Refactoring cloudfactory layer handler into a more generic storage

middleware concept.

This also breaks the dependency the storage package had on goamz
Signed-off-by: David Lawrence <david.lawrence@docker.com> (github: endophage)

cmd/registry/main.go

@@ -17,6 +17,7 @@ import (
 	"github.com/docker/distribution/registry/handlers"
 	_ "github.com/docker/distribution/registry/storage/driver/filesystem"
 	_ "github.com/docker/distribution/registry/storage/driver/inmemory"
+	_ "github.com/docker/distribution/registry/storage/driver/middleware/cloudfront"
 	_ "github.com/docker/distribution/registry/storage/driver/s3"
 	"github.com/docker/distribution/version"
 	gorhandlers "github.com/gorilla/handlers"

configuration/configuration.go

@@ -26,8 +26,8 @@ type Configuration struct {
 	// used to gate requests.
 	Auth Auth `yaml:"auth,omitempty"`
 
-	// LayerHandler specifies a middleware for serving image layers.
+	// Middleware lists all middlewares to be used by the registry.
-	LayerHandler LayerHandler `yaml:"layerhandler,omitempty"`
+	Middleware []Middleware `yaml:"middleware,omitempty"`
 
 	// Reporting is the configuration for error reporting
 	Reporting Reporting `yaml:"reporting,omitempty"`
@@ -295,60 +295,18 @@ type NewRelicReporting struct {
 	Name string `yaml:"name,omitempty"`
 }
 
-// LayerHandler defines the configuration for middleware layer serving
+// Middleware configures named middlewares to be applied at injection points.
-type LayerHandler map[string]Parameters
+type Middleware struct {
-
+	// Name the middleware registers itself as
-// Type returns the layerhandler type
+	Name string `yaml:"name"`
-func (layerHandler LayerHandler) Type() string {
+	// Injection point the middleware should be applied at
-	// Return only key in this map
+	// N.B. ensure the middleware is applicable for the named injection point, middlewares
-	for k := range layerHandler {
+	//      for different injection points are not interchangeable.
-		return k
+	Inject string `yaml:"inject"`
-	}
+	// Flag to disable middleware easily
-	return ""
+	Disabled bool `yaml:"Disabled,omitempty"`
-}
+	// Map of parameters that will be passed to the middleware's initialization function
-
+	Options Parameters `yaml:"options"`
-// Parameters returns the Parameters map for a LayerHandler configuration
-func (layerHandler LayerHandler) Parameters() Parameters {
-	return layerHandler[layerHandler.Type()]
-}
-
-// UnmarshalYAML implements the yaml.Unmarshaler interface
-// Unmarshals a single item map into a Storage or a string into a Storage type with no parameters
-func (layerHandler *LayerHandler) UnmarshalYAML(unmarshal func(interface{}) error) error {
-	var storageMap map[string]Parameters
-	err := unmarshal(&storageMap)
-	if err == nil {
-		if len(storageMap) > 1 {
-			types := make([]string, 0, len(storageMap))
-			for k := range storageMap {
-				types = append(types, k)
-			}
-			return fmt.Errorf("Must provide exactly one layerhandler type. Provided: %v", types)
-		}
-		*layerHandler = storageMap
-		return nil
-	}
-
-	var storageType string
-	err = unmarshal(&storageType)
-	if err == nil {
-		*layerHandler = LayerHandler{storageType: Parameters{}}
-		return nil
-	}
-
-	return err
-}
-
-// MarshalYAML implements the yaml.Marshaler interface
-func (layerHandler LayerHandler) MarshalYAML() (interface{}, error) {
-	if layerHandler.Parameters() == nil {
-		t := layerHandler.Type()
-		if t == "" {
-			return nil, nil
-		}
-		return t, nil
-	}
-	return map[string]Parameters(layerHandler), nil
 }
 
 // Parse parses an input configuration yaml document into a Configuration struct

registry.go

@@ -2,6 +2,7 @@ package distribution
 
 import (
 	"io"
+	"net/http"
 	"time"
 
 	"github.com/docker/distribution/digest"
@@ -106,6 +107,11 @@ type Layer interface {
 
 	// CreatedAt returns the time this layer was created.
 	CreatedAt() time.Time
+
+	// ServeHTTP allows a layer to serve itself, whether by providing
+	// a redirect directly to the content, or by serving the content
+	// itself
+	ServeHTTP(w http.ResponseWriter, r *http.Request)
 }
 
 // LayerUpload provides a handle for working with in-progress uploads.

registry/handlers/app.go

@@ -16,6 +16,7 @@ import (
 	"github.com/docker/distribution/registry/storage"
 	storagedriver "github.com/docker/distribution/registry/storage/driver"
 	"github.com/docker/distribution/registry/storage/driver/factory"
+	storagemiddleware "github.com/docker/distribution/registry/storage/driver/middleware"
 	"github.com/gorilla/mux"
 	"golang.org/x/net/context"
 )
@@ -41,8 +42,6 @@ type App struct {
 		sink   notifications.Sink
 		source notifications.SourceRecord
 	}
-
-	layerHandler storage.LayerHandler // allows dispatch of layer serving to external provider
 }
 
 // Value intercepts calls context.Context.Value, returning the current app id,
@@ -101,14 +100,22 @@ func NewApp(ctx context.Context, configuration configuration.Configuration) *App
 		app.accessController = accessController
 	}
 
-	layerHandlerType := configuration.LayerHandler.Type()
+	for _, mw := range configuration.Middleware {
+		if mw.Inject == "registry" {
+			// registry middleware can director wrap app.registry identically to storage middlewares with driver
+			panic(fmt.Sprintf("unable to configure registry middleware (%s): %v", mw.Name, err))
+		} else if mw.Inject == "repository" {
+			// we have to do something more intelligent with repository middleware, It needs to be staged
+			// for later to be wrapped around the repository at request time.
+			panic(fmt.Sprintf("unable to configure repository middleware (%s): %v", mw.Name, err))
+		} else if mw.Inject == "storage" {
+			smw, err := storagemiddleware.GetStorageMiddleware(mw.Name, mw.Options, app.driver)
 
-	if layerHandlerType != "" {
-		lh, err := storage.GetLayerHandler(layerHandlerType, configuration.LayerHandler.Parameters(), app.driver)
 			if err != nil {
-			panic(fmt.Sprintf("unable to configure layer handler (%s): %v", layerHandlerType, err))
+				panic(fmt.Sprintf("unable to configure storage middleware (%s): %v", mw.Name, err))
+			}
+			app.driver = smw
 		}
-		app.layerHandler = lh
 	}
 
 	return app

registry/handlers/layer.go

@@ -49,8 +49,8 @@ type layerHandler struct {
 // response.
 func (lh *layerHandler) GetLayer(w http.ResponseWriter, r *http.Request) {
 	ctxu.GetLogger(lh).Debug("GetImageLayer")
-	layers := lh.Repository.Layers()
+	layerStore := lh.Repository.Layers()
-	layer, err := layers.Fetch(lh.Digest)
+	layerReader, err := layerStore.Fetch(lh.Digest)
 
 	if err != nil {
 		switch err := err.(type) {
@@ -62,17 +62,6 @@ func (lh *layerHandler) GetLayer(w http.ResponseWriter, r *http.Request) {
 		}
 		return
 	}
-	defer layer.Close()
 
-	w.Header().Set("Docker-Content-Digest", lh.Digest.String())
+	layerReader.ServeHTTP(w, r)
-
-	if lh.layerHandler != nil {
-		handler, _ := lh.layerHandler.Resolve(layer)
-		if handler != nil {
-			handler.ServeHTTP(w, r)
-			return
-		}
-	}
-
-	http.ServeContent(w, r, layer.Digest().String(), layer.CreatedAt(), layer)
 }

registry/storage/delegatelayerhandler.go

@@ -1,95 +0,0 @@
-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))
-}

registry/storage/driver/middleware/cloudfront/middleware.go

@@ -1,34 +1,36 @@
-package storage
+// Package middleware - cloudfront wrapper for storage libs
+// N.B. currently only works with S3, not arbitrary sites
+//
+package middleware
 
 import (
 	"crypto/x509"
 	"encoding/pem"
 	"fmt"
 	"io/ioutil"
-	"net/http"
 	"net/url"
 	"time"
 
 	"github.com/AdRoll/goamz/cloudfront"
-	"github.com/docker/distribution"
 	storagedriver "github.com/docker/distribution/registry/storage/driver"
+	storagemiddleware "github.com/docker/distribution/registry/storage/driver/middleware"
 )
 
-// cloudFrontLayerHandler provides an simple implementation of layerHandler that
+// cloudFrontStorageMiddleware provides an simple implementation of layerHandler that
 // constructs temporary signed CloudFront URLs from the storagedriver layer URL,
 // then issues HTTP Temporary Redirects to this CloudFront content URL.
-type cloudFrontLayerHandler struct {
+type cloudFrontStorageMiddleware struct {
+	storagedriver.StorageDriver
 	cloudfront *cloudfront.CloudFront
-	delegateLayerHandler *delegateLayerHandler
 	duration   time.Duration
 }
 
-var _ LayerHandler = &cloudFrontLayerHandler{}
+var _ storagedriver.StorageDriver = &cloudFrontStorageMiddleware{}
 
 // newCloudFrontLayerHandler constructs and returns a new CloudFront
 // LayerHandler implementation.
 // Required options: baseurl, privatekey, keypairid
-func newCloudFrontLayerHandler(storageDriver storagedriver.StorageDriver, options map[string]interface{}) (LayerHandler, error) {
+func newCloudFrontStorageMiddleware(storageDriver storagedriver.StorageDriver, options map[string]interface{}) (storagedriver.StorageDriver, error) {
 	base, ok := options["baseurl"]
 	if !ok {
 		return nil, fmt.Errorf("No baseurl provided")
@@ -68,12 +70,6 @@ func newCloudFrontLayerHandler(storageDriver storagedriver.StorageDriver, option
 		return nil, err
 	}
 
-	lh, err := newDelegateLayerHandler(storageDriver, options)
-	if err != nil {
-		return nil, err
-	}
-	dlh := lh.(*delegateLayerHandler)
-
 	cf := cloudfront.New(baseURL, privateKey, keypairID)
 
 	duration := 20 * time.Minute
@@ -91,33 +87,33 @@ func newCloudFrontLayerHandler(storageDriver storagedriver.StorageDriver, option
 		}
 	}
 
-	return &cloudFrontLayerHandler{cloudfront: cf, delegateLayerHandler: dlh, duration: duration}, nil
+	return &cloudFrontStorageMiddleware{StorageDriver: storageDriver, cloudfront: cf, 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 *cloudFrontLayerHandler) Resolve(layer distribution.Layer) (http.Handler, error) {
+func (lh *cloudFrontStorageMiddleware) URLFor(path string, options map[string]interface{}) (string, error) {
-	layerURLStr, err := lh.delegateLayerHandler.urlFor(layer, nil)
+	// TODO(endophage): currently only supports S3
+	options["expiry"] = time.Now().Add(lh.duration)
+
+	layerURLStr, err := lh.StorageDriver.URLFor(path, options)
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
 	layerURL, err := url.Parse(layerURLStr)
 	if err != nil {
-		return nil, err
+		return "", err
 	}
 
 	cfURL, err := lh.cloudfront.CannedSignedURL(layerURL.Path, "", time.Now().Add(lh.duration))
 	if err != nil {
-		return nil, err
+		return "", err
 	}
-
+	return cfURL, nil
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		http.Redirect(w, r, cfURL, http.StatusTemporaryRedirect)
-	}), nil
 }
 
 // init registers the cloudfront layerHandler backend.
 func init() {
-	RegisterLayerHandler("cloudfront", LayerHandlerInitFunc(newCloudFrontLayerHandler))
+	storagemiddleware.RegisterStorageMiddleware("cloudfront", storagemiddleware.InitFunc(newCloudFrontStorageMiddleware))
 }

registry/storage/driver/middleware/storagemiddleware.go

@@ -0,0 +1,40 @@
+package storagemiddleware
+
+import (
+	"fmt"
+
+	storagedriver "github.com/docker/distribution/registry/storage/driver"
+)
+
+// InitFunc is the type of a StorageMiddleware factory function and is
+// used to register the contsructor for different StorageMiddleware backends.
+type InitFunc func(storageDriver storagedriver.StorageDriver, options map[string]interface{}) (storagedriver.StorageDriver, error)
+
+var storageMiddlewares map[string]InitFunc
+
+// RegisterStorageMiddleware is used to register an StorageMiddlewareInitFunc for
+// a StorageMiddleware backend with the given name.
+func RegisterStorageMiddleware(name string, initFunc InitFunc) error {
+	if storageMiddlewares == nil {
+		storageMiddlewares = make(map[string]InitFunc)
+	}
+	if _, exists := storageMiddlewares[name]; exists {
+		return fmt.Errorf("name already registered: %s", name)
+	}
+
+	storageMiddlewares[name] = initFunc
+
+	return nil
+}
+
+// GetStorageMiddleware constructs a StorageMiddleware
+// with the given options using the named backend.
+func GetStorageMiddleware(name string, options map[string]interface{}, storageDriver storagedriver.StorageDriver) (storagedriver.StorageDriver, error) {
+	if storageMiddlewares != nil {
+		if initFunc, exists := storageMiddlewares[name]; exists {
+			return initFunc(storageDriver, options)
+		}
+	}
+
+	return nil, fmt.Errorf("no storage middleware registered with name: %s", name)
+}

registry/storage/layerhandler.go

@@ -1,51 +0,0 @@
-package storage
-
-import (
-	"fmt"
-	"net/http"
-
-	"github.com/docker/distribution"
-	storagedriver "github.com/docker/distribution/registry/storage/driver"
-)
-
-// LayerHandler provides middleware for serving the contents of a Layer.
-type LayerHandler interface {
-	// Resolve returns an http.Handler which can serve the contents of a given
-	// Layer if possible, or nil and an error when unsupported. This may
-	// directly serve the contents of the layer or issue a redirect to another
-	// URL hosting the content.
-	Resolve(layer distribution.Layer) (http.Handler, error)
-}
-
-// LayerHandlerInitFunc is the type of a LayerHandler factory function and is
-// used to register the contsructor for different LayerHandler backends.
-type LayerHandlerInitFunc func(storageDriver storagedriver.StorageDriver, options map[string]interface{}) (LayerHandler, error)
-
-var layerHandlers map[string]LayerHandlerInitFunc
-
-// RegisterLayerHandler is used to register an LayerHandlerInitFunc for
-// a LayerHandler backend with the given name.
-func RegisterLayerHandler(name string, initFunc LayerHandlerInitFunc) error {
-	if layerHandlers == nil {
-		layerHandlers = make(map[string]LayerHandlerInitFunc)
-	}
-	if _, exists := layerHandlers[name]; exists {
-		return fmt.Errorf("name already registered: %s", name)
-	}
-
-	layerHandlers[name] = initFunc
-
-	return nil
-}
-
-// GetLayerHandler constructs a LayerHandler
-// with the given options using the named backend.
-func GetLayerHandler(name string, options map[string]interface{}, storageDriver storagedriver.StorageDriver) (LayerHandler, error) {
-	if layerHandlers != nil {
-		if initFunc, exists := layerHandlers[name]; exists {
-			return initFunc(storageDriver, options)
-		}
-	}
-
-	return nil, fmt.Errorf("no layer handler registered with name: %s", name)
-}

registry/storage/layerreader.go

@@ -1,13 +1,14 @@
 package storage
 
 import (
+	"net/http"
 	"time"
 
 	"github.com/docker/distribution"
 	"github.com/docker/distribution/digest"
 )
 
-// layerReadSeeker implements Layer and provides facilities for reading and
+// LayerRead implements Layer and provides facilities for reading and
 // seeking.
 type layerReader struct {
 	fileReader
@@ -17,6 +18,10 @@ type layerReader struct {
 
 var _ distribution.Layer = &layerReader{}
 
+func (lrs *layerReader) Path() string {
+	return lrs.path
+}
+
 func (lrs *layerReader) Digest() digest.Digest {
 	return lrs.digest
 }
@@ -33,3 +38,12 @@ func (lrs *layerReader) CreatedAt() time.Time {
 func (lrs *layerReader) Close() error {
 	return lrs.closeWithErr(distribution.ErrLayerClosed)
 }
+
+func (lrs *layerReader) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Docker-Content-Digest", lrs.digest.String())
+
+	if url, err := lrs.fileReader.driver.URLFor(lrs.Path(), map[string]interface{}{}); err == nil {
+		http.Redirect(w, r, url, http.StatusTemporaryRedirect)
+	}
+	http.ServeContent(w, r, lrs.Digest().String(), lrs.CreatedAt(), lrs)
+}

registry/storage/layerstore.go

@@ -138,7 +138,7 @@ func (ls *layerStore) newLayerUpload(uuid, path string, startedAt time.Time) (di
 		return nil, err
 	}
 
-	return &layerUploadController{
+	return &layerWriter{
 		layerStore:         ls,
 		uuid:               uuid,
 		startedAt:          startedAt,

registry/storage/layerwriter.go

@@ -13,9 +13,11 @@ import (
 	storagedriver "github.com/docker/distribution/registry/storage/driver"
 )
 
-// layerUploadController is used to control the various aspects of resumable
+var _ distribution.LayerUpload = &layerWriter{}
+
+// layerWriter is used to control the various aspects of resumable
 // layer upload. It implements the LayerUpload interface.
-type layerUploadController struct {
+type layerWriter struct {
 	layerStore *layerStore
 
 	uuid      string
@@ -26,65 +28,64 @@ type layerUploadController struct {
 	bufferedFileWriter
 }
 
-var _ distribution.LayerUpload = &layerUploadController{}
+var _ distribution.LayerUpload = &layerWriter{}
 
 // UUID returns the identifier for this upload.
-func (luc *layerUploadController) UUID() string {
+func (lw *layerWriter) UUID() string {
-	return luc.uuid
+	return lw.uuid
 }
 
-func (luc *layerUploadController) StartedAt() time.Time {
+func (lw *layerWriter) StartedAt() time.Time {
-	return luc.startedAt
+	return lw.startedAt
 }
 
 // Finish marks the upload as completed, returning a valid handle to the
 // uploaded layer. The final size and checksum are validated against the
 // contents of the uploaded layer. The checksum should be provided in the
 // format <algorithm>:<hex digest>.
-func (luc *layerUploadController) Finish(digest digest.Digest) (distribution.Layer, error) {
+func (lw *layerWriter) Finish(digest digest.Digest) (distribution.Layer, error) {
-	ctxu.GetLogger(luc.layerStore.repository.ctx).Debug("(*layerUploadController).Finish")
+	ctxu.GetLogger(lw.layerStore.repository.ctx).Debug("(*layerWriter).Finish")
 
-	err := luc.bufferedFileWriter.Close()
+	if err := lw.bufferedFileWriter.Close(); err != nil {
+		return nil, err
+	}
+
+	canonical, err := lw.validateLayer(digest)
 	if err != nil {
 		return nil, err
 	}
 
-	canonical, err := luc.validateLayer(digest)
+	if err := lw.moveLayer(canonical); err != nil {
-	if err != nil {
-		return nil, err
-	}
-
-	if err := luc.moveLayer(canonical); err != nil {
 		// TODO(stevvooe): Cleanup?
 		return nil, err
 	}
 
 	// Link the layer blob into the repository.
-	if err := luc.linkLayer(canonical, digest); err != nil {
+	if err := lw.linkLayer(canonical, digest); err != nil {
 		return nil, err
 	}
 
-	if err := luc.removeResources(); err != nil {
+	if err := lw.removeResources(); err != nil {
 		return nil, err
 	}
 
-	return luc.layerStore.Fetch(canonical)
+	return lw.layerStore.Fetch(canonical)
 }
 
 // Cancel the layer upload process.
-func (luc *layerUploadController) Cancel() error {
+func (lw *layerWriter) Cancel() error {
-	ctxu.GetLogger(luc.layerStore.repository.ctx).Debug("(*layerUploadController).Cancel")
+	ctxu.GetLogger(lw.layerStore.repository.ctx).Debug("(*layerWriter).Cancel")
-	if err := luc.removeResources(); err != nil {
+	if err := lw.removeResources(); err != nil {
 		return err
 	}
 
-	luc.Close()
+	lw.Close()
 	return nil
 }
 
 // validateLayer checks the layer data against the digest, returning an error
 // if it does not match. The canonical digest is returned.
-func (luc *layerUploadController) validateLayer(dgst digest.Digest) (digest.Digest, error) {
+func (lw *layerWriter) validateLayer(dgst digest.Digest) (digest.Digest, error) {
 	digestVerifier, err := digest.NewDigestVerifier(dgst)
 	if err != nil {
 		return "", err
@@ -96,7 +97,7 @@ func (luc *layerUploadController) validateLayer(dgst digest.Digest) (digest.Dige
 	// then only have to fetch the difference.
 
 	// Read the file from the backend driver and validate it.
-	fr, err := newFileReader(luc.bufferedFileWriter.driver, luc.path)
+	fr, err := newFileReader(lw.bufferedFileWriter.driver, lw.path)
 	if err != nil {
 		return "", err
 	}
@@ -125,8 +126,8 @@ func (luc *layerUploadController) validateLayer(dgst digest.Digest) (digest.Dige
 // moveLayer moves the data into its final, hash-qualified destination,
 // identified by dgst. The layer should be validated before commencing the
 // move.
-func (luc *layerUploadController) moveLayer(dgst digest.Digest) error {
+func (lw *layerWriter) moveLayer(dgst digest.Digest) error {
-	blobPath, err := luc.layerStore.repository.registry.pm.path(blobDataPathSpec{
+	blobPath, err := lw.layerStore.repository.registry.pm.path(blobDataPathSpec{
 		digest: dgst,
 	})
 
@@ -135,7 +136,7 @@ func (luc *layerUploadController) moveLayer(dgst digest.Digest) error {
 	}
 
 	// Check for existence
-	if _, err := luc.driver.Stat(blobPath); err != nil {
+	if _, err := lw.driver.Stat(blobPath); err != nil {
 		switch err := err.(type) {
 		case storagedriver.PathNotFoundError:
 			break // ensure that it doesn't exist.
@@ -154,7 +155,7 @@ func (luc *layerUploadController) moveLayer(dgst digest.Digest) error {
 	// the size here and write a zero-length file to blobPath if this is the
 	// case. For the most part, this should only ever happen with zero-length
 	// tars.
-	if _, err := luc.driver.Stat(luc.path); err != nil {
+	if _, err := lw.driver.Stat(lw.path); err != nil {
 		switch err := err.(type) {
 		case storagedriver.PathNotFoundError:
 			// HACK(stevvooe): This is slightly dangerous: if we verify above,
@@ -163,24 +164,24 @@ func (luc *layerUploadController) moveLayer(dgst digest.Digest) error {
 			// prevent this horrid thing, we employ the hack of only allowing
 			// to this happen for the zero tarsum.
 			if dgst == digest.DigestSha256EmptyTar {
-				return luc.driver.PutContent(blobPath, []byte{})
+				return lw.driver.PutContent(blobPath, []byte{})
 			}
 
 			// We let this fail during the move below.
 			logrus.
-				WithField("upload.uuid", luc.UUID()).
+				WithField("upload.uuid", lw.UUID()).
 				WithField("digest", dgst).Warnf("attempted to move zero-length content with non-zero digest")
 		default:
 			return err // unrelated error
 		}
 	}
 
-	return luc.driver.Move(luc.path, blobPath)
+	return lw.driver.Move(lw.path, blobPath)
 }
 
 // linkLayer links a valid, written layer blob into the registry under the
 // named repository for the upload controller.
-func (luc *layerUploadController) linkLayer(canonical digest.Digest, aliases ...digest.Digest) error {
+func (lw *layerWriter) linkLayer(canonical digest.Digest, aliases ...digest.Digest) error {
 	dgsts := append([]digest.Digest{canonical}, aliases...)
 
 	// Don't make duplicate links.
@@ -192,8 +193,8 @@ func (luc *layerUploadController) linkLayer(canonical digest.Digest, aliases ...
 		}
 		seenDigests[dgst] = struct{}{}
 
-		layerLinkPath, err := luc.layerStore.repository.registry.pm.path(layerLinkPathSpec{
+		layerLinkPath, err := lw.layerStore.repository.registry.pm.path(layerLinkPathSpec{
-			name:   luc.layerStore.repository.Name(),
+			name:   lw.layerStore.repository.Name(),
 			digest: dgst,
 		})
 
@@ -201,7 +202,7 @@ func (luc *layerUploadController) linkLayer(canonical digest.Digest, aliases ...
 			return err
 		}
 
-		if err := luc.layerStore.repository.registry.driver.PutContent(layerLinkPath, []byte(canonical)); err != nil {
+		if err := lw.layerStore.repository.registry.driver.PutContent(layerLinkPath, []byte(canonical)); err != nil {
 			return err
 		}
 	}
@@ -212,10 +213,10 @@ func (luc *layerUploadController) linkLayer(canonical digest.Digest, aliases ...
 // removeResources should clean up all resources associated with the upload
 // instance. An error will be returned if the clean up cannot proceed. If the
 // resources are already not present, no error will be returned.
-func (luc *layerUploadController) removeResources() error {
+func (lw *layerWriter) removeResources() error {
-	dataPath, err := luc.layerStore.repository.registry.pm.path(uploadDataPathSpec{
+	dataPath, err := lw.layerStore.repository.registry.pm.path(uploadDataPathSpec{
-		name: luc.layerStore.repository.Name(),
+		name: lw.layerStore.repository.Name(),
-		uuid: luc.uuid,
+		uuid: lw.uuid,
 	})
 
 	if err != nil {
@@ -226,7 +227,7 @@ func (luc *layerUploadController) removeResources() error {
 	// upload related files.
 	dirPath := path.Dir(dataPath)
 
-	if err := luc.driver.Delete(dirPath); err != nil {
+	if err := lw.driver.Delete(dirPath); err != nil {
 		switch err := err.(type) {
 		case storagedriver.PathNotFoundError:
 			break // already gone!