distribution/docs/storage/delegatelayerhandler.go

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package storage
import (
"fmt"
"net/http"
"time"
"github.com/docker/distribution"
storagedriver "github.com/docker/distribution/registry/storage/driver"
)
// 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 distribution.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 distribution.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))
}