net/rpc: don't exit if Accept gets an error

The default implementation of Accept, which spins up a new server
for every new connection, calls log.Fatal if the listener is closed,
stopping any outstanding work. Change that to a non-fatal log
call so work can continue.

There is no programmatic signaling of the problem, just the log,
but that should be enough.

Fixes #11221.

Change-Id: I7c7f6164a0a0143236729eb778d7638c51c34ed1
Reviewed-on: https://go-review.googlesource.com/14185
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/rpc/server.go

@@ -611,13 +611,15 @@ func (server *Server) readRequestHeader(codec ServerCodec) (service *service, mt
 }
 
 // Accept accepts connections on the listener and serves requests
-// for each incoming connection.  Accept blocks; the caller typically
+// for each incoming connection. Accept blocks until the listener
-// invokes it in a go statement.
+// returns a non-nil error. The caller typically invokes Accept in a
+// go statement.
 func (server *Server) Accept(lis net.Listener) {
 	for {
 		conn, err := lis.Accept()
 		if err != nil {
-			log.Fatal("rpc.Serve: accept:", err.Error()) // TODO(r): exit?
+			log.Print("rpc.Serve: accept:", err.Error())
+			return
 		}
 		go server.ServeConn(conn)
 	}

src/net/rpc/server_test.go

@@ -593,6 +593,19 @@ func TestErrorAfterClientClose(t *testing.T) {
 	}
 }
 
+// Tests the fix to issue 11221. Without the fix, this loops forever or crashes.
+func TestAcceptExitAfterListenerClose(t *testing.T) {
+	newServer = NewServer()
+	newServer.Register(new(Arith))
+	newServer.RegisterName("net.rpc.Arith", new(Arith))
+	newServer.RegisterName("newServer.Arith", new(Arith))
+
+	var l net.Listener
+	l, newServerAddr = listenTCP()
+	l.Close()
+	newServer.Accept(l)
+}
+
 func benchmarkEndToEnd(dial func() (*Client, error), b *testing.B) {
 	once.Do(startServer)
 	client, err := dial()