Optimize GzipDecoder (#430)

* Optimize GzipDecoder

 - no heap allocation for footer which has fixed 8-byte size
 - do not store unused header
 - reset CrC instead of reassigning a new one
 - optimize check_crc: rm unnecessary size check

Signed-off-by: Jiahao XU <30436523+NobodyXu@users.noreply.github.com>

* Fix GzipDecoder

Signed-off-by: Jiahao XU <30436523+NobodyXu@users.noreply.github.com>

---------

Signed-off-by: Jiahao XU <30436523+NobodyXu@users.noreply.github.com>

Author: NobodyXu

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

@@ -1,4 +1,4 @@
-use super::header::{self, Header};
+use super::header;
 use crate::{DecodeV2, FlateDecoder};
 use compression_core::util::{PartialBuffer, WriteBuffer};
 use flate2::Crc;
@@ -8,7 +8,7 @@ use std::io::{Error, ErrorKind, Result};
 enum State {
     Header(header::Parser),
     Decoding,
-    Footer(PartialBuffer<Vec<u8>>),
+    Footer(PartialBuffer<[u8; 8]>),
     Done,
 }
 
@@ -17,17 +17,9 @@ pub struct GzipDecoder {
     inner: FlateDecoder,
     crc: Crc,
     state: State,
-    header: Header,
 }
 
-fn check_footer(crc: &Crc, input: &[u8]) -> Result<()> {
-    if input.len() < 8 {
-        return Err(Error::new(
-            ErrorKind::InvalidData,
-            "Invalid gzip footer length",
-        ));
-    }
-
+fn check_footer(crc: &Crc, input: &[u8; 8]) -> Result<()> {
     let crc_sum = crc.sum().to_le_bytes();
     let bytes_read = crc.amount().to_le_bytes();
 
@@ -54,7 +46,6 @@ impl Default for GzipDecoder {
             inner: FlateDecoder::new(false),
             crc: Crc::new(),
             state: State::Header(header::Parser::default()),
-            header: Header::default(),
         }
     }
 }
@@ -73,8 +64,7 @@ impl GzipDecoder {
         loop {
             match &mut self.state {
                 State::Header(parser) => {
-                    if let Some(header) = parser.input(input)? {
-                        self.header = header;
+                    if parser.input(input)?.is_some() {
                         self.state = State::Decoding;
                     }
                 }
@@ -92,16 +82,16 @@ impl GzipDecoder {
                     let done = res?;
 
                     if done {
-                        self.state = State::Footer(vec![0; 8].into())
+                        self.state = State::Footer([0; 8].into());
                     }
                 }
 
                 State::Footer(footer) => {
                     footer.copy_unwritten_from(input);
 
                     if footer.unwritten().is_empty() {
-                        check_footer(&self.crc, footer.written())?;
-                        self.state = State::Done
+                        check_footer(&self.crc, footer.get_mut())?;
+                        self.state = State::Done;
                     }
                 }
 
@@ -122,9 +112,8 @@ impl GzipDecoder {
 impl DecodeV2 for GzipDecoder {
     fn reinit(&mut self) -> Result<()> {
         self.inner.reinit()?;
-        self.crc = Crc::new();
+        self.crc.reset();
         self.state = State::Header(header::Parser::default());
-        self.header = Header::default();
         Ok(())
     }