Allow server sockets to rebind to same port if there is nothing actively listening on that port.

net/socket/tcp_server_socket_libevent.cc

Index: net/socket/tcp_server_socket_libevent.cc
diff --git a/net/socket/tcp_server_socket_libevent.cc b/net/socket/tcp_server_socket_libevent.cc
index ef8d1b1bcbef21f851decf142c01181d9c5e1c30..3249889869f8ce2f263ddc59c9c995b3a683bfc9 100644
--- a/net/socket/tcp_server_socket_libevent.cc
+++ b/net/socket/tcp_server_socket_libevent.cc
@@ -35,6 +35,7 @@ TCPServerSocketLibevent::TCPServerSocketLibevent(
     const net::NetLog::Source& source)
     : socket_(kInvalidSocket),
       accept_socket_(NULL),
+      reuse_address_(false),
       net_log_(BoundNetLog::Make(net_log, NetLog::SOURCE_SOCKET)) {
   net_log_.BeginEvent(NetLog::TYPE_SOCKET_ALIVE,
                       source.ToEventParametersCallback());
@@ -63,11 +64,16 @@ int TCPServerSocketLibevent::Listen(const IPEndPoint& address, int backlog) {
     return result;
   }
 
+  int result = SetSocketOptions();
+  if (result < 0) {

[wtc, 2012/09/13 18:31:55]

result < 0 => result != OK

Note: although SetSocketOptions() and bind()/listen() all
return int, SetSocketOptions() returns a Chrome network
error code, whereas bind()/listen() return 0/-1 (the Unix
system call status values).

[justinlin, 2012/09/14 03:54:40]

Done. Nice catch.

+    return result;
+  }
+
   SockaddrStorage storage;
   if (!address.ToSockAddr(storage.addr, &storage.addr_len))
     return ERR_INVALID_ARGUMENT;
 
-  int result = bind(socket_, storage.addr, storage.addr_len);
+  result = bind(socket_, storage.addr, storage.addr_len);
   if (result < 0) {
     PLOG(ERROR) << "bind() returned an error";
     result = MapSystemError(errno);
@@ -125,6 +131,24 @@ int TCPServerSocketLibevent::Accept(
   return result;
 }
 
+void TCPServerSocketLibevent::AllowAddressReuse() {
+  DCHECK(CalledOnValidThread());
+  DCHECK_EQ(socket_, kInvalidSocket);
+
+  reuse_address_ = true;
+}
+
+int TCPServerSocketLibevent::SetSocketOptions() {
+  int true_value = 1;
+  if (reuse_address_) {
+    int rv = setsockopt(socket_, SOL_SOCKET, SO_REUSEADDR, &true_value,
+                        sizeof(true_value));
+    if (rv < 0)
+      return MapSystemError(errno);

[wtc, 2012/09/13 18:31:55]

Why didn't you copy the following code from tcp_client_socket_libevent.cc?

#if defined(SO_REUSEPORT)
    rv = setsockopt(socket_, SOL_SOCKET, SO_REUSEPORT, &true_value,
                    sizeof(true_value));
    if (rv < 0)
      return MapSystemError(errno);
#endif

[Sergey Ulanov, 2012/09/13 22:08:45]

I actually don't think we really need this. Yuri added it specifically for
broadcast sockets on mac (though I don't know all details of why it's required
there). See my comments on that issue here:
http://codereview.chromium.org/10739002/ . There is also CL in flight to fix it:
http://codereview.chromium.org/10917235/

[wtc, 2012/09/14 02:36:12]

Thank you. Then we should not copy the SO_REUSEPORT code to
TCPServerSocket.

+  }
+  return OK;
+}
+
 int TCPServerSocketLibevent::AcceptInternal(
     scoped_ptr<StreamSocket>* socket) {
   SockaddrStorage storage;