+    }
+  };
+
+  template<std::derived_from<base_ctx> PreRouteCtx>
+  class server {
+    log::logger l_;
+    locale::selector lsel_;
+    middleware_t<base_ctx, PreRouteCtx> global_middleware_;
+    route_tree<routed_ctx<PreRouteCtx>> routes_;
+
+  public:
+    explicit server(log::logger const& l, locale::selector&& lsel, middleware_t<base_ctx, PreRouteCtx> global_middleware, route_tree<routed_ctx<PreRouteCtx>> routes)
+      : l_{l.sub("http_server")}, lsel_{std::move(lsel)}, global_middleware_{std::move(global_middleware)}, routes_{std::move(routes)}
+    {}
+
+    struct match_result {
+      util::not_null<handler_map<basic_route_handler_fn_t<routed_ctx<PreRouteCtx>>> const*> route_handlers;
+      std::vector<std::string> wildcard_matches;
+
+      auto allowed_methods() const -> verb_set {
+        return route_handlers->verbs();
+      }
+    };
+
+    auto match(boost::urls::segments_view segments) const -> std::optional<match_result> {
+      auto const* tree = &routes_;
+      auto wildcard_matches = std::vector<std::string>{};
+      for (auto const& seg : segments) {
+        tree->sub.visit(util::overloaded{
+            [&](route_tree<routed_ctx<PreRouteCtx>>::named_subtrees const& subtrees) {
+              auto it = subtrees.find(seg);
+              tree = it == subtrees.end() ? nullptr : &it->second;
+            },
+            [&](route_tree<routed_ctx<PreRouteCtx>>::wildcard_subtree const& wildcard_subtree) {
+              wildcard_matches.push_back(seg);
+              tree = &*wildcard_subtree;
+            },
+          });
+        if (!tree) return std::nullopt;
+      }
+      if (tree->here.empty()) return std::nullopt;
+      return match_result{
+        .route_handlers   = util::not_null{&tree->here},
+        .wildcard_matches = wildcard_matches,
+      };
+    }
+
+    auto route_request(PreRouteCtx ctx, readable_request r) const -> net::awaitable<presponse> {
+      auto req_base = r.p->get().base();
+
+      auto const bad_request_tpl = problem::tpl{
+        .status   = bhttp::status::bad_request,
+        .title    = translate("Bad request"),
+        .type_uri = "https://routemon.fautchen.eu/problems/bad-request",
+      };
+
+      if (req_base.target() == "*") {
+        // request-target is in asterisk-form (RFC 9112, § 3.2.4),
+        // so the request must be a server-wide OPTIONS request.
+
+        if (req_base.method() != bhttp::verb::options) {
+          auto tpl = problem::tpl{
+            .status   = bhttp::status::method_not_allowed,
+            .title    = translate("Method not allowed"),
+            .type_uri = "https://routemon.fautchen.eu/problems/method-not-allowed",
+          };
+          co_return problem_rsp(ctx, tpl.instantiate(), keep_alive{false});
+        }
+
+        co_return co_await global_options_handler(ctx, r);
+      } else if (auto mreq_url0 = boost::urls::parse_origin_form(req_base.target())) {
+        // request-target is in origin-form (RFC 9112, § 3.2.1),
+        // so it must be a normal request (not a CONNECT or
+        // server-wide OPTIONS request).
+
+        auto req_url = boost::urls::url{*mreq_url0};
+        req_url.normalize();
+        if (!req_url.is_path_absolute()) {
+          auto problem = bad_request_tpl.instantiate().
+            set_detail(translate("Path of normalized (RFC 3986, § 6) "
+                                 "origin-form request-target (RFC "
+                                 "9112, § 3.2.1) should be "
+                                 "absolute"));
+          co_return problem_rsp(ctx, problem, keep_alive{false});
+        }
+
+        auto mres = match(req_url.segments());
+        if (!mres) {
+          auto tpl = problem::tpl{
+            .status   = bhttp::status::not_found,
+            .title    = translate("Not found"),
+            .type_uri = "https://routemon.fautchen.eu/problems/not-found",
+          };
+          co_return problem_rsp(ctx, tpl.instantiate(), keep_alive{false});
+        }
+
+        auto mverb = supported_verb::from(req_base.method());
+        if (!mverb) {
+          // Method not implemented.
+          auto tpl = problem::tpl{
+            .status   = bhttp::status::not_implemented,
+            .title    = translate("Method not implemented"),
+            .type_uri = "https://routemon.fautchen.eu/problems/method-not-implemented",
+          };
+          co_return problem_rsp(ctx, tpl.instantiate(), keep_alive{false});
+        }
+
+        if (auto mhdl = mres->route_handlers->lookup(*mverb)) {
+          auto new_ctx = routed_ctx<PreRouteCtx>{std::move(ctx), mres->allowed_methods()};
+          co_return co_await mhdl(std::move(new_ctx), r, mres->wildcard_matches);
+        } else {
+          // Path recognized, but method not allowed.
+          auto tpl = problem::tpl{
+            .status   = bhttp::status::method_not_allowed,
+            .title    = translate("Method not allowed"),
+            .type_uri = "https://routemon.fautchen.eu/problems/method-not-allowed",
+          };
+          auto rsp = problem_rsp(ctx, tpl.instantiate(), keep_alive{false});
+          rsp.header().set(bhttp::field::allow, mres->allowed_methods().to_string());
+          co_return std::move(rsp);
+        }
+      } else {
+        // We do not accept any other request-target forms.
+
+        auto problem = bad_request_tpl.instantiate().
+          set_detail(translate("Invalid request-target, expected "
+                               "asterisk-form or origin-form "
+                               "(see RFC 9112, § 3.2)"));
+        co_return problem_rsp(ctx, problem, keep_alive{false});
+      }
+    }
+
+    auto handle_request(readable_request r) const -> net::awaitable<presponse> {
+      auto header = r.p->get().base();
+      auto locale = lsel_.select(header[bhttp::field::accept_language]);
+      auto ctx0 = base_ctx{.locale = locale};
+
+      co_return co_await global_middleware_(std::move(ctx0), header, [&](PreRouteCtx ctx) -> net::awaitable<presponse> {
+          co_return co_await route_request(std::move(ctx), std::move(r));
+        });
+    }
+
+    auto do_session(beast::tcp_stream strm) -> net::awaitable<void> {
+      auto buf = beast::flat_buffer{};
+
+      while (true) {
+        auto p0 = bhttp::request_parser<bhttp::empty_body>{};
+        p0.body_limit(boost::none);
+        auto [ec, _] = co_await bhttp::async_read_header(strm, buf, p0, net::as_tuple);
+        if (ec == bhttp::error::end_of_stream) {
+          break;
+        } else if (ec) {
+          throw boost::system::system_error{ec};
+        }
+
+        auto http_version = p0.get().version();
+        auto&& rsp = co_await handle_request(readable_request{
+            .p    = util::not_null{&p0},
+            .strm = util::not_null{&strm},
+            .buf  = util::not_null{&buf},
+          });
+        rsp.header().version(http_version);
+        bool keep_alive = rsp.keep_alive();
+        co_await beast::async_write(strm, std::move(rsp));
+        if (!keep_alive) {
+          break;
+        }
+      }
+
+      strm.socket().shutdown(tcp::socket::shutdown_send);
+    }
+
+    auto do_listen(tcp::endpoint endpoint) -> net::awaitable<void> {
+      auto executor = co_await net::this_coro::executor;
+      auto acceptor = tcp::acceptor{executor, endpoint};
+
+      l_.with("endpoint", endpoint.address().to_string()).
+        with("port", std::to_string(endpoint.port())).
+        info("Serving");
+      while (true) {
+        net::co_spawn(executor,
+                      do_session(beast::tcp_stream{co_await acceptor.async_accept()}),
+                      [this](std::exception_ptr e) {
+                        if (e) {
+                          try {
+                            std::rethrow_exception(e);
+                          } catch (std::exception const& e) {
+                            l_.error("Error in session: {}", e.what());
+                          }
+                        }
+                      });
+      }
+    }
+
+    auto spawn(net::io_context& ioc) -> void {
+      auto const addr = net::ip::make_address("0.0.0.0");
+      auto const endpoint = tcp::endpoint{addr, 8284};
+
+      // TODO: make exception handling as nice as in srv.cpp
+      net::co_spawn(ioc,
+                    do_listen(endpoint),
+                    [this](std::exception_ptr e) {
+                      if (e) {
+                        try {
+                          std::rethrow_exception(e);
+                        } catch (std::exception const& e) {
+                          l_.error("Error: {}", e.what());
+                        }
+                      }
+                    });
+    }
+  };
+
+} // namespace routemon::http
diff --git a/server/src/locale.cppm b/server/src/locale.cppm
new file mode 100644
index 0000000..65ae2ea
--- /dev/null
+++ b/server/src/locale.cppm
@@ -0,0 +1,245 @@
+module;
+
+#include <boost/locale.hpp>
+#include <unicode/localematcher.h>
+
+export module routemon:locale;
+
+import std;
+import :util;
+
+export namespace blocale = boost::locale;
+
+export namespace routemon {
+  using lformat = blocale::format;
+  using blocale::translate;
+  using blocale::gettext;
+} // namespace routemon
+
+namespace routemon::locale {
+
+  struct locale_priority {
+    float weight;
+    std::size_t original_index;
+  };
+
+  auto operator<(locale_priority const& lhs, locale_priority const& rhs) -> bool {
+    if (lhs.weight != rhs.weight)
+      return lhs.weight > rhs.weight;
+    return lhs.original_index < rhs.original_index;
+  }
+
+  struct icu_locale_hash {
+    std::size_t operator()(icu::Locale const& l) const noexcept {
+      static_assert(sizeof(std::int32_t) < sizeof(std::size_t));
+      std::int32_t hash = l.hashCode();
+      if (hash < 0) {
+        return static_cast<std::size_t>(std::numeric_limits<int>::max()) + static_cast<std::size_t>(-hash) + 1;
+      } else {
+        return static_cast<std::size_t>(hash);
+      }
+    }
+  };
+
+  using icu_locale_priority_map = std::unordered_map<icu::Locale, locale_priority, icu_locale_hash>;
+  using icu_priority_locale = std::pair<icu::Locale, locale_priority>;
+
+  auto operator<(icu_priority_locale const& lhs, icu_priority_locale const& rhs) -> bool {
+    return lhs.second < rhs.second;
+  }
+
+  class icu_priority_locale_vec_iterator : public icu::Locale::Iterator {
+    std::size_t i_ = 0uz;
+    std::vector<icu_priority_locale> ls_;
+
+  public:
+    explicit icu_priority_locale_vec_iterator(std::vector<icu_priority_locale>&& ls)
+      : ls_(std::move(ls))
+    {}
+
+    auto hasNext() const -> UBool override {
+      return i_ < ls_.size();
+    }
+
+    auto next() -> icu::Locale const& override {
+      return ls_[i_++].first;
+    }
+
+    ~icu_priority_locale_vec_iterator() override = default;
+  };
+
+  export template<class T>
+  concept locale_input_range =
+    std::ranges::input_range<T> &&
+    std::same_as<std::locale const&, std::ranges::range_const_reference_t<T>>;
+
+  // Helps select a locale based on the Accept-Language header in an
+  // HTTP request.
+  export class selector {
+    std::locale default_;
+    icu::LocaleMatcher matcher_;
+    std::shared_ptr<blocale::generator const> lgen_;
+
+    auto make_matcher(locale_input_range auto supported_locales, std::locale default_locale) {
+      auto builder = icu::LocaleMatcher::Builder{};
+      for (auto const& supported_locale : supported_locales) {
+        auto const& supported_locale_info = std::use_facet<blocale::info>(supported_locale);
+        auto supported_icu_locale = icu::Locale{supported_locale_info.name().c_str()};
+        if (supported_icu_locale.isBogus())
+          throw std::runtime_error{"supported locale gives rise to bogus ICU locale"};
+        builder.addSupportedLocale(supported_icu_locale);
+      }
+      auto const& default_locale_info = std::use_facet<blocale::info>(default_locale);
+      auto default_icu_locale = icu::Locale{default_locale_info.name().c_str()};
+      if (default_icu_locale.isBogus())
+        throw std::runtime_error{"default locale gives rise to bogus ICU locale"};
+      builder.setDefaultLocale(&default_icu_locale);
+      auto ec = UErrorCode::U_ZERO_ERROR;
+      auto matcher = builder.build(ec);
+      if (U_FAILURE(ec))
+        throw std::runtime_error{"failed to build icu::LocaleMatcher"};
+      return matcher;
+    }
+
+    // Trimming optional whitespace as defined in RFC 9110, § 12.4.2.
+    static auto ltrim_ows(std::string_view s) -> std::string_view {
+      if (auto i = s.find_first_not_of(" \t"); i != std::string_view::npos)
+        s.remove_prefix(i);
+      return s;
+    }
+    static auto rtrim_ows(std::string_view s) -> std::string_view {
+      if (auto i = s.find_last_not_of(" \t"); i != std::string_view::npos)
+        return s.substr(0, i + 1);
+      return s;
+    }
+    static auto trim_ows(std::string_view s) -> std::string_view {
+      return rtrim_ows(ltrim_ows(s));
+    }
+
+    auto from_icu_locale(icu::Locale const& l) const -> std::locale {
+      auto posix_name = std::string{l.getLanguage()};
+      if (l.getScript() && std::strlen(l.getScript()) > 0) {
+        posix_name += "_";
+        posix_name += l.getScript();
+      }
+      if (l.getCountry() && std::strlen(l.getCountry()) > 0) {
+        posix_name += "_";
+        posix_name += l.getCountry();
+      }
+      posix_name += ".UTF-8";
+      auto added_at = false;
+      if (l.getVariant() && std::strlen(l.getVariant()) > 0) {
+        added_at = true;
+        posix_name += "@";
+        posix_name += l.getVariant();
+      }
+      auto ec = UErrorCode::U_ZERO_ERROR;
+      auto* keywords = l.createKeywords(ec);
+      if (U_FAILURE(ec))
+        throw std::runtime_error{"failed to create keywords"};
+      if (keywords) {
+        std::int32_t kw_len = 0;
+        char const* kw = nullptr;
+        while (kw = keywords->next(&kw_len, ec), !U_FAILURE(ec) && kw) {
+          auto value = l.getKeywordValue<std::string>(icu::StringPiece(kw, kw_len), ec);
+          if (!added_at) {
+            posix_name += "@";
+            added_at = true;
+          } else {
+            posix_name += ";";
+          }
+          posix_name += kw;
+          posix_name += "=";
+          posix_name += value;
+        }
+        if (U_FAILURE(ec))
+          throw std::runtime_error{"failed to iterate over keywords"};
+        delete keywords;
+      }
+      return lgen_->generate(posix_name);
+    }
+
+  public:
+    // Note: lgen must live at least as long as the selector constructed here!
+    // It is unfortunately not possible to copy/move a blocale::generator.
+    explicit selector(locale_input_range auto locales, std::locale default_, std::shared_ptr<blocale::generator const> lgen)
+      : default_{default_}, matcher_{make_matcher(locales, default_)}, lgen_{lgen}
+    {}
+
+    auto select(std::string_view accept_language) const -> std::locale {
+      using namespace std::literals::string_view_literals;
+      // NOTE: can also contain a *;q=0.1
+      // q should have at most 3 digits after period
+      auto dlpm = icu_locale_priority_map{};
+      for (auto const [i, lang_prio] : accept_language | std::views::split(","sv) | std::views::enumerate) {
+        auto [lang_range_ut, mweight_ut] = util::split_on(std::string_view{lang_prio}, ';');
+        auto lang_range_str = trim_ows(lang_range_ut);
+        auto mweight_str = mweight_ut.transform(trim_ows);
+        if (lang_range_str == "*")
+          break;
+
+        auto ec = UErrorCode::U_ZERO_ERROR;
+        auto icu_locale = icu::Locale::forLanguageTag(lang_range_str, ec);
+        if (U_FAILURE(ec) || icu_locale.isBogus())
+          continue; // ignore this locale
+
+        auto weight = 1.0f;
+        if (mweight_str && mweight_str->starts_with("q=")) {
+          auto weight_str = mweight_str->substr(2, 4);
+          if (auto mweight = util::parse_float(weight_str, std::chars_format::fixed);
+              mweight && 0.0f < *mweight && *mweight < 1.0f) {
+            weight = *mweight;
+          }
+        }
+
+        if (weight > 0.0f) {
+          dlpm[icu_locale] = {
+            .weight = weight,
+            .original_index = static_cast<std::size_t>(i),
+          };
+        } else {
+          dlpm.erase(icu_locale);
+        }
+      }
+
+      auto desired_locales = std::vector<icu_priority_locale>{dlpm.begin(), dlpm.end()};
+      std::sort(desired_locales.begin(), desired_locales.end());
+      auto it = icu_priority_locale_vec_iterator{std::move(desired_locales)};
+      auto ec = UErrorCode::U_ZERO_ERROR;
+      auto res = matcher_.getBestMatchResult(it, ec);
+      if (U_FAILURE(ec))
+        return default_;
+      auto resolved = res.makeResolvedLocale(ec); // TODO: maybe don't?
+      if (U_FAILURE(ec))
+        return from_icu_locale(*res.getSupportedLocale());
+      return from_icu_locale(resolved);
+    }
+  };
+
+  export auto to_bcp47_lang_tag(std::locale locale) -> std::optional<std::string> {
+    auto const& locale_info = std::use_facet<blocale::info>(locale);
+    auto ec = UErrorCode::U_ZERO_ERROR;
+    auto bcp47_lang_tag = icu::Locale{locale_info.name().c_str()}.toLanguageTag<std::string>(ec);
+    if (U_FAILURE(ec))
+      return std::nullopt;
+    return bcp47_lang_tag;
+  }
+
+#ifdef LOCALEDIR
+# define LOCALEDIR_AUX_XSTR(s) LOCALEDIR_AUX_STR(s)
+# define LOCALEDIR_AUX_STR(s) #s
+  constexpr auto messages_path = std::string_view{LOCALEDIR_AUX_XSTR(LOCALEDIR)};
+# undef LOCALEDIR_AUX_STR
+# undef LOCALEDIR_AUX_XSTR
+#else // ifdef LOCALEDIR
+  constexpr auto messages_path = std::string_view{"locale/dev"};
+#endif // ifdef LOCALEDIR
+
+  export auto make_generator() -> std::shared_ptr<blocale::generator const> {
+    auto lgen = std::make_shared<blocale::generator>();
+    lgen->add_messages_path(std::string{messages_path});
+    lgen->add_messages_domain("routemon");
+    return std::static_pointer_cast<blocale::generator const>(lgen);
+  }
+
+} // namespace routemon::locale
diff --git a/server/src/log.cppm b/server/src/log.cppm
new file mode 100644
index 0000000..d7e2bff
--- /dev/null
+++ b/server/src/log.cppm
@@ -0,0 +1,148 @@
+module;
+
+// Seems like ADL for std::quoted is broken with
+//   import std;
+// Might be because the _Quoted_string object is defined in
+// std::__detail, which is not exported by the module.
+#include <iomanip>
+
+export module routemon:log;
+
+import std;
+
+namespace routemon::log {
+
+  export enum class level : std::uint8_t {
+    debug,
+    info,
+    warn,
+    error,
+  };
+
+  namespace {
+
+    auto operator<<(std::ostream& os, level lvl) -> std::ostream& {
+      switch (lvl) {
+      case level::debug: os << "dbg"; break;
+      case level::info:  os << "inf"; break;
+      case level::warn:  os << "wrn"; break;
+      case level::error: os << "err"; break;
+      }
+      return os;
+    }
+
+  } // namespace (unique)
+
+  export class sink {
+    std::atomic<enum level> lvl_;
+    std::ostream& os_ = std::cout;
+
+    struct tmp_message {
+      level lvl;
+      std::string_view component;
+      std::string_view txt;
+      std::map<std::string, std::string> const& attrs;
+    };
+
+    auto write(tmp_message msg) -> void {
+      auto sos = std::osyncstream{os_};
+      sos << "[" << msg.lvl;
+      if (!msg.component.empty())
+        sos << " " << msg.component;
+      sos << "] " << msg.txt;
+      for (auto const& [k, v] : msg.attrs) {
+        sos << " " << k << "=" << std::quoted(v);
+      }
+      sos << '\n';
+    }
+
+    explicit sink(level lvl)
+      : lvl_{lvl}
+    {}
+
+    friend auto make_sink(level lvl) -> std::shared_ptr<sink>;
+    friend class logger;
+
+  public:
+    [[nodiscard]] auto level() const -> enum level {
+      return lvl_;
+    }
+
+    auto set_level(enum level lvl) -> void {
+      lvl_ = lvl;
+    }
+  };
+
+  export auto make_sink(level lvl) -> std::shared_ptr<sink> {
+    return std::shared_ptr<sink>{new sink{lvl}};
+  }
+
+  export class logger {
+    std::shared_ptr<sink> sink_;
+    std::string component_;
+    std::map<std::string, std::string> attrs_;
+
+    template<log::level lvl>
+    auto log_at(std::string_view fmt, std::format_args args) -> logger& {
+      if (sink_->level() <= lvl)
+        sink_->write(sink::tmp_message{
+            .lvl = lvl,
+            .component = component_,
+            .txt = std::vformat(fmt, args),
+            .attrs = attrs_,
+          });
+      return *this;
+    }
+
+  public:
+    explicit logger(std::shared_ptr<sink> const& sink)
+      : sink_{sink}
+    {
+      if (!sink) {
+        throw std::invalid_argument{"logger sink may not be null"};
+      }
+    }
+
+    [[nodiscard]] auto sub(std::string_view component) const -> logger {
+      auto l = *this;
+      if (l.component_.empty()) {
+        l.component_ = component;
+      } else {
+        l.component_ += ".";
+        l.component_ += component;
+      }
+      return l;
+    }
+
+    [[nodiscard]] auto with(std::string const& k, std::string&& v) const -> logger {
+      auto l = *this;
+      l.attrs_[k] = std::move(v);
+      return l;
+    }
+
+    [[nodiscard]] auto with(std::string const& k, std::string_view v) const -> logger {
+      return with(k, std::string{v});
+    }
+
+    template<class... Args>
+    auto debug(std::format_string<Args...> fmt, Args&&... args) -> logger& {
+      return log_at<level::debug>(fmt.get(), std::make_format_args(args...));
+    }
+
+    template<class... Args>
+    auto info(std::format_string<Args...> fmt, Args&&... args) -> logger& {
+      return log_at<level::info>(fmt.get(), std::make_format_args(args...));
+    }
+
+    template<class... Args>
+    auto warn(std::format_string<Args...> fmt, Args&&... args) -> logger& {
+      return log_at<level::warn>(fmt.get(), std::make_format_args(args...));
+    }
+
+    template<class... Args>
+    auto error(std::format_string<Args...> fmt, Args&&... args) -> logger& {
+      return log_at<level::error>(fmt.get(), std::make_format_args(args...));
+    }
+  };
+
+} // namespace routemon::log
diff --git a/server/src/main.cpp b/server/src/main.cpp
new file mode 100644
index 0000000..a40b0b0
--- /dev/null
+++ b/server/src/main.cpp
@@ -0,0 +1,109 @@
+#include <malloc.h>  // for malloc_trim(3)
+#include <boost/asio.hpp>
+
+import std;
+import routemon;
+
+namespace chrono = std::chrono;
+namespace net = boost::asio;
+
+enum class exit_status {
+  failure,
+  bad_usage,
+};
+
+auto real_main(std::span<char const*> args) -> exit_status {
+  auto sink = routemon::log::make_sink(routemon::log::level::info);
+  auto l = routemon::log::logger{sink};
+
+  if (args.size() != 2) {
+    l.error("Fatal: expected exactly one argument (the configuration file location), got {}", args.size() - 1);
+    return exit_status::bad_usage;
+  }
+  auto const* config_filename = args[1];
+
+  auto lgen = routemon::locale::make_generator();
+  auto default_locale = lgen->generate("en_US.UTF-8");
+  auto locales = {
+    default_locale,
+    lgen->generate("nl_NL.UTF-8"),
+    lgen->generate("de_DE.UTF-8"),
+    lgen->generate("en_GB.UTF-8"),
+  };
+  auto lsel = routemon::locale::selector{locales, default_locale, lgen};
+
+  auto ioc = net::io_context{1 /* concurrency hint */};
+
+  auto config = routemon::config::app{};
+  try {
+    config = routemon::config::load_file(config_filename);
+  } catch (std::exception const& e) {
+    l.with("filename", std::string_view{config_filename}).
+      error("Failed to load configuration: {}", e.what());
+    return exit_status::failure;
+  }
+  sink->set_level(config.logger.level);
+  // auto rwgps_client = routemon::rwgps::client{ioc, l, config.rwgps.api_key, config.rwgps.auth_token};
+  // for (auto route : rwgps_client.get_all_routes()) {
+  //   l.info("Route {} (user {}): {} @ {}", route.id, route.user_id, route.name, route.url);
+  // }
+
+  auto dbc = std::shared_ptr<routemon::database::connection>{};
+  try {
+    dbc = routemon::database::open(config.database.sqlite3_filename);
+  } catch (std::exception const& e) {
+    l.with("filename", config.database.sqlite3_filename).
+      error("Failed to open database: {}", e.what());
+    return exit_status::failure;
+  }
+
+  l.with("filename", config.situations.datex2_filename).
+    info("Loading situations");
+  auto const before_load = chrono::steady_clock::now();
+  auto d2loader = routemon::datex2::loader{};
+  auto pub = routemon::datex2::situation_publication{};
+  try {
+    pub = d2loader.load_situation_publication(config.situations.datex2_filename);
+  } catch (std::exception const& e) {
+    l.error("Failed to load DATEX II situations publication: {}", e.what());
+    return exit_status::failure;
+  }
+  if (!d2loader.warnings().empty()) {
+    auto const& warns = d2loader.warnings();
+    l.warn("Encountered {} unique warnings while loading DATEX II situations publication", warns.size());
+    auto i = 0uz;
+    for (auto it = warns.begin(); it != warns.end(); it = warns.upper_bound(*it)) {
+      l.warn("Warning {} (appeared {}×): {}", ++i, warns.count(*it), *it);
+    }
+  }
+  // Processing the feed is by far the most memory-intensive operation
+  // during the run time of this application (at the moment), the
+  // resident set will likely never be this big again. So we ask libc
+  // to return as much memory as possible to the OS.
+  malloc_trim(0);
+  auto const after_load = chrono::steady_clock::now();
+  auto const dur_load = chrono::duration_cast<chrono::milliseconds>(after_load - before_load);
+  l.info("Loading situations finished in {}", dur_load);
+
+  auto handler = routemon::api::handler{l, std::move(pub)};
+  auto http_server = routemon::srv::server{l, std::move(lsel), std::move(handler)};
+  http_server.spawn(ioc);
+  ioc.run();
+
+  l.error("I/O context stopped");
+  return exit_status::failure;
+}
+
+auto main(int argc, char* argv[]) -> int {
+  if (argc < 0) {
+    std::cout << "Fatal: argument count below zero" << std::endl;
+    return EXIT_FAILURE;
+  }
+  auto res = real_main(std::span{const_cast<char const**>(argv), static_cast<std::size_t>(argc)});
+  switch (res) {
+  case exit_status::failure:
+    return EXIT_FAILURE;
+  case exit_status::bad_usage:
+    return 2;
+  }
+}
diff --git a/server/src/problem.cppm b/server/src/problem.cppm
new file mode 100644
index 0000000..8764962
--- /dev/null
+++ b/server/src/problem.cppm
@@ -0,0 +1,60 @@
+module;
+
+#include <boost/beast/http/message.hpp>
+#include <boost/json.hpp>
+#include <boost/locale/message.hpp>
+
+export module routemon:problem;
+
+import std;
+import :locale;
+
+namespace http = boost::beast::http;
+namespace json = boost::json;
+
+namespace routemon::problem {
+
+  export struct details {
+    http::status status;
+    blocale::message title;
+    std::string_view type_uri;
+    std::optional<blocale::message> detail = std::nullopt;
+    std::optional<std::string> instance = std::nullopt;
+
+    auto set_detail(blocale::message detail) -> details& {
+      this->detail = detail;
+      return *this;
+    }
+
+    auto set_instance(std::string&& instance) -> details& {
+      this->instance = instance;
+      return *this;
+    }
+    auto set_instance(std::string_view instance) -> details& {
+      this->instance = std::string{instance};
+      return *this;
+    }
+  };
+
+  export auto tag_invoke(json::value_from_tag, json::value& jv, details const& details, std::locale locale) -> void {
+    auto obj = json::object{
+      {"type",   details.type_uri},
+      {"title",  details.title.str(locale)},
+      {"status", static_cast<unsigned>(details.status)},
+    };
+    if (details.detail)   obj["detail"]   = details.detail->str(locale);
+    if (details.instance) obj["instance"] = *details.instance;
+    jv = obj;
+  }
+
+  export struct tpl {
+    http::status status;
+    blocale::message title;
+    std::string_view type_uri;
+
+    auto instantiate() const -> details {
+      return details{status, title, type_uri};
+    }
+  };
+
+}
diff --git a/server/src/req_ctx.cppm b/server/src/req_ctx.cppm
new file mode 100644
index 0000000..797c51d
--- /dev/null
+++ b/server/src/req_ctx.cppm
@@ -0,0 +1,51 @@
+module;
+
+#include <boost/beast/http/message.hpp>
+#include <boost/beast/http/verb.hpp>
+
+export module routemon:req_ctx;
+
+import :http.common;
+import :trace;
+
+namespace routemon {
+
+  export class req_ctx {
+    trace::id tid_;
+    std::locale locale_;
+    http::verb_set route_verbs_;
+    bool keep_alive_;
+    bhttp::request_header<bhttp::fields> const& req_header_;
+
+  public:
+    explicit req_ctx(trace::id tid, std::locale locale, http::verb_set route_verbs, bool keep_alive, bhttp::request_header<bhttp::fields> const& req_header)
+      : tid_{tid}, locale_{locale}, route_verbs_{route_verbs}, keep_alive_{keep_alive}, req_header_{req_header}
+    {}
+
+    template<typename ReqBody>
+    explicit req_ctx(trace::id tid, std::locale locale, http::verb_set route_verbs, bhttp::request<ReqBody> const& req)
+      : req_ctx{tid, locale, route_verbs, req.keep_alive(), req.base()}
+    {}
+
+    auto trace_id() const -> trace::id {
+      return tid_;
+    }
+
+    auto locale() const -> std::locale {
+      return locale_;
+    }
+
+    auto route_verbs() const -> http::verb_set {
+      return route_verbs_;
+    }
+
+    auto keep_alive() const -> bool {
+      return keep_alive_;
+    }
+
+    auto req_header() const -> bhttp::request_header<bhttp::fields> const& {
+      return req_header_;
+    }
+  };
+
+} // namespace routemon
diff --git a/server/src/routemon.cppm b/server/src/routemon.cppm
new file mode 100644
index 0000000..62db02a
--- /dev/null
+++ b/server/src/routemon.cppm
@@ -0,0 +1,11 @@
+export module routemon;
+export import :api;
+export import :config;
+export import :database;
+export import :datex2;
+export import :gpx;
+export import :locale;
+export import :log;
+export import :srv;
+export import :rwgps;
+export import :util;
diff --git a/server/src/rwgps.cppm b/server/src/rwgps.cppm
new file mode 100644
index 0000000..7ad6605
--- /dev/null
+++ b/server/src/rwgps.cppm
@@ -0,0 +1,137 @@
+module;
+
+#include <boost/beast/core.hpp>
+#include <boost/beast/http.hpp>
+#include <boost/json.hpp>
+
+export module routemon:rwgps;
+
+import std;
+import :http.client;
+import :log;
+
+namespace beast = boost::beast;
+namespace bhttp = beast::http;
+namespace net = boost::asio;
+namespace json = boost::json;
+
+namespace routemon::rwgps {
+
+  export struct route_summary {
+    std::int64_t id;
+    std::int64_t user_id;
+    std::string  url;
+    std::string  name;
+    std::string  description;
+  };
+
+  struct pagination {
+    std::size_t record_count;
+    std::size_t page_count;
+    std::size_t page_size;
+    std::optional<std::string> next_page_url;
+  };
+
+  struct get_routes_meta {
+    pagination pagination;
+  };
+
+  struct get_routes_response {
+    std::vector<route_summary> routes;
+    get_routes_meta meta;
+  };
+
+  auto tag_invoke(json::value_to_tag<route_summary> const&, json::value const& jv) -> route_summary {
+    return {
+      .id          = json::value_to<std::int64_t>(jv.at("id")),
+      .user_id     = json::value_to<std::int64_t>(jv.at("user_id")),
+      .url         = json::value_to<std::string>(jv.at("url")),
+      .name        = json::value_to<std::string>(jv.at("name")),
+      .description = json::value_to<std::string>(jv.at("description")),
+    };
+  }
+
+  auto tag_invoke(json::value_to_tag<pagination> const&, json::value const& jv) -> pagination {
+    return {
+      .record_count  = json::value_to<std::size_t>(jv.at("record_count")),
+      .page_count    = json::value_to<std::size_t>(jv.at("page_count")),
+      .page_size     = json::value_to<std::size_t>(jv.at("page_size")),
+      .next_page_url = json::value_to<std::optional<std::string>>(jv.at("next_page_url")),
+    };
+  }
+
+  auto tag_invoke(json::value_to_tag<get_routes_meta> const&, json::value const& jv) -> get_routes_meta {
+    return {
+      .pagination = json::value_to<pagination>(jv.at("pagination")),
+    };
+  }
+
+  auto tag_invoke(json::value_to_tag<get_routes_response> const&, json::value const& jv) -> get_routes_response {
+    return {
+      .routes = json::value_to<std::vector<route_summary>>(jv.at("routes")),
+      .meta   = json::value_to<get_routes_meta>(jv.at("meta")),
+    };
+  }
+
+  auto json_value_to_get_routes_response(json::value const& jv) -> get_routes_response {
+    return json::value_to<get_routes_response>(jv);
+  }
+
+  export class client {
+    log::logger  l_;
+    http::client hc_;
+    std::string  api_key_;
+    std::string  auth_token_;
+
+    static constexpr std::string host = "ridewithgps.com";
+
+    // TODO: handle failure appropriately
+    auto get_routes_page(std::size_t page) -> get_routes_response {
+      auto req = bhttp::request<bhttp::string_body>{
+        bhttp::verb::get,
+        std::format("/api/v1/routes.json?page_size=200?page={}", page),
+        11, // HTTP 1.1
+      };
+      req.set(bhttp::field::host, host);
+      req.set("x-rwgps-api-key", api_key_);
+      req.set("x-rwgps-auth-token", auth_token_);
+
+      auto rsp = hc_.do_request(req);
+      auto p = json::stream_parser{};
+      for (auto const frag : rsp.body().cdata()) {
+        p.write(static_cast<char const*>(frag.data()), frag.size());
+      }
+      assert(p.done());
+      return json_value_to_get_routes_response(p.release());
+    }
+
+  public:
+    explicit client(net::io_context& ioc, log::logger const& l, std::string api_key, std::string auth_token)
+      : l_{l.sub("rwgps-client")}, hc_{ioc}, api_key_{std::move(api_key)}, auth_token_{std::move(auth_token)}
+    {}
+
+    auto get_all_routes() -> std::vector<route_summary> {
+      // TODO: make sure that there are no duplicates here.
+      // What does RWGPS sort on, by default?
+      // Consider using an associative container instead of a vector.
+      auto record_count = 0uz;
+      auto current_page = 0uz;
+      auto routes = std::vector<route_summary>{};
+
+      while (true) {
+        auto rsp = get_routes_page(current_page);
+        if (rsp.meta.pagination.next_page_url)
+          l_.debug("Next page URL: {}", *rsp.meta.pagination.next_page_url);
+        routes.append_range(rsp.routes);
+        if (rsp.meta.pagination.record_count > 0)
+          record_count = rsp.meta.pagination.record_count;
+        if (rsp.routes.empty() || routes.size() >= record_count) {
+          break;
+        }
+      }
+
+      return routes;
+    }
+  };
+
+} // namespace routemon::rwgps
diff --git a/server/src/sqlite3.cppm b/server/src/sqlite3.cppm
new file mode 100644
index 0000000..f226c6b
--- /dev/null
+++ b/server/src/sqlite3.cppm
@@ -0,0 +1,257 @@
+module;
+
+#include <sqlite3.h>
+
+export module routemon:sqlite3;
+
+import std;
+import :util;
+
+namespace routemon::sqlite3 {
+
+  class mutex_guard {
+    explicit mutex_guard(::sqlite3_mutex* mut) noexcept : mut_{mut} {
+      ::sqlite3_mutex_enter(mut_);
+    }
+
+    friend auto do_guarded(::sqlite3_mutex* mut, std::invocable<mutex_guard const&> auto f) -> decltype(f(std::declval<mutex_guard const&>()));
+
+  public:
+    mutex_guard(mutex_guard const&) = delete;
+    ~mutex_guard() {
+      ::sqlite3_mutex_leave(mut_);
+    }
+
+  private:
+    ::sqlite3_mutex* mut_;
+  };
+
+  auto do_guarded(::sqlite3_mutex* mut, std::invocable<mutex_guard const&> auto f) -> decltype(f(std::declval<mutex_guard const&>())) {
+    return f(mutex_guard{mut});
+  }
+
+  auto do_guarded(::sqlite3* dbc, std::invocable<mutex_guard const&> auto f) -> decltype(f(std::declval<mutex_guard const&>())) {
+    return do_guarded(::sqlite3_db_mutex(dbc), f);
+  }
+
+  class error : public std::exception {
+    int code_;
+    std::string message_;
+
+  public:
+    explicit error(mutex_guard const&, int code, ::sqlite3* dbc)
+      : code_{code}, message_{::sqlite3_errmsg(dbc)}
+    {}
+
+    explicit error(int code)
+      : code_{code}, message_{::sqlite3_errstr(code)}
+    {}
+
+    [[nodiscard]] auto what() const noexcept -> char const* override {
+      return message_.c_str();
+    }
+
+    [[nodiscard]] auto code() const noexcept -> int {
+      return code_;
+    }
+  };
+
+  template<class T, template<class U> concept C>
+  concept optional_of = requires {
+    typename T::value_type;
+    requires std::same_as<T, std::optional<typename T::value_type>>;
+    requires C<typename T::value_type>;
+  };
+
+  template<class T>
+  concept scannable_prim =
+    std::same_as<T, std::string> ||
+    std::same_as<T, double> ||
+    std::same_as<T, std::int64_t>;
+
+  template<class T>
+  concept scannable = scannable_prim<T> || optional_of<T, scannable_prim>;
+
+  class statement {
+    ::sqlite3_stmt* stmt_;
+
+  public:
+    explicit statement(::sqlite3_stmt* stmt) : stmt_{stmt} {}
+    statement(statement const&) = delete;
+    statement(statement&& s) noexcept {
+      stmt_ = s.stmt_;
+      s.stmt_ = nullptr;
+    }
+    ~statement() {
+      ::sqlite3_finalize(stmt_);
+    }
+    auto get() -> ::sqlite3_stmt* {
+      return stmt_;
+    }
+  };
+
+  class row_reader {
+    statement stmt_;
+
+    explicit row_reader(statement stmt) : stmt_{std::move(stmt)} {}
+
+    friend class connection;
+
+    void scan(int col, std::string& s) {
+      if (::sqlite3_column_type(stmt_.get(), col) != SQLITE_TEXT)
+        throw std::invalid_argument{"invalid type for scan"};
+      unsigned char const* chs = ::sqlite3_column_text(stmt_.get(), col);
+      auto size = util::size_from_int(::sqlite3_column_bytes(stmt_.get(), col));
+      if (!size.has_value())
+        throw std::logic_error{"unexpected negative amount of bytes in column"};
+      s = std::string{reinterpret_cast<char const*>(chs), *size};
+    }
+
+    void scan(int col, double& v) {
+      if (::sqlite3_column_type(stmt_.get(), col) != SQLITE_FLOAT)
+        throw std::invalid_argument{"invalid type for scan"};
+      v = ::sqlite3_column_double(stmt_.get(), col);
+    }
+
+    void scan(int col, std::int64_t& v) {
+      if (::sqlite3_column_type(stmt_.get(), col) != SQLITE_INTEGER)
+        throw std::invalid_argument{"invalid type for scan"};
+      v = ::sqlite3_column_int64(stmt_.get(), col);
+    }
+
+    void scan(int col, optional_of<scannable> auto& v) {
+      if (::sqlite3_column_type(stmt_.get(), col) == SQLITE_NULL) {
+        v.reset();
+      } else {
+        typename std::remove_cvref_t<decltype(v)>::value_type tmp;
+        scan(col, tmp);
+        v = std::move(tmp);
+      }
+    }
+
+  public:
+    auto next() -> bool {
+      ::sqlite3* dbc = ::sqlite3_db_handle(stmt_.get());
+      return do_guarded(dbc, [&](auto const& guard) -> bool {
+        auto const s = ::sqlite3_step(stmt_.get());
+        if (s == SQLITE_ROW)
+          return true;
+        if (s == SQLITE_DONE)
+          return false;
+        throw error{guard, s, dbc};
+      });
+    }
+
+    auto scan(scannable auto&... args) -> void {
+      auto const ncols = util::size_from_int(::sqlite3_data_count(stmt_.get()));
+      if (!ncols.has_value())
+        throw std::logic_error{"got unexpected negative amount of columns"};
+      if (sizeof...(args) > *ncols)
+        throw std::invalid_argument{"more scanning arguments provided than columns in result set"};
+      auto col = 0; (..., scan(col++, args));
+    }
+
+    auto scan_single(scannable auto&... args) -> void {
+      if (!next())
+        throw std::logic_error{"no row in result set"};
+      scan(args...);
+      if (next()) {
+        throw std::logic_error{"more than one row in result set"};
+      }
+    }
+  };
+
+  class binder {
+    statement& stmt_;
+
+    explicit binder(statement& stmt) : stmt_{stmt} {}
+
+    friend class connection;
+
+  public:
+    auto text(std::string const& param_name, std::string_view str) -> void {
+      int const i = ::sqlite3_bind_parameter_index(stmt_.get(), param_name.c_str());
+      if (i == 0)
+        throw std::invalid_argument{std::format("bind: no parameter with name {} found", param_name)};
+      auto str_size = util::int_from_size(str.size());
+      if (!str_size.has_value())
+        throw std::invalid_argument{"bind: provided text is too long"};
+      if (auto s = ::sqlite3_bind_text(stmt_.get(), i, str.data(), *str_size, SQLITE_TRANSIENT); s != SQLITE_OK) {
+        throw error{s};
+      }
+    }
+
+    static auto noop(binder&) -> void {}
+  };
+
+  export class connection {
+    ::sqlite3* dbc_;
+    ::sqlite3_mutex* mut_;
+
+    explicit connection(::sqlite3* dbc) : dbc_{dbc}, mut_{::sqlite3_db_mutex(dbc)} {}
+
+    friend auto open(std::string const& filename) -> connection;
+
+  public:
+    connection(connection const&) = delete;
+    connection(connection&& c) noexcept {
+      dbc_ = c.dbc_;
+      mut_ = c.mut_;
+      c.dbc_ = nullptr;
+      c.mut_ = nullptr;
+    }
+
+    [[nodiscard]] auto query(std::string const& sql, std::function<void(binder&)> const& bf = binder::noop) -> row_reader {
+      ::sqlite3_stmt* pstmt = nullptr;
+      char const* sql_tail = nullptr;
+      auto sql_size = util::int_from_size(sql.size());
+      if (!sql_size.has_value() || *sql_size >= std::numeric_limits<int>::max() - 1)
+        throw std::invalid_argument{"provided input text too large"};
+      do_guarded(mut_, [&](auto const& guard) -> void {
+        if (auto s = ::sqlite3_prepare_v2(dbc_, sql.data(), *sql_size + 1, &pstmt, &sql_tail); s != SQLITE_OK) {
+          if (pstmt != nullptr) {
+            // Use contract_assert when having a compiler with contracts available
+            ::sqlite3_finalize(pstmt);
+            throw std::logic_error{"expected stmt to be null after failed preparation"};
+          }
+          throw error{guard, s, dbc_};
+        }
+      });
+      if (!pstmt)
+        throw std::invalid_argument{"provided input text contains no SQL"};
+      auto stmt = statement{pstmt};
+      if (sql_tail && std::strlen(sql_tail) > 0)
+        throw std::invalid_argument{"provided input text contains more than one SQL statement"};
+      auto b = binder{stmt}; bf(b);
+      return row_reader{std::move(stmt)};
+    }
+
+    auto exec(std::string const& sql, std::function<void(binder&)> const& bf = binder::noop) -> void {
+      auto reader = query(sql, bf);
+      while (reader.next());
+    }
+
+    ~connection() {
+      std::ignore = ::sqlite3_close(std::exchange(dbc_, nullptr));
+    }
+  };
+
+  export auto open(std::string const& filename) -> connection {
+    ::sqlite3* dbc = nullptr;
+    auto s = ::sqlite3_open_v2(filename.c_str(), &dbc,
+                              SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE |
+                              SQLITE_OPEN_FULLMUTEX | SQLITE_OPEN_EXRESCODE,
+                              nullptr);
+    if (s != SQLITE_OK) {
+      if (dbc) {
+        do_guarded(dbc, [&](auto const& guard) -> void {
+          throw error{guard, s, dbc};
+        });
+      } else {
+        throw error{s};
+      }
+    }
+    return connection{dbc};
+  }
+
+} // namespace routemon::sqlite3
diff --git a/server/src/srv.cppm b/server/src/srv.cppm
new file mode 100644
index 0000000..2ca48c6
--- /dev/null
+++ b/server/src/srv.cppm
@@ -0,0 +1,221 @@
+module;
+
+#include <boost/config.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/as_tuple.hpp>
+#include <boost/asio/awaitable.hpp>
+#include <boost/asio/co_spawn.hpp>
+#include <boost/beast/core.hpp>
+#include <boost/beast/http.hpp>
+#include <boost/json.hpp>
+#include <boost/locale/generator.hpp>
+
+#include <expat.h>
+
+export module routemon:srv;
+
+import std;
+import :api;
+import :config;
+import :gpx;
+import :http.server;
+import :locale;
+import :log;
+import :problem;
+import :req_ctx;
+import :util;
+
+namespace beast = boost::beast;
+namespace json = boost::json;
+namespace net = boost::asio;
+using tcp = boost::asio::ip::tcp;
+
+namespace routemon::srv {
+
+  class gpx_parse_error_category_impl : public std::error_category {
+  public:
+    char const* name() const noexcept override { return "gpx_parse"; }
+    auto message(int condition) const noexcept -> std::string override {
+      std::ignore = condition;
+      return "failed to parse GPX file";
+    }
+  };
+  auto gpx_parse_error_category() noexcept -> gpx_parse_error_category_impl const& {
+    static auto const inst = gpx_parse_error_category_impl{};
+    return inst;
+  }
+  auto gpx_parse_error() noexcept -> std::error_code {
+    return std::error_code{1, gpx_parse_error_category()};
+  }
+
+  class gpx_parse_result {
+    std::variant<std::exception_ptr, gpx::file> res_;
+
+  public:
+    auto set_exception(std::exception_ptr ex) noexcept {
+      res_ = ex;
+    }
+    auto set_gpx_file(gpx::file&& f) noexcept {
+      res_ = std::move(f);
+    }
+
+    auto unwrap() -> gpx::file&& {
+      return std::visit(util::overloaded{
+          [](std::exception_ptr ex) -> gpx::file&& {
+            if (ex) std::rethrow_exception(ex);
+            else throw std::runtime_error{"no GPX file parse result available"};
+          },
+          [](gpx::file&& f) -> gpx::file&& { return std::move(f); },
+        }, std::move(res_));
+    }
+  };
+
+  struct readable_gpx_body {
+    using value_type = gpx_parse_result;
+
+    class reader {
+      gpx::reader r_;
+      util::not_null<value_type*> res_;
+
+    public:
+      template<bool isRequest, bhttp::concepts::fields Fields>
+      explicit reader(bhttp::header<isRequest, Fields>&, value_type& v)
+        : res_{&v}
+      {}
+
+      // The following methods (which are called by Beast) are marked
+      // noexcept, since Beast does not ensure that exceptions thrown
+      // here are appropriately directed to the caller of
+      // (async_)read(_some), so throwing here might cause the program
+      // to crash.
+
+      auto init(boost::optional<std::uint64_t> /* n */, beast::error_code& ec) noexcept -> void {
+        try {
+          r_.init();
+          ec = {};
+        } catch (std::exception& ex) {
+          res_->set_exception(std::current_exception());
+          ec = gpx_parse_error();
+        }
+      }
+
+      auto put(beast::concepts::const_buffer_sequence auto b, beast::error_code& ec) noexcept -> std::size_t {
+        auto total = 0uz;
+        try {
+          for (auto it = net::buffer_sequence_begin(b); it != net::buffer_sequence_end(b); it++) {
+            r_.put(std::string_view{static_cast<char const*>(it->data()), it->size()});
+            total += it->size();
+          }
+          ec = {};
+        } catch (std::exception& ex) {
+          res_->set_exception(std::current_exception());
+          ec = gpx_parse_error();
+        }
+        return total;
+      }
+
+      auto finish(beast::error_code& ec) noexcept {
+        try {
+          res_->set_gpx_file(r_.finish());
+          ec = {};
+        } catch (std::exception& ex) {
+          res_->set_exception(std::current_exception());
+          ec = gpx_parse_error();
+        }
+      }
+    };
+  };
+  static_assert(bhttp::concepts::body<readable_gpx_body>);
+  static_assert(bhttp::concepts::body_reader<readable_gpx_body>);
+
+  class handler {
+    api::handler inner_;
+
+  public:
+    using outer_ctx = http::trace_id_ctx<http::base_ctx>;
+    using l0_ctx = http::routed_ctx<outer_ctx>;
+
+  private:
+    auto handle_process_gpx(l0_ctx ctx, http::readable_request r) -> net::awaitable<http::presponse> {
+      auto gpx_file = gpx::file{};
+      try {
+        auto req = co_await http::read_request<readable_gpx_body>(ctx, std::move(r));
+        gpx_file = std::move(req->body().unwrap());
+      } catch (std::exception& ex) {
+        // TODO: more detailed problem reporting
+        auto tpl = problem::tpl{
+          .status   = bhttp::status::bad_request,
+          .title    = translate("Failed to parse GPX file"),
+          .type_uri = "https://routemon.fautchen.eu/problems/gpx-parse-failed",
+        };
+        co_return http::problem_rsp(ctx, tpl.instantiate(), http::keep_alive{false});
+      }
+
+      // TODO: catch handler exceptions and return 500 when raised?
+      // (keep-alive depends on whether whole request was read)
+      auto mres = inner_.process_gpx(std::move(gpx_file));
+      if (!mres) {
+        auto tpl = problem::tpl{
+          .status   = bhttp::status::internal_server_error,
+          .title    = translate("Internal server error"),
+          .type_uri = "https://routemon.fautchen.eu/problems/internal-server-error",
+        };
+        co_return http::problem_rsp(ctx, tpl.instantiate(), http::keep_alive{true});
+      }
+
+      auto rsp = http::make_rsp<bhttp::string_body>(bhttp::status::ok, http::keep_alive{true});
+      rsp.set(bhttp::field::content_type, "application/json");
+      rsp.body() = json::serialize(json::value_from(*mres));
+      rsp.prepare_payload();
+      co_return rsp;
+    }
+
+    auto handle_sysinfo(l0_ctx ctx, http::readable_request r) -> net::awaitable<http::presponse> {
+      auto req = co_await http::read_request<bhttp::empty_body>(ctx, std::move(r));
+      auto info = inner_.sysinfo();
+
+      auto rsp = http::make_rsp<bhttp::string_body>(bhttp::status::ok, http::keep_alive{true});
+      rsp.set(bhttp::field::content_type, "application/json");
+      rsp.body() = json::serialize(json::value_from(info));
+      rsp.prepare_payload();
+      co_return rsp;
+    }
+
+  public:
+    handler(api::handler&& inner) : inner_{std::move(inner)} {}
+
+    auto make_routes() -> http::route_tree<http::routed_ctx<outer_ctx>> {
+      auto handler = [this]<class MemFn>(MemFn member) {
+        return std::bind_front(member, this);
+      };
+
+      return http::dtree<http::routed_ctx<outer_ctx>>{}.named_subtrees({
+          {"gpx", http::dtree<l0_ctx>{{
+                .post = handler(&handler::handle_process_gpx),
+              }}.no_subtrees()},
+          {"sysinfo", http::dtree<l0_ctx>{{
+                .get = handler(&handler::handle_sysinfo),
+              }}.no_subtrees()},
+        });
+    }
+  };
+
+  export class server {
+    handler handler_;
+    http::server<handler::outer_ctx> srv_;
+
+    static auto make_global_middleware() -> http::middleware_t<http::base_ctx, handler::outer_ctx> {
+      return http::middleware_compose<http::base_ctx, http::trace_id_ctx<http::base_ctx>, http::trace_id_ctx<http::base_ctx>>(http::trace_id_middleware<http::base_ctx>, http::lax_cors_middleware<http::trace_id_ctx<http::base_ctx>>);
+    }
+
+  public:
+    server(log::logger const& l, locale::selector&& lsel, api::handler&& inner)
+      : handler_{std::move(inner)}, srv_{l, std::move(lsel), make_global_middleware(), handler_.make_routes()}
+    {}
+
+    auto spawn(net::io_context& ioc) -> void {
+      srv_.spawn(ioc);
+    }
+  };
+
+} // namespace routemon::srv
diff --git a/server/src/time.cppm b/server/src/time.cppm
new file mode 100644
index 0000000..767883c
--- /dev/null
+++ b/server/src/time.cppm
@@ -0,0 +1,205 @@
+export module routemon:time;
+
+import std;
+
+export namespace routemon::time {
+
+  using timestamp = std::chrono::time_point<std::chrono::utc_clock>;
+
+  class period {
+    // Assuming [start, end). Unfortunately the DATEX II model is not
+    // clear about this.
+    timestamp start_;
+    timestamp end_;
+
+  public:
+    explicit period(timestamp start, timestamp end)
+      : start_{start}, end_{end}
+    {
+      if (start >= end) {
+        throw std::invalid_argument("period: start should be before end");
+      }
+    }
+
+    [[nodiscard]] auto intersect(period other) const -> std::optional<period> {
+      auto const new_start = start_ < other.start() ? other.start() : start_;
+      auto const new_end   = other.end() < end_     ? other.end()   : end_;
+      return new_start < new_end ? std::make_optional(period{new_start, new_end}) : std::nullopt;
+    }
+
+    [[nodiscard]] auto except(period other) const -> std::pair<std::optional<period>, std::optional<period>> {
+      auto const before_start = start_;
+      auto const before_end   = other.start();
+      auto const after_start  = end_;
+      auto const after_end    = other.end();
+      std::optional<period> before, after;
+      if (before_start < before_end)
+        before = period{before_start, before_end};
+      if (after_start < after_end)
+        after = period{after_end, after_start};
+      return std::make_pair(before, after);
+    }
+
+    [[nodiscard]] auto start() const -> timestamp { return start_; }
+    [[nodiscard]] auto end() const -> timestamp { return end_; }
+  };
+
+  class period_seq {
+    std::vector<period> periods_;
+
+    // The way lt and ge are ordered makes a difference for how the sorting
+    // (insertion based on lower_bound) works. Do not carelessly reorder this.
+    enum lt_ge : std::uint8_t {
+      ge,  // >=
+      lt,  // <
+    };
+
+    // O(n log n)
+    template<std::input_iterator I, std::sentinel_for<I> S>
+    requires std::same_as<std::iter_value_t<I>, period>
+    static auto consolidate(I begin, S end) -> std::vector<period> {
+      auto periods = std::vector<period>{};
+      auto preds = std::vector<std::pair<timestamp, lt_ge>>{};
+
+      for (auto it = begin; it != end; it++) {
+        auto const& period = *it;
+
+        auto const a = std::make_pair(period.start(), ge);
+        auto const b = std::make_pair(period.end(), lt);
+        preds.insert(std::lower_bound(preds.begin(), preds.end(), a), a);
+        preds.insert(std::lower_bound(preds.begin(), preds.end(), b), b);
+      }
+
+      if (preds.empty())
+        return periods;
+
+      if (preds.size() < 2)
+        throw std::logic_error{"period_seq::consolidate: amount of predicates should be >= 2"};
+      if (preds.front().second != ge)
+        throw std::logic_error{"period_seq::consolidate: first element of preds should be a ge-element"};
+      if (preds.back().second != lt)
+        throw std::logic_error{"period_seq::consolidate: last element of preds should be an lt-element"};
+
+      auto period_start = preds[0].first;
+      for (std::size_t i = 1; i < preds.size(); i++) {
+        if (preds[i].second == lt && (i + 1 == preds.size() || preds[i + 1].second == ge)) {
+          auto const period_end = preds[i].first;
+          if (!periods.empty() && periods.back().start() == period_start)
+            periods.back() = period{periods.back().end(), period_end};
+          else
+            periods.emplace_back(period_start, period_end);
+          if (i + 1 != preds.size()) {
+            period_start = preds[i + 1].first;
+            i++;
+          }
+        }
+      }
+
+      return periods;
+    }
+
+    explicit period_seq(std::vector<period> periods)
+      : periods_{std::move(periods)}
+    {
+      for (auto i = 0uz; i < periods_.size(); i++) {
+        if (i + 1 < periods_.size()) {
+          if (periods_[i].end() >= periods_[i + 1].start()) {
+            throw std::logic_error{"period_seq: vector provided to private constructor not ordered properly"};
+          }
+        }
+      }
+    }
+
+  public:
+    template<std::input_iterator I, std::sentinel_for<I> S>
+    requires std::same_as<std::iter_value_t<I>, period>
+    explicit period_seq(I begin, S end)
+      : periods_{consolidate(begin, end)}
+    {}
+
+    explicit period_seq(period singleton)
+      : periods_{singleton}
+    {}
+
+    [[nodiscard]] auto intersect(period_seq const& other) const -> period_seq {
+      auto it1 = periods_.begin(); auto end1 = periods_.end();
+      auto it2 = other.periods_.begin(); auto end2 = other.periods_.end();
+
+      auto res = std::vector<period>{};
+      while (it1 != end1 && it2 != end2) {
+        auto overlap = it1->intersect(*it2);
+        if (overlap) {
+          res.push_back(*overlap);
+          if (it1->end() < it2->end()) {
+            it1++;
+          } else {
+            it2++;
+          }
+        } else {
+          if (it1->end() < it2->start()) {
+            it1++;
+          } else {
+            it2++;
+          }
+        }
+      }
+
+      return period_seq{res};
+    }
+
+    [[nodiscard]] auto except(period_seq const& other) const -> period_seq {
+      // This code was pretty tricky to write, I wouldn't be surprised if it has some bugs in it.
+
+      auto it1 = periods_.begin(); auto end1 = periods_.end();
+      auto it2 = other.periods_.begin(); auto end2 = other.periods_.end();
+
+      auto res = std::vector<period>{};
+      if (it1 == end1)
+        return period_seq{res};
+      if (it2 == end2)
+        return period_seq{periods_};
+      auto period1 = period{*it1++};
+
+      while (it1 != end1 && it2 != end2) {
+        if (period1.end() <= it2->start()) {
+          res.push_back(period1);
+          period1 = *it1++;
+        } else if (it2->end() <= period1.start()) {
+          it2++;
+        } else /* period1.begin() < it2->end() && it2->begin() < period1.end() */ {
+          auto const [mbefore, mafter] = period1.except(*it2);
+          if (mbefore)
+            res.push_back(*mbefore);
+          if (mafter) {
+            period1 = *mafter;
+          } else {
+            period1 = *it1++;
+          }
+        }
+      }
+
+      return period_seq{res};
+    }
+
+    [[nodiscard]] auto periods() const -> std::vector<period> const& {
+      return periods_;
+    }
+  };
+
+  auto operator<<(std::ostream& os, period const& p) -> std::ostream& {
+    return os << "[" << p.start() << ", " << p.end() << ")";
+  }
+
+  auto operator<<(std::ostream &os, period_seq const& ps) -> std::ostream& {
+    os << "{";
+    auto it = ps.periods().begin();
+    while (it != ps.periods().end()) {
+      os << " " << *it;
+      if (++it != ps.periods().end()) {
+        os << ",";
+      }
+    }
+    return os << " }";
+  }
+
+} // namespace routemon::time
diff --git a/server/src/trace.cppm b/server/src/trace.cppm
new file mode 100644
index 0000000..00ecd05
--- /dev/null
+++ b/server/src/trace.cppm
@@ -0,0 +1,79 @@
+module;
+
+// Might as well since we're using OpenSSL
+#include <openssl/err.h>
+#include <openssl/rand.h>
+
+export module routemon:trace;
+
+import std;
+import :util;
+
+namespace routemon::trace {
+
+  class uuid7 {
+    std::uint64_t high_ = 0;
+    std::uint64_t low_  = 0;
+
+  public:
+    uuid7() {
+      namespace chrono = std::chrono;
+      auto const unix_time_ms_signed = static_cast<std::int64_t>(chrono::duration_cast<chrono::milliseconds>(chrono::system_clock::now().time_since_epoch()).count());
+      if (unix_time_ms_signed < 0)
+        throw std::runtime_error{"system time before UNIX epoch"};
+      auto const unix_time_ms = static_cast<std::uint64_t>(unix_time_ms_signed);
+      if (std::countl_zero(unix_time_ms) < 16)
+        throw std::runtime_error{"system time too great"};
+
+      auto rand = std::array<unsigned char, 10>{};
+      int s = RAND_bytes(rand.data(), static_cast<int>(rand.size()));
+      if (s != 1) {
+        unsigned long e = ERR_get_error();
+        throw std::runtime_error{std::format("failed to generate UUID(v7): {} ({}, code {})", ERR_reason_error_string(e), ERR_lib_error_string(e), e)};
+      }
+
+      auto version = std::uint64_t{0b0111};
+      auto variant = std::uint64_t{0b10};
+
+      high_ |= unix_time_ms << 16;
+      high_ |= version << 12;
+      high_ |= std::uint64_t{rand[0]} << 4;
+      high_ |= std::uint64_t{rand[1]};
+      low_  |= variant << 62;
+      low_  |= std::uint64_t{rand[2]} << 54;
+      low_  |= std::uint64_t{rand[3]} << 48;
+      low_  |= std::uint64_t{rand[4]} << 40;
+      low_  |= std::uint64_t{rand[5]} << 32;
+      low_  |= std::uint64_t{rand[6]} << 24;
+      low_  |= std::uint64_t{rand[7]} << 16;
+      low_  |= std::uint64_t{rand[8]} <<  8;
+      low_  |= std::uint64_t{rand[9]};
+    }
+
+    auto format(std::array<char, 37>& target) -> void {
+      auto high_high     = (high_ & 0xffff'ffff'0000'0000) >> 32;
+      auto high_low_high = (high_ & 0x0000'0000'ffff'0000) >> 16;
+      auto low_low_high  = (high_ & 0x0000'0000'0000'ffff) >>  0;
+      auto high_low      = (low_  & 0xffff'0000'0000'0000) >> 48;
+      auto low_low       = (low_  & 0x0000'ffff'ffff'ffff) >>  0;
+
+      std::format_to(target.begin(), "{:0>8x}-{:0>4x}-{:0>4x}-{:0>4x}-{:0>12x}",
+                     high_high, high_low_high, low_low_high, high_low, low_low);
+      target.back() = '\0';
+    }
+  };
+
+  export class id {
+    std::array<char, 37> chars_;
+
+  public:
+    id() {
+      uuid7{}.format(chars_);
+    }
+
+    auto as_string() const -> util::zstring_view {
+      return util::zstring_view{chars_.data(), chars_.size() - 1};
+    }
+  };
+
+} // namespace routemon::trace
diff --git a/server/src/util.cppm b/server/src/util.cppm
new file mode 100644
index 0000000..65f4d67
--- /dev/null
+++ b/server/src/util.cppm
@@ -0,0 +1,254 @@
+// Stuff that doesn't really have a place right now, but that is
+// broadly useful.
+export module routemon:util;
+
+import std;
+
+namespace routemon::util {
+
+  // For use with e.g. std::visit (on std::variant).
+  template<class... Ts>
+  struct overloaded : Ts... {
+    using Ts::operator()...;
+  };
+
+  export constexpr auto parse_double(std::string_view s, std::chars_format fmt = std::chars_format::general) noexcept -> std::optional<double> {
+    auto x = 0.0;
+    auto [_, ec] = std::from_chars(s.data(), s.data() + s.size(), x, fmt);
+    if (ec == std::errc{}) {
+      return x;
+    } else {
+      return std::nullopt;
+    }
+  }
+
+  export constexpr auto parse_float(std::string_view s, std::chars_format fmt = std::chars_format::general) noexcept -> std::optional<float> {
+    auto x = 0.0;
+    auto [_, ec] = std::from_chars(s.data(), s.data() + s.size(), x, fmt);
+    if (ec == std::errc{}) {
+      return x;
+    } else {
+      return std::nullopt;
+    }
+  }
+
+  export template<class T>
+  class aolist : public std::enable_shared_from_this<aolist<T>> {
+    T v_;
+    std::shared_ptr<aolist<T> const> next_;
+
+    explicit aolist(T v, std::shared_ptr<aolist<T> const> next)
+      : v_{v}, next_{next}
+    {}
+
+  public:
+    static auto nil() -> std::shared_ptr<aolist<T>> {
+      return nullptr;
+    }
+
+    static auto cons(T v, std::shared_ptr<aolist<T> const> l) -> std::shared_ptr<aolist<T>> {
+      return std::shared_ptr<aolist<T>>{new aolist<T>{v, l}};
+    }
+
+    auto next() const -> std::shared_ptr<aolist<T> const> {
+      return next_;
+    }
+
+    auto value() const noexcept -> T const& {
+      return v_;
+    }
+  };
+
+  export constexpr auto size_from_int(int x) -> std::optional<std::size_t> {
+    static_assert(sizeof(int) <= sizeof(std::size_t), "cannot cast int to smaller size_t type");
+    if (x < 0)
+      return std::nullopt;
+    return static_cast<std::size_t>(x);
+  }
+
+  export constexpr auto int_from_size(std::size_t x) -> std::optional<int> {
+    constexpr auto int_max = size_from_int(std::numeric_limits<int>::max());
+    static_assert(int_max.has_value());
+    if (x > *int_max)
+      return std::nullopt;
+    return static_cast<int>(x);
+  }
+
+  export class zstring_view {
+    char const* s_;
+    std::size_t length_;
+
+  public:
+    constexpr explicit zstring_view(char const* s, std::size_t length) :
+      s_{s}, length_{length}
+    {}
+
+    constexpr zstring_view(char const* s) :
+      zstring_view{s, std::char_traits<char>::length(s)}
+    {}
+
+    auto length() const -> std::size_t {
+      return length_;
+    }
+
+    auto c_str() const -> char const* {
+      return s_;
+    }
+
+    operator std::string_view() const {
+      return std::string_view{s_, length_};
+    }
+
+    operator char const*() const {
+      return s_;
+    }
+  };
+
+  // View for null-terminated strings for which we might not
+  // necessarily be interested in the length. String length is only
+  // calculated on demand, at most once on each thread (on more than
+  // one thread when racing). May be null.
+  //
+  // It is undefined behavior to assign to a lazy_zstring_view when
+  // it is in use by other threads.
+  export class lazy_zstring_view {
+    static constexpr auto unset_length = std::numeric_limits<std::size_t>::max();
+
+    char const* s_; // nullable
+    mutable std::atomic<std::size_t> length_;
+    static_assert(decltype(length_)::is_always_lock_free);
+
+  public:
+    constexpr explicit lazy_zstring_view(char const* s) :
+      s_{s}, length_{s ? unset_length : 0}
+    {}
+    ~lazy_zstring_view() = default;
+
+    lazy_zstring_view(lazy_zstring_view const& sv) noexcept
+      : s_{sv.s_}, length_{sv.length_.load(std::memory_order_acquire)}
+    {}
+    lazy_zstring_view(lazy_zstring_view&& sv) noexcept
+      : s_{sv.s_}, length_{sv.length_.load(std::memory_order_acquire)}
+    {}
+    auto operator=(lazy_zstring_view const& rhs) noexcept -> lazy_zstring_view& {
+      if (this != &rhs) {
+        s_ = rhs.s_;
+        length_.store(rhs.length_.load(std::memory_order_acquire), std::memory_order_release);
+      }
+      return *this;
+    }
+    auto operator=(lazy_zstring_view&& rhs) noexcept -> lazy_zstring_view& {
+      return *this = rhs; // use the copy assignment operator
+    }
+
+    auto length() const noexcept -> std::size_t {
+      if (auto v = length_.load(std::memory_order_acquire); v != unset_length)
+        return v;
+      auto l = std::char_traits<char>::length(s_);
+      length_.store(l, std::memory_order_release);
+      return l;
+    }
+
+    auto c_str() const noexcept -> char const* {
+      return s_;
+    }
+
+    operator std::string_view() const noexcept {
+      return std::string_view{s_, length()};
+    }
+
+    operator char const*() const noexcept {
+      return s_;
+    }
+
+    auto operator==(std::string_view sv) const noexcept -> bool {
+      if (auto v = length_.load(std::memory_order_acquire); v != unset_length)
+        if (sv.length() != v)
+          return false;
+      auto res = std::char_traits<char>::compare(s_, sv.data(), sv.length());
+      if (res != 0)
+        return false;
+      // Strings are equal for sv.length() characters.
+      if (s_[sv.length()] != '\0')
+        return false;
+      // Strings are actually equal, and we have just found out the
+      // length of this string, so we might as well set it.
+      length_.store(sv.length(), std::memory_order_release);
+      return true;
+    }
+  };
+
+  constexpr auto operator""_zsv(char const* s, std::size_t length) noexcept -> zstring_view {
+    return zstring_view{s, length};
+  }
+
+  auto operator==(zstring_view lhs, zstring_view rhs) -> bool {
+    return std::string_view{lhs} == std::string_view{rhs};
+  }
+
+  export constexpr auto split_on(std::string_view s, char c) -> std::pair<std::string_view, std::optional<std::string_view>> {
+    if (auto i = s.find(c); i != std::string_view::npos)
+      return std::make_pair(s.substr(0, i), s.substr(i + 1));
+    return std::make_pair(s, std::nullopt);
+  }
+
+  export template<class T>
+  class not_null;
+
+  export template<class T>
+  class not_null<T*> {
+    T* p_;
+
+    struct guaranteed_not_null_t {};
+    explicit not_null(T* p, guaranteed_not_null_t) noexcept : p_{p} {}
+
+  public:
+    explicit not_null(T* p)
+      : p_{p}
+    { if (!p_) throw std::runtime_error{"not_null constructed with null pointer"}; }
+    ~not_null() = default;
+
+    not_null(not_null const& other) = default;
+    not_null(not_null&& other) noexcept = default;
+    auto operator=(not_null const& rhs) noexcept -> not_null& = default;
+    auto operator=(not_null&& rhs) noexcept -> not_null& = default;
+
+    friend auto make_not_null(T* p) noexcept -> std::optional<not_null> {
+      if (p) return not_null(p, guaranteed_not_null_t{});
+      else return std::nullopt;
+    }
+
+    [[nodiscard]] auto get() const noexcept -> T* {
+      return p_;
+    }
+
+    auto operator*() const noexcept -> std::add_lvalue_reference_t<T> {
+      return *p_;
+    }
+
+    auto operator->() const noexcept -> T* {
+      return p_;
+    }
+  };
+  export template<class T> explicit not_null(T*) -> not_null<T*>;
+
+  export template<>
+  class not_null<lazy_zstring_view> {
+    lazy_zstring_view s_;
+
+  public:
+    explicit not_null(lazy_zstring_view s)
+      : s_{std::move(s)}
+    { if (!s_) throw std::runtime_error{"not_null constructed with null pointer"}; }
+
+    [[nodiscard]] auto get() const noexcept -> lazy_zstring_view {
+      return s_;
+    }
+
+    operator lazy_zstring_view() const noexcept { return s_; }
+    operator std::string_view() const noexcept { return s_; }
+    operator char const*() const noexcept { return s_; }
+  };
+  export explicit not_null(lazy_zstring_view s) -> not_null<lazy_zstring_view>;
+
+} // namespace routemon::util
diff --git a/server/src/xml.cpp b/server/src/xml.cpp
new file mode 100644
index 0000000..cad42d1
--- /dev/null
+++ b/server/src/xml.cpp
@@ -0,0 +1,61 @@
+module;
+
+#include <cassert>
+#include <expat.h>
+
+module routemon:xml$impl;
+
+import :xml;
+
+namespace routemon::xml {
+
+  auto qname_view::operator==(qname_view const& rhs) const -> bool {
+    return ns_uri == rhs.ns_uri && local == rhs.local;
+  }
+
+  executor::executor() :
+    p_{XML_ParserCreateNS("UTF-8", detail::qname_sep)}
+  {
+    XML_SetUserData(p_, this);
+    XML_SetElementHandler(p_, handle_start_element, handle_end_element);
+    XML_SetCharacterDataHandler(p_, handle_character_data);
+    XML_SetProcessingInstructionHandler(p_, handle_processing_instructions);
+    XML_SetExternalEntityRefHandler(p_, handle_external_entity_ref);
+    XML_SetNamespaceDeclHandler(p_, handle_start_namespace_decl, handle_end_namespace_decl);
+    XML_SetXmlDeclHandler(p_, handle_xml_decl);
+  }
+
+  executor::~executor() {
+    XML_ParserFree(p_);
+  }
+
+  auto executor::start() -> void {
+    continuation_.resume();
+    if (ex_) std::rethrow_exception(ex_);
+  }
+
+  auto executor::read(std::string_view xml, bool is_final) -> void {
+    if (ex_)
+      throw std::runtime_error{"refusing to restart parser that was thrown in"};
+    // TODO: narrow_cast
+    if (auto s = XML_Parse(p_, xml.data(), static_cast<int>(xml.size()), is_final); s != XML_STATUS_OK) {
+      auto errc = XML_GetErrorCode(p_);
+      if (errc == XML_ERROR_ABORTED) {
+        assert(ex_);
+        std::rethrow_exception(ex_);
+      } else {
+        throw std::runtime_error{std::format("failed to parse XML: {}", XML_ErrorString(errc))};
+      }
+    }
+  }
+
+  auto executor::end() -> void {
+    if (ex_)
+      throw std::runtime_error{"refusing to restart parser that was thrown in"};
+    ev_ = eof_event{};
+    advance_ = false;
+    while (continuation_) continuation_.resume();
+    if (ex_) std::rethrow_exception(ex_);
+  }
+
+} // namespace routemon::xml
diff --git a/server/src/xml.cppm b/server/src/xml.cppm
new file mode 100644
index 0000000..957f149
--- /dev/null
+++ b/server/src/xml.cppm
@@ -0,0 +1,632 @@
+module;
+
+#include <cassert>
+#include <expat.h>
+
+export module routemon:xml;
+
+import std;
+import :util;
+
+// XML parsing module.
+//
+// Makes heavy use of C++20 coroutines. Provides combinators to build
+// XML (data format) parsers with. To keep overhead low (and allow for
+// HALO/CoroElide), many non-polymorphic definitions are marked inline
+// (which is not the default in module units). This also has the added
+// benefit of allowing HALO across TU boundaries, which is practically
+// necessary to reduce unnecessary allocations when building parsers
+// using the provided combinators.
+
+// Ensure that Expat is speaking UTF-8
+static_assert(std::is_same_v<XML_Char, char>);
+
+namespace routemon::xml {
+
+  struct qname_view {
+    std::string_view ns_uri;
+    std::string_view local;
+
+    auto operator==(qname_view const& rhs) const -> bool;
+  };
+
+  namespace detail {
+
+    constexpr auto qname_sep = '\xFF';
+    auto split_name(char const* name) noexcept -> qname_view {
+      auto [l, r] = util::split_on(name, qname_sep);
+      if (r) return { .ns_uri = l, .local = *r };
+      else return { .ns_uri = std::string_view{}, .local = l };
+    }
+
+  } // namespace detail
+
+  class attribute_view_iterator {
+    std::string_view default_ns_uri_;
+    char const* const* attrs_;
+
+    auto advance() -> void {
+      attrs_ += 2;
+    }
+
+  public:
+    using difference_type = std::ptrdiff_t;
+    using value_type = std::pair<qname_view, char const*>;
+
+    struct sentinel {
+      friend constexpr auto operator==(attribute_view_iterator const& it, sentinel) noexcept -> bool {
+        return !*it.attrs_;
+      }
+    };
+
+    inline explicit attribute_view_iterator(std::string_view default_ns_uri, char const* const* attrs)
+      : default_ns_uri_{default_ns_uri}, attrs_{attrs}
+    {}
+
+    inline auto operator*() const -> std::pair<qname_view, char const*> {
+      if (!*attrs_)
+        throw std::runtime_error{"end of attribute list"};
+      auto qname = detail::split_name(attrs_[0]);
+      if (qname.ns_uri.empty())
+        qname.ns_uri = default_ns_uri_;
+      return std::make_pair(qname, attrs_[1]);
+    }
+
+    // Pre-increment
+    inline auto operator++() -> attribute_view_iterator& {
+      advance();
+      return *this;
+    }
+
+    // Post-increment
+    inline auto operator++(int) -> attribute_view_iterator {
+      auto pre = *this;
+      advance();
+      return pre;
+    }
+  };
+  static_assert(std::input_iterator<attribute_view_iterator>);
+
+  class attribute_view : std::ranges::view_base {
+    std::string_view default_ns_uri_;
+    char const* const* attrs_;
+
+  public:
+    inline explicit attribute_view(std::string_view default_ns_uri, char const** attrs)
+      : default_ns_uri_{default_ns_uri}, attrs_{const_cast<char const* const*>(attrs)}
+    {}
+
+    [[nodiscard]] inline auto begin() const -> attribute_view_iterator {
+      return attribute_view_iterator{default_ns_uri_, attrs_};
+    }
+
+    [[nodiscard]] inline auto end() const -> attribute_view_iterator::sentinel {
+      return {};
+    }
+
+    inline auto lookup(qname_view want) -> std::optional<util::not_null<util::lazy_zstring_view>> {
+      for (auto const& [name, v] : *this) {
+        if (name == want) {
+          return util::not_null{util::lazy_zstring_view{v}};
+        }
+      }
+      return std::nullopt;
+    }
+  };
+  static_assert(std::ranges::input_range<attribute_view>);
+
+  template<class T> class promise;
+
+  template<class T>
+  struct [[clang::coro_await_elidable, clang::coro_return_type]] parser {
+    using promise_type = promise<T>;
+    using result_type = promise_type::result_type;
+    using handle_type = std::coroutine_handle<promise_type>;
+
+  private:
+    handle_type h_;
+
+  public:
+    explicit parser(handle_type h)
+      : h_{h}
+    { assert(h); }
+
+    parser(const parser&) = delete;
+    parser(parser&& c) noexcept
+      : h_{std::exchange(c.h_, nullptr)}
+    {}
+    auto operator=(const parser&) -> parser& = delete;
+    auto operator=(parser&&) -> parser& = delete;
+
+    [[nodiscard]] auto promise() const -> promise_type& {
+      return h_.promise();
+    }
+
+    ~parser() {
+      if (h_) h_.destroy();
+    }
+  };
+
+  struct start_element_event {
+    qname_view name;
+    attribute_view attrs;
+  };
+  struct end_element_event {
+    qname_view name;
+  };
+  struct character_data_event {
+    std::string_view data;
+  };
+  struct processing_instructions_event {
+    util::lazy_zstring_view target;
+    util::lazy_zstring_view data;
+  };
+  struct xml_decl_event {
+    util::lazy_zstring_view version;
+    util::lazy_zstring_view encoding;
+    std::optional<bool> standalone;
+  };
+  struct eof_event {};
+  using event = std::variant<start_element_event,
+                             end_element_event,
+                             character_data_event,
+                             processing_instructions_event,
+                             xml_decl_event,
+                             eof_event>;
+  template<class T>
+  concept event_type = requires(event ev) { std::get<T>(ev); };
+
+  class executor;
+  using executor_ref = util::not_null<executor*>;
+
+  struct current_event_t {
+    executor_ref executor;
+  };
+  auto current_event(executor_ref executor) -> current_event_t {
+    return current_event_t{executor};
+  }
+
+  class promise_base {
+    executor_ref executor_;
+    std::coroutine_handle<promise_base> continuation_ = nullptr;
+
+  public:
+    // Not having this constructor marked inline messes with coroutine
+    // HALO. (Hours 'wasted': many)
+    inline explicit promise_base(executor_ref executor)
+      : executor_{executor}
+    {}
+
+    [[nodiscard]] inline auto executor() const -> executor& {
+      return *executor_;
+    }
+
+    inline auto base_handle() -> std::coroutine_handle<promise_base> {
+      return std::coroutine_handle<promise_base>::from_promise(*this);
+    }
+
+    [[nodiscard]] inline auto continuation() const -> std::coroutine_handle<promise_base> {
+      return continuation_;
+    }
+    inline auto set_continuation(std::coroutine_handle<promise_base> c) -> void {
+      continuation_ = c;
+    }
+  };
+
+  struct position {
+    std::size_t line;
+    std::size_t col;
+  };
+
+  class executor {
+    XML_Parser p_;
+    std::exception_ptr ex_ = nullptr;
+    std::coroutine_handle<promise_base> continuation_ = nullptr;
+    std::vector<std::optional<std::string>> default_namespace_;
+    std::unordered_map<std::string_view, std::vector<std::string>> namespaces_;
+    std::optional<event> ev_;
+    bool advance_ = true;
+
+    inline auto try_handle_event(event ev) noexcept -> void {
+      assert(!ex_);
+
+      try {
+        ev_ = std::move(ev);
+      } catch (...) {
+        ex_ = std::current_exception();
+        return;
+      }
+      advance_ = false;
+      if (!continuation_) {
+        // Parser returned (all subparsers are done) and has set the continuation to nullptr.
+        if (auto s = XML_StopParser(p_, /* resumable */ false); s != XML_STATUS_OK) {
+          ex_ = std::make_exception_ptr(std::runtime_error{"unexpected error when stopping XML parser"});
+          return;
+        }
+        ex_ = std::make_exception_ptr(std::runtime_error{"parser did not consume entire XML document"});
+        return;
+      }
+      continuation_.resume();
+      if (ex_) {
+        // Not sure if it's useful to report this error.
+        std::ignore = XML_StopParser(p_, /* resumable */ false);
+      }
+    }
+
+    static auto handle_start_element(void* ctx, char const* name, char const** attrs) noexcept -> void {
+      auto qname = detail::split_name(name);
+      static_cast<executor*>(ctx)->try_handle_event(start_element_event{
+          .name = qname,
+          .attrs = attribute_view{qname.ns_uri, attrs},
+        });
+    }
+    static auto handle_end_element(void* ctx, char const* name) noexcept -> void {
+      static_cast<executor*>(ctx)->try_handle_event(end_element_event{
+          .name = detail::split_name(name),
+        });
+    }
+    static auto handle_character_data(void* ctx, char const* s, int len) noexcept -> void {
+      static_cast<executor*>(ctx)->try_handle_event(character_data_event{
+          .data = std::string_view{s, static_cast<std::size_t>(len)},
+        });
+    }
+    static auto handle_processing_instructions(void* ctx, char const* target, char const* data) noexcept -> void {
+      static_cast<executor*>(ctx)->try_handle_event(processing_instructions_event{
+          .target = util::lazy_zstring_view{target},
+          .data = util::lazy_zstring_view{data},
+        });
+    }
+    static auto handle_external_entity_ref(XML_Parser, char const* /* context */, char const* /* base */, char const* /* system_id */, char const* /* public_id */) noexcept -> int {
+      return XML_STATUS_ERROR;
+    }
+    static auto handle_start_namespace_decl(void* ctx, char const* prefix, char const* uri) noexcept -> void {
+      if (prefix) {
+        static_cast<executor*>(ctx)->namespaces_[std::string_view{prefix}].emplace_back(uri);
+      } else {
+        static_cast<executor*>(ctx)->default_namespace_.push_back(uri ? std::make_optional<std::string>(uri) : std::nullopt);
+      }
+    }
+    static auto handle_end_namespace_decl(void* ctx, char const* prefix) noexcept -> void {
+      if (prefix) {
+        static_cast<executor*>(ctx)->namespaces_[std::string_view{prefix}].pop_back();
+      } else {
+        static_cast<executor*>(ctx)->default_namespace_.pop_back();
+      }
+    }
+    static auto handle_xml_decl(void * ctx, char const* version, char const* encoding, int standalone) noexcept -> void {
+      static_cast<executor*>(ctx)->try_handle_event(xml_decl_event{
+          .version = util::lazy_zstring_view{version},
+          .encoding = util::lazy_zstring_view{encoding},
+          .standalone = standalone < 0 ? std::nullopt : std::make_optional(standalone > 0),
+        });
+    }
+
+    inline auto advance_flag() -> bool {
+      return advance_;
+    }
+    inline auto set_exception(std::exception_ptr ex) -> void {
+      ex_ = std::move(ex);
+    }
+    [[nodiscard]] inline auto take_exception() -> std::exception_ptr {
+      return std::exchange(ex_, nullptr);
+    }
+
+    template<class T> friend class promise;
+
+  public:
+    executor();
+
+    executor(executor const&) = delete;
+    executor(executor&&) = delete;
+    auto operator=(executor const&) -> executor& = delete;
+    auto operator=(executor&&) -> executor& = delete;
+
+    ~executor();
+
+    inline auto set_continuation(std::coroutine_handle<promise_base> c) -> void {
+      continuation_ = c;
+    }
+    inline auto set_advance_flag() -> void {
+      if (!ev_ || !std::holds_alternative<eof_event>(ev_.value())) {
+        advance_ = true;
+      }
+    }
+    inline auto event() const -> std::optional<event> const& {
+      return ev_;
+    }
+    inline auto resolve_namespace(std::string_view prefix) -> std::optional<std::string_view> {
+      if (auto it = namespaces_.find(prefix); it != namespaces_.end() && !it->second.empty())
+        return it->second.back();
+      return std::nullopt;
+    }
+    [[nodiscard]] inline auto position() -> position {
+      return {
+        .line = XML_GetCurrentLineNumber(p_),
+        .col = XML_GetCurrentColumnNumber(p_),
+      };
+    }
+
+    auto start() -> void;
+    auto read(std::string_view xml, bool is_final) -> void;
+    auto end() -> void;
+  };
+
+  template<class T>
+  class promise_returnable : public promise_base {
+    std::optional<T> returned_value_;
+
+  public:
+    using result_type = T;
+    using promise_base::promise_base;
+
+    template<class U>
+    auto return_value(U&& v) -> void {
+      returned_value_.emplace(std::forward<U>(v));
+    }
+    auto returned_value() -> T&& {
+      if (!returned_value_)
+        throw std::runtime_error{"XML coroutine did not return"};
+      return std::forward<T>(returned_value_.value());
+    }
+  };
+
+  template<>
+  class promise_returnable<void> : public promise_base {
+  public:
+    using result_type = void;
+    using promise_base::promise_base;
+
+    auto return_void() -> void {}
+  };
+
+  template<class T>
+  class promise : public promise_returnable<T> {
+  public:
+    // Called with all the coroutine's arguments.
+    // Ignoring all but the first argument, which should be the executor.
+    template<class... Args>
+    explicit promise(executor_ref executor, Args&&...)
+      : promise_returnable<T>{executor}
+    {}
+
+    auto handle() -> std::coroutine_handle<promise<T>> {
+      return {parser<T>::handle_type::from_promise(*this)};
+    }
+
+    auto get_return_object() -> parser<T> {
+      return parser<T>{handle()};
+    }
+
+    auto initial_suspend() {
+      return std::suspend_always{};
+    }
+    auto final_suspend() noexcept {
+      struct awaiter {
+        std::coroutine_handle<> h_;
+
+        [[nodiscard]] constexpr auto await_ready() const noexcept -> bool { return false; }
+        auto await_suspend(std::coroutine_handle<>) -> std::coroutine_handle<> { return h_; }
+        constexpr auto await_resume() const noexcept -> void { return; }
+      };
+      if (this->continuation()) {
+        return awaiter{this->continuation()};
+      } else {
+        this->executor().set_continuation(nullptr);
+        return awaiter{std::noop_coroutine()};
+      }
+    }
+
+    auto unhandled_exception() -> void {
+      this->executor().set_exception(std::current_exception());
+    }
+
+    auto await_transform(current_event_t const& req) {
+      struct awaiter {
+        executor_ref executor_;
+
+        [[nodiscard]] constexpr auto await_ready() const noexcept -> bool {
+          return !executor_->advance_flag();
+        }
+        auto await_suspend(std::coroutine_handle<promise<T>> h) -> void {
+          executor_->set_continuation(h.promise().base_handle());
+        }
+        [[nodiscard]] auto await_resume() const -> event {
+          assert(executor_->event());
+          return executor_->event().value();
+        }
+      };
+      return awaiter{req.executor};
+    }
+
+    template<class U>
+    auto await_transform(parser<U> const& coro) {
+      struct [[clang::coro_await_elidable]] awaiter {
+        util::not_null<promise<U>*> next_;
+
+        [[nodiscard]] constexpr auto await_ready() const noexcept -> bool { return false; }
+        auto await_suspend(std::coroutine_handle<promise<T>> h) -> std::coroutine_handle<> {
+          // Passed coroutine handle will be the same as parser<T>::handle_type::from_promise(*this)
+          next_->set_continuation(h.promise().base_handle());
+          return next_->handle();
+        }
+        auto await_resume() -> U {
+          // Promise is still valid since coroutine frame is still alive (and suspended):
+          // control was transferred back to this coroutine via symmetric transfer in
+          // final_suspend(). Assuming that the destructor for coro still needs to run.
+          if (auto ex = next_->executor().take_exception()) {
+            std::rethrow_exception(ex);
+          } else {
+            if constexpr (!std::is_void_v<U>) {
+              return std::move(next_->returned_value());
+            }
+          }
+        }
+      };
+      return awaiter{util::not_null{&coro.promise()}};
+    }
+  };
+
+  // Helpers for handling XML documents. Non-polymorphic functions
+  // should be marked inline to allow HALO across TU boundaries.
+
+  template<class T>
+  concept unconstrained = true;
+
+  template<class T, template<class U> concept C>
+  concept parser_of = requires {
+    typename T::result_type;
+    requires std::same_as<parser<typename T::result_type>, T>;
+      requires C<typename T::result_type>;
+  };
+
+  template<parser_of<unconstrained> T>
+  using parser_result_t = T::result_type;
+
+  template<class T, class... Args>
+  concept parser_invocable = std::invocable<T, Args...> && parser_of<std::invoke_result_t<T, Args...>, unconstrained>;
+
+  template<class Fn, class... Args>
+  requires parser_invocable<Fn, Args...>
+  using parser_invoke_result_t = parser_result_t<std::invoke_result_t<Fn, Args...>>;
+
+  template<event_type T> auto expect_event(executor_ref e) -> parser<T> {
+    auto ev = co_await current_event(e);
+    if (!std::holds_alternative<T>(ev)) {
+      auto pos = e->position();
+      throw std::runtime_error{std::format("at {}:{}: unexpected event type, have {}", pos.line, pos.col, ev.index())};
+    }
+    e->set_advance_flag();
+    co_return std::get<T>(ev);
+  }
+
+  inline auto expect_start_element(executor_ref e, qname_view want) -> parser<attribute_view> {
+    auto ev = co_await expect_event<start_element_event>(e);
+    if (ev.name != want) {
+      auto pos = e->position();
+      throw std::runtime_error{std::format("at {}:{}: unexpected element started", pos.line, pos.col)};
+    }
+    co_return ev.attrs;
+  }
+
+  inline auto allow_start_element(executor_ref e, qname_view want) -> parser<std::optional<attribute_view>> {
+    auto ev = co_await current_event(e);
+    if (auto const* pev = std::get_if<start_element_event>(&ev)) {
+      if (pev->name == want) {
+        e->set_advance_flag();
+        co_return pev->attrs;
+      }
+    }
+    co_return std::nullopt;
+  }
+
+  inline auto expect_end_element(executor_ref e, qname_view want) -> parser<void> {
+    auto ev = co_await expect_event<end_element_event>(e);
+    if (ev.name != want) {
+      throw std::runtime_error{"unexpected element ended"};
+    }
+  }
+
+  inline auto ignore_whitespace(executor_ref e) -> parser<void> {
+    auto all_whitespace = [](std::string_view s) -> bool {
+      for (auto c : s)
+        if (c != ' ' && c != '\r' && c != '\n' && c != '\t')
+          return false;
+      return true;
+    };
+
+    while (true) {
+      auto ev = co_await current_event(e);
+      if (auto const* pev = std::get_if<character_data_event>(&ev); pev && all_whitespace(pev->data)) {
+        e->set_advance_flag();
+      } else {
+        co_return;
+      }
+    }
+  }
+
+  auto expect_element(executor_ref e, qname_view want, parser_invocable<executor_ref, attribute_view> auto p)
+    -> parser<parser_invoke_result_t<decltype(p), executor_ref, attribute_view>>
+  {
+    co_await ignore_whitespace(e);
+    auto attrs = co_await expect_start_element(e, want);
+    auto&& res = co_await p(e, attrs);
+    co_await expect_end_element(e, want);
+    co_await ignore_whitespace(e);
+    co_return std::forward<parser_invoke_result_t<decltype(p), executor_ref, attribute_view>>(res);
+  }
+
+  auto allow_element(executor_ref e, qname_view want, parser_invocable<executor_ref, attribute_view> auto p)
+    -> parser<std::optional<parser_invoke_result_t<decltype(p), executor_ref, attribute_view>>>
+  {
+    co_await ignore_whitespace(e);
+    if (auto mattrs = co_await allow_start_element(e, want)) {
+      auto&& res = co_await p(e, *mattrs);
+      co_await expect_end_element(e, want);
+      co_await ignore_whitespace(e);
+      co_return std::make_optional(std::forward<parser_invoke_result_t<decltype(p), executor_ref, attribute_view>>(res));
+    }
+    co_return std::nullopt;
+  }
+
+  auto allow_element(executor_ref e, qname_view want, parser_invocable<executor_ref, attribute_view> auto p)
+    -> parser<bool>
+    requires std::is_void_v<parser_invoke_result_t<decltype(p), executor_ref, attribute_view>>
+  {
+    co_await ignore_whitespace(e);
+    if (auto mattrs = co_await allow_start_element(e, want)) {
+      co_await p(e, *mattrs);
+      co_await expect_end_element(e, want);
+      co_await ignore_whitespace(e);
+      co_return true;
+    }
+    co_return false;
+  }
+
+  inline auto ignore_contents(executor_ref e, std::optional<qname_view> muntil = std::nullopt) -> parser<void> {
+    std::size_t depth = 0;
+    while (true) {
+      auto ev = co_await current_event(e);
+      if (auto* pev = std::get_if<start_element_event>(&ev)) {
+        if (depth == 0 && muntil && pev->name == *muntil) {
+          co_return;
+        } else {
+          depth++;
+        }
+      } else if (std::holds_alternative<end_element_event>(ev)) {
+        if (depth == 0) {
+          co_return;
+        } else {
+          depth--;
+        }
+      }
+      e->set_advance_flag();
+    }
+  }
+  inline auto ignore_element_contents(executor_ref e, attribute_view) -> parser<void> {
+    co_await ignore_contents(e);
+  }
+
+  inline auto read_string(executor_ref e) -> parser<std::string> {
+    std::string s;
+    while (true) {
+      auto ev = co_await current_event(e);
+      if (auto* pev = std::get_if<character_data_event>(&ev)) {
+        e->set_advance_flag();
+        s += pev->data;
+      } else {
+        co_return s;
+      }
+    }
+  }
+  inline auto read_string_contents(executor_ref e, attribute_view) -> parser<std::string> {
+    co_return co_await read_string(e);
+  }
+
+  template<auto f>
+  auto hohalo() {
+    return []<class... Args>(Args&&... args) -> std::invoke_result_t<decltype(f), Args...> {
+      co_return co_await f(std::forward<Args>(args)...);
+    };
+  }
+
+} // namespace routemon::xml