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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta name="description" content="LuaSocket: Serial port support">
<meta name="keywords" content="Lua, LuaSocket, Serial, Port, TTY, Library, Support">
<title>LuaSocket: Serial port support</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> ·
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<hr>
</div>
<!-- serial +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<h2 id="serial">Serial port support</h2>
<p>
The <tt>socket.serial</tt> module opens a serial device (e.g.
<tt>/dev/ttyUSB0</tt>) and exposes it through the same buffered,
timeout-aware <tt>send</tt>/<tt>receive</tt> interface used by
<a href="tcp.html">TCP</a> and <a href="unix.html">Unix domain</a>
stream objects.
</p>
<p class="note">
Note: This module is only built on Unix-like platforms (Linux, macOS,
BSD, Haiku). It is not available on Windows.
</p>
<p>
Serial port support is a separate module that must be required
explicitly. Unlike most other LuaSocket modules, it returns a
<em>function</em> directly — the constructor — rather than a
table of functions:
</p>
<pre class="example">
-- loads the socket.serial module; note this is the constructor itself
local serial_open = require("socket.serial")
-- open the device
local port = assert(serial_open("/dev/ttyUSB0"))
port:settimeout(1)
assert(port:send("AT\r\n"))
print(port:receive())
port:close()
</pre>
<p class="note">
Note: <b>There is currently no API to configure the serial line itself
— baud rate, parity, data/stop bits or flow control.</b> The device
is opened non-blocking with whatever settings the OS driver or a prior
external configuration (e.g. <tt>stty</tt>) left it in. This is a known
current limitation of the module, not a deliberate protection against
misuse; a future version may add a <tt>setoption</tt>-style API for these
settings the way <a href="tcp.html#setoption"><tt>tcp:setoption</tt></a>
does for TCP.
</p>
<p>
Until such an API exists, the workaround is to configure the line with
the platform's own <tt>stty</tt> utility (via <tt>os.execute</tt>)
<em>before</em> opening the device with <tt>socket.serial</tt>:
</p>
<pre class="example">
local serial_open = require("socket.serial")
local dev = "/dev/ttyUSB0"
-- Linux: stty -F <device> ...
local ok = os.execute(string.format(
"stty -F %s 115200 cs8 -cstopb -parenb raw -echo", dev))
-- macOS/BSD use -f instead of -F:
-- os.execute(string.format("stty -f %s 115200 cs8 -cstopb -parenb raw -echo", dev))
assert(ok, "failed to configure serial line with stty")
local port = assert(serial_open(dev))
port:settimeout(1)
assert(port:send("AT\r\n"))
print(port:receive())
port:close()
</pre>
<p class="note">
Note: <tt>raw -echo</tt> puts the line in raw mode, which matters for
LuaSocket's framing: without it, the TTY driver applies its own line
editing/echo, which can interfere with <a href="#receive"><tt>receive</tt></a>
patterns and <a href="#send"><tt>send</tt></a> content. Adjust the
<tt>stty</tt> flags (baud rate, parity, stop bits, flow control) to match
your device; consult <tt>man stty</tt> for the full option set on your
platform, since flag names and defaults vary between Linux, macOS and the
BSDs.
</p>
<!-- close ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="close">
port:<b>close()</b>
</p>
<p class="description">
Closes a serial object. No further operations (except further calls to
<tt>close</tt>) are allowed on a closed object.
</p>
<p class="note">
Note: Garbage-collected objects are automatically closed before
destruction.
</p>
<!-- dirty +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="dirty">
port:<b>dirty()</b>
</p>
<p class="description">
Check the read buffer status.
</p>
<p class="return">
Returns <tt>true</tt> if there is any data in the read buffer,
<tt>false</tt> otherwise.
</p>
<p class="note">
Note: <b>This is an internal method, use at your own risk.</b>
</p>
<!-- getfd ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="getfd">
port:<b>getfd()</b>
</p>
<p class="description">
Returns the underlying file descriptor associated to the object.
</p>
<p class="return">
The descriptor.
</p>
<p class="note">
Note: <b>This is an internal method. Unlikely to be portable. Use at your
own risk.</b>
</p>
<!-- getstats ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="getstats">
port:<b>getstats()</b>
</p>
<p class="description">
Returns accounting information on the port, useful for throttling of
bandwidth. Works exactly like
<a href="tcp.html#getstats"><tt>tcp:getstats</tt></a>.
</p>
<p class="return">
The method returns the number of bytes received, the number of bytes
sent, and the age of the object in seconds.
</p>
<!-- receive +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="receive">
port:<b>receive(</b>[pattern [, prefix [, maxsize]]]<b>)</b>
</p>
<p class="description">
Reads data from the serial port, according to the specified <em>read
pattern</em>. Works exactly like
<a href="tcp.html#receive"><tt>tcp:receive</tt></a>, including the
<tt>*a</tt>/<tt>*l</tt>/<tt>number</tt> patterns and the
<tt>prefix</tt>/<tt>maxsize</tt> parameters.
</p>
<!-- send +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="send">
port:<b>send(</b>data [, i [, j]]<b>)</b>
</p>
<p class="description">
Sends <tt>data</tt> through the serial port. Works exactly like
<a href="tcp.html#send"><tt>tcp:send</tt></a>, including the optional
<tt>i</tt>/<tt>j</tt> substring selection.
</p>
<!-- setfd ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="setfd">
port:<b>setfd(</b>fd<b>)</b>
</p>
<p class="description">
Sets the underlying file descriptor associated to the object. The current
one is simply replaced, not closed, and no other change to the object
state is made.
</p>
<p class="return">
No return value.
</p>
<p class="note">
Note: <b>This is an internal method. Unlikely to be portable. Use at your
own risk.</b>
</p>
<!-- setstats ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="setstats">
port:<b>setstats(</b>received, sent, age<b>)</b>
</p>
<p class="description">
Resets accounting information on the port, useful for throttling of
bandwidth. Works exactly like
<a href="tcp.html#setstats"><tt>tcp:setstats</tt></a>.
</p>
<p class="return">
The method returns 1 in case of success and <tt><b>nil</b></tt> otherwise.
</p>
<!-- settimeout ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="settimeout">
port:<b>settimeout(</b>value [, mode]<b>)</b>
</p>
<p class="description">
Changes the timeout values for the object. Works exactly like
<a href="tcp.html#settimeout"><tt>tcp:settimeout</tt></a>, including the
'<tt>b</tt>' (block) and '<tt>t</tt>' (total) modes.
</p>
<!-- socket.serial +++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<p class="name" id="socket.serial">
serial_open(<b>path</b>)
</p>
<p class="description">
Opens the serial device at <tt>path</tt> and returns a serial object.
This is the value returned directly by <tt>require("socket.serial")</tt>
— there is no separate module table to index into, unlike
<tt>socket.unix.stream()</tt> or <tt>socket.tcp()</tt>.
</p>
<p class="parameters">
<tt>Path</tt> is a string with the device path (e.g.
<tt>"/dev/ttyUSB0"</tt> or <tt>"/dev/ttyS0"</tt>).
</p>
<p class="return">
In case of success, a new serial object is returned. In case of error,
the function returns <b><tt>nil</tt></b>, followed by an error message,
followed by the numeric <tt>errno</tt> value.
</p>
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