docker-image-store.go

package main

import (
	"fmt"
	"path/filepath"
	"runtime"

	"github.com/docker/distribution/reference"
	"github.com/docker/docker/api/types"
	_ "github.com/docker/docker/daemon/graphdriver/register"
	"github.com/docker/docker/distribution"
	"github.com/docker/docker/distribution/xfer"
	"github.com/docker/docker/image"
	"github.com/docker/docker/layer"
	"github.com/docker/docker/pkg/idtools"
	"github.com/docker/docker/pkg/progress"
	"github.com/docker/docker/plugin"
	"github.com/docker/docker/registry"
	"golang.org/x/net/context"
)

type progressWriter struct {
}

func (writer progressWriter) WriteProgress(prog progress.Progress) error {
	fmt.Println(prog.Message)
	return nil
}

func main() {

	registryService, err := registry.NewService(registry.ServiceOptions{})
	if err != nil {
		return
	}

	mappings, err := idtools.NewIDMappings("pknopf", "users")
	if err != nil {
		return
	}

	pluginStore := plugin.NewStore()

	layerStore, err := layer.NewStoreFromOptions(layer.StoreOptions{
		StorePath:                 "/var/lib/darch",
		MetadataStorePathTemplate: filepath.Join("/var/lib/darch", "image", "%s", "layerdb"),
		GraphDriver:               "vfs",
		GraphDriverOptions:        []string{},
		IDMappings:                mappings,
		PluginGetter:              pluginStore,
		ExperimentalEnabled:       false,
		OS:                        runtime.GOOS,
	})
	if err != nil {
		return
	}

	imageRoot := filepath.Join("/var/lib/darch", "image", "vfs")
	ifs, err := image.NewFSStoreBackend(filepath.Join(imageRoot, "imagedb"))
	if err != nil {
		return
	}

	imageStore, err := image.NewImageStore(ifs, runtime.GOOS, layerStore)
	if err != nil {
		return
	}

	ref, err := reference.ParseNamed("docker.io/library/ubuntu:latest")
	if err != nil {
		return
	}

	progressWriter := progressWriter{}

	imagePullConfig := distribution.ImagePullConfig{}
	imagePullConfig.RegistryService = registryService
	imagePullConfig.RequireSchema2 = true
	imagePullConfig.AuthConfig = &types.AuthConfig{}
	imagePullConfig.ProgressOutput = progressWriter
	imagePullConfig.ImageStore = distribution.NewImageConfigStoreFromStore(imageStore)
	lsMap := make(map[string]layer.Store)
	lsMap[runtime.GOOS] = layerStore
	imagePullConfig.DownloadManager = xfer.NewLayerDownloadManager(lsMap, 100)
	distribution.Pull(context.Background(), ref, &imagePullConfig)
}

This is some sample code that I wrote up that allows you to use an internal image/layer store, using dockerd internals. I will be using this for Darch.