http2: mention bogus header value in error messages

Change-Id: I69d713341b878a2343bb85fb2de2ef49441fd16d
Reviewed-on: https://go-review.googlesource.com/30098
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

http2/transport.go

@@ -624,13 +624,13 @@ func (cc *ClientConn) responseHeaderTimeout() time.Duration {
 // Certain headers are special-cased as okay but not transmitted later.
 func checkConnHeaders(req *http.Request) error {
 	if v := req.Header.Get("Upgrade"); v != "" {
-		return errors.New("http2: invalid Upgrade request header")
+		return fmt.Errorf("http2: invalid Upgrade request header: %q", req.Header["Upgrade"])
 	}
 	if v := req.Header.Get("Transfer-Encoding"); (v != "" && v != "chunked") || len(req.Header["Transfer-Encoding"]) > 1 {
-		return errors.New("http2: invalid Transfer-Encoding request header")
+		return fmt.Errorf("http2: invalid Transfer-Encoding request header: %q", req.Header["Transfer-Encoding"])
 	}
 	if v := req.Header.Get("Connection"); (v != "" && v != "close" && v != "keep-alive") || len(req.Header["Connection"]) > 1 {
-		return errors.New("http2: invalid Connection request header")
+		return fmt.Errorf("http2: invalid Connection request header: %q", req.Header["Connection"])
 	}
 	return nil
 }

http2/transport_test.go

@@ -1707,12 +1707,12 @@ func TestTransportRejectsConnHeaders(t *testing.T) {
 		{
 			key:   "Upgrade",
 			value: []string{"anything"},
-			want:  "ERROR: http2: invalid Upgrade request header",
+			want:  "ERROR: http2: invalid Upgrade request header: [\"anything\"]",
 		},
 		{
 			key:   "Connection",
 			value: []string{"foo"},
-			want:  "ERROR: http2: invalid Connection request header",
+			want:  "ERROR: http2: invalid Connection request header: [\"foo\"]",
 		},
 		{
 			key:   "Connection",
@@ -1722,7 +1722,7 @@ func TestTransportRejectsConnHeaders(t *testing.T) {
 		{
 			key:   "Connection",
 			value: []string{"close", "something-else"},
-			want:  "ERROR: http2: invalid Connection request header",
+			want:  "ERROR: http2: invalid Connection request header: [\"close\" \"something-else\"]",
 		},
 		{
 			key:   "Connection",
@@ -1742,7 +1742,7 @@ func TestTransportRejectsConnHeaders(t *testing.T) {
 		{
 			key:   "Transfer-Encoding",
 			value: []string{"foo"},
-			want:  "ERROR: http2: invalid Transfer-Encoding request header",
+			want:  "ERROR: http2: invalid Transfer-Encoding request header: [\"foo\"]",
 		},
 		{
 			key:   "Transfer-Encoding",
@@ -1752,7 +1752,7 @@ func TestTransportRejectsConnHeaders(t *testing.T) {
 		{
 			key:   "Transfer-Encoding",
 			value: []string{"chunked", "other"},
-			want:  "ERROR: http2: invalid Transfer-Encoding request header",
+			want:  "ERROR: http2: invalid Transfer-Encoding request header: [\"chunked\" \"other\"]",
 		},
 		{
 			key:   "Content-Length",