packer: Communicator Upload/Download return an error

packer/communicator.go

@@ -13,8 +13,8 @@ import (
 // Start or any other method may be called at the same time.
 type Communicator interface {
 	Start(string) (*RemoteCommand, error)
-	Upload(string, io.Reader)
-	Download(string, io.Writer)
+	Upload(string, io.Reader) error
+	Download(string, io.Writer) error
 }
 
 // This struct contains some information about the remote command being

packer/rpc/communicator.go

@@ -87,9 +87,13 @@ func (c *communicator) Start(cmd string) (rc *packer.RemoteCommand, err error) {
 	return
 }
 
-func (c *communicator) Upload(string, io.Reader) {}
+func (c *communicator) Upload(string, io.Reader) error {
+	return nil
+}
 
-func (c *communicator) Download(string, io.Writer) {}
+func (c *communicator) Download(string, io.Writer) error {
+	return nil
+}
 
 func (c *CommunicatorServer) Start(cmd *string, reply *CommunicatorStartResponse) (err error) {
 	// Start executing the command.

packer/rpc/communicator_test.go

@@ -45,9 +45,13 @@ func (t *testCommunicator) Start(cmd string) (*packer.RemoteCommand, error) {
 	return rc, nil
 }
 
-func (t *testCommunicator) Upload(string, io.Reader) {}
+func (t *testCommunicator) Upload(string, io.Reader) error {
+	return nil
+}
 
-func (t *testCommunicator) Download(string, io.Writer) {}
+func (t *testCommunicator) Download(string, io.Writer) error {
+	return nil
+}
 
 func TestCommunicatorRPC(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)