packer/plugin: client to encapsulate logic for starting plugins

packer/plugin/client.go

 package plugin
 
 import (
+	"bufio"
+	"bytes"
+	"errors"
+	"io"
+	"log"
 	"os/exec"
+	"strings"
+	"time"
 )
 
-type Client struct {
+type client struct {
 	cmd *exec.Cmd
+	exited bool
 }
 
-func NewClient(cmd *exec.Cmd) *Client {
-	return &Client{cmd}
+func NewClient(cmd *exec.Cmd) *client {
+	return &client{
+		cmd,
+		false,
+	}
+}
+
+func (c *client) Exited() bool {
+	return c.exited
+}
+
+func (c *client) Start() (address string, err error) {
+	env := []string{
+		"PACKER_PLUGIN_MIN_PORT=10000",
+		"PACKER_PLUGIN_MAX_PORT=25000",
+	}
+
+	stdout := new(bytes.Buffer)
+	stderr := new(bytes.Buffer)
+	c.cmd.Env = append(c.cmd.Env, env...)
+	c.cmd.Stderr = stderr
+	c.cmd.Stdout = stdout
+	err = c.cmd.Start()
+	if err != nil {
+		return
+	}
+
+	// Make sure the command is properly cleaned up if there is an error
+	defer func() {
+		r := recover()
+
+		if err != nil || r != nil {
+			c.cmd.Process.Kill()
+		}
+
+		if r != nil {
+			panic(r)
+		}
+	}()
+
+	// Start goroutine to wait for process to exit
+	go func() {
+		c.cmd.Wait()
+		c.exited = true
+	}()
+
+	// Start goroutine that logs the stderr
+	go c.logStderr(stderr)
+
+	// Some channels for the next step
+	timeout := time.After(1 * time.Minute)
+
+	// Start looking for the address
+	for done := false; !done; {
+		select {
+		case <-timeout:
+			err = errors.New("timeout while waiting for plugin to start")
+			done = true
+		default:
+		}
+
+		if err == nil && c.Exited() {
+			err = errors.New("plugin exited before we could connect")
+			done = true
+		}
+
+		if line, lerr := stdout.ReadBytes('\n'); lerr == nil {
+			// Trim the address and reset the err since we were able
+			// to read some sort of address.
+			address = strings.TrimSpace(string(line))
+			err = nil
+			break
+		}
+
+		// If error is nil from previously, return now
+		if err != nil {
+			return
+		}
+
+		// Wait a bit
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	return
+}
+
+func (c *client) Kill() {
+	c.cmd.Process.Kill()
+}
+
+func (c *client) logStderr(r io.Reader) {
+	buf := bufio.NewReader(r)
+
+	for done := false; !done; {
+		if c.Exited() {
+			done = true
+		}
+
+		var err error
+		for err == nil {
+			var line string
+			line, err = buf.ReadString('\n')
+			if line != "" {
+				log.Print(line)
+			}
+		}
+
+		time.Sleep(10 * time.Millisecond)
+	}
 }

packer/plugin/command.go

 package plugin
 
 import (
-	"bufio"
-	"bytes"
-	"errors"
 	"github.com/mitchellh/packer/packer"
 	"log"
 	"net/rpc"
 	"os/exec"
 	packrpc "github.com/mitchellh/packer/packer/rpc"
-	"strings"
-	"time"
 )
 
 type cmdCommand struct {
 	command packer.Command
-	exited <-chan bool
+	client *client
 }
 
 func (c *cmdCommand) Run(e packer.Environment, args []string) (exitCode int) {
@@ -41,14 +36,11 @@ func (c *cmdCommand) Synopsis() (result string) {
 }
 
 func (c *cmdCommand) checkExit(p interface{}, cb func()) {
-	select {
-	case <-c.exited:
+	if c.client.Exited() {
 		cb()
-	default:
-		if p != nil {
+	} else if p != nil {
 		log.Panic(p)
 	}
-	}
 }
 
 // Returns a valid packer.Command where the command is executed via RPC
@@ -60,17 +52,8 @@ func (c *cmdCommand) checkExit(p interface{}, cb func()) {
 //
 // This function guarantees the subprocess will end in a timely manner.
 func Command(cmd *exec.Cmd) (result packer.Command, err error) {
-	env := []string{
-		"PACKER_PLUGIN_MIN_PORT=10000",
-		"PACKER_PLUGIN_MAX_PORT=25000",
-	}
-
-	stdout := new(bytes.Buffer)
-	stderr := new(bytes.Buffer)
-	cmd.Env = append(cmd.Env, env...)
-	cmd.Stderr = stderr
-	cmd.Stdout = stdout
-	err = cmd.Start()
+	cmdClient := NewClient(cmd)
+	address, err := cmdClient.Start()
 	if err != nil {
 		return
 	}
@@ -78,76 +61,10 @@ func Command(cmd *exec.Cmd) (result packer.Command, err error) {
 	defer func() {
 		// Make sure the command is properly killed in the case of an error
 		if err != nil {
-			cmd.Process.Kill()
+			cmdClient.Kill()
 		}
 	}()
 
-	// Goroutine + channel to signal that the process exited
-	cmdExited := make(chan bool)
-	go func() {
-		cmd.Wait()
-		cmdExited <- true
-	}()
-
-	// Goroutine to log out the output from the command
-	// TODO: All sorts of things wrong with this. First, we're reading from
-	// a channel that can get consumed elsewhere. Second, the app can end
-	// without properly flushing all the log data. BLah.
-	go func() {
-		buf := bufio.NewReader(stderr)
-
-		for done := false; !done; {
-			select {
-			case <-cmdExited:
-				done = true
-			default:
-			}
-
-			var err error
-			for err == nil {
-				var line string
-				line, err = buf.ReadString('\n')
-				if line != "" {
-					log.Print(line)
-				}
-			}
-
-			time.Sleep(10 * time.Millisecond)
-		}
-	}()
-
-	// Timer for a timeout
-	cmdTimeout := time.After(1 * time.Minute)
-
-	var address string
-	for done := false; !done; {
-		select {
-		case <-cmdExited:
-			err = errors.New("plugin exited before we could connect")
-			done = true
-		case <-cmdTimeout:
-			err = errors.New("timeout while waiting for plugin to start")
-			done = true
-		default:
-		}
-
-		if line, lerr := stdout.ReadBytes('\n'); lerr == nil {
-			// Trim the address and reset the err since we were able
-			// to read some sort of address.
-			address = strings.TrimSpace(string(line))
-			err = nil
-			break
-		}
-
-		// If error is nil from previously, return now
-		if err != nil {
-			return
-		}
-
-		// Wait a bit
-		time.Sleep(10 * time.Millisecond)
-	}
-
 	client, err := rpc.Dial("tcp", address)
 	if err != nil {
 		return
@@ -155,7 +72,7 @@ func Command(cmd *exec.Cmd) (result packer.Command, err error) {
 
 	result = &cmdCommand{
 		packrpc.Command(client),
-		cmdExited,
+		cmdClient,
 	}
 
 	return