From b171491a7fcc0eab73dc8f37472a6b956d5f848d Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Thu, 21 Apr 2022 14:29:21 +0100
Subject: [PATCH] return an ErrNotSupported when lazy negotiation fails

---
 lazyClient.go       |  4 ++++
 multistream_test.go | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/lazyClient.go b/lazyClient.go
index 202fd64..76d79ff 100644
--- a/lazyClient.go
+++ b/lazyClient.go
@@ -77,6 +77,10 @@ func (l *lazyClientConn) doReadHandshake() {
 			return
 		}
 
+		if tok == "na" {
+			l.rerr = ErrNotSupported
+			return
+		}
 		if tok != proto {
 			l.rerr = fmt.Errorf("protocol mismatch in lazy handshake ( %s != %s )", tok, proto)
 			return
diff --git a/multistream_test.go b/multistream_test.go
index 5668fa7..8b3c4ec 100644
--- a/multistream_test.go
+++ b/multistream_test.go
@@ -149,6 +149,26 @@ func TestProtocolNegotiationLazy(t *testing.T) {
 	verifyPipe(t, ac, b)
 }
 
+func TestProtocolNegotiationUnsupported(t *testing.T) {
+	a, b := newPipe(t)
+	mux := NewMultistreamMuxer()
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		mux.Negotiate(a)
+	}()
+
+	c := NewMSSelect(b, "/foo")
+	c.Write([]byte("foo protocol data"))
+	_, err := c.Read([]byte{0})
+	if err != ErrNotSupported {
+		t.Fatalf("expected protocol /foo to be unsupported, got: %v", err)
+	}
+	c.Close()
+	<-done
+}
+
 func TestNegLazyStressRead(t *testing.T) {
 	const count = 75