packer/plugin: Much more robust subprocess starting

packer/plugin/command.go

@@ -10,19 +10,10 @@ import (
 	"time"
 )
 
-type processCommand struct {
-	cmd *exec.Cmd
-}
-
-func (c *processCommand) Run(e packer.Environment, args []string) int {
-	return 0
-}
-
-func (c *processCommand) Synopsis() string {
+func Command(cmd *exec.Cmd) packer.Command {
 	out := new(bytes.Buffer)
-	c.cmd.Stdout = out
-	c.cmd.Start()
-	defer c.cmd.Process.Kill()
+	cmd.Stdout = out
+	cmd.Start()
 
 	// TODO: timeout
 	// TODO: check that command is even running
@@ -37,13 +28,10 @@ func (c *processCommand) Synopsis() string {
 		time.Sleep(10 * time.Millisecond)
 	}
 
-	client, _ := rpc.Dial("tcp", address)
-	defer client.Close()
-
-	realCommand := packrpc.Command(client)
-	return realCommand.Synopsis()
-}
+	client, err := rpc.Dial("tcp", address)
+	if err != nil {
+		panic(err)
+	}
 
-func Command(cmd *exec.Cmd) packer.Command {
-	return &processCommand{cmd}
+	return packrpc.Command(client)
 }

packer/plugin/plugin.go

@@ -6,26 +6,42 @@ package plugin
 import (
 	"fmt"
 	"github.com/mitchellh/packer/packer"
+	"net"
+	"net/rpc"
 	"os"
 	packrpc "github.com/mitchellh/packer/packer/rpc"
 )
 
-// This serves the plugin by starting the RPC server and serving requests.
-// This function never returns.
-func serve(server *packrpc.Server) {
-	// Start up the server
-	server.Start()
+// This serves a single RPC connection on the given RPC server on
+// a random port.
+func serve(server *rpc.Server) (err error) {
+	listener, err := net.Listen("tcp", ":2345")
+	if err != nil {
+		return
+	}
+	defer listener.Close()
 
 	// Output the address to stdout
-	fmt.Println(server.Address())
+	fmt.Println(":2345")
 	os.Stdout.Sync()
 
-	// Never return, wait on a channel that never gets a message
-	<-make(chan bool)
+	// Accept a connection
+	conn, err := listener.Accept()
+	if err != nil {
+		return
+	}
+
+	// Serve a single connection
+	server.ServeConn(conn)
+	return
 }
 
+// Serves a command from a plugin.
 func ServeCommand(command packer.Command) {
-	server := packrpc.NewServer()
-	server.RegisterCommand(command)
-	serve(server)
+	server := rpc.NewServer()
+	packrpc.RegisterCommand(server, command)
+
+	if err := serve(server); err != nil {
+		panic(err)
+	}
 }

packer/rpc/command.go

@@ -31,12 +31,20 @@ func Command(client *rpc.Client) *ClientCommand {
 func (c *ClientCommand) Run(env packer.Environment, args []string) (result int) {
 	// TODO: Environment
 	rpcArgs := &CommandRunArgs{nil, args}
-	c.client.Call("Command.Run", rpcArgs, &result)
+	err := c.client.Call("Command.Run", rpcArgs, &result)
+	if err != nil {
+		panic(err)
+	}
+
 	return
 }
 
 func (c *ClientCommand) Synopsis() (result string) {
-	c.client.Call("Command.Synopsis", CommandSynopsisArgs(0), &result)
+	err := c.client.Call("Command.Synopsis", CommandSynopsisArgs(0), &result)
+	if err != nil {
+		panic(err)
+	}
+
 	return
 }
 

packer/rpc/server.go

@@ -7,6 +7,10 @@ import (
 	"net/rpc"
 )
 
+func RegisterCommand(s *rpc.Server, c packer.Command) {
+	s.RegisterName("Command", &ServerCommand{c})
+}
+
 // A Server is a Golang RPC server that has helper methods for automatically
 // setting up the endpoints for Packer interfaces.
 type Server struct {