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<div id="header">
<h1>IPC interface (interprocess communication)</h1>
<span id="author">Michael Stapelberg</span><br />
<span id="email"><tt><<a href="mailto:michael+i3@stapelberg.de">michael+i3@stapelberg.de</a>></tt></span><br />
<span id="revdate">March 2010</span>
<div id="toc">
<div id="toctitle">Table of Contents</div>
<noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>This document describes how to interface with i3 from a separate process. This
is useful for example to remote-control i3 (to write test cases for example) or
to get various information like the current workspaces to implement an external
workspace bar.</p></div>
<div class="paragraph"><p>The method of choice for IPC in our case is a unix socket because it has very
little overhead on both sides and is usually available without headaches in
most languages. In the default configuration file, no ipc-socket path is
specified and thus no socket is created. The standard path (which <tt>i3-msg</tt> and
<tt>i3-input</tt> use) is <tt>~/.i3/ipc.sock</tt>.</p></div>
</div>
</div>
<h2 id="_establishing_a_connection">1. Establishing a connection</h2>
<div class="sectionbody">
<div class="paragraph"><p>To establish a connection, simply open the IPC socket. The following code
snippet illustrates this in Perl:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>use IO::Socket::UNIX;
my $sock = IO::Socket::UNIX->new(Peer => '~/.i3/ipc.sock');</tt></pre>
</div></div>
</div>
<h2 id="_sending_messages_to_i3">2. Sending messages to i3</h2>
<div class="sectionbody">
<div class="paragraph"><p>To send a message to i3, you have to format in the binary message format which
i3 expects. This format specifies a magic string in the beginning to ensure
the integrity of messages (to prevent follow-up errors). Following the magic
string comes the length of the payload of the message as 32-bit integer, and
the type of the message as 32-bit integer (the integers are not converted, so
they are in native byte order).</p></div>
<div class="paragraph"><p>The magic string currently is "i3-ipc" and will only be changed when a change
in the IPC API is done which breaks compatibility (we hope that we don’t need
to do that).</p></div>
<div class="paragraph"><p>Currently implemented message types are the following:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
COMMAND (0)
</dt>
<dd>
<p>
The payload of the message is a command for i3 (like the commands you
can bind to keys in the configuration file) and will be executed
directly after receiving it. There is no reply to this message.
</p>
</dd>
<dt class="hdlist1">
GET_WORKSPACES (1)
</dt>
<dd>
<p>
Gets the current workspaces. The reply will be a JSON-encoded list of
workspaces (see the reply section).
</p>
</dd>
<dt class="hdlist1">
SUBSCRIBE (2)
</dt>
<dd>
<p>
Subscribes your connection to certain events. See <a href="#events">[events]</a> for a
description of this message and the concept of events.
</p>
</dd>
<dt class="hdlist1">
GET_OUTPUTS (3)
</dt>
<dd>
<p>
Gets the current outputs. The reply will be a JSON-encoded list of outputs
(see the reply section).
</p>
</dd>
</dl></div>
<div class="paragraph"><p>So, a typical message could look like this:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>"i3-ipc" <message length> <message type> <payload></tt></pre>
</div></div>
<div class="paragraph"><p>Or, as a hexdump:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
00000010 69 74 0a |it.|</tt></pre>
</div></div>
<div class="paragraph"><p>To generate and send such a message, you could use the following code in Perl:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>sub format_ipc_command {
my ($msg) = @_;
my $len;
# Get the real byte count (vs. amount of characters)
{ use bytes; $len = length($msg); }
return "i3-ipc" . pack("LL", $len, 0) . $msg;
}
$sock->write(format_ipc_command("exit"));</tt></pre>
</div></div>
</div>
<h2 id="_receiving_replies_from_i3">3. Receiving replies from i3</h2>
<div class="sectionbody">
<div class="paragraph"><p>Replies from i3 usually consist of a simple string (the length of the string
is the message_length, so you can consider them length-prefixed) which in turn
contain the JSON serialization of a data structure. For example, the
GET_WORKSPACES message returns an array of workspaces (each workspace is a map
with certain attributes).</p></div>
<h3 id="_reply_format">3.1. Reply format</h3><div style="clear:left"></div>
<div class="paragraph"><p>The reply format is identical to the normal message format. There also is
the magic string, then the message length, then the message type and the
payload.</p></div>
<div class="paragraph"><p>The following reply types are implemented:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
COMMAND (0)
</dt>
<dd>
<p>
Confirmation/Error code for the COMMAND message.
</p>
</dd>
<dt class="hdlist1">
GET_WORKSPACES (1)
</dt>
<dd>
<p>
Reply to the GET_WORKSPACES message.
</p>
</dd>
<dt class="hdlist1">
SUBSCRIBE (2)
</dt>
<dd>
<p>
Confirmation/Error code for the SUBSCRIBE message.
</p>
</dd>
<dt class="hdlist1">
GET_OUTPUTS (3)
</dt>
<dd>
<p>
Reply to the GET_OUTPUTS message.
</p>
</dd>
</dl></div>
<h3 id="_command_reply">3.2. COMMAND reply</h3><div style="clear:left"></div>
<div class="paragraph"><p>The reply consists of a single serialized map. At the moment, the only
property is <tt>success (bool)</tt>, but this will be expanded in future versions.</p></div>
<div class="paragraph"><p><strong>Example:</strong></p></div>
<div class="listingblock">
<div class="content">
<pre><tt>{ "success": true }</tt></pre>
</div></div>
<h3 id="_get_workspaces_reply">3.3. GET_WORKSPACES reply</h3><div style="clear:left"></div>
<div class="paragraph"><p>The reply consists of a serialized list of workspaces. Each workspace has the
following properties:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
num (integer)
</dt>
<dd>
<p>
The logical number of the workspace. Corresponds to the command
to switch to this workspace.
</p>
</dd>
<dt class="hdlist1">
name (string)
</dt>
<dd>
<p>
The name of this workspace (by default num+1), as changed by the
user. Encoded in UTF-8.
</p>
</dd>
<dt class="hdlist1">
visible (boolean)
</dt>
<dd>
<p>
Whether this workspace is currently visible on an output (multiple
workspaces can be visible at the same time).
</p>
</dd>
<dt class="hdlist1">
focused (boolean)
</dt>
<dd>
<p>
Whether this workspace currently has the focus (only one workspace
can have the focus at the same time).
</p>
</dd>
<dt class="hdlist1">
urgent (boolean)
</dt>
<dd>
<p>
Whether a window on this workspace has the "urgent" flag set.
</p>
</dd>
<dt class="hdlist1">
rect (map)
</dt>
<dd>
<p>
The rectangle of this workspace (equals the rect of the output it
is on), consists of x, y, width, height.
</p>
</dd>
<dt class="hdlist1">
output (string)
</dt>
<dd>
<p>
The video output this workspace is on (LVDS1, VGA1, …).
</p>
</dd>
</dl></div>
<div class="paragraph"><p><strong>Example:</strong></p></div>
<div class="listingblock">
<div class="content">
<pre><tt>[
{
"num": 0,
"name": "1",
"visible": true,
"focused": true,
"urgent": false,
"rect": {
"x": 0,
"y": 0,
"width": 1280,
"height": 800
},
"output": "LVDS1"
},
{
"num": 1,
"name": "2",
"visible": false,
"focused": false,
"urgent": false,
"rect": {
"x": 0,
"y": 0,
"width": 1280,
"height": 800
},
"output": "LVDS1"
}
]</tt></pre>
</div></div>
<h3 id="_subscribe_reply">3.4. SUBSCRIBE reply</h3><div style="clear:left"></div>
<div class="paragraph"><p>The reply consists of a single serialized map. The only property is
<tt>success (bool)</tt>, indicating whether the subscription was successful (the
default) or whether a JSON parse error occurred.</p></div>
<div class="paragraph"><p><strong>Example:</strong></p></div>
<div class="listingblock">
<div class="content">
<pre><tt>{ "success": true }</tt></pre>
</div></div>
<h3 id="_get_outputs_reply">3.5. GET_OUTPUTS reply</h3><div style="clear:left"></div>
<div class="paragraph"><p>The reply consists of a serialized list of outputs. Each output has the
following properties:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
name (string)
</dt>
<dd>
<p>
The name of this output (as seen in <tt>xrandr(1)</tt>). Encoded in UTF-8.
</p>
</dd>
<dt class="hdlist1">
active (boolean)
</dt>
<dd>
<p>
Whether this output is currently active (has a valid mode).
</p>
</dd>
<dt class="hdlist1">
current_workspace (integer)
</dt>
<dd>
<p>
The current workspace which is visible on this output. <tt>null</tt> if the
output is not active.
</p>
</dd>
<dt class="hdlist1">
rect (map)
</dt>
<dd>
<p>
The rectangle of this output (equals the rect of the output it
is on), consists of x, y, width, height.
</p>
</dd>
</dl></div>
<div class="paragraph"><p><strong>Example:</strong></p></div>
<div class="listingblock">
<div class="content">
<pre><tt>[
{
"name": "LVDS1",
"active": true,
"current_workspace": 4,
"rect": {
"x": 0,
"y": 0,
"width": 1280,
"height": 800
}
},
{
"name": "VGA1",
"active": true,
"current_workspace": 1,
"rect": {
"x": 1280,
"y": 0,
"width": 1280,
"height": 1024
},
}
]</tt></pre>
</div></div>
</div>
<h2 id="_events">4. Events</h2>
<div class="sectionbody">
<div class="paragraph" id="events"><p>To get informed when certain things happen in i3, clients can subscribe to
events. Events consist of a name (like "workspace") and an event reply type
(like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
as replies to specific commands.</p></div>
<div class="paragraph"><p>Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
that the requests to i3 are processed in order. This means, the following
situation can happen: You send a GET_WORKSPACES request but you receive a
"workspace" event before receiving the reply to GET_WORKSPACES. If your
program does not want to cope which such kinds of race conditions (an
event based library may not have a problem here), I suggest you create a
separate connection to receive events.</p></div>
<h3 id="_subscribing_to_events">4.1. Subscribing to events</h3><div style="clear:left"></div>
<div class="paragraph"><p>By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
you can register to an event.</p></div>
<div class="paragraph"><p><strong>Example:</strong></p></div>
<div class="listingblock">
<div class="content">
<pre><tt>type: SUBSCRIBE
payload: [ "workspace", "focus" ]</tt></pre>
</div></div>
<h3 id="_available_events">4.2. Available events</h3><div style="clear:left"></div>
<div class="dlist"><dl>
<dt class="hdlist1">
workspace
</dt>
<dd>
<p>
Sent when the user switches to a different workspace, when a new
workspace is initialized or when a workspace is removed (because the
last client vanished).
</p>
</dd>
<dt class="hdlist1">
output
</dt>
<dd>
<p>
Sent when RandR issues a change notification (of either screens,
outputs, CRTCs or output properties).
</p>
</dd>
</dl></div>
<h3 id="_workspace_event">4.3. workspace event</h3><div style="clear:left"></div>
<div class="paragraph"><p>This event consists of a single serialized map containing a property
<tt>change (string)</tt> which indicates the type of the change ("focus", "init",
"empty", "urgent").</p></div>
<div class="paragraph"><p><strong>Example:</strong></p></div>
<div class="listingblock">
<div class="content">
<pre><tt>{ "change": "focus" }</tt></pre>
</div></div>
<h3 id="_output_event">4.4. output event</h3><div style="clear:left"></div>
<div class="paragraph"><p>This event consists of a single serialized map containing a property
<tt>change (string)</tt> which indicates the type of the change (currently only
"unspecified").</p></div>
<div class="paragraph"><p><strong>Example:</strong></p></div>
<div class="listingblock">
<div class="content">
<pre><tt>{ "change": "unspecified" }</tt></pre>
</div></div>
</div>
<h2 id="_see_also">5. See also</h2>
<div class="sectionbody">
<div class="paragraph"><p>For some languages, libraries are available (so you don’t have to implement
all this on your own). This list names some (if you wrote one, please let me
know):</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
C
</dt>
<dd>
<p>
i3 includes a headerfile <tt>i3/ipc.h</tt> which provides you all constants.
However, there is no library yet.
</p>
</dd>
<dt class="hdlist1">
Ruby
</dt>
<dd>
<p>
<a href="http://github.com/badboy/i3-ipc">http://github.com/badboy/i3-ipc</a>
</p>
</dd>
<dt class="hdlist1">
Perl
</dt>
<dd>
<p>
<a href="http://search.cpan.org/search?query=AnyEvent::I3">http://search.cpan.org/search?query=AnyEvent::I3</a>
</p>
</dd>
</dl></div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
Last updated 2010-06-07 12:23:49 CEST
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