@@ -226,7 +226,7 @@ func (srv *Server) CmdStop(stdin io.ReadCloser, stdout io.Writer, args ...string

 			if err := container.Stop(); err != nil {

 				return err

 			}

-			fmt.Fprintln(stdout, container.Id)

+			fmt.Fprintln(stdout, container.ShortId())

 		} else {

 			return fmt.Errorf("No such container: %s", name)

 		}

@@ -248,7 +248,7 @@ func (srv *Server) CmdRestart(stdin io.ReadCloser, stdout io.Writer, args ...str

 			if err := container.Restart(); err != nil {

 				return err

 			}

-			fmt.Fprintln(stdout, container.Id)

+			fmt.Fprintln(stdout, container.ShortId())

 		} else {

 			return fmt.Errorf("No such container: %s", name)

 		}

@@ -270,7 +270,7 @@ func (srv *Server) CmdStart(stdin io.ReadCloser, stdout io.Writer, args ...strin

 			if err := container.Start(); err != nil {

 				return err

 			}

-			fmt.Fprintln(stdout, container.Id)

+			fmt.Fprintln(stdout, container.ShortId())

 		} else {

 			return fmt.Errorf("No such container: %s", name)

 		}

@@ -659,7 +659,7 @@ func (srv *Server) CmdPs(stdin io.ReadCloser, stdout io.Writer, args ...string)

 				command = Trunc(command, 20)

 			}

 			for idx, field := range []string{

-				/* ID */ container.Id,

+				/* ID */ container.ShortId(),

 				/* IMAGE */ srv.runtime.repositories.ImageName(container.Image),

 				/* COMMAND */ command,

 				/* CREATED */ HumanDuration(time.Now().Sub(container.Created)) + " ago",

@@ -674,7 +674,7 @@ func (srv *Server) CmdPs(stdin io.ReadCloser, stdout io.Writer, args ...string)

 			}

 			w.Write([]byte{'\n'})

 		} else {

-			stdout.Write([]byte(container.Id + "\n"))

+			stdout.Write([]byte(container.ShortId() + "\n"))

 		}

 	}

 	if !*quiet {

@@ -965,7 +965,7 @@ func (srv *Server) CmdRun(stdin io.ReadCloser, stdout io.Writer, args ...string)

 		if err := container.Start(); err != nil {

 			return err

 		}

-		fmt.Fprintln(stdout, container.Id)

+		fmt.Fprintln(stdout, container.ShortId())

 	}

 	return nil

 }

@@ -555,6 +555,18 @@ func (container *Container) Unmount() error {

 	return Unmount(container.RootfsPath())

 }

+// ShortId returns a shorthand version of the container's id for convenience.

+// A collision with other container shorthands is very unlikely, but possible.

+// 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]

+}

+

 func (container *Container) logPath(name string) string {

 	return path.Join(container.root, fmt.Sprintf("%s-%s.log", container.Id, name))

 }

@@ -21,6 +21,7 @@ type Runtime struct {

 	graph          *Graph

 	repositories   *TagStore

 	authConfig     *auth.AuthConfig

+	idIndex        *TruncIndex

 }

 var sysInitPath string

@@ -47,7 +48,11 @@ func (runtime *Runtime) getContainerElement(id string) *list.Element {

 	return nil

 }

-func (runtime *Runtime) Get(id string) *Container {

+func (runtime *Runtime) Get(name string) *Container {

+	id, err := runtime.idIndex.Get(name)

+	if err != nil {

+		return nil

+	}

 	e := runtime.getContainerElement(id)

 	if e == nil {

 		return nil

@@ -72,6 +77,7 @@ func (runtime *Runtime) Create(config *Config) (*Container, error) {

 	// Generate id

 	id := GenerateId()

 	// Generate default hostname

+	// FIXME: the lxc template no longer needs to set a default hostname

 	if config.Hostname == "" {

 		config.Hostname = id[:12]

 	}

@@ -142,6 +148,7 @@ func (runtime *Runtime) Register(container *Container) error {

 	}

 	// done

 	runtime.containers.PushBack(container)

+	runtime.idIndex.Add(container.Id)

 	return nil

 }

@@ -171,6 +178,7 @@ func (runtime *Runtime) Destroy(container *Container) error {

 		}

 	}

 	// Deregister the container before removing its directory, to avoid race conditions

+	runtime.idIndex.Delete(container.Id)

 	runtime.containers.Remove(element)

 	if err := os.RemoveAll(container.root); err != nil {

 		return fmt.Errorf("Unable to remove filesystem for %v: %v", container.Id, err)

@@ -222,6 +230,7 @@ func (runtime *Runtime) restore() error {

 	return nil

 }

+// FIXME: harmonize with NewGraph()

 func NewRuntime() (*Runtime, error) {

 	return NewRuntimeFromDirectory("/var/lib/docker")

 }

@@ -259,6 +268,7 @@ func NewRuntimeFromDirectory(root string) (*Runtime, error) {

 		graph:          g,

 		repositories:   repositories,

 		authConfig:     authConfig,

+		idIndex:        NewTruncIndex(),

 	}

 	if err := runtime.restore(); err != nil {

@@ -6,6 +6,7 @@ import (

 	"errors"

 	"fmt"

 	"github.com/dotcloud/docker/rcli"

+	"index/suffixarray"

 	"io"

 	"io/ioutil"

 	"net/http"

@@ -270,3 +271,66 @@ func getTotalUsedFds() int {

 	}

 	return -1

 }

+

+// TruncIndex allows the retrieval of string identifiers by any of their unique prefixes.

+// This is used to retrieve image and container IDs by more convenient shorthand prefixes.

+type TruncIndex struct {

+	index *suffixarray.Index

+	ids   map[string]bool

+	bytes []byte

+}

+

+func NewTruncIndex() *TruncIndex {

+	return &TruncIndex{

+		index: suffixarray.New([]byte{' '}),

+		ids:   make(map[string]bool),

+		bytes: []byte{' '},

+	}

+}

+

+func (idx *TruncIndex) Add(id string) error {

+	if strings.Contains(id, " ") {

+		return fmt.Errorf("Illegal character: ' '")

+	}

+	if _, exists := idx.ids[id]; exists {

+		return fmt.Errorf("Id already exists: %s", id)

+	}

+	idx.ids[id] = true

+	idx.bytes = append(idx.bytes, []byte(id+" ")...)

+	idx.index = suffixarray.New(idx.bytes)

+	return nil

+}

+

+func (idx *TruncIndex) Delete(id string) error {

+	if _, exists := idx.ids[id]; !exists {

+		return fmt.Errorf("No such id: %s", id)

+	}

+	before, after, err := idx.lookup(id)

+	if err != nil {

+		return err

+	}

+	delete(idx.ids, id)

+	idx.bytes = append(idx.bytes[:before], idx.bytes[after:]...)

+	idx.index = suffixarray.New(idx.bytes)

+	return nil

+}

+

+func (idx *TruncIndex) lookup(s string) (int, int, error) {

+	offsets := idx.index.Lookup([]byte(" "+s), -1)

+	//log.Printf("lookup(%s): %v (index bytes: '%s')\n", s, offsets, idx.index.Bytes())

+	if offsets == nil || len(offsets) == 0 || len(offsets) > 1 {

+		return -1, -1, fmt.Errorf("No such id: %s", s)

+	}

+	offsetBefore := offsets[0] + 1

+	offsetAfter := offsetBefore + strings.Index(string(idx.bytes[offsetBefore:]), " ")

+	return offsetBefore, offsetAfter, nil

+}

+

+func (idx *TruncIndex) Get(s string) (string, error) {

+	before, after, err := idx.lookup(s)

+	//log.Printf("Get(%s) bytes=|%s| before=|%d| after=|%d|\n", s, idx.bytes, before, after)

+	if err != nil {

+		return "", err

+	}

+	return string(idx.bytes[before:after]), err

+}

@@ -124,3 +124,85 @@ func TestWriteBroadcaster(t *testing.T) {

 	writer.Close()

 }

+

+// Test the behavior of TruncIndex, an index for querying IDs from a non-conflicting prefix.

+func TestTruncIndex(t *testing.T) {

+	index := NewTruncIndex()

+	// Get on an empty index

+	if _, err := index.Get("foobar"); err == nil {

+		t.Fatal("Get on an empty index should return an error")

+	}

+

+	// Spaces should be illegal in an id

+	if err := index.Add("I have a space"); err == nil {

+		t.Fatalf("Adding an id with ' ' should return an error")

+	}

+

+	id := "99b36c2c326ccc11e726eee6ee78a0baf166ef96"

+	// Add an id

+	if err := index.Add(id); err != nil {

+		t.Fatal(err)

+	}

+	// Get a non-existing id

+	assertIndexGet(t, index, "abracadabra", "", true)

+	// Get the exact id

+	assertIndexGet(t, index, id, id, false)

+	// The first letter should match

+	assertIndexGet(t, index, id[:1], id, false)

+	// The first half should match

+	assertIndexGet(t, index, id[:len(id)/2], id, false)

+	// The second half should NOT match

+	assertIndexGet(t, index, id[len(id)/2:], "", true)

+

+	id2 := id[:6] + "blabla"

+	// Add an id

+	if err := index.Add(id2); err != nil {

+		t.Fatal(err)

+	}

+	// Both exact IDs should work

+	assertIndexGet(t, index, id, id, false)

+	assertIndexGet(t, index, id2, id2, false)

+

+	// 6 characters or less should conflict

+	assertIndexGet(t, index, id[:6], "", true)

+	assertIndexGet(t, index, id[:4], "", true)

+	assertIndexGet(t, index, id[:1], "", true)

+

+	// 7 characters should NOT conflict

+	assertIndexGet(t, index, id[:7], id, false)

+	assertIndexGet(t, index, id2[:7], id2, false)

+

+	// Deleting a non-existing id should return an error

+	if err := index.Delete("non-existing"); err == nil {

+		t.Fatalf("Deleting a non-existing id should return an error")

+	}

+

+	// Deleting id2 should remove conflicts

+	if err := index.Delete(id2); err != nil {

+		t.Fatal(err)

+	}

+	// id2 should no longer work

+	assertIndexGet(t, index, id2, "", true)

+	assertIndexGet(t, index, id2[:7], "", true)

+	assertIndexGet(t, index, id2[:11], "", true)

+

+	// conflicts between id and id2 should be gone

+	assertIndexGet(t, index, id[:6], id, false)

+	assertIndexGet(t, index, id[:4], id, false)

+	assertIndexGet(t, index, id[:1], id, false)

+

+	// non-conflicting substrings should still not conflict

+	assertIndexGet(t, index, id[:7], id, false)

+	assertIndexGet(t, index, id[:15], id, false)

+	assertIndexGet(t, index, id, id, false)

+}

+

+func assertIndexGet(t *testing.T, index *TruncIndex, input, expectedResult string, expectError bool) {

+	if result, err := index.Get(input); err != nil && !expectError {

+		t.Fatalf("Unexpected error getting '%s': %s", input, err)

+	} else if err == nil && expectError {

+		t.Fatalf("Getting '%s' should return an error", input)

+	} else if result != expectedResult {

+		t.Fatalf("Getting '%s' returned '%s' instead of '%s'", input, result, expectedResult)

+	}

+}