Question

I was looking at some code in Python (I know nothing about Python) and I came across this portion:

def do_req(body):
    global host, req
    data = ""
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((host, 80))
    s.sendall(req % (len(body), body))
    tmpdata = s.recv(8192)
    while len(tmpdata) > 0:
        data += tmpdata
        tmpdata = s.recv(8192)
    s.close()
    return data

This is then called later on with body of huge size, as in over 500,000 bytes. This is sent to an Apache server that has the max request size on the default 8190 bytes.

My question is what is happening at the “s.sendall()” part? Obviously the entire body cannot be sent at once and I’m guessing it is reduced by way of the modulus operator. I don’t know how it works in Python, though. Can anyone explain? Thanks.

Answer 1

No, body is not reduced here, because % is format operator, when operates on strings.

http://docs.python.org/release/2.5.2/lib/typesseq-strings.html

All the data is sent by sendall method by parts.

socket.sendall works like that:

do {
        n = sendsegmented(s->sock_fd, buf, len, flags);
        len -= n;
} while (len > 0);

where sendsegmented sends data and returns len or SEGMENT_SIZE