source: trunk/essentials/dev-lang/python/Doc/howto/sockets.tex@ 3298

\documentclass{howto}

\title{Socket Programming HOWTO}

\release{0.00}

\author{Gordon McMillan}
\authoraddress{\email{[email protected]}}

\begin{document}
\maketitle

\begin{abstract}
\noindent
Sockets are used nearly everywhere, but are one of the most severely
misunderstood technologies around. This is a 10,000 foot overview of
sockets. It's not really a tutorial - you'll still have work to do in
getting things operational. It doesn't cover the fine points (and there
are a lot of them), but I hope it will give you enough background to
begin using them decently.

This document is available from the Python HOWTO page at
\url{http://www.python.org/doc/howto}.

\end{abstract}

\tableofcontents

\section{Sockets}

Sockets are used nearly everywhere, but are one of the most severely
misunderstood technologies around. This is a 10,000 foot overview of
sockets. It's not really a tutorial - you'll still have work to do in
getting things working. It doesn't cover the fine points (and there
are a lot of them), but I hope it will give you enough background to
begin using them decently.

I'm only going to talk about INET sockets, but they account for at
least 99\% of the sockets in use. And I'll only talk about STREAM
sockets - unless you really know what you're doing (in which case this
HOWTO isn't for you!), you'll get better behavior and performance from
a STREAM socket than anything else. I will try to clear up the mystery
of what a socket is, as well as some hints on how to work with
blocking and non-blocking sockets. But I'll start by talking about
blocking sockets. You'll need to know how they work before dealing
with non-blocking sockets.

Part of the trouble with understanding these things is that "socket"
can mean a number of subtly different things, depending on context. So
first, let's make a distinction between a "client" socket - an
endpoint of a conversation, and a "server" socket, which is more like
a switchboard operator. The client application (your browser, for
example) uses "client" sockets exclusively; the web server it's
talking to uses both "server" sockets and "client" sockets.


\subsection{History}

Of the various forms of IPC (\emph{Inter Process Communication}),
sockets are by far the most popular.  On any given platform, there are
likely to be other forms of IPC that are faster, but for
cross-platform communication, sockets are about the only game in town.

They were invented in Berkeley as part of the BSD flavor of Unix. They
spread like wildfire with the Internet. With good reason --- the
combination of sockets with INET makes talking to arbitrary machines
around the world unbelievably easy (at least compared to other