static work

src/lib.rs

@@ -1,3 +1,5 @@
+use std::ffi::CStr;
+
 struct Bitstream<'a> {
     data: &'a [u8],
     pos_bit: usize,
@@ -9,15 +11,18 @@ impl Bitstream<'_> {
 
         let mut result = 0;
 
+        let mut read = 0;
+
         while len > 0 {
             if self.data.is_empty() {
                 return Err(Error::Incomplete);
             }
 
             let to_read_from_current_byte = std::cmp::min(len % 8, 8 - self.pos_bit);
-            result <<= to_read_from_current_byte;
-            result |=
-                ((self.data[0] >> self.pos_bit) & ((1 << to_read_from_current_byte) - 1)) as u16;
+            result |= (((self.data[0] >> self.pos_bit) & ((1 << to_read_from_current_byte) - 1))
+                as u16)
+                << read;
+            read += to_read_from_current_byte;
             len -= to_read_from_current_byte;
             self.pos_bit += to_read_from_current_byte;
 
@@ -235,11 +240,78 @@ impl HuffmanTree {
     }
 }
 
+#[derive(Debug)]
+pub enum GzipError {
+    InvalidHeader,
+    UnexpectedHeaderValue {
+        value: u8,
+        expected: u8,
+        kind: &'static str,
+    },
+    Deflate(Error),
+}
+
+pub fn inflate_gzip(data: &[u8], out: &mut Vec<u8>) -> Result<(), GzipError> {
+    if data.len() < 10 {
+        return Err(GzipError::InvalidHeader);
+    }
+    if data[0] != 31 {
+        return Err(GzipError::UnexpectedHeaderValue {
+            value: data[0],
+            expected: 31,
+            kind: "ID",
+        });
+    }
+    if data[1] != 139 {
+        return Err(GzipError::UnexpectedHeaderValue {
+            value: data[1],
+            expected: 31,
+            kind: "ID",
+        });
+    }
+    if data[2] != 8 {
+        return Err(GzipError::UnexpectedHeaderValue {
+            value: data[2],
+            expected: 8,
+            kind: "compression method",
+        });
+    }
+
+    let flg = data[3];
+
+    if flg != 8 && flg != 0 {
+        return Err(GzipError::UnexpectedHeaderValue {
+            value: flg,
+            expected: 8,
+            kind: "FLG",
+        });
+    }
+
+    let mut data_start = 10;
+
+    if flg & 0b1000 != 0 {
+        let fname =
+            CStr::from_bytes_until_nul(&data[10..]).map_err(|_| GzipError::InvalidHeader)?;
+        data_start += fname.count_bytes() + 1;
+    }
+
+    let blocks = &data.get((data_start)..).ok_or(GzipError::InvalidHeader)?;
+    let blocks = &blocks
+        .get(..(blocks.len() - 8))
+        .ok_or(GzipError::InvalidHeader)?; // crc32 and isize
+
+    inflate(blocks, out).map_err(GzipError::Deflate)?;
+
+    Ok(())
+}
+
 #[derive(Debug)]
 pub enum Error {
     ReservedBlockType,
     Incomplete,
     InvalidCode,
+    InvalidDistance,
+    InvalidLength,
 }
 
 // https://datatracker.ietf.org/doc/html/rfc1951
@@ -347,10 +419,6 @@ pub fn inflate(data: &[u8], out: &mut Vec<u8>) -> Result<(), Error> {
                         let mut compute_value =
                             |first_code, extra_bits_amount, value_start| -> Result<u16, Error> {
                                 assert_eq!(extra_bits_amount, 3);
-                                dbg!(data.read_bits(1).unwrap());
-                                dbg!(data.read_bits(1).unwrap());
-                                dbg!(data.read_bits(1).unwrap());
-                                std::process::exit(1);
 
                                 // TODO: read_bits is broken (i suspect the byte parts are reversed)
 
@@ -399,7 +467,19 @@ pub fn inflate(data: &[u8], out: &mut Vec<u8>) -> Result<(), Error> {
                             _ => return Err(Error::InvalidCode),
                         }?;
 
-                        dbg!((length, dist_value, distance));
+                        let base = out
+                            .len()
+                            .checked_sub(distance as usize)
+                            .ok_or(Error::InvalidDistance)?;
+
+                        let length = length as usize;
+                        let end = base + length;
+
+                        if end >= out.len() {
+                            return Err(Error::InvalidLength);
+                        }
+
+                        out.extend_from_within(base..end);
                     }
                     286.. => return Err(Error::InvalidCode),
                 }
@@ -416,20 +496,42 @@ pub fn inflate(data: &[u8], out: &mut Vec<u8>) -> Result<(), Error> {
 
 #[cfg(test)]
 mod tests {
+    mod helpers {
         use crate::HuffmanTree;
 
         #[test]
-    fn bitstream() {
-        let bytes = [0b110_010_01_u8, 0b010_111_01];
-        let mut stream = super::Bitstream {
+        fn bitstream_single() {
+            let bytes = [0b10010_u8];
+            let mut stream = crate::Bitstream {
                 data: &bytes,
                 pos_bit: 0,
             };
-        assert_eq!(stream.read_bits(2).unwrap(), 0b01);
-        assert_eq!(stream.read_bits(3).unwrap(), 0b010);
-        assert_eq!(stream.read_bits(5).unwrap(), 0b11001);
-        assert_eq!(stream.read_bits(3).unwrap(), 0b111);
-        assert_eq!(stream.read_bits(3).unwrap(), 0b010);
+            assert_eq!(stream.read_bits(1).unwrap(), 0);
+            assert_eq!(stream.read_bits(1).unwrap(), 1);
+            assert_eq!(stream.read_bits(1).unwrap(), 0);
+            assert_eq!(stream.read_bits(1).unwrap(), 0);
+            assert_eq!(stream.read_bits(1).unwrap(), 1);
+        }
+
+        #[test]
+        fn bitstream_extra_bits() {
+            let bytes = [0b1110_u8];
+            let mut stream = crate::Bitstream {
+                data: &bytes,
+                pos_bit: 0,
+            };
+            assert_eq!(stream.read_bits(4).unwrap(), 0b1110);
+        }
+
+        #[test]
+        fn bitstream_extra_bits_byte_overlap() {
+            let bytes = [0b10_000000, 0b000000_11];
+            let mut stream = crate::Bitstream {
+                data: &bytes,
+                pos_bit: 0,
+            };
+            stream.read_bits(6).unwrap();
+            assert_eq!(stream.read_bits(4).unwrap(), 0b1110);
         }
 
         #[test]
@@ -438,3 +540,31 @@ mod tests {
             HuffmanTree::from_lengths(&lengths);
         }
     }
+
+    mod decode {
+        #[test]
+        fn cargo_toml_gzip() {
+            let data = [
+  0x1f, 0x8b, 0x08, 0x08, 0x7f, 0x27, 0xb4, 0x68, 0x00, 0x03, 0x43, 0x61,
+  0x72, 0x67, 0x6f, 0x2e, 0x74, 0x6f, 0x6d, 0x6c, 0x00, 0x8b, 0x2e, 0x48,
+  0x4c, 0xce, 0x4e, 0x4c, 0x4f, 0x8d, 0xe5, 0xca, 0x4b, 0xcc, 0x4d, 0x55,
+  0xb0, 0x55, 0x50, 0xaa, 0x2a, 0x4f, 0x2d, 0x4a, 0xcf, 0xc9, 0x54, 0xe2,
+  0x2a, 0x4b, 0x2d, 0x2a, 0xce, 0xcc, 0xcf, 0x03, 0x89, 0x19, 0xe8, 0x19,
+  0xea, 0x19, 0x28, 0x71, 0xa5, 0xa6, 0x64, 0x96, 0x40, 0x45, 0x8c, 0x0c,
+  0x8c, 0x4c, 0x94, 0xb8, 0xb8, 0xa2, 0x53, 0x52, 0x0b, 0x52, 0xf3, 0x52,
+  0x52, 0xf3, 0x92, 0x33, 0x53, 0x8b, 0x63, 0xb9, 0x00, 0x5f, 0x81, 0x28,
+  0x59, 0x4e, 0x00, 0x00, 0x00
+            ];
+            let mut out = Vec::new();
+            crate::inflate_gzip(&data, &mut out).unwrap();
+            let out = String::from_utf8(out).unwrap();
+            assert_eq!(out, r#"[package]
+name = "zwergli"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+"#)
+        }
+    }
+}

src/main.rs

@@ -1,31 +1,16 @@
-use std::ffi::CStr;
-
 fn main() {
-    let gz = std::env::args().nth(1).expect("must provide a cli argument");
+    let gz = std::env::args()
+        .nth(1)
+        .expect("must provide a cli argument");
     let gz = std::fs::read(gz).unwrap();
 
     assert_eq!(gz[0], 31, "ID");
     assert_eq!(gz[1], 139, "ID");
     assert_eq!(gz[2], 8, "compression method");
 
-    let flg = gz[3];
+    let mut out: Vec<u8> = Vec::new();
 
-    assert!(flg == 8 || flg == 0); // only FLG.FNAME
-
-    let mut data_start = 10;
-
-    if flg & 0b1000 != 0 {
-        let fname = CStr::from_bytes_until_nul(&gz[10..]).unwrap();
-        dbg!(fname);
-        data_start += fname.count_bytes() + 1;
-    }
-
-    let blocks = &gz[(data_start)..];
-    let blocks = &blocks[..(blocks.len() - 8)]; // crc32 and isize
-
-    let mut out = Vec::new();
-
-    zwergli::inflate(blocks, &mut out);
+    zwergli::inflate_gzip(&gz, &mut out).unwrap();
 
     dbg!(String::from_utf8(out)).ok();
 }