No content-type on no body response code (#1011)

* No content-type on no body response code

Author: juliens

gzhttp/compress.go

@@ -324,6 +324,20 @@ func (w *GzipResponseWriter) init() {
 w.gw = w.gwFactory.New(w.ResponseWriter, w.level)
 }
 
+// bodyAllowedForStatus reports whether a given response status code
+// permits a body. See RFC 7230, section 3.3.
+func bodyAllowedForStatus(status int) bool {
+switch {
+case status >= 100 && status <= 199:
+return false
+case status == 204:
+return false
+case status == 304:
+return false
+}
+return true
+}
+
 // Close will close the gzip.Writer and will put it back in the gzipWriterPool.
 func (w *GzipResponseWriter) Close() error {
 if w.ignore {
@@ -340,7 +354,7 @@ func (w *GzipResponseWriter) Close() error {
 
 // Handles the intended case of setting a nil Content-Type (as for http/server or http/fs)
 // Set the header only if the key does not exist
-if _, ok := w.Header()[contentType]; w.setContentType && !ok {
+if _, ok := w.Header()[contentType]; bodyAllowedForStatus(w.code) && w.setContentType && !ok {
 w.Header().Set(contentType, ct)
 }
 }

gzhttp/compress_test.go

@@ -662,7 +662,7 @@ func TestFlushAfterWrite3(t *testing.T) {
 }
 handler := gz(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
 rw.WriteHeader(http.StatusOK)
-//rw.Write(nil)
+// rw.Write(nil)
 rw.(http.Flusher).Flush()
 }))
 r := httptest.NewRequest(http.MethodGet, "/", nil)
@@ -1598,6 +1598,25 @@ var sniffTests = []struct {
 {"Incorrect RAR v5+", []byte("Rar \x1A\x07\x01\x00"), "application/octet-stream"},
 }
 
+func TestNoContentTypeWhenNoContent(t *testing.T) {
+handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+w.WriteHeader(http.StatusNoContent)
+})
+
+wrapper, err := NewWrapper()
+assertNil(t, err)
+
+req, _ := http.NewRequest("GET", "/", nil)
+req.Header.Set("Accept-Encoding", "gzip")
+resp := httptest.NewRecorder()
+wrapper(handler).ServeHTTP(resp, req)
+res := resp.Result()
+
+assertEqual(t, http.StatusNoContent, res.StatusCode)
+assertEqual(t, "", res.Header.Get("Content-Type"))
+
+}
+
 func TestContentTypeDetect(t *testing.T) {
 for _, tt := range sniffTests {
 t.Run(tt.desc, func(t *testing.T) {