Question

I’ve seen several uses of sockets where programmers send a command or some information over a TCP/IP socket, and expect it to be received in one call on the receiving side.

For eg, transmitting

mySocket.Send("SomeSpecificCommand")

They assume the receive side will receive all the data in one call. For eg:

Dim data(255) As Byte   
Dim nReceived As Long = s.Receive(data, 0, data.Count, SocketFlags.None)
Dim str As String = Encoding.ASCII.GetString(data, 0, n)
If str = "SomeSpecificCommand" Then
    DoStuff()
    ...

The example above doesn’t use any terminator, so the programmer is relying on the fact that the sockets implementation is not allowed, for example, to return “SomeSpecif” in a first call to Receive(), and “cCommand” in a later call to Receive(). (NOTE – In the example, the buffer is sized to be larger than the expected string).

I’ve never before given this much thought and had just assumed that this type of coding is unsafe and have always used delimiters. Have I been wasting my time (and processor cycles)?

Answer 1

There is no guarantee that it will all arrive at the same time. The code (the app’s protocol) needs to deal with the possibility that data from one send may arrive in multiple pieces or the possibility that data from more than one send could arrive in one receive.