From c49ba0c5cb53bc55d48e374e33f2268c72b54231 Mon Sep 17 00:00:00 2001
From: "Johan T. Halseth" <johanth@gmail.com>
Date: Fri, 2 Nov 2018 11:33:01 +0100
Subject: [PATCH] rpcServer: ensure we don't get blocked on bidirectional
 payment errors

This commit fixes a potential issue in the bidirectional sendPayment
case, where multiple goroutines could be sending on an errChan with
buffer 1. Instead we select on default as well, as it is enough to
handle the first error that was received.
---
 rpcserver.go | 44 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/rpcserver.go b/rpcserver.go
index ff02ea0d..43f7f762 100644
--- a/rpcserver.go
+++ b/rpcserver.go
@@ -3707,10 +3707,12 @@ func (r *rpcServer) sendPayment(stream *paymentStream) error {
 					errChan <- nil
 					return
 				} else if err != nil {
+					rpcsLog.Errorf("Failed receiving from "+
+						"stream: %v", err)
+
 					select {
 					case errChan <- err:
-					case <-reqQuit:
-						return
+					default:
 					}
 					return
 				}
@@ -3728,18 +3730,22 @@ func (r *rpcServer) sendPayment(stream *paymentStream) error {
 						PaymentError: err.Error(),
 						PaymentHash:  payIntent.rHash[:],
 					}); err != nil {
+						rpcsLog.Errorf("Failed "+
+							"sending on "+
+							"stream: %v", err)
+
 						select {
 						case errChan <- err:
-						case <-reqQuit:
-							return
+						default:
 						}
+						return
 					}
 					continue
 				}
 
 				// If the payment was well formed, then we'll
 				// send to the dispatch goroutine, or exit,
-				// which ever comes first
+				// which ever comes first.
 				select {
 				case payChan <- &payIntent:
 				case <-reqQuit:
@@ -3751,6 +3757,9 @@ func (r *rpcServer) sendPayment(stream *paymentStream) error {
 
 	for {
 		select {
+
+		// If we encounter and error either during sending or
+		// receiving, we return directly, closing the stream.
 		case err := <-errChan:
 			return err
 
@@ -3779,7 +3788,13 @@ func (r *rpcServer) sendPayment(stream *paymentStream) error {
 				// payment, then we'll return the error to the
 				// user, and terminate.
 				case saveErr != nil:
-					errChan <- saveErr
+					rpcsLog.Errorf("Failed dispatching "+
+						"payment intent: %v", saveErr)
+
+					select {
+					case errChan <- saveErr:
+					default:
+					}
 					return
 
 				// If we receive payment error than, instead of
@@ -3791,7 +3806,14 @@ func (r *rpcServer) sendPayment(stream *paymentStream) error {
 						PaymentHash:  payIntent.rHash[:],
 					})
 					if err != nil {
-						errChan <- err
+						rpcsLog.Errorf("Failed "+
+							"sending error "+
+							"response: %v", err)
+
+						select {
+						case errChan <- err:
+						default:
+						}
 					}
 					return
 				}
@@ -3811,7 +3833,13 @@ func (r *rpcServer) sendPayment(stream *paymentStream) error {
 					PaymentRoute:    marshalledRouted,
 				})
 				if err != nil {
-					errChan <- err
+					rpcsLog.Errorf("Failed sending "+
+						"response: %v", err)
+
+					select {
+					case errChan <- err:
+					default:
+					}
 					return
 				}
 			}()