@@ -145,8 +145,55 @@ func (builder *Builder) Commit(container *Container, repository, tag, comment, a

 	return img, nil

 }

-func (builder *Builder) Build(dockerfile io.Reader, stdout io.Writer) error {

-	var image, base *Image

+func (builder *Builder) clearTmp(containers, images map[string]struct{}) {

+	for c := range containers {

+		tmp := builder.runtime.Get(c)

+		builder.runtime.Destroy(tmp)

+		Debugf("Removing container %s", c)

+	}

+	for i := range images {

+		builder.runtime.graph.Delete(i)

+		Debugf("Removing image %s", i)

+	}

+}

+

+func (builder *Builder) getCachedImage(image *Image, config *Config) (*Image, error) {

+	// Retrieve all images

+	images, err := builder.graph.All()

+	if err != nil {

+		return nil, err

+	}

+

+	// Store the tree in a map of map (map[parentId][childId])

+	imageMap := make(map[string]map[string]struct{})

+	for _, img := range images {

+		if _, exists := imageMap[img.Parent]; !exists {

+			imageMap[img.Parent] = make(map[string]struct{})

+		}

+		imageMap[img.Parent][img.Id] = struct{}{}

+	}

+

+	// Loop on the children of the given image and check the config

+	for elem := range imageMap[image.Id] {

+		img, err := builder.graph.Get(elem)

+		if err != nil {

+			return nil, err

+		}

+		if CompareConfig(&img.ContainerConfig, config) {

+			return img, nil

+		}

+	}

+	return nil, nil

+}

+

+func (builder *Builder) Build(dockerfile io.Reader, stdout io.Writer) (*Image, error) {

+	var (

+		image, base   *Image

+		maintainer    string

+		tmpContainers map[string]struct{} = make(map[string]struct{})

+		tmpImages     map[string]struct{} = make(map[string]struct{})

+	)

+	defer builder.clearTmp(tmpContainers, tmpImages)

 	file := bufio.NewReader(dockerfile)

 	for {

@@ -204,6 +251,14 @@ func (builder *Builder) Build(dockerfile io.Reader, stdout io.Writer) error {

 				return err

 			}

+			if cache, err := builder.getCachedImage(image, config); err != nil {

+				return nil, err

+			} else if cache != nil {

+				image = cache

+				fmt.Fprintf(stdout, "===> %s\n", image.ShortId())

+				break

+			}

+

 			// Create the container and start it

 			c, err := builder.Create(config)

 			if err != nil {

@@ -276,10 +331,16 @@ func (builder *Builder) Build(dockerfile io.Reader, stdout io.Writer) error {

 			fmt.Fprintf(stdout, "Skipping unknown op %s\n", tmp[0])

 		}

 	}

-	if base != nil {

-		fmt.Fprintf(stdout, "Build finished. image id: %s\n", base.Id)

-	} else {

-		fmt.Fprintf(stdout, "An error occured during the build\n")

+	if image != nil {

+		// The build is successful, keep the temporary containers and images

+		for i := range tmpImages {

+			delete(tmpImages, i)

+		}

+		for i := range tmpContainers {

+			delete(tmpContainers, i)

+		}

+		fmt.Fprintf(stdout, "Build finished. image id: %s\n", image.ShortId())

+		return image, nil

 	}

-	return nil

+	return nil, fmt.Errorf("An error occured during the build\n")

 }

@@ -474,3 +474,50 @@ func FindCgroupMountpoint(cgroupType string) (string, error) {

 	return "", fmt.Errorf("cgroup mountpoint not found for %s", cgroupType)

 }

+

+// Compare two Config struct. Do not compare the "Image" nor "Hostname" fields

+// If OpenStdin is set, then it differs

+func CompareConfig(a, b *Config) bool {

+	if a == nil || b == nil ||

+		a.OpenStdin || b.OpenStdin {

+		return false

+	}

+	if a.AttachStdout != b.AttachStdout ||

+		a.AttachStderr != b.AttachStderr ||

+		a.User != b.User ||

+		a.Memory != b.Memory ||

+		a.MemorySwap != b.MemorySwap ||

+		a.OpenStdin != b.OpenStdin ||

+		a.Tty != b.Tty {

+		return false

+	}

+	if len(a.Cmd) != len(b.Cmd) ||

+		len(a.Dns) != len(b.Dns) ||

+		len(a.Env) != len(b.Env) ||

+		len(a.PortSpecs) != len(b.PortSpecs) {

+		return false

+	}

+

+	for i := 0; i < len(a.Cmd); i++ {

+		if a.Cmd[i] != b.Cmd[i] {

+			return false

+		}

+	}

+	for i := 0; i < len(a.Dns); i++ {

+		if a.Dns[i] != b.Dns[i] {

+			return false

+		}

+	}

+	for i := 0; i < len(a.Env); i++ {

+		if a.Env[i] != b.Env[i] {

+			return false

+		}

+	}

+	for i := 0; i < len(a.PortSpecs); i++ {

+		if a.PortSpecs[i] != b.PortSpecs[i] {

+			return false

+		}

+	}

+

+	return true

+}