Question

Consider the following line of code mySocket.recv(10000). The socket is valid and connected. I know for a fact that the data I am waiting for is at least 10000 bytes in size. Nevertheless, the recv() function returns only 1000 bytes. What happened (assuming the socket did not become disconnected)? What should be done about it?

This is the full question. There is no code for it.

Answer 1

1. Typically, client server send & receive program is written like this -

send program:

bytesWritten = send(socketFd, buf, bytesToSend, flags);

recieve program:

recvedBytes = Recv(sockFd, readBuf, maxBufSize, flag, flags);

Please note that maxBufSize (in your case is 10000bytes) is the maximum size of the read buffer. It is not the maximum size of the data to read. If the send-program is sending 1000bytes then receive program will receive only 1000.

2. What can be done about this?

The receiving program should be in the loop to read till it reaches its target size.

Example:

recieve program:

total_bytes_recv = 10000;

while (total_bytes_recv <= 0) {

recvedBytes = Recv(sockFd, readBuf, maxBufSize, flag, flags);

total_bytes_recv = total_bytes_recv – recvedBytes;

            }

       Additional information:

1. In client-server network program, that data is sent over the packet/datagram. MTU is called maximum transfer unit, it is typically 1400 bytes. This is including transport, IP & ethernet header. So typically, the application will send packet less than 1400 bytes to avoid the IP fragmentation.
2. If the socket program uses the TCP, then there is no concept like message boundary like in UDP. Recieve program will receive in the stream, that is of any size.