Repository: distribution/distribution (go)

Issue:
Feature Request: Shutdown() method on registry.Registry struct
### Description

I am working on a project that embeds the Distribution Registry. Unless I missed something, there is no way to gracefully shutdown the registry HTTP server from code. The registry server expects a signal on the `quit` channel, which is in a global variable that is private to the package.

I would like to have a shutdown method on the registry.Registry struct so that I can gracefully shutdown an embedded registry HTTP server.

Opening a PR shortly.

Pull request description:
Add Shutdown method to registry.Registry
Adds a Shutdown method to `registry.Registry`. Enables gracefully shutting down an embedded registry HTTP server.

Closes #4337.

Patch:
diff --git a/registry/registry.go b/registry/registry.go
index 96f68b12..b7989f02 100644
--- a/registry/registry.go
+++ b/registry/registry.go
@@ -81,9 +81,6 @@ var tlsVersions = map[string]uint16{
 // defaultLogFormatter is the default formatter to use for logs.
 const defaultLogFormatter = "text"
 
-// this channel gets notified when process receives signal. It is global to ease unit testing
-var quit = make(chan os.Signal, 1)
-
 // HandlerFunc defines an http middleware
 type HandlerFunc func(config *configuration.Configuration, handler http.Handler) http.Handler
 
@@ -130,6 +127,7 @@ type Registry struct {
 	config *configuration.Configuration
 	app    *handlers.App
 	server *http.Server
+	quit   chan os.Signal
 }
 
 // NewRegistry creates a new registry from a context and configuration struct.
@@ -173,6 +171,7 @@ func NewRegistry(ctx context.Context, config *configuration.Configuration) (*Reg
 		app:    app,
 		config: config,
 		server: server,
+		quit:   make(chan os.Signal, 1),
 	}, nil
 }
 
@@ -313,7 +312,7 @@ func (registry *Registry) ListenAndServe() error {
 	}
 
 	// setup channel to get notified on SIGTERM signal
-	signal.Notify(quit, syscall.SIGTERM)
+	signal.Notify(registry.quit, syscall.SIGTERM)
 	serveErr := make(chan error)
 
 	// Start serving in goroutine and listen for stop signal in main thread
@@ -324,15 +323,20 @@ func (registry *Registry) ListenAndServe() error {
 	select {
 	case err := <-serveErr:
 		return err
-	case <-quit:
+	case <-registry.quit:
 		dcontext.GetLogger(registry.app).Info("stopping server gracefully. Draining connections for ", config.HTTP.DrainTimeout)
 		// shutdown the server with a grace period of configured timeout
 		c, cancel := context.WithTimeout(context.Background(), config.HTTP.DrainTimeout)
 		defer cancel()
-		return registry.server.Shutdown(c)
+		return registry.Shutdown(c)
 	}
 }
 
+// Shutdown gracefully shuts down the registry's HTTP server.
+func (registry *Registry) Shutdown(ctx context.Context) error {
+	return registry.server.Shutdown(ctx)
+}
+
 func configureDebugServer(config *configuration.Configuration) {
 	if config.HTTP.Debug.Addr != "" {
 		go func(addr string) {


Test patch:
diff --git a/registry/registry_test.go b/registry/registry_test.go
index 98dd6c94..ea23b9db 100644
--- a/registry/registry_test.go
+++ b/registry/registry_test.go
@@ -103,7 +103,7 @@ func TestGracefulShutdown(t *testing.T) {
 	fmt.Fprintf(conn, "GET /v2/ ")
 
 	// send stop signal
-	quit <- os.Interrupt
+	registry.quit <- os.Interrupt
 	time.Sleep(100 * time.Millisecond)
 
 	// try connecting again. it shouldn't
@@ -325,7 +325,7 @@ func TestRegistrySupportedCipherSuite(t *testing.T) {
 	}
 
 	// send stop signal
-	quit <- os.Interrupt
+	registry.quit <- os.Interrupt
 	time.Sleep(100 * time.Millisecond)
 }
 
@@ -369,7 +369,7 @@ func TestRegistryUnsupportedCipherSuite(t *testing.T) {
 	}
 
 	// send stop signal
-	quit <- os.Interrupt
+	registry.quit <- os.Interrupt
 	time.Sleep(100 * time.Millisecond)
 }