Test that server socket cannot reuse port

net/socket/tcp_server_socket_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/socket/tcp_server_socket.h"
 
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "net/base/address_list.h"
 #include "net/base/io_buffer.h"
 #include "net/base/ip_endpoint.h"
 #include "net/base/net_errors.h"
 #include "net/base/test_completion_callback.h"
 #include "net/socket/tcp_client_socket.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 
 namespace net {
 
 namespace {
 const int kListenBacklog = 5;
+const int kListenPort = 31373;
 
 class TCPServerSocketTest : public PlatformTest {
  protected:
   TCPServerSocketTest()
       : socket_(NULL, NetLog::Source()) {
   }
 
   void SetUpIPv4() {
     IPEndPoint address;
     ParseAddress("127.0.0.1", 0, &address);
@@ skipping 203 matching lines @@
     ASSERT_TRUE(read_result >= 0);
     ASSERT_TRUE(bytes_read + read_result <= message.size());
     memmove(&buffer[bytes_read], read_buffer->data(), read_result);
     bytes_read += read_result;
   }
 
   std::string received_message(buffer.begin(), buffer.end());
   ASSERT_EQ(message, received_message);
 }
 
+TEST_F(TCPServerSocketTest, Rebind) {
+  IPEndPoint address;
+  ParseAddress("127.0.0.1", kListenPort, &address);

[wtc, 2013/07/25 18:03:56]

Using a constant listen port may prevent another person from running
this unit test on the same machine at the same time. This could be
problematic for a shared machine such as a try bot.

I suggest the following solution:

1. Have |socket| bind to port 0, and call socket.GetLocalAddress
to get the actual port number. Then, have |conflict_socket| bind to
that port number.

This still leaves a small window (after |socket.reset(NULL)| and before
the unit test ends) when |socket| releases the port, and another user
who runs the same test may grab that port.

2. Use a port number based on process id (PID), so that different
processes will use different port numbers.

3. Use a random port number. There is still a small probability that
the port numbers will collide.

[Bei Zhang, 2013/07/26 05:10:40]

Done. I think no solution is perfect here. I cannot really assure that the port
number derived from PID will not duplicate as well, it might also conflict with
existing program.

+
+  scoped_ptr<TCPServerSocket> socket(
+      new TCPServerSocket(NULL, NetLog::Source()));
+  ASSERT_EQ(OK, socket->Listen(address, kListenBacklog));
+
+  scoped_ptr<TCPServerSocket> conflict_socket(
+      new TCPServerSocket(NULL, NetLog::Source()));
+  ASSERT_NE(OK, conflict_socket->Listen(address, kListenBacklog));
+
+  // Unbind
+  socket.reset(NULL);
+
+  ASSERT_EQ(OK, conflict_socket->Listen(address, kListenBacklog));
+}
+
 }  // namespace
 
 }  // namespace net