packer/rpc: make servers use odd seqnums, clients even [GH-727]

packer/rpc/client.go

@@ -17,7 +17,7 @@ type Client struct {
 }
 
 func NewClient(rwc io.ReadWriteCloser) (*Client, error) {
-	result, err := NewClientWithMux(NewMuxConn(rwc), 0)
+	result, err := NewClientWithMux(NewMuxConn(rwc, 0), 0)
 	if err != nil {
 		return nil, err
 	}

packer/rpc/muxconn.go

@@ -41,11 +41,12 @@ const (
 )
 
 // Create a new MuxConn around any io.ReadWriteCloser.
-func NewMuxConn(rwc io.ReadWriteCloser) *MuxConn {
+func NewMuxConn(rwc io.ReadWriteCloser, startId uint32) *MuxConn {
 	m := &MuxConn{
 		rwc:     rwc,
 		streams: make(map[uint32]*Stream),
 		doneCh:  make(chan struct{}),
+		curId:   startId,
 	}
 
 	go m.cleaner()
@@ -145,7 +146,7 @@ func (m *MuxConn) NextId() uint32 {
 
 	for {
 		result := m.curId
-		m.curId++
+		m.curId += 2
 		if _, ok := m.streams[result]; !ok {
 			return result
 		}

packer/rpc/muxconn_test.go

@@ -33,7 +33,7 @@ func testMux(t *testing.T) (client *MuxConn, server *MuxConn) {
 			t.Fatalf("err: %s", err)
 		}
 
-		server = NewMuxConn(conn)
+		server = NewMuxConn(conn, 1)
 	}()
 
 	// Client side
@@ -41,7 +41,7 @@ func testMux(t *testing.T) (client *MuxConn, server *MuxConn) {
 	if err != nil {
 		t.Fatalf("err: %s", err)
 	}
-	client = NewMuxConn(conn)
+	client = NewMuxConn(conn, 0)
 
 	// Wait for the server
 	<-doneCh
@@ -241,7 +241,14 @@ func TestMuxConnNextId(t *testing.T) {
 	a := client.NextId()
 	b := client.NextId()
 
-	if a != 0 || b != 1 {
+	if a != 0 || b != 2 {
 		t.Fatalf("IDs should increment")
 	}
+
+	a = server.NextId()
+	b = server.NextId()
+
+	if a != 1 || b != 3 {
+		t.Fatalf("IDs should increment: %d %d", a, b)
+	}
 }

packer/rpc/server.go

@@ -36,7 +36,7 @@ type Server struct {
 
 // NewServer returns a new Packer RPC server.
 func NewServer(conn io.ReadWriteCloser) *Server {
-	result := NewServerWithMux(NewMuxConn(conn), 0)
+	result := NewServerWithMux(NewMuxConn(conn, 1), 0)
 	result.closeMux = true
 	return result
 }