packer/rpc: tests passing

packer/rpc/client_test.go

 package rpc
 
 import (
+	"net"
 	"testing"
 )
 
 func testClient(t *testing.T, server *Server) *Client {
-	return nil
+	l, err := net.Listen("tcp", ":0")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	go func() {
+		conn, err := l.Accept()
+		if err != nil {
+			t.Fatalf("err: %s", err)
+		}
+		server.ServeConn(conn)
+	}()
+
+	clientConn, err := net.Dial("tcp", l.Addr().String())
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	client, err := NewClient(clientConn)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	return client
 }

packer/rpc/server_new.go

@@ -34,8 +34,8 @@ func (s *Server) ServeConn(conn io.ReadWriteCloser) {
 	mux := NewMuxConn(conn)
 	defer mux.Close()
 
-	// Get stream ID 0, which we always use as the stream for serving
-	// our RPC server on.
+	// Accept a connection on stream ID 0, which is always used for
+	// normal client to server connections.
 	stream, err := mux.Accept(0)
 	if err != nil {
 		log.Printf("[ERR] Error retrieving stream for serving: %s", err)