Add an API to AsyncUDPSocket to set DF bit

Summary: Some application requires IP not to fragment the the datagram. Add an API to AsyncUDPSocket to set such option.

Reviewed By: siyengar

Differential Revision: D5421406

fbshipit-source-id: 6cd3ab262f1420e22eb0948e0e2bfef77b7b6e92

folly/io/async/AsyncUDPSocket.cpp

@@ -132,6 +132,32 @@ void AsyncUDPSocket::bind(const folly::SocketAddress& address) {
   }
 }
 
+void AsyncUDPSocket::dontFragment(bool df) {
+#ifdef IP_MTU_DISCOVER
+  if (address().getFamily() == AF_INET) {
+    int v4 = df ? IP_PMTUDISC_DO : IP_PMTUDISC_WANT;
+    if (fsp::setsockopt(fd_, IPPROTO_IP, IP_MTU_DISCOVER, &v4, sizeof(v4))) {
+      throw AsyncSocketException(
+          AsyncSocketException::NOT_OPEN,
+          "Failed to set DF with IP_MTU_DISCOVER",
+          errno);
+    }
+  }
+#endif
+#ifdef IPV6_MTU_DISCOVER
+  if (address().getFamily() == AF_INET6) {
+    int v6 = df ? IPV6_PMTUDISC_DO : IPV6_PMTUDISC_WANT;
+    if (fsp::setsockopt(
+            fd_, IPPROTO_IPV6, IPV6_MTU_DISCOVER, &v6, sizeof(v6))) {
+      throw AsyncSocketException(
+          AsyncSocketException::NOT_OPEN,
+          "Failed to set DF with IPV6_MTU_DISCOVER",
+          errno);
+    }
+  }
+#endif
+}
+
 void AsyncUDPSocket::setFD(int fd, FDOwnership ownership) {
   CHECK_EQ(-1, fd_) << "Already bound to another FD";
 

folly/io/async/AsyncUDPSocket.h

@@ -162,6 +162,18 @@ class AsyncUDPSocket : public EventHandler {
     return eventBase_;
   }
 
+  /**
+   * Enable or disable fragmentation on the socket.
+   *
+   * On Linux, this sets IP(V6)_MTU_DISCOVER to IP(V6)_PMTUDISC_DO when enabled,
+   * and to IP(V6)_PMTUDISC_WANT when disabled. IP(V6)_PMTUDISC_WANT will use
+   * per-route setting to set DF bit. It may be more desirable to use
+   * IP(V6)_PMTUDISC_PROBE as opposed to IP(V6)_PMTUDISC_DO for apps that has
+   * its own PMTU Discovery mechanism.
+   * Note this doesn't work on Apple.
+   */
+  virtual void dontFragment(bool df);
+
  protected:
   virtual ssize_t sendmsg(int socket, const struct msghdr* message, int flags) {
     return ::sendmsg(socket, message, flags);

folly/io/async/test/MockAsyncUDPSocket.h

@@ -39,6 +39,7 @@ struct MockAsyncUDPSocket : public AsyncUDPSocket {
   MOCK_CONST_METHOD0(getFD, int());
   MOCK_METHOD1(setReusePort, void(bool));
   MOCK_METHOD1(setReuseAddr, void(bool));
+  MOCK_METHOD1(dontFragment, void(bool));
 };
 
 }}