2 files changed, 358 insertions, 0 deletions

diff --git a/gitolfs3-common/Cargo.toml b/gitolfs3-common/Cargo.toml
new file mode 100644
index 0000000..5724732
--- /dev/null
+++ b/gitolfs3-common/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "gitolfs3-common"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+chrono = "0.4"
+hmac-sha256 = "1.1"
+subtle = "2.5"
+serde = { version = "1", features = ["derive"] }
diff --git a/gitolfs3-common/src/lib.rs b/gitolfs3-common/src/lib.rs
new file mode 100644
index 0000000..917f566
--- /dev/null
+++ b/gitolfs3-common/src/lib.rs
@@ -0,0 +1,348 @@
+use chrono::{DateTime, Utc};
+use serde::{de, Deserialize, Serialize};
+use std::{
+    fmt::{self, Write},
+    ops,
+    str::FromStr,
+};
+use subtle::ConstantTimeEq;
+
+#[repr(u8)]
+enum AuthType {
+    BatchApi = 1,
+    Download = 2,
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct Claims<'a> {
+    pub specific_claims: SpecificClaims,
+    pub repo_path: &'a str,
+    pub expires_at: DateTime<Utc>,
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum SpecificClaims {
+    BatchApi(Operation),
+    Download(Oid),
+}
+
+pub type Oid = Digest<32>;
+
+#[derive(Debug, Eq, PartialEq, Copy, Clone, Serialize, Deserialize)]
+#[repr(u8)]
+pub enum Operation {
+    #[serde(rename = "download")]
+    Download = 1,
+    #[serde(rename = "upload")]
+    Upload = 2,
+}
+
+/// Returns None if the claims are invalid. Repo path length may be no more than 100 bytes.
+pub fn generate_tag(claims: Claims, key: impl AsRef<[u8]>) -> Option<Digest<32>> {
+    if claims.repo_path.len() > 100 {
+        return None;
+    }
+
+    let mut hmac = hmac_sha256::HMAC::new(key);
+    match claims.specific_claims {
+        SpecificClaims::BatchApi(operation) => {
+            hmac.update([AuthType::BatchApi as u8]);
+            hmac.update([operation as u8]);
+        }
+        SpecificClaims::Download(oid) => {
+            hmac.update([AuthType::Download as u8]);
+            hmac.update(oid.as_bytes());
+        }
+    }
+    hmac.update([claims.repo_path.len() as u8]);
+    hmac.update(claims.repo_path.as_bytes());
+    hmac.update(claims.expires_at.timestamp().to_be_bytes());
+    Some(hmac.finalize().into())
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub struct ParseOperationError;
+
+impl fmt::Display for ParseOperationError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "operation should be 'download' or 'upload'")
+    }
+}
+
+impl FromStr for Operation {
+    type Err = ParseOperationError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "upload" => Ok(Self::Upload),
+            "download" => Ok(Self::Download),
+            _ => Err(ParseOperationError),
+        }
+    }
+}
+
+/// None means out of range.
+fn decode_nibble(c: u8) -> Option<u8> {
+    if c.is_ascii_digit() {
+        Some(c - b'0')
+    } else if (b'a'..=b'f').contains(&c) {
+        Some(c - b'a' + 10)
+    } else if (b'A'..=b'F').contains(&c) {
+        Some(c - b'A' + 10)
+    } else {
+        None
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct HexByte(pub u8);
+
+impl<'de> Deserialize<'de> for HexByte {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let str = <&str>::deserialize(deserializer)?;
+        let &[b1, b2] = str.as_bytes() else {
+            return Err(de::Error::invalid_length(
+                str.len(),
+                &"two hexadecimal characters",
+            ));
+        };
+        let (Some(b1), Some(b2)) = (decode_nibble(b1), decode_nibble(b2)) else {
+            return Err(de::Error::invalid_value(
+                de::Unexpected::Str(str),
+                &"two hexadecimal characters",
+            ));
+        };
+        Ok(HexByte((b1 << 4) | b2))
+    }
+}
+
+impl fmt::Display for HexByte {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let &HexByte(b) = self;
+        HexFmt(&[b]).fmt(f)
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub enum ParseHexError {
+    UnevenNibbles,
+    InvalidCharacter,
+    TooShort,
+    TooLong,
+}
+
+impl fmt::Display for ParseHexError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::UnevenNibbles => {
+                write!(f, "uneven amount of nibbles (chars in range [a-zA-Z0-9])")
+            }
+            Self::InvalidCharacter => write!(f, "non-hex character encountered"),
+            Self::TooShort => write!(f, "unexpected end of hex sequence"),
+            Self::TooLong => write!(f, "longer hex sequence than expected"),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum ReadHexError {
+    Io(std::io::Error),
+    Format(ParseHexError),
+}
+
+impl fmt::Display for ReadHexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Self::Io(e) => e.fmt(f),
+            Self::Format(e) => e.fmt(f),
+        }
+    }
+}
+
+fn parse_hex_exact(value: &str, buf: &mut [u8]) -> Result<(), ParseHexError> {
+    if value.bytes().len() % 2 == 1 {
+        return Err(ParseHexError::UnevenNibbles);
+    }
+    if value.bytes().len() < 2 * buf.len() {
+        return Err(ParseHexError::TooShort);
+    }
+    if value.bytes().len() > 2 * buf.len() {
+        return Err(ParseHexError::TooLong);
+    }
+    for (i, c) in value.bytes().enumerate() {
+        if let Some(b) = decode_nibble(c) {
+            if i % 2 == 0 {
+                buf[i / 2] = b << 4;
+            } else {
+                buf[i / 2] |= b;
+            }
+        } else {
+            return Err(ParseHexError::InvalidCharacter);
+        }
+    }
+    Ok(())
+}
+
+pub type Key = SafeByteArray<64>;
+
+pub fn load_key(path: &str) -> Result<Key, ReadHexError> {
+    let key_str = std::fs::read_to_string(path).map_err(ReadHexError::Io)?;
+    key_str.trim().parse().map_err(ReadHexError::Format)
+}
+
+pub struct SafeByteArray<const N: usize> {
+    inner: [u8; N],
+}
+
+impl<const N: usize> SafeByteArray<N> {
+    pub fn new() -> Self {
+        Self { inner: [0; N] }
+    }
+}
+
+impl<const N: usize> Default for SafeByteArray<N> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<const N: usize> AsRef<[u8]> for SafeByteArray<N> {
+    fn as_ref(&self) -> &[u8] {
+        &self.inner
+    }
+}
+
+impl<const N: usize> AsMut<[u8]> for SafeByteArray<N> {
+    fn as_mut(&mut self) -> &mut [u8] {
+        &mut self.inner
+    }
+}
+
+impl<const N: usize> Drop for SafeByteArray<N> {
+    fn drop(&mut self) {
+        self.inner.fill(0)
+    }
+}
+
+impl<const N: usize> FromStr for SafeByteArray<N> {
+    type Err = ParseHexError;
+
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        let mut sba = Self { inner: [0u8; N] };
+        parse_hex_exact(value, &mut sba.inner)?;
+        Ok(sba)
+    }
+}
+
+pub struct HexFmt<B: AsRef<[u8]>>(pub B);
+
+impl<B: AsRef<[u8]>> fmt::Display for HexFmt<B> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let HexFmt(buf) = self;
+        for b in buf.as_ref() {
+            let (high, low) = (b >> 4, b & 0xF);
+            let highc = if high < 10 {
+                high + b'0'
+            } else {
+                high - 10 + b'a'
+            };
+            let lowc = if low < 10 {
+                low + b'0'
+            } else {
+                low - 10 + b'a'
+            };
+            f.write_char(highc as char)?;
+            f.write_char(lowc as char)?;
+        }
+        Ok(())
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct Digest<const N: usize> {
+    inner: [u8; N],
+}
+
+impl<const N: usize> ops::Index<usize> for Digest<N> {
+    type Output = u8;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.inner[index]
+    }
+}
+
+impl<const N: usize> Digest<N> {
+    pub fn as_bytes(&self) -> &[u8; N] {
+        &self.inner
+    }
+}
+
+impl<const N: usize> fmt::Display for Digest<N> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        HexFmt(&self.inner).fmt(f)
+    }
+}
+
+impl<const N: usize> Digest<N> {
+    pub fn new(data: [u8; N]) -> Self {
+        Self { inner: data }
+    }
+}
+
+impl<const N: usize> From<[u8; N]> for Digest<N> {
+    fn from(value: [u8; N]) -> Self {
+        Self::new(value)
+    }
+}
+
+impl<const N: usize> From<Digest<N>> for [u8; N] {
+    fn from(val: Digest<N>) -> Self {
+        val.inner
+    }
+}
+
+impl<const N: usize> FromStr for Digest<N> {
+    type Err = ParseHexError;
+
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        let mut buf = [0u8; N];
+        parse_hex_exact(value, &mut buf)?;
+        Ok(buf.into())
+    }
+}
+
+impl<const N: usize> ConstantTimeEq for Digest<N> {
+    fn ct_eq(&self, other: &Self) -> subtle::Choice {
+        self.inner.ct_eq(&other.inner)
+    }
+}
+
+impl<const N: usize> PartialEq for Digest<N> {
+    fn eq(&self, other: &Self) -> bool {
+        self.ct_eq(other).into()
+    }
+}
+
+impl<const N: usize> Eq for Digest<N> {}
+
+impl<'de, const N: usize> Deserialize<'de> for Digest<N> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let hex = <&str>::deserialize(deserializer)?;
+        Digest::from_str(hex).map_err(de::Error::custom)
+    }
+}
+
+impl<const N: usize> Serialize for Digest<N> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.serialize_str(&format!("{self}"))
+    }
+}