optimise: use byteBuffer pool in decompression

pkg/kgo/compression.go

@@ -255,38 +255,43 @@ type zstdDecoder struct {
 }
 
 func (d *decompressor) decompress(src []byte, codec byte) ([]byte, error) {
-	switch codecType(codec) {
-	case codecNone:
+	// Early return in case there is no compression
+	compCodec := codecType(codec)
+	if compCodec == codecNone {
 		return src, nil
+	}
+	out := byteBuffers.Get().(*bytes.Buffer)
+	out.Reset()
+	defer byteBuffers.Put(out)
+
+	switch compCodec {
 	case codecGzip:
 		ungz := d.ungzPool.Get().(*gzip.Reader)
 		defer d.ungzPool.Put(ungz)
 		if err := ungz.Reset(bytes.NewReader(src)); err != nil {
 			return nil, err
 		}
-		out := new(bytes.Buffer)
 		if _, err := io.Copy(out, ungz); err != nil {
 			return nil, err
 		}
-		return out.Bytes(), nil
+		return append([]byte(nil), out.Bytes()...), nil
 	case codecSnappy:
 		if len(src) > 16 && bytes.HasPrefix(src, xerialPfx) {
 			return xerialDecode(src)
 		}
-		return s2.Decode(nil, src)
+		return s2.Decode(out.Bytes(), src)
 	case codecLZ4:
 		unlz4 := d.unlz4Pool.Get().(*lz4.Reader)
 		defer d.unlz4Pool.Put(unlz4)
 		unlz4.Reset(bytes.NewReader(src))
-		out := new(bytes.Buffer)
 		if _, err := io.Copy(out, unlz4); err != nil {
 			return nil, err
 		}
-		return out.Bytes(), nil
+		return append([]byte(nil), out.Bytes()...), nil
 	case codecZstd:
 		unzstd := d.unzstdPool.Get().(*zstdDecoder)
 		defer d.unzstdPool.Put(unzstd)
-		return unzstd.inner.DecodeAll(src, nil)
+		return unzstd.inner.DecodeAll(src, out.Bytes())
 	default:
 		return nil, errors.New("unknown compression codec")
 	}