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" + note + "</div>"; spans[i].innerHTML = "[<a id='_footnoteref_" + n + "' href='#_footnote_" + n + "' title='View footnote' class='footnote'>" + n + "</a>]"; var id =spans[i].getAttribute("id"); if (id != null) refs["#"+id] = n; } } if (n == 0) noteholder.parentNode.removeChild(noteholder); else { // Process footnoterefs. for (i=0; i<spans.length; i++) { if (spans[i].className == "footnoteref") { var href = spans[i].getElementsByTagName("a")[0].getAttribute("href"); href = href.match(/#.*/)[0]; // Because IE return full URL. n = refs[href]; spans[i].innerHTML = "[<a href='#_footnote_" + n + "' title='View footnote' class='footnote'>" + n + "</a>]"; } } } } } /*]]>*/ </script> </head> <body> <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 </div> </div> </body> </html>