From 7bde9aea068072e08c41148fc230393872d9c49c Mon Sep 17 00:00:00 2001
From: Nao Yonashiro <owan.orisano@gmail.com>
Date: Wed, 15 Dec 2021 17:15:13 +0900
Subject: [PATCH] Fixed a problem that returned wrong content-encoding when the
 gzip compressed content was empty (#1921)

Fixed a problem that returned wrong content-encoding when the gzip compressed content was empty
---
 middleware/compress.go      |  9 ++++-----
 middleware/compress_test.go | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/middleware/compress.go b/middleware/compress.go
index 6ae19745..ac6672e9 100644
--- a/middleware/compress.go
+++ b/middleware/compress.go
@@ -27,6 +27,7 @@ type (
 	gzipResponseWriter struct {
 		io.Writer
 		http.ResponseWriter
+		wroteBody bool
 	}
 )
 
@@ -78,8 +79,9 @@ func GzipWithConfig(config GzipConfig) echo.MiddlewareFunc {
 				}
 				rw := res.Writer
 				w.Reset(rw)
+				grw := &gzipResponseWriter{Writer: w, ResponseWriter: rw}
 				defer func() {
-					if res.Size == 0 {
+					if !grw.wroteBody {
 						if res.Header().Get(echo.HeaderContentEncoding) == gzipScheme {
 							res.Header().Del(echo.HeaderContentEncoding)
 						}
@@ -92,7 +94,6 @@ func GzipWithConfig(config GzipConfig) echo.MiddlewareFunc {
 					w.Close()
 					pool.Put(w)
 				}()
-				grw := &gzipResponseWriter{Writer: w, ResponseWriter: rw}
 				res.Writer = grw
 			}
 			return next(c)
@@ -101,9 +102,6 @@ func GzipWithConfig(config GzipConfig) echo.MiddlewareFunc {
 }
 
 func (w *gzipResponseWriter) WriteHeader(code int) {
-	if code == http.StatusNoContent { // Issue #489
-		w.ResponseWriter.Header().Del(echo.HeaderContentEncoding)
-	}
 	w.Header().Del(echo.HeaderContentLength) // Issue #444
 	w.ResponseWriter.WriteHeader(code)
 }
@@ -112,6 +110,7 @@ func (w *gzipResponseWriter) Write(b []byte) (int, error) {
 	if w.Header().Get(echo.HeaderContentType) == "" {
 		w.Header().Set(echo.HeaderContentType, http.DetectContentType(b))
 	}
+	w.wroteBody = true
 	return w.Writer.Write(b)
 }
 
diff --git a/middleware/compress_test.go b/middleware/compress_test.go
index d16ffca4..b62bffef 100644
--- a/middleware/compress_test.go
+++ b/middleware/compress_test.go
@@ -106,6 +106,27 @@ func TestGzipNoContent(t *testing.T) {
 	}
 }
 
+func TestGzipEmpty(t *testing.T) {
+	e := echo.New()
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.Header.Set(echo.HeaderAcceptEncoding, gzipScheme)
+	rec := httptest.NewRecorder()
+	c := e.NewContext(req, rec)
+	h := Gzip()(func(c echo.Context) error {
+		return c.String(http.StatusOK, "")
+	})
+	if assert.NoError(t, h(c)) {
+		assert.Equal(t, gzipScheme, rec.Header().Get(echo.HeaderContentEncoding))
+		assert.Equal(t, "text/plain; charset=UTF-8", rec.Header().Get(echo.HeaderContentType))
+		r, err := gzip.NewReader(rec.Body)
+		if assert.NoError(t, err) {
+			var buf bytes.Buffer
+			buf.ReadFrom(r)
+			assert.Equal(t, "", buf.String())
+		}
+	}
+}
+
 func TestGzipErrorReturned(t *testing.T) {
 	e := echo.New()
 	e.Use(Gzip())