Move storage package under registry package

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/storage/delegatelayerhandler.go

@@ -0,0 +1,94 @@
+package storage
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/docker/distribution/storagedriver"
+)
+
+// delegateLayerHandler provides a simple implementation of layerHandler that
+// simply issues HTTP Temporary Redirects to the URL provided by the
+// storagedriver for a given Layer.
+type delegateLayerHandler struct {
+	storageDriver storagedriver.StorageDriver
+	pathMapper    *pathMapper
+	duration      time.Duration
+}
+
+var _ LayerHandler = &delegateLayerHandler{}
+
+func newDelegateLayerHandler(storageDriver storagedriver.StorageDriver, options map[string]interface{}) (LayerHandler, error) {
+	duration := 20 * time.Minute
+	d, ok := options["duration"]
+	if ok {
+		switch d := d.(type) {
+		case time.Duration:
+			duration = d
+		case string:
+			dur, err := time.ParseDuration(d)
+			if err != nil {
+				return nil, fmt.Errorf("Invalid duration: %s", err)
+			}
+			duration = dur
+		}
+	}
+
+	return &delegateLayerHandler{storageDriver: storageDriver, pathMapper: defaultPathMapper, duration: duration}, nil
+}
+
+// Resolve returns an http.Handler which can serve the contents of the given
+// Layer, or an error if not supported by the storagedriver.
+func (lh *delegateLayerHandler) Resolve(layer Layer) (http.Handler, error) {
+	// TODO(bbland): This is just a sanity check to ensure that the
+	// storagedriver supports url generation. It would be nice if we didn't have
+	// to do this twice for non-GET requests.
+	layerURL, err := lh.urlFor(layer, map[string]interface{}{"method": "GET"})
+	if err != nil {
+		return nil, err
+	}
+
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != "GET" {
+			layerURL, err = lh.urlFor(layer, map[string]interface{}{"method": r.Method})
+			if err != nil {
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+		}
+
+		http.Redirect(w, r, layerURL, http.StatusTemporaryRedirect)
+	}), nil
+}
+
+// urlFor returns a download URL for the given layer, or the empty string if
+// unsupported.
+func (lh *delegateLayerHandler) urlFor(layer Layer, options map[string]interface{}) (string, error) {
+	// Crack open the layer to get at the layerStore
+	layerRd, ok := layer.(*layerReader)
+	if !ok {
+		// TODO(stevvooe): We probably want to find a better way to get at the
+		// underlying filesystem path for a given layer. Perhaps, the layer
+		// handler should have its own layer store but right now, it is not
+		// request scoped.
+		return "", fmt.Errorf("unsupported layer type: cannot resolve blob path: %v", layer)
+	}
+
+	if options == nil {
+		options = make(map[string]interface{})
+	}
+	options["expiry"] = time.Now().Add(lh.duration)
+
+	layerURL, err := lh.storageDriver.URLFor(layerRd.path, options)
+	if err != nil {
+		return "", err
+	}
+
+	return layerURL, nil
+}
+
+// init registers the delegate layerHandler backend.
+func init() {
+	RegisterLayerHandler("delegate", LayerHandlerInitFunc(newDelegateLayerHandler))
+}