builder/virtualbox: guest-additions_url can use Version var [GH-272]

CHANGELOG.md

@@ -10,6 +10,8 @@ IMPROVEMENTS:
 
 * core: built with Go 1.1.2
 * core: packer help output now loads much faster.
+* builder/virtualbox: guest_additions_url can now use the `Version`
+  variable to get the VirtualBox version. [GH-272]
 * builder/virtualbox: Do not check for VirtualBox as part of template
   validation; only check at execution.
 * builder/vmware: Do not check for VMware as part of template validation;

builder/virtualbox/builder.go

@@ -132,8 +132,6 @@ func (b *Builder) Prepare(raws ...interface{}) error {
 
 	// Errors
 	templates := map[string]*string{
-		"guest_additions_path":    &b.config.GuestAdditionsPath,
-		"guest_additions_url":     &b.config.GuestAdditionsURL,
 		"guest_additions_sha256":  &b.config.GuestAdditionsSHA256,
 		"guest_os_type":           &b.config.GuestOSType,
 		"http_directory":          &b.config.HTTPDir,
@@ -160,6 +158,18 @@ func (b *Builder) Prepare(raws ...interface{}) error {
 		}
 	}
 
+	validates := map[string]*string{
+		"guest_additions_path": &b.config.GuestAdditionsPath,
+		"guest_additions_url":  &b.config.GuestAdditionsURL,
+	}
+
+	for n, ptr := range validates {
+		if err := b.config.tpl.Validate(*ptr); err != nil {
+			errs = packer.MultiErrorAppend(
+				errs, fmt.Errorf("Error parsing %s: %s", n, err))
+		}
+	}
+
 	for i, command := range b.config.BootCommand {
 		if err := b.config.tpl.Validate(command); err != nil {
 			errs = packer.MultiErrorAppend(errs,

builder/virtualbox/step_download_guest_additions.go

@@ -21,6 +21,10 @@ var additionsVersionMap = map[string]string{
 	"4.1.23": "4.1.22",
 }
 
+type guestAdditionsUrlTemplate struct {
+	Version string
+}
+
 // This step uploads a file containing the VirtualBox version, which
 // can be useful for various provisioning reasons.
 //
@@ -69,7 +73,19 @@ func (s *stepDownloadGuestAdditions) Run(state map[string]interface{}) multistep
 
 	// Use the provided source (URL or file path) or generate it
 	url := config.GuestAdditionsURL
-	if url == "" {
+	if url != "" {
+		tplData := &guestAdditionsUrlTemplate{
+			Version: version,
+		}
+
+		url, err = config.tpl.Process(url, tplData)
+		if err != nil {
+			err := fmt.Errorf("Error preparing guest additions url: %s", err)
+			state["error"] = err
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+	} else {
 		url = fmt.Sprintf(
 			"http://download.virtualbox.org/virtualbox/%s/%s",
 			version,