Initial implementation of Layer API

The http API has its first set of endpoints to implement the core aspects of
fetching and uploading layers. Uploads can be started and completed in a single
chunk and the content can be fetched via tarsum. Most proposed error conditions
should be represented but edge cases likely remain.

In this version, note that the layers are still called layers, even though the
routes are pointing to blobs. This will change with backend refactoring over
the next few weeks.

The unit tests are a bit of a shamble but these need to be carefully written
along with the core specification process. As the the client-server interaction
solidifies, we can port this into a verification suite for registry providers.

app.go

@@ -3,7 +3,11 @@ package registry
 import (
 	"net/http"
 
+	"github.com/docker/docker-registry/storagedriver"
+	"github.com/docker/docker-registry/storagedriver/factory"
+
 	"github.com/docker/docker-registry/configuration"
+	"github.com/docker/docker-registry/storage"
 
 	log "github.com/Sirupsen/logrus"
 	"github.com/gorilla/mux"
@@ -16,6 +20,12 @@ type App struct {
 	Config configuration.Configuration
 
 	router *mux.Router
+
+	// driver maintains the app global storage driver instance.
+	driver storagedriver.StorageDriver
+
+	// services contains the main services instance for the application.
+	services *storage.Services
 }
 
 // NewApp takes a configuration and returns a configured app, ready to serve
@@ -29,11 +39,23 @@ func NewApp(configuration configuration.Configuration) *App {
 
 	// Register the handler dispatchers.
 	app.register(routeNameImageManifest, imageManifestDispatcher)
-	app.register(routeNameBlob, layerDispatcher)
 	app.register(routeNameTags, tagsDispatcher)
+	app.register(routeNameBlob, layerDispatcher)
 	app.register(routeNameBlobUpload, layerUploadDispatcher)
 	app.register(routeNameBlobUploadResume, layerUploadDispatcher)
 
+	driver, err := factory.Create(configuration.Storage.Type(), configuration.Storage.Parameters())
+
+	if err != nil {
+		// TODO(stevvooe): Move the creation of a service into a protected
+		// method, where this is created lazily. Its status can be queried via
+		// a health check.
+		panic(err)
+	}
+
+	app.driver = driver
+	app.services = storage.NewServices(app.driver)
+
 	return app
 }
 
@@ -64,6 +86,22 @@ type dispatchFunc func(ctx *Context, r *http.Request) http.Handler
 // TODO(stevvooe): dispatchers should probably have some validation error
 // chain with proper error reporting.
 
+// singleStatusResponseWriter only allows the first status to be written to be
+// the valid request status. The current use case of this class should be
+// factored out.
+type singleStatusResponseWriter struct {
+	http.ResponseWriter
+	status int
+}
+
+func (ssrw *singleStatusResponseWriter) WriteHeader(status int) {
+	if ssrw.status != 0 {
+		return
+	}
+	ssrw.status = status
+	ssrw.ResponseWriter.WriteHeader(status)
+}
+
 // dispatcher returns a handler that constructs a request specific context and
 // handler, using the dispatch factory function.
 func (app *App) dispatcher(dispatch dispatchFunc) http.Handler {
@@ -80,14 +118,17 @@ func (app *App) dispatcher(dispatch dispatchFunc) http.Handler {
 		context.log = log.WithField("name", context.Name)
 		handler := dispatch(context, r)
 
+		ssrw := &singleStatusResponseWriter{ResponseWriter: w}
 		context.log.Infoln("handler", resolveHandlerName(r.Method, handler))
-		handler.ServeHTTP(w, r)
+		handler.ServeHTTP(ssrw, r)
 
 		// Automated error response handling here. Handlers may return their
 		// own errors if they need different behavior (such as range errors
 		// for layer upload).
-		if len(context.Errors.Errors) > 0 {
-			w.WriteHeader(http.StatusBadRequest)
+		if context.Errors.Len() > 0 {
+			if ssrw.status == 0 {
+				w.WriteHeader(http.StatusBadRequest)
+			}
 			serveJSON(w, context.Errors)
 		}
 	})