On Thursday 02 August 2007, Walker Lindley wrote: > OK, I'm back with another networking question. I'm trying to seend large > amounts of information over TCP (the length of data being given to send() > is on the order of 16000 characters in length). Unfortunately on the > receiving end, the packets appear to be truncated. So I wrote some code > that continuously tries to send bigger and bigger packets until it fails > and noticed that it never fails at the same length. I'm not even sure these > two things are related, but is there some undocumented (or documented and I > missed it) maximum size for data you can pass to send()?
First off, very long messages, that is messages whose length cannot be represented in a C size_t, are probably right out ;-) from the send(2) manual page on my Debian system: > If the message is too long to pass atomically through the underlying > protocol, the error EMSGSIZE is returned, and the message is not trans‐ > mitted. from the Python socket.send documentation [1] > Send data to the socket. The socket must be connected to a remote socket. > The optional flags argument has the same meaning as for recv() above. > Returns the number of bytes sent. Applications are responsible for checking > that all data has been sent; if only some of the data was transmitted, the > application needs to attempt delivery of the remaining data. that makes it quite clear that it's possible that not all data was transmitted. That you were unable to find a fixed size may be explainable in many ways - it might just be the way your operating system's TCP/IP stack works. If you just want to send data in some way or another, do yourself a favour and use socket.sendall instead of socket.send. Docs for socket.sendall: [1] > Send data to the socket. The socket must be connected to a remote socket. > The optional flags argument has the same meaning as for recv() above. > Unlike send(), this method continues to send data from string until either > all data has been sent or an error occurs. None is returned on success. On > error, an exception is raised, and there is no way to determine how much > data, if any, was successfully sent. [1]: http://docs.python.org/lib/socket-objects.html -- Regards, Thomas Jollans GPG key: 0xF421434B may be found on various keyservers, eg pgp.mit.edu Hacker key <http://hackerkey.com/>: v4sw6+8Yhw4/5ln3pr5Ock2ma2u7Lw2Nl7Di2e2t3/4TMb6HOPTen5/6g5OPa1XsMr9p-7/-6
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