From d2e85b5806bf24c182a243c40732166960bf58f5 Mon Sep 17 00:00:00 2001
From: Ian Denhardt <ian@zenhack.net>
Date: Mon, 13 Feb 2023 19:32:28 -0500
Subject: [PATCH] Hold lock while accessing c.stream.err

For some reason I'd been under the impression that startCall acquired
this and released it in finish(), but that's not the case.
---
 capability.go | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/capability.go b/capability.go
index fb5b9d18..1708ce4c 100644
--- a/capability.go
+++ b/capability.go
@@ -327,8 +327,13 @@ func (c Client) SendCall(ctx context.Context, s Send) (*Answer, ReleaseFunc) {
 		return ErrorAnswer(s.Method, errors.New("call on null client")), func() {}
 	}
 
-	if c.stream.err != nil {
-		return ErrorAnswer(s.Method, exc.WrapError("stream error", c.stream.err)), func() {}
+	var err error
+	syncutil.With(&c.mu, func() {
+		err = c.stream.err
+	})
+
+	if err != nil {
+		return ErrorAnswer(s.Method, exc.WrapError("stream error", err)), func() {}
 	}
 
 	limiter := c.GetFlowLimiter()