From 973aec43ea54bbf95b64fbcb636403401d1ca60e Mon Sep 17 00:00:00 2001
From: Rutger Broekhoff
Date: Fri, 28 Aug 2026 18:03:05 +0200
Subject: Import from e4b104792206ee7ea64bf39c6b7d2c0c230f9d14

---
 server/src/xml.cppm | 632 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 632 insertions(+)
 create mode 100644 server/src/xml.cppm

(limited to 'server/src/xml.cppm')

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
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