feat(binary): add git binary patch support

.github/workflows/ci.yml

@@ -23,13 +23,14 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        rust: [stable, beta, nightly, 1.70.0]
+        rust: [stable, beta, nightly, 1.75.0]
 
     steps:
       - uses: actions/checkout@v6
       - run: rustup toolchain install ${{ matrix.rust }} --profile minimal
       - run: cargo +${{ matrix.rust }} check --all-targets --all-features
       - run: cargo +${{ matrix.rust }} test
+      - run: cargo +${{ matrix.rust }} test -F binary
 
   lint:
     runs-on: ubuntu-latest

.github/workflows/replay.yml

@@ -67,7 +67,7 @@ jobs:
             exit 1
           fi
       - run: rustup toolchain install stable --profile minimal
-      - run: cargo test --release --test replay -- --ignored --nocapture
+      - run: cargo test --release --test replay -F binary -- --ignored --nocapture
         env:
           DIFFY_TEST_REPO: ${{ inputs.repo_url == '' && '.' || 'target/test-repo' }}
           DIFFY_TEST_COMMITS: ${{ inputs.commits }}

Cargo.toml

@@ -9,14 +9,16 @@ repository = "https://github.com/bmwill/diffy"
 readme = "README.md"
 keywords = ["diff", "patch", "merge"]
 categories = ["text-processing"]
-rust-version = "1.70.0"
+rust-version = "1.75.0"
 edition = "2021"
 
 [features]
+binary = ["dep:flate2"]
 color = ["dep:anstyle"]
 
 [dependencies]
 anstyle = { version = "1.0.13", optional = true }
+flate2 = { version = "1.1.9", optional = true, default-features = false, features = ["zlib-rs"] }
 
 [dev-dependencies]
 rayon = "1.10.0"
@@ -25,3 +27,11 @@ snapbox = { version = "0.6.24", features = ["dir"] }
 [[example]]
 name = "patch_formatter"
 required-features = ["color"]
+
+[[test]]
+name = "compat"
+required-features = ["binary"]
+
+[[test]]
+name = "replay"
+required-features = ["binary"]

deny.toml

@@ -91,6 +91,7 @@ ignore = [
 allow = [
     "MIT",
     "Apache-2.0",
+    "Zlib",
     #"Apache-2.0 WITH LLVM-exception",
 ]
 # The confidence threshold for detecting a license from license text.

src/binary/base85.rs

@@ -0,0 +1,227 @@
+//! Base85 encoding and decoding using the character set defined in [RFC 1924].
+//!
+//! ## References
+//!
+//! * [RFC 1924]
+//! * [Wikipedia: Ascii85 § RFC 1924 version](https://en.wikipedia.org/wiki/Ascii85#RFC_1924_version)
+//!
+//! [RFC 1924]: https://datatracker.ietf.org/doc/html/rfc1924
+
+use std::fmt;
+
+/// Base85 character set (RFC 1924).
+const ALPHABET: &[u8; 85] = b"0123456789\
+    ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz\
+    !#$%&()*+-;<=>?@^_`{|}~";
+
+/// Pre-computed lookup table for Base85 decoding.
+///
+/// Maps ASCII byte value → digit value or `0xFF` for invalid characters.
+/// This provides O(1) lookup.
+const TABLE: [u8; 256] = {
+    let mut table = [0xFFu8; 256];
+    let mut i = 0usize;
+    while i < 85 {
+        table[ALPHABET[i] as usize] = i as u8;
+        i += 1;
+    }
+    table
+};
+
+/// Error type for Base85 operations.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Base85Error {
+    /// Invalid character that is not in RFC 1924 alphabet.
+    InvalidCharacter(char),
+    /// Invalid input length for the operation.
+    InvalidLength,
+}
+
+impl fmt::Display for Base85Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Base85Error::InvalidCharacter(c) => write!(f, "invalid base85 character: {:?}", c),
+            Base85Error::InvalidLength => write!(f, "invalid input length"),
+        }
+    }
+}
+
+impl std::error::Error for Base85Error {}
+
+/// Decodes a Base85 string to the provided output.
+///
+/// ## Limitations
+///
+/// The input length must be a multiple of 5.
+///
+/// This function does not handle padding for partial chunks.
+/// When decoding data where the original byte count isn't a multiple of 4,
+/// callers must handle truncation at a higher level.
+/// For example, via a length indicator in Git binary patch.
+pub fn decode_into(input: &[u8], output: &mut impl Extend<u8>) -> Result<(), Base85Error> {
+    if input.len() % 5 != 0 {
+        return Err(Base85Error::InvalidLength);
+    }
+
+    // TODO: Use `as_chunks::<5>()` when MSRV >= 1.88
+    for chunk in input.chunks_exact(5) {
+        let mut value: u32 = 0;
+        for &byte in chunk {
+            let digit = TABLE[byte as usize];
+            if digit == 0xFF {
+                return Err(Base85Error::InvalidCharacter(byte as char));
+            }
+            value = value * 85 + digit as u32;
+        }
+
+        output.extend(value.to_be_bytes());
+    }
+
+    Ok(())
+}
+
+/// Encodes bytes in Base85 to the provided output.
+///
+/// ## Limitations
+///
+/// The input length must be a multiple of 4.
+///
+/// This function does not handle padding for partial chunks.
+/// Callers encoding data where the byte count isn't a multiple of 4
+/// must handle padding at a higher level.
+/// For example, via a length indicator in Git binary patch format.
+#[allow(dead_code)] // will be used for patch formatting
+pub fn encode_into(input: &[u8], output: &mut impl Extend<char>) -> Result<(), Base85Error> {
+    if input.len() % 4 != 0 {
+        return Err(Base85Error::InvalidLength);
+    }
+
+    // TODO: Use `as_chunks::<4>()` when MSRV >= 1.88
+    for chunk in input.chunks_exact(4) {
+        let mut value = u32::from_be_bytes(chunk.try_into().unwrap());
+
+        // Extract 5 base85 digits (least to most significant order)
+        let mut digits = [0u8; 5];
+        for digit in digits.iter_mut().rev() {
+            *digit = ALPHABET[(value % 85) as usize];
+            value /= 85;
+        }
+        output.extend(digits.iter().map(|&b| b as char));
+    }
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn decode(input: &str) -> Result<Vec<u8>, Base85Error> {
+        let mut result = Vec::with_capacity((input.len() / 5) * 4);
+        decode_into(input.as_bytes(), &mut result)?;
+        Ok(result)
+    }
+
+    fn encode(input: &[u8]) -> Result<String, Base85Error> {
+        let mut result = String::with_capacity((input.len() / 4) * 5);
+        encode_into(input, &mut result)?;
+        Ok(result)
+    }
+
+    const TEST_VECTORS: &[(&[u8], &str)] = &[
+        (b"", ""),
+        (&[0x00, 0x00, 0x00, 0x00], "00000"),
+        (&[0xff, 0xff, 0xff, 0xff], "|NsC0"),
+        // Rust ecosystem phrases
+        (b"Rust", "Qgw55"),
+        (b"Fearless concurrency", "MrC1gY-MwEAY*TCV|8+JWo~16"),
+        (b"memory safe!", "ZDnn5a(N(gVP<6^"),
+        (b"blazing fast", "Vr*f0X>MmAW?^%5"),
+        (
+            b"zero-cost abstraction!??",
+            "dS!BNEn{zUbRc13b98cHV{~b6ZXrKE",
+        ),
+    ];
+
+    #[test]
+    fn table_covers_all_alphabet_chars() {
+        for (i, &c) in ALPHABET.iter().enumerate() {
+            assert_eq!(
+                TABLE[c as usize], i as u8,
+                "mismatch for char '{}' at index {}",
+                c as char, i
+            );
+        }
+    }
+
+    #[test]
+    fn table_rejects_invalid_chars() {
+        let invalid_chars = b" \t\n\r\"'\\[],:";
+        for &c in invalid_chars {
+            assert_eq!(
+                TABLE[c as usize], 0xFF,
+                "char '{}' should be invalid",
+                c as char
+            );
+        }
+    }
+
+    #[test]
+    fn decode_test_vectors() {
+        for (bytes, encoded) in TEST_VECTORS {
+            let result = decode(encoded).unwrap();
+            assert_eq!(&result, *bytes, "decode({:?}) failed", encoded);
+        }
+    }
+
+    #[test]
+    fn encode_test_vectors() {
+        for (bytes, encoded) in TEST_VECTORS {
+            let result = encode(bytes).unwrap();
+            assert_eq!(result, *encoded, "encode({:?}) failed", bytes);
+        }
+    }
+
+    #[test]
+    fn decode_invalid_length() {
+        assert!(matches!(decode("0000"), Err(Base85Error::InvalidLength)));
+        assert!(matches!(decode("000"), Err(Base85Error::InvalidLength)));
+        assert!(matches!(decode("00"), Err(Base85Error::InvalidLength)));
+        assert!(matches!(decode("0"), Err(Base85Error::InvalidLength)));
+    }
+
+    #[test]
+    fn decode_invalid_character() {
+        assert!(matches!(
+            decode("0000 "),
+            Err(Base85Error::InvalidCharacter(' '))
+        ));
+        assert!(matches!(
+            decode("0000\""),
+            Err(Base85Error::InvalidCharacter('"'))
+        ));
+    }
+
+    #[test]
+    fn encode_invalid_length() {
+        assert!(matches!(encode(&[0]), Err(Base85Error::InvalidLength)));
+        assert!(matches!(encode(&[0, 0]), Err(Base85Error::InvalidLength)));
+        assert!(matches!(
+            encode(&[0, 0, 0]),
+            Err(Base85Error::InvalidLength)
+        ));
+        assert!(matches!(
+            encode(&[0, 0, 0, 0, 0]),
+            Err(Base85Error::InvalidLength)
+        ));
+    }
+
+    #[test]
+    fn round_trip() {
+        for (bytes, _) in TEST_VECTORS {
+            let encoded = encode(bytes).unwrap();
+            let decoded = decode(&encoded).unwrap();
+            assert_eq!(&decoded, *bytes, "round-trip failed for {:?}", bytes);
+        }
+    }
+}