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, the ipc-socket gets created
14 in +/tmp/i3-%u/ipc-socket.%p+ where +%u+ is your UNIX username and +%p+ is the
17 All i3 utilities, like +i3-msg+ and +i3-input+ will read the +I3_SOCKET_PATH+
18 X11 property, stored on the X11 root window.
20 == Establishing a connection
22 To establish a connection, simply open the IPC socket. The following code
23 snippet illustrates this in Perl:
25 -------------------------------------------------------------
27 my $sock = IO::Socket::UNIX->new(Peer => '/tmp/i3-ipc.sock');
28 -------------------------------------------------------------
30 == Sending messages to i3
32 To send a message to i3, you have to format in the binary message format which
33 i3 expects. This format specifies a magic string in the beginning to ensure
34 the integrity of messages (to prevent follow-up errors). Following the magic
35 string comes the length of the payload of the message as 32-bit integer, and
36 the type of the message as 32-bit integer (the integers are not converted, so
37 they are in native byte order).
39 The magic string currently is "i3-ipc" and will only be changed when a change
40 in the IPC API is done which breaks compatibility (we hope that we don’t need
43 Currently implemented message types are the following:
46 The payload of the message is a command for i3 (like the commands you
47 can bind to keys in the configuration file) and will be executed
48 directly after receiving it. There is no reply to this message.
50 Gets the current workspaces. The reply will be a JSON-encoded list of
51 workspaces (see the reply section).
53 Subscribes your connection to certain events. See <<events>> for a
54 description of this message and the concept of events.
56 Gets the current outputs. The reply will be a JSON-encoded list of outputs
57 (see the reply section).
59 So, a typical message could look like this:
60 --------------------------------------------------
61 "i3-ipc" <message length> <message type> <payload>
62 --------------------------------------------------
65 ------------------------------------------------------------------------------
66 00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
67 00000010 69 74 0a |it.|
68 ------------------------------------------------------------------------------
70 To generate and send such a message, you could use the following code in Perl:
71 ------------------------------------------------------------
72 sub format_ipc_command {
75 # Get the real byte count (vs. amount of characters)
76 { use bytes; $len = length($msg); }
77 return "i3-ipc" . pack("LL", $len, 0) . $msg;
80 $sock->write(format_ipc_command("exit"));
81 ------------------------------------------------------------------------------
83 == Receiving replies from i3
85 Replies from i3 usually consist of a simple string (the length of the string
86 is the message_length, so you can consider them length-prefixed) which in turn
87 contain the JSON serialization of a data structure. For example, the
88 GET_WORKSPACES message returns an array of workspaces (each workspace is a map
89 with certain attributes).
93 The reply format is identical to the normal message format. There also is
94 the magic string, then the message length, then the message type and the
97 The following reply types are implemented:
100 Confirmation/Error code for the COMMAND message.
102 Reply to the GET_WORKSPACES message.
104 Confirmation/Error code for the SUBSCRIBE message.
106 Reply to the GET_OUTPUTS message.
110 The reply consists of a single serialized map. At the moment, the only
111 property is +success (bool)+, but this will be expanded in future versions.
118 === GET_WORKSPACES reply
120 The reply consists of a serialized list of workspaces. Each workspace has the
121 following properties:
124 The logical number of the workspace. Corresponds to the command
125 to switch to this workspace.
127 The name of this workspace (by default num+1), as changed by the
128 user. Encoded in UTF-8.
130 Whether this workspace is currently visible on an output (multiple
131 workspaces can be visible at the same time).
133 Whether this workspace currently has the focus (only one workspace
134 can have the focus at the same time).
136 Whether a window on this workspace has the "urgent" flag set.
138 The rectangle of this workspace (equals the rect of the output it
139 is on), consists of x, y, width, height.
141 The video output this workspace is on (LVDS1, VGA1, …).
179 The reply consists of a single serialized map. The only property is
180 +success (bool)+, indicating whether the subscription was successful (the
181 default) or whether a JSON parse error occurred.
188 === GET_OUTPUTS reply
190 The reply consists of a serialized list of outputs. Each output has the
191 following properties:
194 The name of this output (as seen in +xrandr(1)+). Encoded in UTF-8.
196 Whether this output is currently active (has a valid mode).
197 current_workspace (integer)::
198 The current workspace which is visible on this output. +null+ if the
199 output is not active.
201 The rectangle of this output (equals the rect of the output it
202 is on), consists of x, y, width, height.
210 "current_workspace": 4,
221 "current_workspace": 1,
236 To get informed when certain things happen in i3, clients can subscribe to
237 events. Events consist of a name (like "workspace") and an event reply type
238 (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
239 as replies to specific commands. However, the highest bit of the message type
240 is set to 1 to indicate that this is an event reply instead of a normal reply.
242 Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
243 that the requests to i3 are processed in order. This means, the following
244 situation can happen: You send a GET_WORKSPACES request but you receive a
245 "workspace" event before receiving the reply to GET_WORKSPACES. If your
246 program does not want to cope which such kinds of race conditions (an
247 event based library may not have a problem here), I suggest you create a
248 separate connection to receive events.
250 === Subscribing to events
252 By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
253 you can register to an event.
256 ---------------------------------
258 payload: [ "workspace", "focus" ]
259 ---------------------------------
264 The numbers in parenthesis is the event type (keep in mind that you need to
265 strip the highest bit first).
268 Sent when the user switches to a different workspace, when a new
269 workspace is initialized or when a workspace is removed (because the
270 last client vanished).
272 Sent when RandR issues a change notification (of either screens,
273 outputs, CRTCs or output properties).
276 --------------------------------------------------------------------
277 # the appropriate 4 bytes read from the socket are stored in $input
279 # unpack a 32-bit unsigned integer
280 my $message_type = unpack("L", $input);
282 # check if the highest bit is 1
283 my $is_event = (($message_type >> 31) == 1);
286 my $event_type = ($message_type & 0x7F);
289 say "Received event of type $event_type";
291 --------------------------------------------------------------------
295 This event consists of a single serialized map containing a property
296 +change (string)+ which indicates the type of the change ("focus", "init",
300 ---------------------
301 { "change": "focus" }
302 ---------------------
306 This event consists of a single serialized map containing a property
307 +change (string)+ which indicates the type of the change (currently only
311 ---------------------------
312 { "change": "unspecified" }
313 ---------------------------
317 For some languages, libraries are available (so you don’t have to implement
318 all this on your own). This list names some (if you wrote one, please let me
322 i3 includes a headerfile +i3/ipc.h+ which provides you all constants.
323 However, there is no library yet.
325 http://github.com/badboy/i3-ipc
327 http://search.cpan.org/search?query=AnyEvent::I3
329 http://github.com/thepub/i3ipc