Add a SetDoNotFragment() method to DatagramSocket, and call this for

net/udp/udp_socket_posix.cc

Index: net/udp/udp_socket_posix.cc
diff --git a/net/udp/udp_socket_posix.cc b/net/udp/udp_socket_posix.cc
index 797e1a0bc1352b5a4a9a43c8c663c7acb05ab374..f3d51a2d5feeeac0787df5a30cc4e8b4367035c3 100644
--- a/net/udp/udp_socket_posix.cc
+++ b/net/udp/udp_socket_posix.cc
@@ -425,6 +425,36 @@ int UDPSocketPosix::SetSendBufferSize(int32_t size) {
   return rv == 0 ? OK : MapSystemError(errno);
 }
 
+int UDPSocketPosix::SetDoNotFragment() {
+  DCHECK_NE(socket_, kInvalidSocket);
+  DCHECK(CalledOnValidThread());
+
+#if !defined(IP_PMTUDISC_DO)
+  return OK;
+#else
+  int v6_only = false;
+  if (addr_family_ == AF_INET6) {
+    socklen_t v6_only_len = sizeof(v6_only);
+    getsockopt(socket_, IPPROTO_IPV6, IPV6_V6ONLY, &v6_only, &v6_only_len);
+  }
+
+  int rv;
+  if (addr_family_ == AF_INET6) {
+    DCHECK_EQ(addr_family_, AF_INET6);

[Jeremy Dorfman, 2016/08/12 17:23:41]

This line seems redundant.

[Ryan Hamilton, 2016/08/12 17:40:52]

Heh, whoops. Done.

+    int val = IPV6_PMTUDISC_DO;
+    rv =
+        setsockopt(socket_, IPPROTO_IPV6, IPV6_MTU_DISCOVER, &val, sizeof(val));
+    if (rv != 0)
+      return MapSystemError(errno);
+  }
+  if (!v6_only) {
+    int val = IP_PMTUDISC_DO;
+    rv = setsockopt(socket_, IPPROTO_IP, IP_MTU_DISCOVER, &val, sizeof(val));
+  }
+  return rv == 0 ? OK : MapSystemError(errno);
+#endif
+}
+
 int UDPSocketPosix::AllowAddressReuse() {
   DCHECK_NE(socket_, kInvalidSocket);
   DCHECK(CalledOnValidThread());