net/http: update bundled http2, fix Transport memory leak

Updates x/net/http2 to git rev 644ffc for three CLs since the last update:

http2: don't add *Response to activeRes in Transport on Headers.END_STREAM
https://golang.org/cl/19134

http2: add mechanism to send undeclared Trailers mid handler
https://golang.org/cl/19131

http2: remove unused variable
https://golang.org/cl/18936

The first in the list above is the main fix that's necessary. The
other are two are in the git history but along for the cmd/bundle
ride. The middle CL is well-tested, small (mostly comments),
non-tricky, and almost never seen (since nobody really uses Trailers).
The final CL is just deleting an unused global variable.

Fixes #14084 again (with more tests)

Change-Id: Iac51350acee9c51d32bf7779d57e9d5a5482b928
Reviewed-on: https://go-review.googlesource.com/19135
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

src/net/http/clientserver_test.go

@@ -1001,13 +1001,17 @@ func TestTransportDiscardsUnneededConns(t *testing.T) {
 }
 
 // tests that Transport doesn't retain a pointer to the provided request.
-func TestTransportGCRequest_h1(t *testing.T) { testTransportGCRequest(t, h1Mode) }
-func TestTransportGCRequest_h2(t *testing.T) { testTransportGCRequest(t, h2Mode) }
-func testTransportGCRequest(t *testing.T, h2 bool) {
+func TestTransportGCRequest_Body_h1(t *testing.T)   { testTransportGCRequest(t, h1Mode, true) }
+func TestTransportGCRequest_Body_h2(t *testing.T)   { testTransportGCRequest(t, h2Mode, true) }
+func TestTransportGCRequest_NoBody_h1(t *testing.T) { testTransportGCRequest(t, h1Mode, false) }
+func TestTransportGCRequest_NoBody_h2(t *testing.T) { testTransportGCRequest(t, h2Mode, false) }
+func testTransportGCRequest(t *testing.T, h2, body bool) {
 	defer afterTest(t)
 	cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
 		ioutil.ReadAll(r.Body)
-		io.WriteString(w, "Hello.")
+		if body {
+			io.WriteString(w, "Hello.")
+		}
 	}))
 	defer cst.close()
 

src/net/http/h2_bundle.go

@@ -2851,8 +2851,6 @@ func (sc *http2serverConn) logf(format string, args ...interface{}) {
 	}
 }
 
-var http2uintptrType = reflect.TypeOf(uintptr(0))
-
 // errno returns v's underlying uintptr, else 0.
 //
 // TODO: remove this helper function once http2 can use build
@@ -4220,7 +4218,9 @@ func (rws *http2responseWriterState) declareTrailer(k string) {
 
 		return
 	}
-	rws.trailers = append(rws.trailers, k)
+	if !http2strSliceContains(rws.trailers, k) {
+		rws.trailers = append(rws.trailers, k)
+	}
 }
 
 // writeChunk writes chunks from the bufio.Writer. But because
@@ -4288,6 +4288,10 @@ func (rws *http2responseWriterState) writeChunk(p []byte) (n int, err error) {
 		return 0, nil
 	}
 
+	if rws.handlerDone {
+		rws.promoteUndeclaredTrailers()
+	}
+
 	endStream := rws.handlerDone && !rws.hasTrailers()
 	if len(p) > 0 || endStream {
 
@@ -4308,6 +4312,53 @@ func (rws *http2responseWriterState) writeChunk(p []byte) (n int, err error) {
 	return len(p), nil
 }
 
+// TrailerPrefix is a magic prefix for ResponseWriter.Header map keys
+// that, if present, signals that the map entry is actually for
+// the response trailers, and not the response headers. The prefix
+// is stripped after the ServeHTTP call finishes and the values are
+// sent in the trailers.
+//
+// This mechanism is intended only for trailers that are not known
+// prior to the headers being written. If the set of trailers is fixed
+// or known before the header is written, the normal Go trailers mechanism
+// is preferred:
+//    https://golang.org/pkg/net/http/#ResponseWriter
+//    https://golang.org/pkg/net/http/#example_ResponseWriter_trailers
+const http2TrailerPrefix = "Trailer:"
+
+// promoteUndeclaredTrailers permits http.Handlers to set trailers
+// after the header has already been flushed. Because the Go
+// ResponseWriter interface has no way to set Trailers (only the
+// Header), and because we didn't want to expand the ResponseWriter
+// interface, and because nobody used trailers, and because RFC 2616
+// says you SHOULD (but not must) predeclare any trailers in the
+// header, the official ResponseWriter rules said trailers in Go must
+// be predeclared, and then we reuse the same ResponseWriter.Header()
+// map to mean both Headers and Trailers.  When it's time to write the
+// Trailers, we pick out the fields of Headers that were declared as
+// trailers. That worked for a while, until we found the first major
+// user of Trailers in the wild: gRPC (using them only over http2),
+// and gRPC libraries permit setting trailers mid-stream without
+// predeclarnig them. So: change of plans. We still permit the old
+// way, but we also permit this hack: if a Header() key begins with
+// "Trailer:", the suffix of that key is a Trailer. Because ':' is an
+// invalid token byte anyway, there is no ambiguity. (And it's already
+// filtered out) It's mildly hacky, but not terrible.
+//
+// This method runs after the Handler is done and promotes any Header
+// fields to be trailers.
+func (rws *http2responseWriterState) promoteUndeclaredTrailers() {
+	for k, vv := range rws.handlerHeader {
+		if !strings.HasPrefix(k, http2TrailerPrefix) {
+			continue
+		}
+		trailerKey := strings.TrimPrefix(k, http2TrailerPrefix)
+		rws.declareTrailer(trailerKey)
+		rws.handlerHeader[CanonicalHeaderKey(trailerKey)] = vv
+	}
+	sort.Strings(rws.trailers)
+}
+
 func (w *http2responseWriter) Flush() {
 	rws := w.rws
 	if rws == nil {
@@ -5611,10 +5662,10 @@ func (rl *http2clientConnReadLoop) processHeaderBlockFragment(frag []byte, strea
 			res.ContentLength = -1
 			res.Body = &http2gzipReader{body: res.Body}
 		}
+		rl.activeRes[cs.ID] = cs
 	}
 
 	cs.resTrailer = &res.Trailer
-	rl.activeRes[cs.ID] = cs
 	cs.resc <- http2resAndError{res: res}
 	rl.nextRes = nil
 	return nil
@@ -6258,8 +6309,16 @@ func http2encodeHeaders(enc *hpack.Encoder, h Header, keys []string) {
 	for _, k := range keys {
 		vv := h[k]
 		k = http2lowerHeader(k)
+		if !http2validHeaderFieldName(k) {
+
+			continue
+		}
 		isTE := k == "transfer-encoding"
 		for _, v := range vv {
+			if !http2validHeaderFieldValue(v) {
+
+				continue
+			}
 
 			if isTE && v != "trailers" {
 				continue