Question

I’m writing client and server programs and I’m looking for a way to ensure all bytes are read and all bytes are sent when using read() or write() to/from the sockets opened by the client/server.

I’m assuming I’ll have to use a loop to check the number of bytes returned from the read or write functions.

Something like this probably:

#define BUFFER 20
char buffer[BUFFER];

while (I haven't read all bytes from the buffer){
       int bytesRead = read(theSocket, myWord, BUFFER);
 }

And how would I ensure that all the bytes I am trying to transmit using write() have been transmitted?

Thanks for any help!

Answer 1

Yes, exactly like that. Typical read logic goes like this:

1) Call read.

2) Did we get EOF or error? If so, return.

3) Did we receive all the bytes? If so, return.

4) Go to step 1.

Note that when you call read, you’ll need to pass it a pointer to the buffer after the data that was already read, and you’ll need to try to read an appropriate amount of bytes that won’t overflow the buffer. Also, how you tell if you received all the bytes depends on the protocol.

To write:

1) Call write, passing it a pointer to the first unwritten byte and the number of unwritten bytes.

2) Did we get zero or error? If so, return.

3) Did we write all the bytes? If so, return.

4) Go to step 1.

Note that you have to adjust appropriately for blocking or non-blocking sockets. For example, for non-blocking sockets, you have to handle EWOULDBLOCK.