Question

I’m interested in the behavior of send function when using a blocking socket.

The manual specifies nothing about this case explicitly.

From my tests (and documentation) it results that when using send on a blocking socket I have 2 cases:

• all the data is sent
• an error is returned and nothing is sent

In lines of code (in C for example) this translate like this:

    // everything is allocated and initilized     int socket_fd;     char *buffer;      size_t buffer_len;     ssize_t nret;      nret = send(socket_fd, buffer, buffer_len, 0);     if(nret < 0)     {           // error - nothing was sent (at least we cannot assume anything)     }     else     {           // in case of blocking socket everything is sent (buffer_len == nret)     } 

Am I right?

I’m interested about this behavior on all platforms (Windows, Linux, *nix).

Answer 1

From the man page. (http://linux.die.net/man/2/send)

‘On success, these calls return the number of characters sent. On error, -1 is returned, and errno is set appropriately. ‘

You have three conditions.

• -1 is a local error in the socket or it’s binding.

• Some number < the length: not all the bytes were sent. This is usually the case when the socket is marked non-blocking and the requested operation would block; the errno value is EAGAIN.

  You probably won’t see this because you’re doing blocking I/O.

  However, the other end of the socket could close the connection prematurely, which may lead to this. The errno value would probably be EPIPE.

• Some number == the length: all the bytes were sent.