Show shorthand image IDs for convenience. Shorthand IDs (or any non-conflicting prefix) can be used to lookup images

commands.go

@@ -372,7 +372,7 @@ func (srv *Server) CmdHistory(stdin io.ReadCloser, stdout io.Writer, args ...str
 	fmt.Fprintf(w, "ID\tCREATED\tCREATED BY\n")
 	return image.WalkHistory(func(img *Image) error {
 		fmt.Fprintf(w, "%s\t%s\t%s\n",
-			srv.runtime.repositories.ImageName(img.Id),
+			srv.runtime.repositories.ImageName(img.ShortId()),
 			HumanDuration(time.Now().Sub(img.Created))+" ago",
 			strings.Join(img.ContainerConfig.Cmd, " "),
 		)
@@ -458,7 +458,7 @@ func (srv *Server) CmdImport(stdin io.ReadCloser, stdout io.Writer, args ...stri
 			return err
 		}
 	}
-	fmt.Fprintln(stdout, img.Id)
+	fmt.Fprintln(stdout, img.ShortId())
 	return nil
 }
 
@@ -591,7 +591,7 @@ func (srv *Server) CmdImages(stdin io.ReadCloser, stdout io.Writer, args ...stri
 				for idx, field := range []string{
 					/* REPOSITORY */ name,
 					/* TAG */ tag,
-					/* ID */ id,
+					/* ID */ TruncateId(id),
 					/* CREATED */ HumanDuration(time.Now().Sub(image.Created)) + " ago",
 					/* PARENT */ srv.runtime.repositories.ImageName(image.Parent),
 				} {
@@ -603,7 +603,7 @@ func (srv *Server) CmdImages(stdin io.ReadCloser, stdout io.Writer, args ...stri
 				}
 				w.Write([]byte{'\n'})
 			} else {
-				stdout.Write([]byte(image.Id + "\n"))
+				stdout.Write([]byte(image.ShortId() + "\n"))
 			}
 		}
 	}
@@ -614,7 +614,7 @@ func (srv *Server) CmdImages(stdin io.ReadCloser, stdout io.Writer, args ...stri
 				for idx, field := range []string{
 					/* REPOSITORY */ "<none>",
 					/* TAG */ "<none>",
-					/* ID */ id,
+					/* ID */ TruncateId(id),
 					/* CREATED */ HumanDuration(time.Now().Sub(image.Created)) + " ago",
 					/* PARENT */ srv.runtime.repositories.ImageName(image.Parent),
 				} {
@@ -626,7 +626,7 @@ func (srv *Server) CmdImages(stdin io.ReadCloser, stdout io.Writer, args ...stri
 				}
 				w.Write([]byte{'\n'})
 			} else {
-				stdout.Write([]byte(image.Id + "\n"))
+				stdout.Write([]byte(image.ShortId() + "\n"))
 			}
 		}
 	}
@@ -700,7 +700,7 @@ func (srv *Server) CmdCommit(stdin io.ReadCloser, stdout io.Writer, args ...stri
 	if err != nil {
 		return err
 	}
-	fmt.Fprintln(stdout, img.Id)
+	fmt.Fprintln(stdout, img.ShortId())
 	return nil
 }
 

container.go

@@ -566,11 +566,7 @@ func (container *Container) Unmount() error {
 // In case of a collision a lookup with Runtime.Get() will fail, and the caller
 // will need to use a langer prefix, or the full-length container Id.
 func (container *Container) ShortId() string {
-	shortLen := 12
-	if len(container.Id) < shortLen {
-		shortLen = len(container.Id)
-	}
-	return container.Id[:shortLen]
+	return TruncateId(container.Id)
 }
 
 func (container *Container) logPath(name string) string {

graph.go

@@ -12,7 +12,8 @@ import (
 
 // A Graph is a store for versioned filesystem images, and the relationship between them.
 type Graph struct {
-	Root string
+	Root    string
+	idIndex *TruncIndex
 }
 
 // NewGraph instanciates a new graph at the given root path in the filesystem.
@@ -26,9 +27,26 @@ func NewGraph(root string) (*Graph, error) {
 	if err := os.Mkdir(root, 0700); err != nil && !os.IsExist(err) {
 		return nil, err
 	}
-	return &Graph{
-		Root: abspath,
-	}, nil
+	graph := &Graph{
+		Root:    abspath,
+		idIndex: NewTruncIndex(),
+	}
+	if err := graph.restore(); err != nil {
+		return nil, err
+	}
+	return graph, nil
+}
+
+func (graph *Graph) restore() error {
+	dir, err := ioutil.ReadDir(graph.Root)
+	if err != nil {
+		return err
+	}
+	for _, v := range dir {
+		id := v.Name()
+		graph.idIndex.Add(id)
+	}
+	return nil
 }
 
 // FIXME: Implement error subclass instead of looking at the error text
@@ -47,7 +65,11 @@ func (graph *Graph) Exists(id string) bool {
 }
 
 // Get returns the image with the given id, or an error if the image doesn't exist.
-func (graph *Graph) Get(id string) (*Image, error) {
+func (graph *Graph) Get(name string) (*Image, error) {
+	id, err := graph.idIndex.Get(name)
+	if err != nil {
+		return nil, err
+	}
 	// FIXME: return nil when the image doesn't exist, instead of an error
 	img, err := LoadImage(graph.imageRoot(id))
 	if err != nil {
@@ -101,6 +123,7 @@ func (graph *Graph) Register(layerData Archive, img *Image) error {
 		return err
 	}
 	img.graph = graph
+	graph.idIndex.Add(img.Id)
 	return nil
 }
 
@@ -143,8 +166,11 @@ func (graph *Graph) Delete(id string) error {
 	if err != nil {
 		return err
 	}
+	graph.idIndex.Delete(id)
 	err = os.Rename(graph.imageRoot(id), garbage.imageRoot(id))
 	if err != nil {
+		// FIXME: this introduces a race condition in Delete() if the image is already present
+		// in garbage. Let's store at random names in grabage instead.
 		if isNotEmpty(err) {
 			Debugf("The image %s is already present in garbage. Removing it.", id)
 			if err = os.RemoveAll(garbage.imageRoot(id)); err != nil {
@@ -170,7 +196,11 @@ func (graph *Graph) Undelete(id string) error {
 	if err != nil {
 		return err
 	}
-	return os.Rename(garbage.imageRoot(id), graph.imageRoot(id))
+	if err := os.Rename(garbage.imageRoot(id), graph.imageRoot(id)); err != nil {
+		return err
+	}
+	graph.idIndex.Add(id)
+	return nil
 }
 
 // GarbageCollect definitely deletes all images moved to the garbage

image.go

@@ -150,6 +150,10 @@ func (image *Image) Changes(rw string) ([]Change, error) {
 	return Changes(layers, rw)
 }
 
+func (image *Image) ShortId() string {
+	return TruncateId(image.Id)
+}
+
 func ValidateId(id string) error {
 	if id == "" {
 		return fmt.Errorf("Image id can't be empty")

tags.go

@@ -106,7 +106,7 @@ func (store *TagStore) ImageName(id string) string {
 	if names, exists := store.ById()[id]; exists && len(names) > 0 {
 		return names[0]
 	}
-	return id
+	return TruncateId(id)
 }
 
 func (store *TagStore) Set(repoName, tag, imageName string, force bool) error {

utils.go

@@ -334,3 +334,15 @@ func (idx *TruncIndex) Get(s string) (string, error) {
 	}
 	return string(idx.bytes[before:after]), err
 }
+
+// TruncateId returns a shorthand version of a string identifier for convenience.
+// A collision with other shorthands is very unlikely, but possible.
+// In case of a collision a lookup with TruncIndex.Get() will fail, and the caller
+// will need to use a langer prefix, or the full-length Id.
+func TruncateId(id string) string {
+	shortLen := 12
+	if len(id) < shortLen {
+		shortLen = len(id)
+	}
+	return id[:shortLen]
+}