Add Crc checksum validation for gzip::header::Parser (Nullus157#432)

Ensure the header is valid, [gzip
wikipedia](https://en.wikipedia.org/wiki/Gzip) says that:

> Two least significant bytes of the
[CRC-32](https://en.wikipedia.org/wiki/CRC-32) (ISO 3309) of all bytes
in the gzip file up to (not including) this field.

---------

Signed-off-by: Jiahao XU <[email protected]>

Author: NobodyXu

crates/compression-codecs/src/gzip/decoder.rs

@@ -64,7 +64,8 @@ impl GzipDecoder {
         loop {
             match &mut self.state {
                 State::Header(parser) => {
-                    if parser.input(input)?.is_some() {
+                    if parser.input(&mut self.crc, input)?.is_some() {
+                        self.crc.reset();
                         self.state = State::Decoding;
                     }
                 }

crates/compression-codecs/src/gzip/header.rs

@@ -1,4 +1,5 @@
 use compression_core::util::PartialBuffer;
+use flate2::Crc;
 use std::io;
 
 #[derive(Debug, Default)]
@@ -61,18 +62,39 @@ impl Header {
     }
 }
 
+fn consume_input(crc: &mut Crc, n: usize, input: &mut PartialBuffer<&[u8]>) {
+    crc.update(&input.unwritten()[..n]);
+    input.advance(n);
+}
+
+fn consume_cstr(crc: &mut Crc, input: &mut PartialBuffer<&[u8]>) -> Option<()> {
+    if let Some(len) = memchr::memchr(0, input.unwritten()) {
+        consume_input(crc, len + 1, input);
+        Some(())
+    } else {
+        consume_input(crc, input.unwritten().len(), input);
+        None
+    }
+}
+
 impl Parser {
-    pub(super) fn input(&mut self, input: &mut PartialBuffer<&[u8]>) -> io::Result<Option<Header>> {
+    pub(super) fn input(
+        &mut self,
+        crc: &mut Crc,
+        input: &mut PartialBuffer<&[u8]>,
+    ) -> io::Result<Option<Header>> {
         loop {
             match &mut self.state {
                 State::Fixed(data) => {
                     data.copy_unwritten_from(input);
 
                     if data.unwritten().is_empty() {
-                        self.header = Header::parse(&data.take().into_inner())?;
+                        let data = data.get_mut();
+                        crc.update(data);
+                        self.header = Header::parse(data)?;
                         self.state = State::ExtraLen(<_>::default());
                     } else {
-                        return Ok(None);
+                        break Ok(None);
                     }
                 }
 
@@ -85,22 +107,24 @@ impl Parser {
                     data.copy_unwritten_from(input);
 
                     if data.unwritten().is_empty() {
-                        let len = u16::from_le_bytes(data.take().into_inner());
+                        let data = data.get_mut();
+                        crc.update(data);
+                        let len = u16::from_le_bytes(*data);
                         self.state = State::Extra(len.into());
                     } else {
-                        return Ok(None);
+                        break Ok(None);
                     }
                 }
 
                 State::Extra(bytes_to_consume) => {
                     let n = input.unwritten().len().min(*bytes_to_consume);
                     *bytes_to_consume -= n;
-                    input.advance(n);
+                    consume_input(crc, n, input);
 
                     if *bytes_to_consume == 0 {
                         self.state = State::Filename;
                     } else {
-                        return Ok(None);
+                        break Ok(None);
                     }
                 }
 
@@ -110,13 +134,11 @@ impl Parser {
                         continue;
                     }
 
-                    if let Some(len) = memchr::memchr(0, input.unwritten()) {
-                        input.advance(len + 1);
-                        self.state = State::Comment;
-                    } else {
-                        input.advance(input.unwritten().len());
-                        return Ok(None);
+                    if consume_cstr(crc, input).is_none() {
+                        break Ok(None);
                     }
+
+                    self.state = State::Comment;
                 }
 
                 State::Comment => {
@@ -125,35 +147,43 @@ impl Parser {
                         continue;
                     }
 
-                    if let Some(len) = memchr::memchr(0, input.unwritten()) {
-                        input.advance(len + 1);
-                        self.state = State::Crc(<_>::default());
-                    } else {
-                        input.advance(input.unwritten().len());
-                        return Ok(None);
+                    if consume_cstr(crc, input).is_none() {
+                        break Ok(None);
                     }
+
+                    self.state = State::Crc(<_>::default());
                 }
 
                 State::Crc(data) => {
+                    let header = std::mem::take(&mut self.header);
+
                     if !self.header.flags.crc {
                         self.state = State::Done;
-                        return Ok(Some(std::mem::take(&mut self.header)));
+                        break Ok(Some(header));
                     }
 
                     data.copy_unwritten_from(input);
 
-                    if data.unwritten().is_empty() {
+                    break if data.unwritten().is_empty() {
+                        let data = data.take().into_inner();
                         self.state = State::Done;
-                        return Ok(Some(std::mem::take(&mut self.header)));
+                        let checksum = crc.sum().to_le_bytes();
+
+                        if data == checksum[..2] {
+                            Ok(Some(header))
+                        } else {
+                            Err(io::Error::new(
+                                io::ErrorKind::InvalidData,
+                                "CRC computed for header does not match",
+                            ))
+                        }
                     } else {
-                        return Ok(None);
-                    }
+                        Ok(None)
+                    };
                 }
 
-                State::Done => {
-                    return Err(io::Error::other("parser used after done"));
-                }
-            };
+                State::Done => break Err(io::Error::other("parser used after done")),
+            }
         }
     }
 }