Merge pull request #7 from grammarly/issue-6

#6 provide `-id` parameter

src/cmd/rocker/main.go

@@ -110,6 +110,10 @@ func main() {
 			Name:  "print",
 			Usage: "just print the Rockerfile after template processing and stop",
 		},
+		cli.StringFlag{
+			Name:  "id",
+			Usage: "override the default id generation strategy for current build",
+		},
 	}
 
 	app.Commands = []cli.Command{
@@ -229,6 +233,7 @@ func buildCommand(c *cli.Context) {
 		OutStream:    os.Stdout,
 		Docker:       dockerClient,
 		AddMeta:      c.Bool("meta"),
+		Id:           c.String("id"),
 	}
 
 	if _, err := builder.Build(); err != nil {

src/rocker/build/builder.go

@@ -53,6 +53,7 @@ type Builder struct {
 	Rockerfile        string
 	RockerfileContent string
 	ContextDir        string
+	Id                string
 	OutStream         io.Writer
 	InStream          io.ReadCloser
 	Docker            *docker.Client
@@ -360,16 +361,24 @@ func (builder *Builder) getTmpPrefix() string {
 	return ".rockertmp"
 }
 
+// getIdentifier returns the sequence that is unique to the current Rockerfile
+func (builder *Builder) getIdentifier() string {
+	if builder.Id != "" {
+		return builder.Id
+	}
+	return builder.ContextDir + ":" + builder.Rockerfile
+}
+
 // mountsContainerName returns the name of volume container that will be used for a particular MOUNT
 func (builder *Builder) mountsContainerName(destinations []string) string {
 	// TODO: should mounts be reused between different FROMs ?
-	mountID := builder.ContextDir + ":" + builder.Rockerfile + ":" + strings.Join(destinations, ":")
+	mountID := builder.getIdentifier() + ":" + strings.Join(destinations, ":")
 	return fmt.Sprintf("rocker_mount_%.6x", md5.Sum([]byte(mountID)))
 }
 
 // exportsContainerName return the name of volume container that will be used for EXPORTs
 func (builder *Builder) exportsContainerName() string {
-	mountID := builder.ContextDir + ":" + builder.Rockerfile
+	mountID := builder.getIdentifier()
 	return fmt.Sprintf("rocker_exports_%.6x", md5.Sum([]byte(mountID)))
 }