How to find out how many bytes in socket before recv in Python?

Question

I have a TCP handling streams of data. It takes 4096 bytes at a time, but I need a way to find out the whole socket size before it recv. This is so I can determine how many times the socket will be read before it switches socket. It will also notify that this is the last recv of this socket so that I can do something with it before select switches to the other socket when it becomes available.

def handle_tcp(self, sock, remote):  
    fdset = [sock, remote]  
    while True:  
        r, w, e = select.select(fdset, [], [])  
        # How to find out how much bytes need to be read from socket?
        if sock in r:  
            non_blocking_calculation()
            if remote.send(sock.recv(4096)) <= 0: break  
        if remote in r: 
            non_blocking_calculation() 
            if sock.send(remote.recv(4096)) <= 0: break  

Answer 1

You beated me to it. In accordance with Igor Kalinosvkiy way. You can either Use FIONREAD to do this or use MSG_PEEK and keep reading until empty. For example, after select().

import fcntl, termios, array, math
...
sock_size = array.array('i', [0])  # initialise outside While loop
if sock in r:
    fcntl.ioctl(sock, termios.FIONREAD, sock_size)
    count = ceil(sock_size[0] / float(BUF_SIZE))
    print("Socket size: {} and count: {}".format(sock_size[0], count)