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 Gets the layout tree. i3 uses a tree as data structure which includes
60 every container. The reply will be the JSON-encoded tree (see the reply
63 Gets a list of marks (identifiers for containers to easily jump to them
64 later). The reply will be a JSON-encoded list of window marks (see
67 So, a typical message could look like this:
68 --------------------------------------------------
69 "i3-ipc" <message length> <message type> <payload>
70 --------------------------------------------------
73 ------------------------------------------------------------------------------
74 00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
75 00000010 69 74 0a |it.|
76 ------------------------------------------------------------------------------
78 To generate and send such a message, you could use the following code in Perl:
79 ------------------------------------------------------------
80 sub format_ipc_command {
83 # Get the real byte count (vs. amount of characters)
84 { use bytes; $len = length($msg); }
85 return "i3-ipc" . pack("LL", $len, 0) . $msg;
88 $sock->write(format_ipc_command("exit"));
89 ------------------------------------------------------------------------------
91 == Receiving replies from i3
93 Replies from i3 usually consist of a simple string (the length of the string
94 is the message_length, so you can consider them length-prefixed) which in turn
95 contain the JSON serialization of a data structure. For example, the
96 GET_WORKSPACES message returns an array of workspaces (each workspace is a map
97 with certain attributes).
101 The reply format is identical to the normal message format. There also is
102 the magic string, then the message length, then the message type and the
105 The following reply types are implemented:
108 Confirmation/Error code for the COMMAND message.
110 Reply to the GET_WORKSPACES message.
112 Confirmation/Error code for the SUBSCRIBE message.
114 Reply to the GET_OUTPUTS message.
116 Reply to the GET_TREE message.
118 Reply to the GET_MARKS message.
122 The reply consists of a single serialized map. At the moment, the only
123 property is +success (bool)+, but this will be expanded in future versions.
130 === GET_WORKSPACES reply
132 The reply consists of a serialized list of workspaces. Each workspace has the
133 following properties:
136 The logical number of the workspace. Corresponds to the command
137 to switch to this workspace.
139 The name of this workspace (by default num+1), as changed by the
140 user. Encoded in UTF-8.
142 Whether this workspace is currently visible on an output (multiple
143 workspaces can be visible at the same time).
145 Whether this workspace currently has the focus (only one workspace
146 can have the focus at the same time).
148 Whether a window on this workspace has the "urgent" flag set.
150 The rectangle of this workspace (equals the rect of the output it
151 is on), consists of x, y, width, height.
153 The video output this workspace is on (LVDS1, VGA1, …).
191 The reply consists of a single serialized map. The only property is
192 +success (bool)+, indicating whether the subscription was successful (the
193 default) or whether a JSON parse error occurred.
200 === GET_OUTPUTS reply
202 The reply consists of a serialized list of outputs. Each output has the
203 following properties:
206 The name of this output (as seen in +xrandr(1)+). Encoded in UTF-8.
208 Whether this output is currently active (has a valid mode).
209 current_workspace (integer)::
210 The current workspace which is visible on this output. +null+ if the
211 output is not active.
213 The rectangle of this output (equals the rect of the output it
214 is on), consists of x, y, width, height.
222 "current_workspace": 4,
233 "current_workspace": 1,
246 The reply consists of a serialized tree. Each node in the tree (representing
247 one container) has at least the properties listed below. While the nodes might
248 have more properties, please do not use any properties which are not documented
249 here. They are not yet finalized and will probably change!
252 The internal ID (actually a C pointer value) of this container. Do not
253 make any assumptions about it. You can use it to (re-)identify and
254 address containers when talking to i3.
256 The internal name of this container. For all containers which are part
257 of the tree structure down to the workspace contents, this is set to a
258 nice human-readable name of the container.
259 For all other containers, the content is not defined (yet).
261 Can be either "normal", "none" or "1pixel", dependending on the
262 container’s border style.
264 Can be either "default", "stacked", "tabbed", "dockarea" or "output".
265 Other values might be possible in the future, should we add new
267 orientation (string)::
268 Can be either "none" (for non-split containers), "horizontal" or
271 The percentage which this container takes in its parent. A value of
272 +null+ means that the percent property does not make sense for this
273 container, for example for the root container.
275 The absolute display coordinates for this container. Display
276 coordinates means that when you have two 1600x1200 monitors on a single
277 X11 Display (the standard way), the coordinates of the first window on
278 the second monitor are +{ "x": 1600, "y": 0, "width": 1600, "height":
281 The coordinates of the *actual client window* inside its container.
282 These coordinates are relative to the container and do not include the
283 window decoration (which is actually rendered on the parent container).
284 So, when using the +default+ layout, you will have a 2 pixel border on
285 each side, making the window_rect +{ "x": 2, "y": 0, "width": 632,
286 "height": 366 }+ (for example).
288 The original geometry the window specified when i3 mapped it. Used when
289 switching a window to floating mode, for example.
291 Whether this container (window or workspace) has the urgency hint set.
293 Whether this container is currently focused.
295 Please note that in the following example, I have left out some keys/values
296 which are not relevant for the type of the node. Otherwise, the example would
297 be by far too long (it already is quite long, despite showing only 1 window and
300 It is useful to have an overview of the structure before taking a look at the
314 -----------------------
341 "layout": "dockarea",
342 "orientation": "vertical",
365 "orientation": "horizontal",
372 "floating_nodes": [],
396 "name": "bottomdock",
397 "layout": "dockarea",
398 "orientation": "vertical",
429 The reply consists of a single array of strings for each container that has a
430 mark. The order of that array is undefined. If more than one container has the
431 same mark, it will be represented multiple times in the reply (the array
432 contents are not unique).
434 If no window has a mark the response will be the empty array [].
435 ------------------------
442 To get informed when certain things happen in i3, clients can subscribe to
443 events. Events consist of a name (like "workspace") and an event reply type
444 (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
445 as replies to specific commands. However, the highest bit of the message type
446 is set to 1 to indicate that this is an event reply instead of a normal reply.
448 Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
449 that the requests to i3 are processed in order. This means, the following
450 situation can happen: You send a GET_WORKSPACES request but you receive a
451 "workspace" event before receiving the reply to GET_WORKSPACES. If your
452 program does not want to cope which such kinds of race conditions (an
453 event based library may not have a problem here), I suggest you create a
454 separate connection to receive events.
456 === Subscribing to events
458 By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
459 you can register to an event.
462 ---------------------------------
464 payload: [ "workspace", "focus" ]
465 ---------------------------------
470 The numbers in parenthesis is the event type (keep in mind that you need to
471 strip the highest bit first).
474 Sent when the user switches to a different workspace, when a new
475 workspace is initialized or when a workspace is removed (because the
476 last client vanished).
478 Sent when RandR issues a change notification (of either screens,
479 outputs, CRTCs or output properties).
482 --------------------------------------------------------------------
483 # the appropriate 4 bytes read from the socket are stored in $input
485 # unpack a 32-bit unsigned integer
486 my $message_type = unpack("L", $input);
488 # check if the highest bit is 1
489 my $is_event = (($message_type >> 31) == 1);
492 my $event_type = ($message_type & 0x7F);
495 say "Received event of type $event_type";
497 --------------------------------------------------------------------
501 This event consists of a single serialized map containing a property
502 +change (string)+ which indicates the type of the change ("focus", "init",
506 ---------------------
507 { "change": "focus" }
508 ---------------------
512 This event consists of a single serialized map containing a property
513 +change (string)+ which indicates the type of the change (currently only
517 ---------------------------
518 { "change": "unspecified" }
519 ---------------------------
523 For some languages, libraries are available (so you don’t have to implement
524 all this on your own). This list names some (if you wrote one, please let me
528 i3 includes a headerfile +i3/ipc.h+ which provides you all constants.
529 However, there is no library yet.
531 http://github.com/badboy/i3-ipc
533 http://search.cpan.org/search?query=AnyEvent::I3
535 http://github.com/thepub/i3ipc