Add code to set TCP keep alive delay on OSX.

net/socket/tcp_socket_libevent.cc

 // Copyright 2013 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_socket.h"
 
 #include <errno.h>
 #include <netinet/tcp.h>
 #include <sys/socket.h>
 
@@ skipping 39 matching lines @@
 // `man 7 tcp`.
 bool SetTCPNoDelay(int fd, bool no_delay) {
   int on = no_delay ? 1 : 0;
   int error = setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &on, sizeof(on));
   return error == 0;
 }
 
 // SetTCPKeepAlive sets SO_KEEPALIVE.
 bool SetTCPKeepAlive(int fd, bool enable, int delay) {
   int on = enable ? 1 : 0;
   if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on))) {

[Jana, 2015/04/06 23:20:00]

Nit: Perhaps add a comment here to say that this setsockopt is applied towards
all platforms?

[mmenke, 2015/04/07 15:28:06]

Done.

     PLOG(ERROR) << "Failed to set SO_KEEPALIVE on fd: " << fd;
     return false;
   }
 
   // If we disabled TCP keep alive, our work is done here.
   if (!enable)
     return true;
 
 #if defined(OS_LINUX) || defined(OS_ANDROID)
   // Set seconds until first TCP keep alive.
   if (setsockopt(fd, SOL_TCP, TCP_KEEPIDLE, &delay, sizeof(delay))) {
     PLOG(ERROR) << "Failed to set TCP_KEEPIDLE on fd: " << fd;
     return false;
   }
   // Set seconds between TCP keep alives.
   if (setsockopt(fd, SOL_TCP, TCP_KEEPINTVL, &delay, sizeof(delay))) {
     PLOG(ERROR) << "Failed to set TCP_KEEPINTVL on fd: " << fd;
     return false;
   }
+#elif defined(OS_MACOSX) || defined(OS_IOS)
+  if (setsockopt(fd, IPPROTO_TCP, TCP_KEEPALIVE, &delay, sizeof(delay))) {
+    PLOG(ERROR) << "Failed to set TCP_KEEPALIVE on fd: " << fd;
+    return false;
+  }
 #endif

[Jana, 2015/04/06 23:20:00]

Should there be a #else? What are the platforms that are left out? FreeBSD
should have the same semantics as MACOSX (I think ... I'll take a look).

[mmenke, 2015/04/07 15:28:06]

There's also ChromeOS, but I believe that has OS_LINUX defined, given the huge
number of "#if defined(OS_LINUX) && !defined(OS_CHROMEOS)"

There's also OS_NACL, which I believe also has OS_LINUX set.

And then there's OS_FREEBSD, OS_SOLARIS, OS_QNX, OS_OPENBSD.  I think figuring
out which code each (unsupported) platform should use is beyond the scope of
this CL, particularly since we have no trybots, and I'm not going to try and
build them all manually.

For what it's worth, looks like FreeBSD should use the Linux path: 
http://svnweb.freebsd.org/base/head/sys/netinet/tcp.h?view=markup#l165

[Jana, 2015/04/07 19:47:19]

I think that the FBSD code is close to the MacOS code, but MacOS collapses some
of the options that FBSD needs explicit setting. See the setsockopt code 
for FBSD: http://fxr.watson.org/fxr/source/netinet/tcp_usrreq.c#L1492
and for MacOS:
http://fxr.watson.org/fxr/source/bsd/netinet/tcp_usrreq.c?v=xnu-2050.18.24#L1452

MacOS uses a single timer value for keepalives, when it's turned on, where FBSD
uses two different user defined values for the first keepalive and for intervals
between keepalives. That said, as you pointed out, this is not for this CL, so
I'll stop digging further :-)

   return true;
 }
 
 #if defined(OS_LINUX) || defined(OS_ANDROID)
 // Checks if the kernel supports TCP FastOpen.
 bool SystemSupportsTCPFastOpen() {
   const base::FilePath::CharType kTCPFastOpenProcFilePath[] =
       "/proc/sys/net/ipv4/tcp_fastopen";
   std::string system_supports_tcp_fastopen;
   if (!base::ReadFileToString(base::FilePath(kTCPFastOpenProcFilePath),
@@ skipping 641 matching lines @@
     }
   } else {
     tcp_fastopen_status_ =
         (tcp_fastopen_status_ == TCP_FASTOPEN_FAST_CONNECT_RETURN ?
          TCP_FASTOPEN_SYN_DATA_GETSOCKOPT_FAILED :
          TCP_FASTOPEN_NO_SYN_DATA_GETSOCKOPT_FAILED);
   }
 }
 
 }  // namespace net