net/http: remove Content-Encoding in writeNotModified

Additional header to remove if set before calling http.ServeContent.

The API of ServeContent is that one should set Content-Encoding before calling it, if the content is encoded (e.g., compressed). But then, if content has not been modified, that header should be removed, according to RFC 7232 section 4.1.

Change-Id: If51b35b7811a4dbb19de2ddb73f40c5e68fcec7e
GitHub-Last-Rev: 53df6e73c44b63f351f7aeeb45cab82d706311eb
GitHub-Pull-Request: golang/go#50903
Reviewed-on: https://go-review.googlesource.com/c/go/+/381955
Run-TryBot: hopehook <hopehook@qq.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>

diff --git a/src/net/http/fs.go b/src/net/http/fs.go
index 7a1d5f4be5f6e229c05e451ea5423883f8fe3efb..4f144ebad2530ffb94cc1aa629a9d4fa874e5536 100644 (file)
--- a/src/net/http/fs.go
+++ b/src/net/http/fs.go
@@ -541,6 +541,7 @@ func writeNotModified(w ResponseWriter) {
        h := w.Header()
        delete(h, "Content-Type")
        delete(h, "Content-Length")
+       delete(h, "Content-Encoding")
        if h.Get("Etag") != "" {
                delete(h, "Last-Modified")
        }

diff --git a/src/net/http/fs_test.go b/src/net/http/fs_test.go
index d627dfd4be965287cb1d929ba8dc5621c02525cc..4be561cdfa1fa7864240a7e5e515db23b1a36454 100644 (file)
--- a/src/net/http/fs_test.go
+++ b/src/net/http/fs_test.go
@@ -564,6 +564,60 @@ func testServeFileWithContentEncoding(t *testing.T, h2 bool) {
        }
 }
 
+// Tests that ServeFile does not generate representation metadata when
+// file has not been modified, as per RFC 7232 section 4.1.
+func TestServeFileNotModified_h1(t *testing.T) { testServeFileNotModified(t, h1Mode) }
+func TestServeFileNotModified_h2(t *testing.T) { testServeFileNotModified(t, h2Mode) }
+func testServeFileNotModified(t *testing.T, h2 bool) {
+       defer afterTest(t)
+       cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
+               w.Header().Set("Content-Type", "application/json")
+               w.Header().Set("Content-Encoding", "foo")
+               w.Header().Set("Etag", `"123"`)
+               ServeFile(w, r, "testdata/file")
+
+               // Because the testdata is so small, it would fit in
+               // both the h1 and h2 Server's write buffers. For h1,
+               // sendfile is used, though, forcing a header flush at
+               // the io.Copy. http2 doesn't do a header flush so
+               // buffers all 11 bytes and then adds its own
+               // Content-Length. To prevent the Server's
+               // Content-Length and test ServeFile only, flush here.
+               w.(Flusher).Flush()
+       }))
+       defer cst.close()
+       req, err := NewRequest("GET", cst.ts.URL, nil)
+       if err != nil {
+               t.Fatal(err)
+       }
+       req.Header.Set("If-None-Match", `"123"`)
+       resp, err := cst.c.Do(req)
+       if err != nil {
+               t.Fatal(err)
+       }
+       b, err := io.ReadAll(resp.Body)
+       resp.Body.Close()
+       if err != nil {
+               t.Fatal("reading Body:", err)
+       }
+       if len(b) != 0 {
+               t.Errorf("non-empty body")
+       }
+       if g, e := resp.StatusCode, StatusNotModified; g != e {
+               t.Errorf("status mismatch: got %d, want %d", g, e)
+       }
+       // HTTP1 transport sets ContentLength to 0.
+       if g, e1, e2 := resp.ContentLength, int64(-1), int64(0); g != e1 && g != e2 {
+               t.Errorf("Content-Length mismatch: got %d, want %d or %d", g, e1, e2)
+       }
+       if resp.Header.Get("Content-Type") != "" {
+               t.Errorf("Content-Type present, but it should not be")
+       }
+       if resp.Header.Get("Content-Encoding") != "" {
+               t.Errorf("Content-Encoding present, but it should not be")
+       }
+}
+
 func TestServeIndexHtml(t *testing.T) {
        defer afterTest(t)