Use pool for buffer

http/middleware/gzip/gzip.go

@@ -35,7 +35,7 @@ type gzipResponseWriter struct {
 	wroteBody         bool
 	minLength         int
 	minLengthExceeded bool
-	buffer            bytes.Buffer
+	buffer            *bytes.Buffer
 	code              int
 }
 
@@ -101,6 +101,7 @@ func NewWithConfig(config Config) echo.MiddlewareFunc {
 	}
 
 	pool := gzipPool(config)
+	bpool := bufferPool()
 
 	return func(next echo.HandlerFunc) echo.HandlerFunc {
 		return func(c echo.Context) error {
@@ -119,7 +120,11 @@ func NewWithConfig(config Config) echo.MiddlewareFunc {
 				}
 				rw := res.Writer
 				w.Reset(rw)
-				grw := &gzipResponseWriter{Writer: w, ResponseWriter: rw, minLength: config.MinLength}
+
+				buf := bpool.Get().(*bytes.Buffer)
+				buf.Reset()
+
+				grw := &gzipResponseWriter{Writer: w, ResponseWriter: rw, minLength: config.MinLength, buffer: buf}
 
 				defer func() {
 					if !grw.wroteBody {
@@ -141,6 +146,7 @@ func NewWithConfig(config Config) echo.MiddlewareFunc {
 						w.Reset(io.Discard)
 					}
 					w.Close()
+					bpool.Put(buf)
 					pool.Put(w)
 				}()
 
@@ -232,3 +238,12 @@ func gzipPool(config Config) sync.Pool {
 		},
 	}
 }
+
+func bufferPool() sync.Pool {
+	return sync.Pool{
+		New: func() interface{} {
+			b := &bytes.Buffer{}
+			return b
+		},
+	}
+}