server: Pass the assigner to the Finish method of a Service

This is a breaking change to the Service interface. It extends the Finish
method to receive the assigner that was passed to the server, along with the
server exit status. This permits the implementation to clean up per-assigner
state when the server exits.

Author: creachadair

server/example_test.go

@@ -41,7 +41,7 @@ func (Service) Assigner() (jrpc2.Assigner, error) {
 	})}, nil
 }
 
-func (s Service) Finish(stat jrpc2.ServerStatus) {
+func (s Service) Finish(_ jrpc2.Assigner, stat jrpc2.ServerStatus) {
 	fmt.Printf("SERVICE FINISHED err=%v\n", stat.Err)
 	close(s.done)
 }

server/loop.go

@@ -16,17 +16,19 @@ type Service interface {
 	Assigner() (jrpc2.Assigner, error)
 
 	// This method is called when the server for this service has exited.
-	Finish(jrpc2.ServerStatus)
+	// The arguments are the assigner returned by the Assigner method and the
+	// server exit status.
+	Finish(jrpc2.Assigner, jrpc2.ServerStatus)
 }
 
 // Static wraps a jrpc2.Assigner to trivially implement the Service interface.
 func Static(m jrpc2.Assigner) func() Service { return static{methods: m}.New }
 
 type static struct{ methods jrpc2.Assigner }
 
-func (s static) New() Service                      { return s }
-func (s static) Assigner() (jrpc2.Assigner, error) { return s.methods, nil }
-func (static) Finish(jrpc2.ServerStatus)           {}
+func (s static) New() Service                            { return s }
+func (s static) Assigner() (jrpc2.Assigner, error)       { return s.methods, nil }
+func (static) Finish(jrpc2.Assigner, jrpc2.ServerStatus) {}
 
 // Loop obtains connections from lst and starts a server for each with the
 // given service constructor and options, running in a new goroutine. If accept
@@ -66,7 +68,7 @@ func Loop(lst net.Listener, newService func() Service, opts *LoopOptions) error
 			}
 			srv := jrpc2.NewServer(assigner, serverOpts).Start(ch)
 			stat := srv.WaitStatus()
-			svc.Finish(stat)
+			svc.Finish(assigner, stat)
 			if stat.Err != nil {
 				log("Server exit: %v", stat.Err)
 			}

server/loop_test.go

@@ -49,7 +49,10 @@ func (t *testSession) Assigner() (jrpc2.Assigner, error) {
 	}, nil
 }
 
-func (t *testSession) Finish(stat jrpc2.ServerStatus) {
+func (t *testSession) Finish(assigner jrpc2.Assigner, stat jrpc2.ServerStatus) {
+	if _, ok := assigner.(handler.Map); !ok {
+		t.t.Errorf("Finished assigner: got %+v, want handler.Map", assigner)
+	}
 	if !t.init {
 		t.t.Error("Service finished without being initialized")
 	}

server/run.go

@@ -18,6 +18,6 @@ func Run(ch channel.Channel, svc Service, opts *jrpc2.ServerOptions) error {
 	}
 	srv := jrpc2.NewServer(assigner, opts).Start(ch)
 	stat := srv.WaitStatus()
-	svc.Finish(stat)
+	svc.Finish(assigner, stat)
 	return stat.Err
 }

server/run_test.go

@@ -21,7 +21,7 @@ func (t *testService) Assigner() (jrpc2.Assigner, error) {
 	return t.assigner, nil
 }
 
-func (t *testService) Finish(stat jrpc2.ServerStatus) {
+func (t *testService) Finish(_ jrpc2.Assigner, stat jrpc2.ServerStatus) {
 	t.finishCalled = true
 	t.stat = stat
 }