使用TCP / IP进行套接字编程：recv（）块

Question

I am developing a simple Client/Server project which moves a chunk of data from client to server. I use TCP/IP.

The server sets up a listening socket and the client connects. First a short 16 byte "header" is transmitted containing some information including the amount of data to be transmitted after. Afterwards the big chunk is transmitted (around 2MB), namely

send( socketDesc, (void *) myBuffer, bigChunkSize, 0 );

and

recv( socketDescPeer, (void *) myBuffer, bigChunkSize, 0 )

First i implemented the client side under windows using winsock2, which works without problems. I now tried to port this implementation to linux, in which case the server side never returns from the recv() call (the "header" however is transmitted correctly). I then tried to send the data in smaller chunks of fixed size like this

unsigned int byteSent = 0;
while( byteSent < bigChunkSize ) {
    int result = send( socketDesc, (void *) myBuffer, smallChunkSize, 0 );
    if ( result < 0 ) {...} else { byteSent += result; }
}

Now, the server receives the first few number of chunks but then again, blocks.

Any ideas? Keep in mind that transmission works without problems using winsock2! Thanks a lot!

Answer 1

Did you check the return code of send to check, how many bytes were really send? Neither send nor recv are guaranteed to send/receive the given number of bytes. They can handle less and you have to call send/recv again to handle the rest.

So if you actually send less bytes than expected it explains, why the recv will block waiting for more data (which were not send).