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<h1>IPC interface (interprocess communication)</h1>\r
<span id="author">Michael Stapelberg</span><br />\r
<span id="email"><tt><<a href="mailto:michael@i3wm.org">michael@i3wm.org</a>></tt></span><br />\r
-<span id="revdate">October 2014</span>\r
+<span id="revdate">September 2017</span>\r
<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 class="paragraph"><p>The magic string currently is "i3-ipc" and will only be changed when a change\r
in the IPC API is done which breaks compatibility (we hope that we don’t need\r
to do that).</p></div>\r
-<div class="paragraph"><p>Currently implemented message types are the following:</p></div>\r
-<div class="dlist"><dl>\r
-<dt class="hdlist1">\r
-COMMAND (0)\r
-</dt>\r
-<dd>\r
-<p>\r
- The payload of the message is a command for i3 (like the commands you\r
- can bind to keys in the configuration file) and will be executed\r
- directly after receiving it.\r
-</p>\r
-</dd>\r
-<dt class="hdlist1">\r
-GET_WORKSPACES (1)\r
-</dt>\r
-<dd>\r
-<p>\r
- Gets the current workspaces. The reply will be a JSON-encoded list of\r
- workspaces (see the reply section).\r
-</p>\r
-</dd>\r
-<dt class="hdlist1">\r
-SUBSCRIBE (2)\r
-</dt>\r
-<dd>\r
-<p>\r
- Subscribes your connection to certain events. See <a href="#events">[events]</a> for a\r
- description of this message and the concept of events.\r
-</p>\r
-</dd>\r
-<dt class="hdlist1">\r
-GET_OUTPUTS (3)\r
-</dt>\r
-<dd>\r
-<p>\r
- Gets the current outputs. The reply will be a JSON-encoded list of outputs\r
- (see the reply section).\r
-</p>\r
-</dd>\r
-<dt class="hdlist1">\r
-GET_TREE (4)\r
-</dt>\r
-<dd>\r
-<p>\r
- Gets the layout tree. i3 uses a tree as data structure which includes\r
- every container. The reply will be the JSON-encoded tree (see the reply\r
- section).\r
-</p>\r
-</dd>\r
-<dt class="hdlist1">\r
-GET_MARKS (5)\r
-</dt>\r
-<dd>\r
-<p>\r
- Gets a list of marks (identifiers for containers to easily jump to them\r
- later). The reply will be a JSON-encoded list of window marks (see\r
- reply section).\r
-</p>\r
-</dd>\r
-<dt class="hdlist1">\r
-GET_BAR_CONFIG (6)\r
-</dt>\r
-<dd>\r
-<p>\r
- Gets the configuration (as JSON map) of the workspace bar with the\r
- given ID. If no ID is provided, an array with all configured bar IDs is\r
- returned instead.\r
-</p>\r
-</dd>\r
-<dt class="hdlist1">\r
-GET_VERSION (7)\r
-</dt>\r
-<dd>\r
-<p>\r
- Gets the version of i3. The reply will be a JSON-encoded dictionary\r
- with the major, minor, patch and human-readable version.\r
-</p>\r
-</dd>\r
-</dl></div>\r
+<div class="tableblock">\r
+<table rules="all"\r
+width="100%"\r
+frame="border"\r
+cellspacing="0" cellpadding="4">\r
+<caption class="title">Table 1. Currently implemented message types</caption>\r
+<col width="10%" />\r
+<col width="20%" />\r
+<col width="20%" />\r
+<col width="50%" />\r
+<thead>\r
+<tr>\r
+<th align="center" valign="top"> Type (numeric) </th>\r
+<th align="center" valign="top"> Type (name) </th>\r
+<th align="center" valign="top"> Reply type </th>\r
+<th align="center" valign="top"> Purpose</th>\r
+</tr>\r
+</thead>\r
+<tbody>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">0</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>RUN_COMMAND</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_command_reply">COMMAND</a></p></td>\r
+<td align="center" valign="top"><p class="table">Run the payload as an i3 command (like the commands you can bind to keys).</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">1</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>GET_WORKSPACES</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_workspaces_reply">WORKSPACES</a></p></td>\r
+<td align="center" valign="top"><p class="table">Get the list of current workspaces.</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">2</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>SUBSCRIBE</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_subscribe_reply">SUBSCRIBE</a></p></td>\r
+<td align="center" valign="top"><p class="table">Subscribe this IPC connection to the event types specified in the message payload. See <a href="#events">[events]</a>.</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">3</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>GET_OUTPUTS</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_outputs_reply">OUTPUTS</a></p></td>\r
+<td align="center" valign="top"><p class="table">Get the list of current outputs.</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">4</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>GET_TREE</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_tree_reply">TREE</a></p></td>\r
+<td align="center" valign="top"><p class="table">Get the i3 layout tree.</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">5</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>GET_MARKS</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_marks_reply">MARKS</a></p></td>\r
+<td align="center" valign="top"><p class="table">Gets the names of all currently set marks.</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">6</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>GET_BAR_CONFIG</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_bar_config_reply">BAR_CONFIG</a></p></td>\r
+<td align="center" valign="top"><p class="table">Gets the specified bar configuration or the names of all bar configurations if payload is empty.</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">7</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>GET_VERSION</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_version_reply">VERSION</a></p></td>\r
+<td align="center" valign="top"><p class="table">Gets the i3 version.</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">8</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>GET_BINDING_MODES</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_binding_modes_reply">BINDING_MODES</a></p></td>\r
+<td align="center" valign="top"><p class="table">Gets the names of all currently configured binding modes.</p></td>\r
+</tr>\r
+<tr>\r
+<td align="center" valign="top"><p class="table">9</p></td>\r
+<td align="center" valign="top"><p class="table"><tt>GET_CONFIG</tt></p></td>\r
+<td align="center" valign="top"><p class="table"><a href="#_config_reply">CONFIG</a></p></td>\r
+<td align="center" valign="top"><p class="table">Returns the last loaded i3 config.</p></td>\r
+</tr>\r
+</tbody>\r
+</table>\r
+</div>\r
<div class="paragraph"><p>So, a typical message could look like this:</p></div>\r
<div class="listingblock">\r
<div class="content">\r
</dt>\r
<dd>\r
<p>\r
- Confirmation/Error code for the COMMAND message.\r
+ Confirmation/Error code for the RUN_COMMAND message.\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
Reply to the GET_VERSION message.\r
</p>\r
</dd>\r
+<dt class="hdlist1">\r
+BINDING_MODES (8)\r
+</dt>\r
+<dd>\r
+<p>\r
+ Reply to the GET_BINDING_MODES message.\r
+</p>\r
+</dd>\r
+<dt class="hdlist1">\r
+GET_CONFIG (9)\r
+</dt>\r
+<dd>\r
+<p>\r
+ Reply to the GET_CONFIG message.\r
+</p>\r
+</dd>\r
</dl></div>\r
</div>\r
<div class="sect2">\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
+primary (boolean)\r
+</dt>\r
+<dd>\r
+<p>\r
+ Whether this output is currently the primary output.\r
+</p>\r
+</dd>\r
+<dt class="hdlist1">\r
current_workspace (string)\r
</dt>\r
<dd>\r
"y": 0,\r
"width": 1280,\r
"height": 1024\r
- },\r
+ }\r
}\r
]</tt></pre>\r
</div></div>\r
</dt>\r
<dd>\r
<p>\r
- Can be either "normal", "none" or "1pixel", dependending on the\r
+ Can be either "normal", "none" or "pixel", depending on the\r
container’s border style.\r
</p>\r
</dd>\r
</dt>\r
<dd>\r
<p>\r
- Whether this container (window or workspace) has the urgency hint set.\r
+ Whether this container (window, split container, floating container or\r
+ workspace) has the urgency hint set, directly or indirectly. All parent\r
+ containers up until the workspace container will be marked urgent if they\r
+ have at least one urgent child.\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
Whether this container is currently focused.\r
</p>\r
</dd>\r
+<dt class="hdlist1">\r
+focus (array of integer)\r
+</dt>\r
+<dd>\r
+<p>\r
+ List of child node IDs (see <tt>nodes</tt>, <tt>floating_nodes</tt> and <tt>id</tt>) in focus\r
+ order. Traversing the tree by following the first entry in this array\r
+ will result in eventually reaching the one node with <tt>focused</tt> set to\r
+ true.\r
+</p>\r
+</dd>\r
+<dt class="hdlist1">\r
+nodes (array of node)\r
+</dt>\r
+<dd>\r
+<p>\r
+ The tiling (i.e. non-floating) child containers of this node.\r
+</p>\r
+</dd>\r
+<dt class="hdlist1">\r
+floating_nodes (array of node)\r
+</dt>\r
+<dd>\r
+<p>\r
+ The floating child containers of this node. Only non-empty on nodes with\r
+ type <tt>workspace</tt>.\r
+</p>\r
+</dd>\r
</dl></div>\r
<div class="paragraph"><p>Please note that in the following example, I have left out some keys/values\r
which are not relevant for the type of the node. Otherwise, the example would\r
"y": 0,\r
"width": 1280,\r
"height": 0\r
- },\r
+ }\r
},\r
\r
{\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
-focused_workspace_text/focused_workspace_bg\r
+focused_background\r
+</dt>\r
+<dd>\r
+<p>\r
+ Background color of the bar on the currently focused monitor output.\r
+</p>\r
+</dd>\r
+<dt class="hdlist1">\r
+focused_statusline\r
+</dt>\r
+<dd>\r
+<p>\r
+ Text color to be used for the statusline on the currently focused\r
+ monitor output.\r
+</p>\r
+</dd>\r
+<dt class="hdlist1">\r
+focused_separator\r
</dt>\r
<dd>\r
<p>\r
- Text color/background color for a workspace button when the workspace\r
+ Text color to be used for the separator on the currently focused\r
+ monitor output.\r
+</p>\r
+</dd>\r
+<dt class="hdlist1">\r
+focused_workspace_text/focused_workspace_bg/focused_workspace_border\r
+</dt>\r
+<dd>\r
+<p>\r
+ Text/background/border color for a workspace button when the workspace\r
has focus.\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
-active_workspace_text/active_workspace_bg\r
+active_workspace_text/active_workspace_bg/active_workspace_border\r
</dt>\r
<dd>\r
<p>\r
- Text color/background color for a workspace button when the workspace\r
+ Text/background/border color for a workspace button when the workspace\r
is active (visible) on some output, but the focus is on another one.\r
You can only tell this apart from the focused workspace when you are\r
using multiple monitors.\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
-inactive_workspace_text/inactive_workspace_bg\r
+inactive_workspace_text/inactive_workspace_bg/inactive_workspace_border\r
</dt>\r
<dd>\r
<p>\r
- Text color/background color for a workspace button when the workspace\r
+ Text/background/border color for a workspace button when the workspace\r
does not have focus and is not active (visible) on any output. This\r
will be the case for most workspaces.\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
-urgent_workspace_text/urgent_workspace_bar\r
+urgent_workspace_text/urgent_workspace_bg/urgent_workspace_border\r
</dt>\r
<dd>\r
<p>\r
- Text color/background color for workspaces which contain at least one\r
+ Text/background/border color for workspaces which contain at least one\r
window with the urgency hint set.\r
</p>\r
</dd>\r
+<dt class="hdlist1">\r
+binding_mode_text/binding_mode_bg/binding_mode_border\r
+</dt>\r
+<dd>\r
+<p>\r
+ Text/background/border color for the binding mode indicator.\r
+</p>\r
+</dd>\r
</dl></div>\r
<div class="paragraph"><p><strong>Example of configured bars:</strong></p></div>\r
<div class="listingblock">\r
this is what <tt>i3 --version</tt> displays, too).\r
</p>\r
</dd>\r
+<dt class="hdlist1">\r
+loaded_config_file_name (string)\r
+</dt>\r
+<dd>\r
+<p>\r
+ The current config path.\r
+</p>\r
+</dd>\r
</dl></div>\r
<div class="paragraph"><p><strong>Example:</strong></p></div>\r
<div class="listingblock">\r
<div class="content">\r
<pre><tt>{\r
"human_readable" : "4.2-169-gf80b877 (2012-08-05, branch \"next\")",\r
+ "loaded_config_file_name" : "/home/hwangcc23/.i3/config",\r
"minor" : 2,\r
"patch" : 0,\r
"major" : 4\r
}</tt></pre>\r
</div></div>\r
</div>\r
+<div class="sect2">\r
+<h3 id="_binding_modes_reply">3.10. BINDING_MODES reply</h3>\r
+<div class="paragraph"><p>The reply consists of an array of all currently configured binding modes.</p></div>\r
+<div class="paragraph"><p><strong>Example:</strong></p></div>\r
+<div class="listingblock">\r
+<div class="content">\r
+<pre><tt>["default", "resize"]</tt></pre>\r
+</div></div>\r
+</div>\r
+<div class="sect2">\r
+<h3 id="_config_reply">3.11. CONFIG reply</h3>\r
+<div class="paragraph"><p>The config reply is a map which currently only contains the "config" member,\r
+which is a string containing the config file as loaded by i3 most recently.</p></div>\r
+<div class="paragraph"><p><strong>Example:</strong></p></div>\r
+<div class="listingblock">\r
+<div class="content">\r
+<pre><tt>{ "config": "font pango:monospace 8\nbindsym Mod4+q exit\n" }</tt></pre>\r
+</div></div>\r
+</div>\r
</div>\r
</div>\r
<div class="sect1">\r
mouse\r
</p>\r
</dd>\r
+<dt class="hdlist1">\r
+shutdown (6)\r
+</dt>\r
+<dd>\r
+<p>\r
+ Sent when the ipc shuts down because of a restart or exit by user command\r
+</p>\r
+</dd>\r
</dl></div>\r
<div class="paragraph"><p><strong>Example:</strong></p></div>\r
<div class="listingblock">\r
<h3 id="_workspace_event">4.3. workspace event</h3>\r
<div class="paragraph"><p>This event consists of a single serialized map containing a property\r
<tt>change (string)</tt> which indicates the type of the change ("focus", "init",\r
-"empty", "urgent"). A <tt>current (object)</tt> property will be present with the\r
-affected workspace whenever the type of event affects a workspace (otherwise,\r
-it will be +null).</p></div>\r
+"empty", "urgent", "reload", "rename", "restored", "move"). A\r
+<tt>current (object)</tt> property will be present with the affected workspace\r
+whenever the type of event affects a workspace (otherwise, it will be +null).</p></div>\r
<div class="paragraph"><p>When the change is "focus", an <tt>old (object)</tt> property will be present with the\r
previous workspace. When the first switch occurs (when i3 focuses the\r
workspace visible at the beginning) there is no previous workspace, and the\r
<div class="paragraph"><p>This event consists of a single serialized map containing a property\r
<tt>change (string)</tt> which holds the name of current mode in use. The name\r
is the same as specified in config when creating a mode. The default\r
-mode is simply named default.</p></div>\r
+mode is simply named default. It contains a second property, <tt>pango_markup</tt>, which\r
+defines whether pango markup shall be used for displaying this mode.</p></div>\r
<div class="paragraph"><p><strong>Example:</strong></p></div>\r
<div class="listingblock">\r
<div class="content">\r
-<pre><tt>{ "change": "default" }</tt></pre>\r
+<pre><tt>{\r
+ "change": "default",\r
+ "pango_markup": true\r
+}</tt></pre>\r
</div></div>\r
</div>\r
<div class="sect2">\r
<div class="ulist"><ul>\r
<li>\r
<p>\r
-<tt>new</tt> - the window has become managed by i3\r
+<tt>new</tt> – the window has become managed by i3\r
+</p>\r
+</li>\r
+<li>\r
+<p>\r
+<tt>close</tt> – the window has closed\r
</p>\r
</li>\r
<li>\r
<p>\r
-<tt>close</tt> - the window has closed\r
+<tt>focus</tt> – the window has received input focus\r
</p>\r
</li>\r
<li>\r
<p>\r
-<tt>focus</tt> - the window has received input focus\r
+<tt>title</tt> – the window’s title has changed\r
</p>\r
</li>\r
<li>\r
<p>\r
-<tt>title</tt> - the window’s title has changed\r
+<tt>fullscreen_mode</tt> – the window has entered or exited fullscreen mode\r
</p>\r
</li>\r
<li>\r
<p>\r
-<tt>fullscreen_mode</tt> - the window has entered or exited fullscreen mode\r
+<tt>move</tt> – the window has changed its position in the tree\r
</p>\r
</li>\r
<li>\r
<p>\r
-<tt>move</tt> - the window has changed its position in the tree\r
+<tt>floating</tt> – the window has transitioned to or from floating\r
</p>\r
</li>\r
<li>\r
<p>\r
-<tt>floating</tt> - the window has transitioned to or from floating\r
+<tt>urgent</tt> – the window has become urgent or lost its urgent status\r
</p>\r
</li>\r
<li>\r
<p>\r
-<tt>urgent</tt> - the window has become urgent or lost its urgent status\r
+<tt>mark</tt> – a mark has been added to or removed from the window\r
</p>\r
</li>\r
</ul></div>\r
<div class="sect2">\r
<h3 id="_binding_event">4.8. binding event</h3>\r
<div class="paragraph"><p>This event consists of a single serialized map reporting on the details of a\r
-binding that ran a command because of user input. The <tt>change (sring)</tt> field\r
+binding that ran a command because of user input. The <tt>change (string)</tt> field\r
indicates what sort of binding event was triggered (right now it will always be\r
<tt>"run"</tt> but may be expanded in the future).</p></div>\r
<div class="paragraph"><p>The <tt>binding (object)</tt> field contains details about the binding that was run:</p></div>\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
-mods (array of strings)\r
+event_state_mask (array of strings)\r
</dt>\r
<dd>\r
<p>\r
- The modifier keys that were configured with this binding.\r
+ The group and modifier keys that were configured with this binding.\r
</p>\r
</dd>\r
<dt class="hdlist1">\r
"change": "run",\r
"binding": {\r
"command": "nop",\r
- "mods": [\r
+ "event_state_mask": [\r
"shift",\r
"ctrl"\r
],\r
}</tt></pre>\r
</div></div>\r
</div>\r
+<div class="sect2">\r
+<h3 id="_shutdown_event">4.9. shutdown event</h3>\r
+<div class="paragraph"><p>This event is triggered when the connection to the ipc is about to shutdown\r
+because of a user action such as a <tt>restart</tt> or <tt>exit</tt> command. The <tt>change\r
+(string)</tt> field indicates why the ipc is shutting down. It can be either\r
+<tt>"restart"</tt> or <tt>"exit"</tt>.</p></div>\r
+<div class="paragraph"><p><strong>Example:</strong></p></div>\r
+<div class="listingblock">\r
+<div class="content">\r
+<pre><tt>{\r
+ "change": "restart"\r
+}</tt></pre>\r
+</div></div>\r
+</div>\r
</div>\r
</div>\r
<div class="sect1">\r
</ul></div>\r
</dd>\r
<dt class="hdlist1">\r
+C++\r
+</dt>\r
+<dd>\r
+<div class="ulist"><ul>\r
+<li>\r
+<p>\r
+<a href="https://github.com/drmgc/i3ipcpp">https://github.com/drmgc/i3ipcpp</a>\r
+</p>\r
+</li>\r
+</ul></div>\r
+</dd>\r
+<dt class="hdlist1">\r
Go\r
</dt>\r
<dd>\r
<div class="ulist"><ul>\r
<li>\r
<p>\r
-<a href="https://github.com/proxypoke/i3ipc">https://github.com/proxypoke/i3ipc</a>\r
+<a href="https://github.com/mdirkse/i3ipc-go">https://github.com/mdirkse/i3ipc-go</a>\r
</p>\r
</li>\r
</ul></div>\r
</li>\r
<li>\r
<p>\r
+<a href="https://github.com/Ceryn/i3msg-python">https://github.com/Ceryn/i3msg-python</a>\r
+</p>\r
+</li>\r
+<li>\r
+<p>\r
<a href="https://github.com/whitelynx/i3ipc">https://github.com/whitelynx/i3ipc</a> (not maintained)\r
</p>\r
</li>\r
<div class="ulist"><ul>\r
<li>\r
<p>\r
-<a href="http://github.com/badboy/i3-ipc">http://github.com/badboy/i3-ipc</a>\r
+<a href="https://github.com/veelenga/i3ipc-ruby">https://github.com/veelenga/i3ipc-ruby</a>\r
+</p>\r
+</li>\r
+<li>\r
+<p>\r
+<a href="https://github.com/badboy/i3-ipc">https://github.com/badboy/i3-ipc</a> (not maintained)\r
+</p>\r
+</li>\r
+</ul></div>\r
+</dd>\r
+<dt class="hdlist1">\r
+Rust\r
+</dt>\r
+<dd>\r
+<div class="ulist"><ul>\r
+<li>\r
+<p>\r
+<a href="https://github.com/tmerr/i3ipc-rs">https://github.com/tmerr/i3ipc-rs</a>\r
+</p>\r
+</li>\r
+</ul></div>\r
+</dd>\r
+<dt class="hdlist1">\r
+OCaml\r
+</dt>\r
+<dd>\r
+<div class="ulist"><ul>\r
+<li>\r
+<p>\r
+<a href="https://github.com/Armael/ocaml-i3ipc">https://github.com/Armael/ocaml-i3ipc</a>\r
</p>\r
</li>\r
</ul></div>\r
</dl></div>\r
</div>\r
</div>\r
+<div class="sect1">\r
+<h2 id="_appendix_a_detecting_byte_order_in_memory_safe_languages">6. Appendix A: Detecting byte order in memory-safe languages</h2>\r
+<div class="sectionbody">\r
+<div class="paragraph"><p>Some programming languages such as Go don’t offer a way to serialize data in the\r
+native byte order of the machine they’re running on without resorting to tricks\r
+involving the <tt>unsafe</tt> package.</p></div>\r
+<div class="paragraph"><p>The following technique can be used (and will not be broken by changes to i3) to\r
+detect the byte order i3 is using:</p></div>\r
+<div class="olist arabic"><ol class="arabic">\r
+<li>\r
+<p>\r
+The byte order dependent fields of an IPC message are message type and\r
+ payload length.\r
+</p>\r
+<div class="ulist"><ul>\r
+<li>\r
+<p>\r
+The message type <tt>RUN_COMMAND</tt> (0) is the same in big and little endian, so\r
+ we can use it in either byte order to elicit a reply from i3.\r
+</p>\r
+</li>\r
+<li>\r
+<p>\r
+The payload length 65536 + 256 (<tt>0x00 01 01 00</tt>) is the same in big and\r
+ little endian, and also small enough to not worry about memory allocations\r
+ of that size. We must use payloads of length 65536 + 256 in every message\r
+ we send, so that i3 will be able to read the entire message regardless of\r
+ the byte order it uses.\r
+</p>\r
+</li>\r
+</ul></div>\r
+</li>\r
+<li>\r
+<p>\r
+Send a big endian encoded message of type <tt>SUBSCRIBE</tt> (2) with payload <tt>[]</tt>\r
+ followed by 65536 + 256 - 2 <tt>SPACE</tt> (ASCII 0x20) bytes.\r
+</p>\r
+<div class="ulist"><ul>\r
+<li>\r
+<p>\r
+If i3 is running in big endian, this message is treated as a noop,\r
+ resulting in a <tt>SUBSCRIBE</tt> reply with payload <tt>{"success":true}</tt>\r
+ <span class="footnote"><br />[A small payload is important: that way, we circumvent dealing\r
+ with UNIX domain socket buffer sizes, whose size depends on the\r
+ implementation/operating system. Exhausting such a buffer results in an i3\r
+ deadlock unless you concurrently read and write, which — depending on the\r
+ programming language — makes the technique much more complicated.]<br /></span>.\r
+</p>\r
+</li>\r
+<li>\r
+<p>\r
+If i3 is running in little endian, this message is read in its entirety due\r
+ to the byte order independent payload length, then\r
+ <a href="https://github.com/i3/i3/blob/d726d09d496577d1c337a4b97486f2c9fbc914f1/src/ipc.c#L1188">silently\r
+ discarded</a> due to the unknown message type.\r
+</p>\r
+</li>\r
+</ul></div>\r
+</li>\r
+<li>\r
+<p>\r
+Send a byte order independent message, i.e. type <tt>RUN_COMMAND</tt> (0) with\r
+ payload <tt>nop byte order detection. padding:</tt>, padded to 65536 + 256 bytes\r
+ with <tt>a</tt> (ASCII 0x61) bytes. i3 will reply to this message with a reply of\r
+ type <tt>COMMAND</tt> (0).\r
+</p>\r
+<div class="ulist"><ul>\r
+<li>\r
+<p>\r
+The human-readable prefix is in there to not confuse readers of the i3 log.\r
+</p>\r
+</li>\r
+<li>\r
+<p>\r
+This messages serves as a synchronization primitive so that we know whether\r
+ i3 discarded the <tt>SUBSCRIBE</tt> message or didn’t answer it yet.\r
+</p>\r
+</li>\r
+</ul></div>\r
+</li>\r
+<li>\r
+<p>\r
+Receive a message header from i3, decoding the message type as big endian.\r
+</p>\r
+<div class="ulist"><ul>\r
+<li>\r
+<p>\r
+If the message’s reply type is <tt>COMMAND</tt> (0), i3 is running in little\r
+ endian (because the <tt>SUBSCRIBE</tt> message was discarded). Decode the message\r
+ payload length as little endian, receive the message payload.\r
+</p>\r
+</li>\r
+<li>\r
+<p>\r
+If the message’s reply type is anything else, i3 is running in big endian\r
+ (because our big endian encoded <tt>SUBSCRIBE</tt> message was answered). Decode\r
+ the message payload length in big endian, receive the message\r
+ payload. Then, receive the pending <tt>COMMAND</tt> message reply in big endian.\r
+</p>\r
+</li>\r
+</ul></div>\r
+</li>\r
+<li>\r
+<p>\r
+From here on out, send/receive all messages using the detected byte order.\r
+</p>\r
+</li>\r
+</ol></div>\r
+</div>\r
+</div>\r
</div>\r
<div id="footnotes"><hr /></div>\r
<div id="footer" lang="de">\r
projects / i3 / i3.github.io / blobdiff