Fix a listener leak when a server is stopped before it starts

If server.Stop() and server.Serve() race, Serve() can return without
closing the listener. This in turn can lead to clients timing out trying
to connect to a server that is neither accepting nor rejecting
connections.

server.go

@@ -257,12 +257,14 @@ func (s *Server) useTransportAuthenticator(rawConn net.Conn) (net.Conn, credenti
 // Serve accepts incoming connections on the listener lis, creating a new
 // ServerTransport and service goroutine for each. The service goroutines
 // read gRPC requests and then call the registered handlers to reply to them.
-// Service returns when lis.Accept fails.
+// Service returns when lis.Accept fails. lis will be closed when
+// this method returns.
 func (s *Server) Serve(lis net.Listener) error {
 	s.mu.Lock()
 	s.printf("serving")
 	if s.lis == nil {
 		s.mu.Unlock()
+		lis.Close()
 		return ErrServerStopped
 	}
 	s.lis[lis] = true

server_test.go

@@ -0,0 +1,61 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+package grpc
+
+import (
+	"net"
+	"strings"
+	"testing"
+)
+
+func TestStopBeforeServe(t *testing.T) {
+	lis, err := net.Listen("tcp", "localhost:0")
+	if err != nil {
+		t.Fatalf("failed to create listener: %v", err)
+	}
+
+	server := NewServer()
+	server.Stop()
+	err = server.Serve(lis)
+	if err != ErrServerStopped {
+		t.Fatalf("server.Serve() error = %v, want %v", err, ErrServerStopped)
+	}
+
+	// server.Serve is responsible for closing the listener, even if the
+	// server was already stopped.
+	err = lis.Close()
+	if got, want := ErrorDesc(err), "use of closed network connection"; !strings.Contains(got, want) {
+		t.Errorf("Close() error = %q, want %q", got, want)
+	}
+}