334 lines
12 KiB
HTML
334 lines
12 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
|
|
"http://www.w3.org/TR/html4/strict.dtd">
|
|
<html>
|
|
|
|
<head>
|
|
<meta name="description" content="LuaSocket: Introduction to the core">
|
|
<meta name="keywords" content="Lua, LuaSocket, TCP, UDP, Network,
|
|
Library, Support">
|
|
<title>LuaSocket: Introduction to the core</title>
|
|
<link rel="stylesheet" href="reference.css" type="text/css">
|
|
</head>
|
|
|
|
<body>
|
|
|
|
<!-- header +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
|
|
|
|
<div class=header>
|
|
<hr>
|
|
<center>
|
|
<table summary="LuaSocket logo">
|
|
<tr><td align=center><a href="http://www.lua.org">
|
|
<img width=128 height=128 border=0 alt="LuaSocket" src="luasocket.png">
|
|
</a></td></tr>
|
|
<tr><td align=center valign=top>Network support for the Lua language
|
|
</td></tr>
|
|
</table>
|
|
<p class=bar>
|
|
<a href="index.html">home</a> ·
|
|
<a href="index.html#download">download</a> ·
|
|
<a href="installation.html">installation</a> ·
|
|
<a href="introduction.html">introduction</a> ·
|
|
<a href="reference.html">reference</a>
|
|
</p>
|
|
</center>
|
|
<hr>
|
|
</div>
|
|
|
|
<!-- introduction +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
|
|
|
|
<h2>Introduction</h2>
|
|
|
|
<p>
|
|
LuaSocket is a <a href="http://www.lua.org">Lua</a> extension library
|
|
that is composed by two parts: a C core that provides support for the TCP
|
|
and UDP transport layers, and a set of Lua modules that add support for
|
|
the SMTP (sending e-mails), HTTP (WWW access) and FTP (uploading and
|
|
downloading files) protocols and other functionality commonly needed by
|
|
applications that deal with the Internet. This introduction is about the C
|
|
core.
|
|
</p>
|
|
|
|
<p>
|
|
Communication in LuaSocket is performed via I/O objects. These can
|
|
represent different network domains. Currently, support is provided for TCP
|
|
and UDP, but nothing prevents other developers from implementing SSL, Local
|
|
Domain, Pipes, File Descriptors etc. I/O objects provide a standard
|
|
interface to I/O across different domains and operating systems.
|
|
</p>
|
|
|
|
<p>
|
|
The API design had two goals in mind. First, users
|
|
experienced with the C API to sockets should feel comfortable using LuaSocket.
|
|
Second, the simplicity and the feel of the Lua language should be
|
|
preserved. To achieve these goals, the LuaSocket API keeps the function names and semantics the C API whenever possible, but their usage in Lua has been greatly simplified.
|
|
</p>
|
|
|
|
|
|
<p>
|
|
One of the simplifications is the receive pattern capability.
|
|
Applications can read data from stream domains (such as TCP)
|
|
line by line, block by block, or until the connection is closed.
|
|
All I/O reads are buffered and the performance differences between
|
|
different receive patterns are negligible.
|
|
</p>
|
|
|
|
<p>
|
|
Another advantage is the flexible timeout control
|
|
mechanism. As in C, all I/O operations are blocking by default. For
|
|
example, the <a href=tcp.html#send><tt>send</tt></a>,
|
|
<a href=tcp.html#receive><tt>receive</tt></a> and
|
|
<a href=tcp.html#accept><tt>accept</tt></a> methods
|
|
of the TCP domain will block the caller application until
|
|
the operation is completed (if ever!). However, with a call to the
|
|
<a href=tcp.html#settimeout><tt>settimeout</tt></a>
|
|
method, an application can specify upper limits on
|
|
the time it can be blocked by LuaSocket (the "<tt>total</tt>" timeout), on
|
|
the time LuaSocket can internally be blocked by any OS call (the
|
|
"<tt>block</tt>" timeout) or a combination of the two. Each LuaSocket
|
|
call might perform several OS calls, so that the two timeout values are
|
|
<em>not</em> equivalent.
|
|
</p>
|
|
|
|
<p>
|
|
Finally, the host name resolution is transparent, meaning that most
|
|
functions and methods accept both IP addresses and host names. In case a
|
|
host name is given, the library queries the system's resolver and
|
|
tries the main IP address returned. Note that direct use of IP addresses
|
|
is more efficient, of course. The
|
|
<a href=dns.html#toip><tt>toip</tt></a>
|
|
and <a href=dns.html#tohostname><tt>tohostname</tt></a>
|
|
functions from the DNS module are provided to convert between host names and IP addresses.
|
|
</p>
|
|
|
|
<p>
|
|
Together, these changes make network programming in LuaSocket much simpler
|
|
than it is in C, as the following sections will show.
|
|
</p>
|
|
|
|
<!-- tcp ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
|
|
|
|
<h3 id=tcp>TCP</h3>
|
|
|
|
<p>
|
|
TCP (Transfer Control Protocol) is reliable stream protocol. In other
|
|
words, applications communicating through TCP can send and receive data as
|
|
an error free stream of bytes. Data is split in one end and
|
|
reassembled transparently on the other end. There are no boundaries in
|
|
the data transfers. The library allows users to read data from the
|
|
sockets in several different granularities: patterns are available for
|
|
lines, arbitrary sized blocks or "read up to connection closed", all with
|
|
good performance.
|
|
</p>
|
|
|
|
<p>
|
|
The library distinguishes three types of TCP sockets: <em>master</em>,
|
|
<em>client</em> and <em>server</em> sockets.
|
|
</p>
|
|
|
|
<p>
|
|
Master sockets are newly created TCP sockets returned by the function
|
|
<a href=tcp.html#tcp><tt>socket.tcp</tt></a>. A master socket is
|
|
transformed into a server socket
|
|
after it is associated with a <em>local</em> address by a call to the
|
|
<a href=tcp.html#bind><tt>bind</tt></a> method followed by a call to the
|
|
<a href=tcp.html#listen><tt>listen</tt></a>. Conversely, a master socket
|
|
can be changed into a client socket with the method
|
|
<a href=tcp.html#connect><tt>connect</tt></a>,
|
|
which associates it with a <em>remote</em> address.
|
|
</p>
|
|
|
|
<p>
|
|
On server sockets, applications can use the
|
|
<a href=tcp.html#accept><tt>accept</tt></a> method
|
|
to wait for a client connection. Once a connection is established, a
|
|
client socket object is returned representing this connection. The
|
|
other methods available for server socket objects are
|
|
<a href=tcp.html#getsockname><tt>getsockname</tt></a>,
|
|
<a href=tcp.html#setoption><tt>setoption</tt></a>,
|
|
<a href=tcp.html#settimeout><tt>settimeout</tt></a>, and
|
|
<a href=tcp.html#close><tt>close</tt></a>.
|
|
</p>
|
|
|
|
<p>
|
|
Client sockets are used to exchange data between two applications over
|
|
the Internet. Applications can call the methods
|
|
<a href=tcp.html#send><tt>send</tt></a> and
|
|
<a href=tcp.html#receive><tt>receive</tt></a>
|
|
to send and receive data. The other methods
|
|
available for client socket objects are
|
|
<a href=tcp.html#getsockname><tt>getsockname</tt></a>,
|
|
<a href=tcp.html#getpeername><tt>getpeername</tt></a>,
|
|
<a href=tcp.html#setoption><tt>setoption</tt></a>,
|
|
<a href=tcp.html#settimeout><tt>settimeout</tt></a>,
|
|
<a href=tcp.html#shutdown><tt>shutdown</tt></a>, and
|
|
<a href=tcp.html#close><tt>close</tt></a>.
|
|
</p>
|
|
|
|
<p>
|
|
Example:
|
|
</p>
|
|
<blockquote>
|
|
<p>
|
|
A simple echo server, using LuaSocket. The program binds to an ephemeral
|
|
port (one that is chosen by the operating system) on the local host and
|
|
awaits client connections on that port. When a connection is established,
|
|
the program reads a line from the remote end and sends it back, closing
|
|
the connection immediately. You can test it using the telnet
|
|
program.
|
|
</p>
|
|
|
|
<pre class=example>
|
|
-- load namespace
|
|
local socket = require("socket")
|
|
-- create a TCP socket and bind it to the local host, at any port
|
|
local server = assert(socket.bind("*", 0))
|
|
-- find out which port the OS chose for us
|
|
local ip, port = server:getsockname()
|
|
-- print a message informing what's up
|
|
print("Please telnet to localhost on port " .. port)
|
|
print("After connecting, you have 10s to enter a line to be echoed")
|
|
-- loop forever waiting for clients
|
|
while 1 do
|
|
-- wait for a connection from any client
|
|
local client = server:accept()
|
|
-- make sure we don't block waiting for this client's line
|
|
client:settimeout(10)
|
|
-- receive the line
|
|
local line, err = client:receive()
|
|
-- if there was no error, send it back to the client
|
|
if not err then client:send(line .. "\n") end
|
|
-- done with client, close the object
|
|
client:close()
|
|
end
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<!-- udp ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
|
|
|
|
<h3 id=udp>UDP</h3>
|
|
|
|
<p>
|
|
UDP (User Datagram Protocol) is a non-reliable datagram protocol. In
|
|
other words, applications communicating through UDP send and receive
|
|
data as independent blocks, which are not guaranteed to reach the other
|
|
end. Even when they do reach the other end, they are not guaranteed to be
|
|
error free. Data transfers are atomic, one datagram at a time. Reading
|
|
only part of a datagram discards the rest, so that the following read
|
|
operation will act on the next datagram. The advantages are in
|
|
simplicity (no connection setup) and performance (no error checking or
|
|
error correction).
|
|
</p>
|
|
|
|
<p>
|
|
Note that although no guarantees are made, these days
|
|
networks are so good that, under normal circumstances, few errors
|
|
happen in practice.
|
|
</p>
|
|
|
|
<p>
|
|
An UDP socket object is created by the
|
|
<a href=udp.html#udp><tt>socket.udp</tt></a> function. UDP
|
|
sockets do not need to be connected before use. The method
|
|
<a href=udp.html#sendto><tt>sendto</tt></a>
|
|
can be used immediately after creation to
|
|
send a datagram to IP address and port. Host names are not allowed
|
|
because performing name resolution for each packet would be forbiddingly
|
|
slow. Methods
|
|
<a href=udp.html#receive><tt>receive</tt></a> and
|
|
<a href=udp.html#receivefrom><tt>receivefrom</tt></a>
|
|
can be used to retrieve datagrams, the latter returning the IP and port of
|
|
the sender as extra return values (thus being slightly less
|
|
efficient).
|
|
</p>
|
|
|
|
<p>
|
|
When communication is performed repeatedly with a single peer, an
|
|
application should call the
|
|
<a href=udp.html#setpeername><tt>setpeername</tt></a> method to specify a
|
|
permanent partner. Methods
|
|
<a href=udp.html#sendto><tt>sendto</tt></a> and
|
|
<a href=udp.html#receivefrom><tt>receivefrom</tt></a>
|
|
can no longer be used, but the method
|
|
<a href=udp.html#send><tt>send</tt></a> can be used to send data
|
|
directly to the peer, and the method
|
|
<a href=udp.html#receive><tt>receive</tt></a>
|
|
will only return datagrams originating
|
|
from that peer. There is about 30% performance gain due to this practice.
|
|
</p>
|
|
|
|
<p>
|
|
To associate an UDP socket with a local address, an application calls the
|
|
<a href=udp.html#setsockname><tt>setsockname</tt></a>
|
|
method <em>before</em> sending any datagrams. Otherwise, the socket is
|
|
automatically bound to an ephemeral address before the first data
|
|
transmission and once bound the local address cannot be changed.
|
|
The other methods available for UDP sockets are
|
|
<a href=udp.html#getpeername><tt>getpeername</tt></a>,
|
|
<a href=udp.html#getsockname><tt>getsockname</tt></a>,
|
|
<a href=udp.html#settimeout><tt>settimeout</tt></a>,
|
|
<a href=udp.html#setoption><tt>setoption</tt></a> and
|
|
<a href=udp.html#close><tt>close</tt></a>.
|
|
</p>
|
|
|
|
<p>
|
|
Example:
|
|
</p>
|
|
<blockquote>
|
|
<p>
|
|
A simple daytime client, using LuaSocket. The program connects to a remote
|
|
server and tries to retrieve the daytime, printing the answer it got or an
|
|
error message.
|
|
</p>
|
|
|
|
<pre class=example>
|
|
-- change here to the host an port you want to contact
|
|
local host, port = "localhost", 13
|
|
-- load namespace
|
|
local socket = require("socket")
|
|
-- convert host name to ip address
|
|
local ip = assert(socket.dns.toip(host))
|
|
-- create a new UDP object
|
|
local udp = assert(socket.udp())
|
|
-- contact daytime host
|
|
assert(udp:sendto("anything", ip, port))
|
|
-- retrieve the answer and print results
|
|
io.write(assert(udp:receive()))
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<!-- More +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
|
|
|
|
<h3 id=more>Support modules</h3>
|
|
|
|
<p> Although not covered in the introduction, LuaSocket offers
|
|
much more than TCP and UDP functionality. As the library
|
|
evolved, support for <a href=http.html>HTTP</a>, <a href=ftp.html>FTP</a>,
|
|
and <a href=smtp.html>SMTP</a> were built on top of these. These modules
|
|
and many others are covered by the <a href=reference.html>reference manual</a>.
|
|
</p>
|
|
|
|
<!-- footer +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
|
|
|
|
<div class=footer>
|
|
<hr>
|
|
<center>
|
|
<p class=bar>
|
|
<a href="index.html">home</a> ·
|
|
<a href="index.html#down">download</a> ·
|
|
<a href="installation.html">installation</a> ·
|
|
<a href="introduction.html">introduction</a> ·
|
|
<a href="reference.html">reference</a>
|
|
</p>
|
|
<p>
|
|
<small>
|
|
Last modified by Diego Nehab on <br>
|
|
Thu Apr 20 00:25:36 EDT 2006
|
|
</small>
|
|
</p>
|
|
</center>
|
|
</div>
|
|
|
|
</body>
|
|
</html>
|