fix: use Header().Add instead of Header() for setting Vary header (#99)

- Modify middleware to add "Vary: Origin" header before applying gzip compression
- Add a new test to verify the "Vary" header is correctly set and gzip compression is applied
- Update handler to use `Header().Add` instead of `Header()` for setting "Vary" header

Signed-off-by: appleboy <[email protected]>

Author: appleboy

_example/main.go

@@ -12,10 +12,14 @@ import (
 
 func main() {
 	r := gin.Default()
-	r.Use(gzip.Gzip(
-		gzip.DefaultCompression,
-		gzip.WithExcludedPaths([]string{"/ping2"}),
-	))
+	r.Use(
+		func(c *gin.Context) {
+			c.Writer.Header().Add("Vary", "Origin")
+		},
+		gzip.Gzip(
+			gzip.DefaultCompression,
+			gzip.WithExcludedPaths([]string{"/ping2"}),
+		))
 	r.Use(func(c *gin.Context) {
 		log.Println("Request received")
 		c.Next()

gzip_test.go

@@ -59,12 +59,41 @@ func newServer() *gin.Engine {
 		c.Header("Content-Length", strconv.Itoa(len(testResponse)))
 		c.String(200, testResponse)
 	})
+	router.GET("/ping", func(c *gin.Context) {
+		c.Writer.Header().Add("Vary", "Origin")
+	}, func(c *gin.Context) {
+		c.Header("Content-Length", strconv.Itoa(len(testResponse)))
+		c.String(200, testResponse)
+	})
 	router.Any("/reverse", func(c *gin.Context) {
 		rp.ServeHTTP(c.Writer, c.Request)
 	})
 	return router
 }
 
+func TestVaryHeader(t *testing.T) {
+	req, _ := http.NewRequestWithContext(context.Background(), "GET", "/ping", nil)
+	req.Header.Add(headerAcceptEncoding, "gzip")
+
+	w := httptest.NewRecorder()
+	r := newServer()
+	r.ServeHTTP(w, req)
+
+	assert.Equal(t, 200, w.Code)
+	assert.Equal(t, "gzip", w.Header().Get(headerContentEncoding))
+	assert.Equal(t, []string{headerAcceptEncoding, "Origin"}, w.Header().Values(headerVary))
+	assert.NotEqual(t, "0", w.Header().Get("Content-Length"))
+	assert.NotEqual(t, 19, w.Body.Len())
+	assert.Equal(t, w.Header().Get("Content-Length"), fmt.Sprint(w.Body.Len()))
+
+	gr, err := gzip.NewReader(w.Body)
+	assert.NoError(t, err)
+	defer gr.Close()
+
+	body, _ := io.ReadAll(gr)
+	assert.Equal(t, testResponse, string(body))
+}
+
 func TestGzip(t *testing.T) {
 	req, _ := http.NewRequestWithContext(context.Background(), "GET", "/", nil)
 	req.Header.Add(headerAcceptEncoding, "gzip")

handler.go

@@ -85,7 +85,7 @@ func (g *gzipHandler) Handle(c *gin.Context) {
 	gz.Reset(c.Writer)
 
 	c.Header(headerContentEncoding, "gzip")
-	c.Header(headerVary, headerAcceptEncoding)
+	c.Writer.Header().Add(headerVary, headerAcceptEncoding)
 	c.Writer = &gzipWriter{c.Writer, gz}
 	defer func() {
 		if c.Writer.Size() < 0 {