Added asynchronous udp receive function (#193)

* Added asynchronous udp receive function

* Remove receive_async and added low level recv, which is non-blocking.

* Remove thread include

* Moved unix include to IXNetSystem.h

ixwebsocket/IXUdpSocket.cpp

@@ -44,6 +44,18 @@ namespace ix
         return err;
     }
 
+    bool UdpSocket::isWaitNeeded()
+    {
+        int err = getErrno();
+
+        if (err == EWOULDBLOCK || err == EAGAIN || err == EINPROGRESS)
+        {
+            return true;
+        }
+
+        return false;
+    }
+
     void UdpSocket::closeSocket(int fd)
     {
 #ifdef _WIN32
@@ -62,6 +74,13 @@ namespace ix
             return false;
         }
 
+#ifdef _WIN32
+        unsigned long nonblocking = 1;
+        ioctlsocket(sockfd, FIONBIO, &nonblocking);
+#else
+        fcntl(_sockfd, F_SETFL, O_NONBLOCK); // make socket non blocking
+#endif
+
         memset(&_server, 0, sizeof(_server));
         _server.sin_family = AF_INET;
         _server.sin_port = htons(port);
@@ -93,4 +112,11 @@ namespace ix
         return (ssize_t)::sendto(
             _sockfd, buffer.data(), buffer.size(), 0, (struct sockaddr*) &_server, sizeof(_server));
     }
+
+    ssize_t UdpSocket::recvfrom(void* buffer, size_t length)
+    {
+        uint32_t add_len = sizeof(_server);
+        return (ssize_t)::recvfrom(
+            _sockfd, buffer, length, 0, (struct sockaddr*) &_server, &add_len);
+    }
 } // namespace ix