Socket.ReceiveFrom Method (Byte, Int32, Int32, SocketFlags, EndPoint)
Receives the specified number of bytes of data into the specified location of the data buffer, using the specified SocketFlags, and stores the endpoint.
Assembly: System (in System.dll)
member ReceiveFrom : buffer:byte * offset:int * size:int * socketFlags:SocketFlags * remoteEP:EndPoint byref -> int
- Type: System.Int32
The position in the buffer parameter to store the received data.
- Type: System.Int32
The number of bytes to receive.
Return ValueType: System.Int32
The number of bytes received.
buffer is a null reference (Nothing in Visual Basic).
remoteEP is a null reference (Nothing in Visual Basic).
offset is less than 0.
offset is greater than the length of buffer.
size is less than 0.
size is greater than the length of the buffer minus the value of the offset parameter.
socketFlags is not a valid combination of values.
The LocalEndPoint property was not set.
An error occurred when attempting to access the socket. See the Remarks section for more information.
The Socket has been closed.
The ReceiveFrom method reads data into the buffer parameter, returns the number of bytes successfully read, and captures the remote host endpoint from which the data was sent. This method is useful if you intend to receive connectionless datagrams from an unknown host or multiple hosts.
With connectionless protocols, ReceiveFrom will read the first enqueued datagram received into the local network buffer. If the datagram you receive is larger than the size of buffer, the ReceiveFrom method will fill buffer with as much of the message as is possible, and throw a SocketException. If you are using an unreliable protocol, the excess data will be lost. If you are using a reliable protocol, the excess data will be retained by the service provider and you can retrieve it by calling the ReceiveFrom method with a large enough buffer.
If no data is available for reading, the ReceiveFrom method will block until data is available. If you are in non-blocking mode, and there is no data available in the in the protocol stack buffer, the ReceiveFrom method will complete immediately and throw a SocketException. You can use the Available property to determine if data is available for reading. When Available is non-zero, retry the receive operation.
Although ReceiveFrom is intended for connectionless protocols, you can use a connection-oriented protocol as well. If you choose to do so, you must first either establish a remote host connection by calling the Connect method or accept an incoming remote host connection by calling the Accept method. If you do not establish or accept a connection before calling the ReceiveFrom method, you will get a SocketException. You can also establish a default remote host for a connectionless protocol prior to calling the ReceiveFrom method. In either of these cases, the ReceiveFrom method will ignore the remoteEP parameter and only receive data from the connected or default remote host.
With connection-oriented sockets, ReceiveFrom will read as much data as is available up to the amount of bytes specified by the size parameter. If the remote host shuts down the Socket connection with the Shutdown method, and all available data has been Received, the ReceiveFrom method will complete immediately and return zero bytes.
Before calling ReceiveFrom, you must explicitly bind the Socket to a local endpoint using the Bind method. If you do not, ReceiveFrom will throw a SocketException. If you receive a SocketException, use the SocketException.ErrorCode property to obtain the specific error code. After you have obtained this code, refer to the Windows Sockets version 2 API error code documentation in the MSDN library for a detailed description of the error.
This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing in the .NET Framework.