1 IPC interface (interprocess communication)
2 ==========================================
3 Michael Stapelberg <michael+i3@stapelberg.de>
6 This document describes how to interface with i3 from a separate process. This
7 is useful for example to remote-control i3 (to write test cases for example) or
8 to get various information like the current workspaces to implement an external
11 The method of choice for IPC in our case is a unix socket because it has very
12 little overhead on both sides and is usually available without headaches in
13 most languages. In the default configuration file, no ipc-socket path is
14 specified and thus no socket is created. The standard path (which +i3-msg+ and
15 +i3-input+ use) is +/tmp/i3-ipc.sock+.
17 == Establishing a connection
19 To establish a connection, simply open the IPC socket. The following code
20 snippet illustrates this in Perl:
22 -------------------------------------------------------------
24 my $sock = IO::Socket::UNIX->new(Peer => '/tmp/i3-ipc.sock');
25 -------------------------------------------------------------
27 == Sending messages to i3
29 To send a message to i3, you have to format in the binary message format which
30 i3 expects. This format specifies a magic string in the beginning to ensure
31 the integrity of messages (to prevent follow-up errors). Afterwards follows
32 the length of the payload of the message as 32-bit integer and the type of
33 the message as 32-bit integer (the integers are not converted, so they are
34 in native byte order).
36 The magic string currently is "i3-ipc" and will only be changed when a change
37 in the IPC API is done which breaks compatibility (we hope that we don’t need
40 Currently implemented message types are the following:
43 The payload of the message is a command for i3 (like the commands you
44 can bind to keys in the configuration file) and will be executed
45 directly after receiving it. There is no reply to this message.
47 Gets the current workspaces. The reply will be a JSON-encoded list of
48 workspaces (see the reply section).
50 Subscribes your connection to certain events. See <<events>> for a
51 description of this message and the concept of events.
53 So, a typical message could look like this:
54 --------------------------------------------------
55 "i3-ipc" <message length> <message type> <payload>
56 --------------------------------------------------
59 ------------------------------------------------------------------------------
60 00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
61 00000010 69 74 0a |it.|
62 ------------------------------------------------------------------------------
64 To generate and send such a message, you could use the following code in Perl:
65 ------------------------------------------------------------
66 sub format_ipc_command {
69 # Get the real byte count (vs. amount of characters)
70 { use bytes; $len = length($msg); }
71 return "i3-ipc" . pack("LL", $len, 0) . $msg;
74 $sock->write(format_ipc_command("exit"));
75 ------------------------------------------------------------
77 == Receiving replies from i3
79 Replies of i3 usually consist of a simple string (the length of the string
80 is the message_length, so you can consider them length-prefixed) which in turn
81 contain the JSON serialization of a data structure. For example, the
82 GET_WORKSPACES message returns an array of workspaces (each workspace is a map
83 with certain attributes).
87 The reply format is identical to the normal message format. There also is
88 the magic string, then the message length, then the message type and the
91 The following reply types are implemented:
94 Confirmation/Error code for the COMMAND message.
96 Reply to the GET_WORKSPACES message.
98 Confirmation/Error code for the SUBSCRIBE message.
102 The reply consists of a single serialized map. At the moment, the only
103 property is +success (bool)+, but this will be expanded in future versions.
110 === GET_WORKSPACES reply
112 The reply consists of a serialized list of workspaces. Each workspace has the
113 following properties:
116 The logical number of the workspace. Corresponds to the command
117 to switch to this workspace.
119 The name of this workspace (by default num+1), as changed by the
120 user. Encoded in UTF-8.
122 Whether this workspace is currently visible on an output (multiple
123 workspaces can be visible at the same time).
125 Whether this workspace currently has the focus (only one workspace
126 can have the focus at the same time).
128 The rectangle of this workspace (equals the rect of the output it
129 is on), consists of x, y, width, height.
131 The video output this workspace is on (LVDS1, VGA1, …).
167 The reply consists of a single serialized map. The only property is
168 +success (bool)+, indicating whether the subscription was successful (the
169 default) or whether a JSON parse error occurred.
180 To get informed when certain things happen in i3, clients can subscribe to
181 events. Events consist of a name (like "workspace") and an event reply type
182 (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
183 as replies to specific commands.
185 Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
186 that the requests to i3 are processed in order. This means, the following
187 situation can happen: You send a GET_WORKSPACES request but you receive a
188 "workspace" event before receiving the reply to GET_WORKSPACES. If your
189 program does not want to cope which such kinds of race conditions (an
190 event based library may not have a problem here), I advise to create a separate
191 connection to receive events.
193 === Subscribing to events
195 By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
196 you can register to an event.
199 ---------------------------------
201 payload: [ "workspace", "focus" ]
202 ---------------------------------
207 Sent when the user switches to a different workspace, when a new
208 workspace is initialized or when a workspace is removed (because the
209 last client vanished).
213 This event consists of a single serialized map containing a property
214 +change (string)+ which indicates the type of the change ("focus", "init",
218 ---------------------
219 { "change": "focus" }
220 ---------------------
224 For some languages, libraries are available (so you don’t have to implement
225 all this on your own). This list names some (if you wrote one, please let me
229 http://github.com/badboy/i3-ipc
231 http://search.cpan.org/search?query=AnyEvent::I3