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21 <a href="/"><h1 id="title">i3 - improved tiling WM</h1></a>
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31 <h1>IPC interface (interprocess communication)</h1>
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32 <span id="author">Michael Stapelberg</span><br />
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33 <span id="email"><tt><<a href="mailto:michael+i3@stapelberg.de">michael+i3@stapelberg.de</a>></tt></span><br />
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34 <span id="revdate">March 2010</span>
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36 <div id="toctitle">Table of Contents</div>
37 <noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
41 <div class="sectionbody">
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42 <div class="paragraph"><p>This document describes how to interface with i3 from a separate process. This
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43 is useful for example to remote-control i3 (to write test cases for example) or
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44 to get various information like the current workspaces to implement an external
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45 workspace bar.</p></div>
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46 <div class="paragraph"><p>The method of choice for IPC in our case is a unix socket because it has very
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47 little overhead on both sides and is usually available without headaches in
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48 most languages. In the default configuration file, the ipc-socket gets created
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49 in <tt>/tmp/i3-%u/ipc-socket.%p</tt> where <tt>%u</tt> is your UNIX username and <tt>%p</tt> is the
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50 PID of i3.</p></div>
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51 <div class="paragraph"><p>All i3 utilities, like <tt>i3-msg</tt> and <tt>i3-input</tt> will read the <tt>I3_SOCKET_PATH</tt>
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52 X11 property, stored on the X11 root window.</p></div>
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56 <h2 id="_establishing_a_connection">1. Establishing a connection</h2>
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57 <div class="sectionbody">
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58 <div class="paragraph"><p>To establish a connection, simply open the IPC socket. The following code
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59 snippet illustrates this in Perl:</p></div>
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60 <div class="listingblock">
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61 <div class="content">
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62 <pre><tt>use IO::Socket::UNIX;
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63 my $sock = IO::Socket::UNIX->new(Peer => '/tmp/i3-ipc.sock');</tt></pre>
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68 <h2 id="_sending_messages_to_i3">2. Sending messages to i3</h2>
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69 <div class="sectionbody">
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70 <div class="paragraph"><p>To send a message to i3, you have to format in the binary message format which
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71 i3 expects. This format specifies a magic string in the beginning to ensure
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72 the integrity of messages (to prevent follow-up errors). Following the magic
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73 string comes the length of the payload of the message as 32-bit integer, and
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74 the type of the message as 32-bit integer (the integers are not converted, so
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75 they are in native byte order).</p></div>
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76 <div class="paragraph"><p>The magic string currently is "i3-ipc" and will only be changed when a change
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77 in the IPC API is done which breaks compatibility (we hope that we don’t need
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78 to do that).</p></div>
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79 <div class="paragraph"><p>Currently implemented message types are the following:</p></div>
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80 <div class="dlist"><dl>
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81 <dt class="hdlist1">
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86 The payload of the message is a command for i3 (like the commands you
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87 can bind to keys in the configuration file) and will be executed
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88 directly after receiving it. There is no reply to this message.
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91 <dt class="hdlist1">
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96 Gets the current workspaces. The reply will be a JSON-encoded list of
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97 workspaces (see the reply section).
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100 <dt class="hdlist1">
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105 Subscribes your connection to certain events. See <a href="#events">[events]</a> for a
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106 description of this message and the concept of events.
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109 <dt class="hdlist1">
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114 Gets the current outputs. The reply will be a JSON-encoded list of outputs
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115 (see the reply section).
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118 <dt class="hdlist1">
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123 Gets the layout tree. i3 uses a tree as data structure which includes
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124 every container. The reply will be the JSON-encoded tree (see the reply
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129 <div class="paragraph"><p>So, a typical message could look like this:</p></div>
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130 <div class="listingblock">
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131 <div class="content">
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132 <pre><tt>"i3-ipc" <message length> <message type> <payload></tt></pre>
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134 <div class="paragraph"><p>Or, as a hexdump:</p></div>
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135 <div class="listingblock">
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136 <div class="content">
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137 <pre><tt>00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
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138 00000010 69 74 0a |it.|</tt></pre>
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140 <div class="paragraph"><p>To generate and send such a message, you could use the following code in Perl:</p></div>
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141 <div class="listingblock">
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142 <div class="content">
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143 <pre><tt>sub format_ipc_command {
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146 # Get the real byte count (vs. amount of characters)
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147 { use bytes; $len = length($msg); }
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148 return "i3-ipc" . pack("LL", $len, 0) . $msg;
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151 $sock->write(format_ipc_command("exit"));</tt></pre>
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155 <div class="sect1">
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156 <h2 id="_receiving_replies_from_i3">3. Receiving replies from i3</h2>
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157 <div class="sectionbody">
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158 <div class="paragraph"><p>Replies from i3 usually consist of a simple string (the length of the string
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159 is the message_length, so you can consider them length-prefixed) which in turn
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160 contain the JSON serialization of a data structure. For example, the
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161 GET_WORKSPACES message returns an array of workspaces (each workspace is a map
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162 with certain attributes).</p></div>
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163 <div class="sect2">
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164 <h3 id="_reply_format">3.1. Reply format</h3>
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165 <div class="paragraph"><p>The reply format is identical to the normal message format. There also is
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166 the magic string, then the message length, then the message type and the
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168 <div class="paragraph"><p>The following reply types are implemented:</p></div>
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169 <div class="dlist"><dl>
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170 <dt class="hdlist1">
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175 Confirmation/Error code for the COMMAND message.
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178 <dt class="hdlist1">
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183 Reply to the GET_WORKSPACES message.
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186 <dt class="hdlist1">
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191 Confirmation/Error code for the SUBSCRIBE message.
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194 <dt class="hdlist1">
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199 Reply to the GET_OUTPUTS message.
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202 <dt class="hdlist1">
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207 Reply to the GET_TREE message.
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212 <div class="sect2">
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213 <h3 id="_command_reply">3.2. COMMAND reply</h3>
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214 <div class="paragraph"><p>The reply consists of a single serialized map. At the moment, the only
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215 property is <tt>success (bool)</tt>, but this will be expanded in future versions.</p></div>
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216 <div class="paragraph"><p><strong>Example:</strong></p></div>
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217 <div class="listingblock">
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218 <div class="content">
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219 <pre><tt>{ "success": true }</tt></pre>
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222 <div class="sect2">
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223 <h3 id="_get_workspaces_reply">3.3. GET_WORKSPACES reply</h3>
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224 <div class="paragraph"><p>The reply consists of a serialized list of workspaces. Each workspace has the
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225 following properties:</p></div>
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226 <div class="dlist"><dl>
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227 <dt class="hdlist1">
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232 The logical number of the workspace. Corresponds to the command
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233 to switch to this workspace.
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236 <dt class="hdlist1">
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241 The name of this workspace (by default num+1), as changed by the
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242 user. Encoded in UTF-8.
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245 <dt class="hdlist1">
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250 Whether this workspace is currently visible on an output (multiple
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251 workspaces can be visible at the same time).
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254 <dt class="hdlist1">
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259 Whether this workspace currently has the focus (only one workspace
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260 can have the focus at the same time).
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263 <dt class="hdlist1">
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268 Whether a window on this workspace has the "urgent" flag set.
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271 <dt class="hdlist1">
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276 The rectangle of this workspace (equals the rect of the output it
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277 is on), consists of x, y, width, height.
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280 <dt class="hdlist1">
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285 The video output this workspace is on (LVDS1, VGA1, …).
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289 <div class="paragraph"><p><strong>Example:</strong></p></div>
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290 <div class="listingblock">
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291 <div class="content">
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324 <div class="sect2">
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325 <h3 id="_subscribe_reply">3.4. SUBSCRIBE reply</h3>
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326 <div class="paragraph"><p>The reply consists of a single serialized map. The only property is
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327 <tt>success (bool)</tt>, indicating whether the subscription was successful (the
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328 default) or whether a JSON parse error occurred.</p></div>
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329 <div class="paragraph"><p><strong>Example:</strong></p></div>
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330 <div class="listingblock">
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331 <div class="content">
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332 <pre><tt>{ "success": true }</tt></pre>
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335 <div class="sect2">
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336 <h3 id="_get_outputs_reply">3.5. GET_OUTPUTS reply</h3>
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337 <div class="paragraph"><p>The reply consists of a serialized list of outputs. Each output has the
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338 following properties:</p></div>
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339 <div class="dlist"><dl>
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340 <dt class="hdlist1">
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345 The name of this output (as seen in <tt>xrandr(1)</tt>). Encoded in UTF-8.
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348 <dt class="hdlist1">
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353 Whether this output is currently active (has a valid mode).
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356 <dt class="hdlist1">
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357 current_workspace (integer)
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361 The current workspace which is visible on this output. <tt>null</tt> if the
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362 output is not active.
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365 <dt class="hdlist1">
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370 The rectangle of this output (equals the rect of the output it
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371 is on), consists of x, y, width, height.
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375 <div class="paragraph"><p><strong>Example:</strong></p></div>
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376 <div class="listingblock">
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377 <div class="content">
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382 "current_workspace": 4,
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393 "current_workspace": 1,
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404 <div class="sect2">
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405 <h3 id="_get_tree_reply">3.6. GET_TREE reply</h3>
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406 <div class="paragraph"><p>The reply consists of a serialized tree. Each node in the tree (representing
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407 one container) has at least the properties listed below. While the nodes might
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408 have more properties, please do not use any properties which are not documented
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409 here. They are not yet finalized and will probably change!</p></div>
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410 <div class="dlist"><dl>
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411 <dt class="hdlist1">
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416 The internal ID (actually a C pointer value) of this container. Do not
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417 make any assumptions about it. You can use it to (re-)identify and
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418 address containers when talking to i3.
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421 <dt class="hdlist1">
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426 The internal name of this container. For all containers which are part
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427 of the tree structure down to the workspace contents, this is set to a
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428 nice human-readable name of the container.
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429 For all other containers, the content is not defined (yet).
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432 <dt class="hdlist1">
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437 Can be either "normal", "none" or "1pixel", dependending on the
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438 container’s border style.
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441 <dt class="hdlist1">
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446 Can be either "default", "stacked", "tabbed", "dockarea" or "output".
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447 Other values might be possible in the future, should we add new
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451 <dt class="hdlist1">
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452 orientation (string)
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456 Can be either "none" (for non-split containers), "horizontal" or
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460 <dt class="hdlist1">
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465 The percentage which this container takes in its parent. A value of
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466 <tt>null</tt> means that the percent property does not make sense for this
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467 container, for example for the root container.
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470 <dt class="hdlist1">
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475 The absolute display coordinates for this container. Display
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476 coordinates means that when you have two 1600x1200 monitors on a single
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477 X11 Display (the standard way), the coordinates of the first window on
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478 the second monitor are <tt>{ "x": 1600, "y": 0, "width": 1600, "height":
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482 <dt class="hdlist1">
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487 The coordinates of the <strong>actual client window</strong> inside its container.
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488 These coordinates are relative to the container and do not include the
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489 window decoration (which is actually rendered on the parent container).
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490 So, when using the <tt>default</tt> layout, you will have a 2 pixel border on
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491 each side, making the window_rect <tt>{ "x": 2, "y": 0, "width": 632,
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492 "height": 366 }</tt> (for example).
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495 <dt class="hdlist1">
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500 The original geometry the window specified when i3 mapped it. Used when
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501 switching a window to floating mode, for example.
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504 <dt class="hdlist1">
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509 Whether this container (window or workspace) has the urgency hint set.
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512 <dt class="hdlist1">
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517 Whether this container is currently focused.
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521 <div class="paragraph"><p>Please note that in the following example, I have left out some keys/values
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522 which are not relevant for the type of the node. Otherwise, the example would
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523 be by far too long (it already is quite long, despite showing only 1 window and
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524 one dock window).</p></div>
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525 <div class="paragraph"><p>It is useful to have an overview of the structure before taking a look at the
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526 JSON dump:</p></div>
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527 <div class="ulist"><ul>
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532 <div class="ulist"><ul>
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537 <div class="ulist"><ul>
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547 <div class="ulist"><ul>
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552 <div class="ulist"><ul>
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566 <div class="ulist"><ul>
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584 <div class="paragraph"><p><strong>Example:</strong></p></div>
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585 <div class="listingblock">
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586 <div class="content">
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601 "layout": "output",
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613 "layout": "dockarea",
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614 "orientation": "vertical",
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637 "orientation": "horizontal",
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644 "floating_nodes": [],
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650 "border": "normal",
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668 "name": "bottomdock",
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669 "layout": "dockarea",
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670 "orientation": "vertical",
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701 <div class="sect1">
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702 <h2 id="_events">4. Events</h2>
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703 <div class="sectionbody">
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704 <div class="paragraph" id="events"><p>To get informed when certain things happen in i3, clients can subscribe to
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705 events. Events consist of a name (like "workspace") and an event reply type
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706 (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
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707 as replies to specific commands. However, the highest bit of the message type
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708 is set to 1 to indicate that this is an event reply instead of a normal reply.</p></div>
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709 <div class="paragraph"><p>Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
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710 that the requests to i3 are processed in order. This means, the following
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711 situation can happen: You send a GET_WORKSPACES request but you receive a
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712 "workspace" event before receiving the reply to GET_WORKSPACES. If your
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713 program does not want to cope which such kinds of race conditions (an
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714 event based library may not have a problem here), I suggest you create a
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715 separate connection to receive events.</p></div>
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716 <div class="sect2">
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717 <h3 id="_subscribing_to_events">4.1. Subscribing to events</h3>
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718 <div class="paragraph"><p>By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
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719 you can register to an event.</p></div>
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720 <div class="paragraph"><p><strong>Example:</strong></p></div>
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721 <div class="listingblock">
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722 <div class="content">
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723 <pre><tt>type: SUBSCRIBE
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724 payload: [ "workspace", "focus" ]</tt></pre>
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727 <div class="sect2">
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728 <h3 id="_available_events">4.2. Available events</h3>
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729 <div class="paragraph"><p>The numbers in parenthesis is the event type (keep in mind that you need to
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730 strip the highest bit first).</p></div>
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731 <div class="dlist"><dl>
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732 <dt class="hdlist1">
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737 Sent when the user switches to a different workspace, when a new
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738 workspace is initialized or when a workspace is removed (because the
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739 last client vanished).
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742 <dt class="hdlist1">
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747 Sent when RandR issues a change notification (of either screens,
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748 outputs, CRTCs or output properties).
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752 <div class="paragraph"><p><strong>Example:</strong></p></div>
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753 <div class="listingblock">
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754 <div class="content">
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755 <pre><tt># the appropriate 4 bytes read from the socket are stored in $input
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757 # unpack a 32-bit unsigned integer
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758 my $message_type = unpack("L", $input);
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760 # check if the highest bit is 1
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761 my $is_event = (($message_type >> 31) == 1);
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763 # use the other bits
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764 my $event_type = ($message_type & 0x7F);
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767 say "Received event of type $event_type";
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771 <div class="sect2">
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772 <h3 id="_workspace_event">4.3. workspace event</h3>
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773 <div class="paragraph"><p>This event consists of a single serialized map containing a property
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774 <tt>change (string)</tt> which indicates the type of the change ("focus", "init",
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775 "empty", "urgent").</p></div>
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776 <div class="paragraph"><p><strong>Example:</strong></p></div>
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777 <div class="listingblock">
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778 <div class="content">
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779 <pre><tt>{ "change": "focus" }</tt></pre>
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782 <div class="sect2">
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783 <h3 id="_output_event">4.4. output event</h3>
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784 <div class="paragraph"><p>This event consists of a single serialized map containing a property
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785 <tt>change (string)</tt> which indicates the type of the change (currently only
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786 "unspecified").</p></div>
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787 <div class="paragraph"><p><strong>Example:</strong></p></div>
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788 <div class="listingblock">
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789 <div class="content">
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790 <pre><tt>{ "change": "unspecified" }</tt></pre>
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795 <div class="sect1">
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796 <h2 id="_see_also">5. See also</h2>
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797 <div class="sectionbody">
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798 <div class="paragraph"><p>For some languages, libraries are available (so you don’t have to implement
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799 all this on your own). This list names some (if you wrote one, please let me
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801 <div class="dlist"><dl>
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802 <dt class="hdlist1">
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807 i3 includes a headerfile <tt>i3/ipc.h</tt> which provides you all constants.
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808 However, there is no library yet.
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811 <dt class="hdlist1">
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816 <a href="http://github.com/badboy/i3-ipc">http://github.com/badboy/i3-ipc</a>
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819 <dt class="hdlist1">
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824 <a href="http://search.cpan.org/search?query=AnyEvent::I3">http://search.cpan.org/search?query=AnyEvent::I3</a>
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827 <dt class="hdlist1">
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832 <a href="http://github.com/thepub/i3ipc">http://github.com/thepub/i3ipc</a>
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839 <div id="footnotes"><hr /></div>
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840 <div id="footer" lang="de">
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841 © 2009-2011 Michael Stapelberg, <a href="/impress.html">Impressum</a>
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projects / i3 / i3.github.io / blob