Support builders in config, packer/rpc, packer/plugin

config.go

@@ -64,6 +64,17 @@ func (c *config) CommandNames() (result []string) {
 	return
 }
 
+func (c *config) LoadBuilder(name string) (packer.Builder, error) {
+	log.Printf("Loading builder: %s\n", name)
+	bin, ok := c.Builders[name]
+	if !ok {
+		log.Printf("Builder not found: %s\n", name)
+		return nil, nil
+	}
+
+	return plugin.Builder(exec.Command(bin))
+}
+
 // This is a proper packer.CommandFunc that can be used to load packer.Command
 // implementations from the defined plugins.
 func (c *config) LoadCommand(name string) (packer.Command, error) {

packer.go

@@ -84,6 +84,7 @@ func main() {
 	}
 
 	envConfig := packer.DefaultEnvironmentConfig()
+	envConfig.BuilderFunc = config.LoadBuilder
 	envConfig.Commands = config.CommandNames()
 	envConfig.CommandFunc = config.LoadCommand
 

packer/plugin/builder.go

@@ -0,0 +1,76 @@
+package plugin
+
+import (
+	"github.com/mitchellh/packer/packer"
+	"log"
+	"net/rpc"
+	"os/exec"
+	packrpc "github.com/mitchellh/packer/packer/rpc"
+)
+
+type cmdBuilder struct {
+	builder packer.Builder
+	client *client
+}
+
+func (b *cmdBuilder) Prepare(config interface{}) {
+	defer func() {
+		r := recover()
+		b.checkExit(r, nil)
+	}()
+
+	b.builder.Prepare(config)
+}
+
+func (b *cmdBuilder) Run(build packer.Build, ui packer.Ui) {
+	defer func() {
+		r := recover()
+		b.checkExit(r, nil)
+	}()
+
+	b.builder.Run(build, ui)
+}
+
+func (c *cmdBuilder) checkExit(p interface{}, cb func()) {
+	if c.client.Exited() && cb != nil {
+		cb()
+	} else if p != nil {
+		log.Panic(p)
+	}
+}
+
+
+// Returns a valid packer.Builder where the builder is executed via RPC
+// to a plugin that is within a subprocess.
+//
+// This method will start the given exec.Cmd, which should point to
+// the plugin binary to execute. Some configuration will be done to
+// the command, such as overriding Stdout and some environmental variables.
+//
+// This function guarantees the subprocess will end in a timely manner.
+func Builder(cmd *exec.Cmd) (result packer.Builder, err error) {
+	cmdClient := NewManagedClient(cmd)
+	address, err := cmdClient.Start()
+	if err != nil {
+		return
+	}
+
+	defer func() {
+		// Make sure the command is properly killed in the case of an error
+		if err != nil {
+			cmdClient.Kill()
+		}
+	}()
+
+	client, err := rpc.Dial("tcp", address)
+	if err != nil {
+		return
+	}
+
+	result = &cmdBuilder{
+		packrpc.Builder(client),
+		cmdClient,
+	}
+
+	return
+}

packer/rpc/builder.go

@@ -7,7 +7,7 @@ import (
 
 // An implementation of packer.Builder where the builder is actually executed
 // over an RPC connection.
-type Builder struct {
+type builder struct {
 	client *rpc.Client
 }
 
@@ -25,11 +25,15 @@ type BuilderRunArgs struct {
 	RPCAddress string
 }
 
-func (b *Builder) Prepare(config interface{}) {
+func Builder(client *rpc.Client) *builder {
+	return &builder{client}
+}
+
+func (b *builder) Prepare(config interface{}) {
 	b.client.Call("Builder.Prepare", &BuilderPrepareArgs{config}, new(interface{}))
 }
 
-func (b *Builder) Run(build packer.Build, ui packer.Ui) {
+func (b *builder) Run(build packer.Build, ui packer.Ui) {
 	// Create and start the server for the Build and UI
 	// TODO: Error handling
 	server := rpc.NewServer()

packer/rpc/environment.go

@@ -33,7 +33,7 @@ func (e *Environment) Builder(name string) (b packer.Builder, err error) {
 		return
 	}
 
-	b = &Builder{client}
+	b = Builder(client)
 	return
 }