From adaa228f563cb48e9cf15e50b1b2087b209928d6 Mon Sep 17 00:00:00 2001
From: Steven Allen <steven@stebalien.com>
Date: Thu, 15 Nov 2018 21:11:10 -0800
Subject: [PATCH] warn when we encounter a useless transport

---
 swarm_transport.go |  4 ++++
 transport_test.go  | 47 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 transport_test.go

diff --git a/swarm_transport.go b/swarm_transport.go
index c96a079..0431488 100644
--- a/swarm_transport.go
+++ b/swarm_transport.go
@@ -70,6 +70,10 @@ func (s *Swarm) TransportForListening(a ma.Multiaddr) transport.Transport {
 func (s *Swarm) AddTransport(t transport.Transport) error {
 	protocols := t.Protocols()
 
+	if len(protocols) == 0 {
+		return fmt.Errorf("useless transport handles no protocols: %T", t)
+	}
+
 	s.transports.Lock()
 	defer s.transports.Unlock()
 	var registered []string
diff --git a/transport_test.go b/transport_test.go
new file mode 100644
index 0000000..018775b
--- /dev/null
+++ b/transport_test.go
@@ -0,0 +1,47 @@
+package swarm_test
+
+import (
+	"context"
+	"testing"
+
+	swarmt "github.com/libp2p/go-libp2p-swarm/testing"
+
+	peer "github.com/libp2p/go-libp2p-peer"
+	transport "github.com/libp2p/go-libp2p-transport"
+	ma "github.com/multiformats/go-multiaddr"
+)
+
+type dummyTransport struct {
+	protocols []int
+	proxy     bool
+}
+
+func (dt *dummyTransport) Dial(ctx context.Context, raddr ma.Multiaddr, p peer.ID) (transport.Conn, error) {
+	panic("unimplemented")
+}
+
+func (dt *dummyTransport) CanDial(addr ma.Multiaddr) bool {
+	panic("unimplemented")
+}
+
+func (dt *dummyTransport) Listen(laddr ma.Multiaddr) (transport.Listener, error) {
+	panic("unimplemented")
+}
+
+func (dt *dummyTransport) Proxy() bool {
+	return dt.proxy
+}
+
+func (dt *dummyTransport) Protocols() []int {
+	return dt.protocols
+}
+
+func TestUselessTransport(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	swarm := swarmt.GenSwarm(t, ctx)
+	err := swarm.AddTransport(new(dummyTransport))
+	if err == nil {
+		t.Fatal("adding a transport that supports no protocols should have failed")
+	}
+}
-- 
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