The ReceiveMessageFromAsync method is used primarily to receive message data on a connectionless socket. The socket's local address must be known. This method can only be used with datagram and raw sockets. The socket must be initialized with the socket type set to Dgram or Raw before calling this method. This can be done when the socket is constructed using Socket.
The caller must set the SocketAsyncEventArgs..::.RemoteEndPoint property to the IPEndPoint of the remote host from which the data is to be received.
The following properties and events on the System.Net.Sockets..::.SocketAsyncEventArgs object are required to successfully call this method:
The caller may set the SocketAsyncEventArgs..::.UserToken property to any user state object desired before calling the ReceiveMessageFromAsync method, so that the information will be retrievable in the callback method. If the callback needs more information than a single object, a small class can be created to hold the other required state information as members.
For message-oriented sockets, an incoming message is placed into the buffer up to the total size of the buffer. The SocketAsyncEventArgs..::.Count and SocketAsyncEventArgs..::.Offset properties determine where in the buffer the data is placed and the amount of data.
The ReceiveMessageFromAsync method automatically sets the PacketInformation socket option to true the first time it is called for a given Socket. However, the IPPacketInformation object will only be valid for packets which arrive at the local computer after the socket option has been set. If a socket is sent packets between when the socket is bound to a local endpoint (explicitly by the Bind method or implicitly by one of the Connect, ConnectAsync, SendTo, or SendToAsync methods) and the first call to the ReceiveMessageFromAsync method, calls to ReceiveMessageFromAsync method will result in invalid IPPacketInformation objects for these packets.
To ensure that all IPPacketInformation objects are valid, an application should set the PacketInformation socket option to true before it is bound to a local endpoint using the SetSocketOption(SocketOptionLevel, SocketOptionName, Boolean) method.
An application can examine the resulting IPPacketInformation objects if it needs to know if the datagram was sent using a unicast, multicast, or broadcast address.