use set protos in identify protocol knowledge gathering

p2p/host/basic/basic_host_test.go

@@ -241,3 +241,62 @@ func TestNewDialOld(t *testing.T) {
 
 	s.Close()
 }
+
+func TestProtoDowngrade(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	h1, h2 := getHostPair(ctx, t)
+	defer h1.Close()
+	defer h2.Close()
+
+	connectedOn := make(chan protocol.ID, 16)
+	h1.SetStreamHandler("/testing/1.0.0", func(s inet.Stream) {
+		connectedOn <- s.Protocol()
+		s.Close()
+	})
+
+	s, err := h2.NewStream(ctx, h1.ID(), "/testing/1.0.0", "/testing")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assertWait(t, connectedOn, "/testing/1.0.0")
+
+	if s.Protocol() != "/testing/1.0.0" {
+		t.Fatal("shoould have gotten /testing")
+	}
+	s.Close()
+
+	h1.Network().ConnsToPeer(h2.ID())[0].Close()
+
+	time.Sleep(time.Millisecond * 50) // allow notifications to propogate
+	h1.RemoveStreamHandler("/testing/1.0.0")
+	h1.SetStreamHandler("/testing", func(s inet.Stream) {
+		connectedOn <- s.Protocol()
+		s.Close()
+	})
+
+	h2pi := h2.Peerstore().PeerInfo(h2.ID())
+	if err := h1.Connect(ctx, h2pi); err != nil {
+		t.Fatal(err)
+	}
+
+	s2, err := h2.NewStream(ctx, h1.ID(), "/testing/1.0.0", "/testing")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = s2.Write(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assertWait(t, connectedOn, "/testing")
+
+	if s2.Protocol() != "/testing" {
+		t.Fatal("shoould have gotten /testing")
+	}
+	s2.Close()
+
+}

p2p/protocol/identify/id.go

@@ -193,7 +193,7 @@ func (ids *IDService) consumeMessage(mes *pb.Identify, c inet.Conn) {
 	p := c.RemotePeer()
 
 	// mes.Protocols
-	ids.Host.Peerstore().AddProtocols(p, mes.Protocols...)
+	ids.Host.Peerstore().SetProtocols(p, mes.Protocols...)
 
 	// mes.ObservedAddr
 	ids.consumeObservedAddress(mes.GetObservedAddr(), c)