packer: RemoteCommand.ExitChan() and tests

TODO.md

@@ -4,6 +4,7 @@
 * communicator/ssh: Ability to re-establish connection
 * communicator/ssh: Download()
 * packer: Communicator should have Close() method
+* packer: RemoteCommand.ExitChan() should be more efficient
 * packer: Ui input
 * packer/plugin: Better error messages/detection if plugin crashes
 * packer/plugin: Testing of client struct/methods

packer/communicator.go

@@ -36,6 +36,32 @@ type RemoteCommand struct {
 	ExitStatus int
 }
 
+// StdoutStream returns a channel that will be sent all the output
+// of stdout as it comes. The output isn't guaranteed to be a full line.
+// When the channel is closed, the process is exited.
+func (r *RemoteCommand) StdoutChan() (<-chan string) {
+	return nil
+}
+
+// ExitChan returns a channel that will be sent the exit status once
+// the process exits. This can be used in cases such a select statement
+// waiting on the process to end.
+func (r *RemoteCommand) ExitChan() (<-chan int) {
+	// TODO(mitchellh): lock
+	// TODO(mitchellh): Something more efficient than multiple Wait() calls
+
+	// Make a single buffered channel so that the send doesn't block.
+	exitChan := make(chan int, 1)
+
+	go func() {
+		defer close(exitChan)
+		r.Wait()
+		exitChan <- r.ExitStatus
+	}()
+
+	return exitChan
+}
+
 // Wait waits for the command to exit.
 func (r *RemoteCommand) Wait() {
 	// Busy wait on being exited. We put a sleep to be kind to the

packer/communicator_test.go

@@ -5,6 +5,31 @@ import (
 	"time"
 )
 
+func TestRemoteCommand_ExitChan(t *testing.T) {
+	t.Parallel()
+
+	rc := &RemoteCommand{}
+	exitChan := rc.ExitChan()
+
+	// Set the exit data so that it is sent
+	rc.ExitStatus = 42
+	rc.Exited = true
+
+	select {
+	case exitCode := <-exitChan:
+		if exitCode != 42 {
+			t.Fatal("invalid exit code")
+		}
+
+		_, ok := <-exitChan
+		if ok {
+			t.Fatal("exit channel should be closed")
+		}
+	case <-time.After(500 * time.Millisecond):
+		t.Fatal("exit channel never sent")
+	}
+}
+
 func TestRemoteCommand_WaitBlocks(t *testing.T) {
 	t.Parallel()