Relay should handle error frames, and finish relays after errors

connection.go

@@ -742,7 +742,7 @@ func (c *Connection) readFrames(_ uint32) {
 func (c *Connection) handleFrameRelay(frame *Frame) bool {
 	// TODO: handle error frames.
 	switch frame.Header.messageType {
-	case messageTypeCallReq, messageTypeCallReqContinue, messageTypeCallRes, messageTypeCallResContinue:
+	case messageTypeCallReq, messageTypeCallReqContinue, messageTypeCallRes, messageTypeCallResContinue, messageTypeError:
 		if err := c.relay.Relay(frame); err != nil {
 			c.log.WithFields(
 				LogField{"header", frame.Header},

relay.go

@@ -244,10 +244,11 @@ func frameTypeFor(f *Frame) frameType {
 // this RPC req-res.
 func finishesCall(f *Frame) bool {
 	switch f.messageType() {
+	case messageTypeError:
+		return true
 	case messageTypeCallRes, messageTypeCallResContinue:
 		flags := f.Payload[_flagsIndex]
 		return flags&hasMoreFragmentsFlag == 0
-	// TODO: errors should also terminate an RPC.
 	default:
 		return false
 	}

relay_test.go

@@ -213,5 +213,24 @@ func TestRelayErrorUnknownPeer(t *testing.T) {
 		assert.Equal(t, ErrCodeDeclined, se.Code(), "Expected Declined error")
 		assert.Contains(t, err.Error(), `no peers for "random-service"`, "Unexpected error")
 	})
+}
+
+func TestErrorFrameEndsRelay(t *testing.T) {
+	// withRelayTest validates that there are no relay items left after the given func.
+	withRelayTest(t, func(rt *relayTest) {
+		rt.newServer("svc", testutils.NewOpts().AddLogFilter("Couldn't find handler", 1))
+		client := rt.newClient("client", nil)
+
+		err := testutils.CallEcho(client, rt.relay.PeerInfo().HostPort, "svc", nil)
+		if !assert.Error(t, err, "Expected error due to unknown method") {
+			return
+		}
 
+		se, ok := err.(SystemError)
+		if !assert.True(t, ok, "err should be a SystemError, got %T", err) {
+			return
+		}
+
+		assert.Equal(t, ErrCodeBadRequest, se.Code(), "Expected BadRequest error")
+	})
 }