Allow unsetting errmsgcallback

Summary:
Unset the error message callbacks when err
message so that we dont deliver errors when
not needed

Reviewed By: yfeldblum

Differential Revision: D7661052

fbshipit-source-id: 5a2330b2cd11f844649d56343307e2c75b626bdc

folly/io/async/AsyncUDPSocket.cpp

@@ -199,7 +199,7 @@ void AsyncUDPSocket::dontFragment(bool df) {
 void AsyncUDPSocket::setErrMessageCallback(
     ErrMessageCallback* errMessageCallback) {
   errMessageCallback_ = errMessageCallback;
-  int err = 1;
+  int err = (errMessageCallback_ != nullptr);
 #if defined(IP_RECVERR)
   if (address().getFamily() == AF_INET &&
       fsp::setsockopt(fd_, IPPROTO_IP, IP_RECVERR, &err, sizeof(err))) {

folly/io/async/test/AsyncUDPSocketTest.cpp

@@ -359,6 +359,18 @@ TEST_F(AsyncUDPSocketTest, TestErrToNonExistentServer) {
   EXPECT_TRUE(errRecvd);
 }
 
+TEST_F(AsyncUDPSocketTest, TestUnsetErrCallback) {
+  socket_->resumeRead(&readCb);
+  socket_->setErrMessageCallback(&err);
+  socket_->setErrMessageCallback(nullptr);
+  folly::SocketAddress addr("127.0.0.1", 10000);
+  EXPECT_CALL(err, errMessage(_)).Times(0);
+  socket_->write(addr, folly::IOBuf::copyBuffer("hey"));
+  evb_.timer().scheduleTimeoutFn(
+      [&] { evb_.terminateLoopSoon(); }, std::chrono::milliseconds(30));
+  evb_.loopForever();
+}
+
 TEST_F(AsyncUDPSocketTest, CloseInErrorCallback) {
   socket_->resumeRead(&readCb);
   socket_->setErrMessageCallback(&err);