http2: stop rejecting outgoing paths beginning with two slashes

Updates golang/go#19103 (fixes after bundle into std)

Change-Id: I847133e289e210dedf2b89ab529478edc5de11d1
Reviewed-on: https://go-review.googlesource.com/45773
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

http2/http2.go

@@ -376,12 +376,16 @@ func (s *sorter) SortStrings(ss []string) {
 // validPseudoPath reports whether v is a valid :path pseudo-header
 // value. It must be either:
 //
-//     *) a non-empty string starting with '/', but not with with "//",
+//     *) a non-empty string starting with '/'
 //     *) the string '*', for OPTIONS requests.
 //
 // For now this is only used a quick check for deciding when to clean
 // up Opaque URLs before sending requests from the Transport.
 // See golang.org/issue/16847
+//
+// We used to enforce that the path also didn't start with "//", but
+// Google's GFE accepts such paths and Chrome sends them, so ignore
+// that part of the spec. See golang.org/issue/19103.
 func validPseudoPath(v string) bool {
-	return (len(v) > 0 && v[0] == '/' && (len(v) == 1 || v[1] != '/')) || v == "*"
+	return (len(v) > 0 && v[0] == '/') || v == "*"
 }

http2/transport_test.go

@@ -2529,7 +2529,7 @@ func TestTransportBodyDoubleEndStream(t *testing.T) {
 	}
 }
 
-// golangorg/issue/16847
+// golang.org/issue/16847, golang.org/issue/19103
 func TestTransportRequestPathPseudo(t *testing.T) {
 	type result struct {
 		path string
@@ -2549,9 +2549,9 @@ func TestTransportRequestPathPseudo(t *testing.T) {
 			},
 			want: result{path: "/foo"},
 		},
-		// I guess we just don't let users request "//foo" as
-		// a path, since it's illegal to start with two
-		// slashes....
+		// In Go 1.7, we accepted paths of "//foo".
+		// In Go 1.8, we rejected it (issue 16847).
+		// In Go 1.9, we accepted it again (issue 19103).
 		1: {
 			req: &http.Request{
 				Method: "GET",
@@ -2560,7 +2560,7 @@ func TestTransportRequestPathPseudo(t *testing.T) {
 					Path: "//foo",
 				},
 			},
-			want: result{err: `invalid request :path "//foo"`},
+			want: result{path: "//foo"},
 		},
 
 		// Opaque with //$Matching_Hostname/path