Optimize GzipEncoder to not allocate for header and footer (#431)

Fixed #397

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

Author: NobodyXu

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

@@ -5,9 +5,9 @@ use std::io;
 
 #[derive(Debug)]
 enum State {
-    Header(PartialBuffer<Vec<u8>>),
+    Header(PartialBuffer<[u8; 10]>),
     Encoding,
-    Footer(PartialBuffer<Vec<u8>>),
+    Footer(PartialBuffer<[u8; 8]>),
     Done,
 }
 
@@ -18,7 +18,7 @@ pub struct GzipEncoder {
     state: State,
 }
 
-fn header(level: Compression) -> Vec<u8> {
+fn header(level: Compression) -> [u8; 10] {
     let level_byte = if level.level() >= Compression::best().level() {
         0x02
     } else if level.level() <= Compression::fast().level() {
@@ -27,7 +27,7 @@ fn header(level: Compression) -> Vec<u8> {
         0x00
     };
 
-    vec![0x1f, 0x8b, 0x08, 0, 0, 0, 0, 0, level_byte, 0xff]
+    [0x1f, 0x8b, 0x08, 0, 0, 0, 0, 0, level_byte, 0xff]
 }
 
 impl GzipEncoder {
@@ -39,11 +39,11 @@ impl GzipEncoder {
         }
     }
 
-    fn footer(&mut self) -> Vec<u8> {
-        let mut output = Vec::with_capacity(8);
+    fn footer(&mut self) -> [u8; 8] {
+        let mut output = [0; 8];
 
-        output.extend(&self.crc.sum().to_le_bytes());
-        output.extend(&self.crc.amount().to_le_bytes());
+        output[..4].copy_from_slice(&self.crc.sum().to_le_bytes());
+        output[4..].copy_from_slice(&self.crc.amount().to_le_bytes());
 
         output
     }