net/http, net/http/httptest: make http2's TrailerPrefix work for http1

Go's http1 implementation originally had a mechanism to send HTTP
trailers based on pre-declaring the trailer keys whose values you'd
later let after the header was written.

http2 copied the same mechanism, but it was found to be unsufficient
for gRPC's wire protocol. A second trailer mechanism was added later
(but only to http2) for handlers that want to send a trailer without
knowing in advance they'd need to.

Copy the same mechanism back to http1 and document it.

Fixes #15754

Change-Id: I8c40d55e28b0e5b7087d3d1a904a392c56ee1f9b
Reviewed-on: https://go-review.googlesource.com/32479
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/src/net/http/clientserver_test.go b/src/net/http/clientserver_test.go
index f552424189..d01e7558dc 100644
--- a/src/net/http/clientserver_test.go
+++ b/src/net/http/clientserver_test.go
@@ -1270,3 +1270,34 @@ func testNoSniffExpectRequestBody(t *testing.T, h2 bool) {
 		t.Errorf("status code = %v; want %v", res.StatusCode, StatusUnauthorized)
 	}
 }
+
+func TestServerUndeclaredTrailers_h1(t *testing.T) { testServerUndeclaredTrailers(t, h1Mode) }
+func TestServerUndeclaredTrailers_h2(t *testing.T) { testServerUndeclaredTrailers(t, h2Mode) }
+func testServerUndeclaredTrailers(t *testing.T, h2 bool) {
+	defer afterTest(t)
+	cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
+		w.Header().Set("Foo", "Bar")
+		w.Header().Set("Trailer:Foo", "Baz")
+		w.(Flusher).Flush()
+		w.Header().Add("Trailer:Foo", "Baz2")
+		w.Header().Set("Trailer:Bar", "Quux")
+	}))
+	defer cst.close()
+	res, err := cst.c.Get(cst.ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := io.Copy(ioutil.Discard, res.Body); err != nil {
+		t.Fatal(err)
+	}
+	res.Body.Close()
+	delete(res.Header, "Date")
+	delete(res.Header, "Content-Type")
+
+	if want := (Header{"Foo": {"Bar"}}); !reflect.DeepEqual(res.Header, want) {
+		t.Errorf("Header = %#v; want %#v", res.Header, want)
+	}
+	if want := (Header{"Foo": {"Baz", "Baz2"}, "Bar": {"Quux"}}); !reflect.DeepEqual(res.Trailer, want) {
+		t.Errorf("Trailer = %#v; want %#v", res.Trailer, want)
+	}
+}