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

commands.go

@@ -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
 }

container.go

@@ -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))
 }

runtime.go

@@ -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 {

utils.go

@@ -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
+}

utils_test.go

@@ -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)
+	}
+}