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
15 PID of i3. You can get the socketpath from i3 by calling +i3 --get-socketpath+.
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 chomp(my $path = qx(i3 --get-socketpath));
28 my $sock = IO::Socket::UNIX->new(Peer => $path);
29 -------------------------------------------------------------
31 == Sending messages to i3
33 To send a message to i3, you have to format in the binary message format which
34 i3 expects. This format specifies a magic string in the beginning to ensure
35 the integrity of messages (to prevent follow-up errors). Following the magic
36 string comes the length of the payload of the message as 32-bit integer, and
37 the type of the message as 32-bit integer (the integers are not converted, so
38 they are in native byte order).
40 The magic string currently is "i3-ipc" and will only be changed when a change
41 in the IPC API is done which breaks compatibility (we hope that we don’t need
44 Currently implemented message types are the following:
47 The payload of the message is a command for i3 (like the commands you
48 can bind to keys in the configuration file) and will be executed
49 directly after receiving it. There is no reply to this message.
51 Gets the current workspaces. The reply will be a JSON-encoded list of
52 workspaces (see the reply section).
54 Subscribes your connection to certain events. See <<events>> for a
55 description of this message and the concept of events.
57 Gets the current outputs. The reply will be a JSON-encoded list of outputs
58 (see the reply section).
60 Gets the layout tree. i3 uses a tree as data structure which includes
61 every container. The reply will be the JSON-encoded tree (see the reply
64 Gets a list of marks (identifiers for containers to easily jump to them
65 later). The reply will be a JSON-encoded list of window marks (see
68 So, a typical message could look like this:
69 --------------------------------------------------
70 "i3-ipc" <message length> <message type> <payload>
71 --------------------------------------------------
74 ------------------------------------------------------------------------------
75 00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
76 00000010 69 74 0a |it.|
77 ------------------------------------------------------------------------------
79 To generate and send such a message, you could use the following code in Perl:
80 ------------------------------------------------------------
81 sub format_ipc_command {
84 # Get the real byte count (vs. amount of characters)
85 { use bytes; $len = length($msg); }
86 return "i3-ipc" . pack("LL", $len, 0) . $msg;
89 $sock->write(format_ipc_command("exit"));
90 ------------------------------------------------------------------------------
92 == Receiving replies from i3
94 Replies from i3 usually consist of a simple string (the length of the string
95 is the message_length, so you can consider them length-prefixed) which in turn
96 contain the JSON serialization of a data structure. For example, the
97 GET_WORKSPACES message returns an array of workspaces (each workspace is a map
98 with certain attributes).
102 The reply format is identical to the normal message format. There also is
103 the magic string, then the message length, then the message type and the
106 The following reply types are implemented:
109 Confirmation/Error code for the COMMAND message.
111 Reply to the GET_WORKSPACES message.
113 Confirmation/Error code for the SUBSCRIBE message.
115 Reply to the GET_OUTPUTS message.
117 Reply to the GET_TREE message.
119 Reply to the GET_MARKS message.
123 The reply consists of a single serialized map. At the moment, the only
124 property is +success (bool)+, but this will be expanded in future versions.
131 === GET_WORKSPACES reply
133 The reply consists of a serialized list of workspaces. Each workspace has the
134 following properties:
137 The logical number of the workspace. Corresponds to the command
138 to switch to this workspace.
140 The name of this workspace (by default num+1), as changed by the
141 user. Encoded in UTF-8.
143 Whether this workspace is currently visible on an output (multiple
144 workspaces can be visible at the same time).
146 Whether this workspace currently has the focus (only one workspace
147 can have the focus at the same time).
149 Whether a window on this workspace has the "urgent" flag set.
151 The rectangle of this workspace (equals the rect of the output it
152 is on), consists of x, y, width, height.
154 The video output this workspace is on (LVDS1, VGA1, …).
192 The reply consists of a single serialized map. The only property is
193 +success (bool)+, indicating whether the subscription was successful (the
194 default) or whether a JSON parse error occurred.
201 === GET_OUTPUTS reply
203 The reply consists of a serialized list of outputs. Each output has the
204 following properties:
207 The name of this output (as seen in +xrandr(1)+). Encoded in UTF-8.
209 Whether this output is currently active (has a valid mode).
210 current_workspace (integer)::
211 The current workspace which is visible on this output. +null+ if the
212 output is not active.
214 The rectangle of this output (equals the rect of the output it
215 is on), consists of x, y, width, height.
223 "current_workspace": 4,
234 "current_workspace": 1,
247 The reply consists of a serialized tree. Each node in the tree (representing
248 one container) has at least the properties listed below. While the nodes might
249 have more properties, please do not use any properties which are not documented
250 here. They are not yet finalized and will probably change!
253 The internal ID (actually a C pointer value) of this container. Do not
254 make any assumptions about it. You can use it to (re-)identify and
255 address containers when talking to i3.
257 The internal name of this container. For all containers which are part
258 of the tree structure down to the workspace contents, this is set to a
259 nice human-readable name of the container.
260 For all other containers, the content is not defined (yet).
262 Can be either "normal", "none" or "1pixel", dependending on the
263 container’s border style.
265 Can be either "default", "stacked", "tabbed", "dockarea" or "output".
266 Other values might be possible in the future, should we add new
268 orientation (string)::
269 Can be either "none" (for non-split containers), "horizontal" or
272 The percentage which this container takes in its parent. A value of
273 +null+ means that the percent property does not make sense for this
274 container, for example for the root container.
276 The absolute display coordinates for this container. Display
277 coordinates means that when you have two 1600x1200 monitors on a single
278 X11 Display (the standard way), the coordinates of the first window on
279 the second monitor are +{ "x": 1600, "y": 0, "width": 1600, "height":
282 The coordinates of the *actual client window* inside its container.
283 These coordinates are relative to the container and do not include the
284 window decoration (which is actually rendered on the parent container).
285 So, when using the +default+ layout, you will have a 2 pixel border on
286 each side, making the window_rect +{ "x": 2, "y": 0, "width": 632,
287 "height": 366 }+ (for example).
289 The original geometry the window specified when i3 mapped it. Used when
290 switching a window to floating mode, for example.
292 Whether this container (window or workspace) has the urgency hint set.
294 Whether this container is currently focused.
296 Please note that in the following example, I have left out some keys/values
297 which are not relevant for the type of the node. Otherwise, the example would
298 be by far too long (it already is quite long, despite showing only 1 window and
301 It is useful to have an overview of the structure before taking a look at the
315 -----------------------
342 "layout": "dockarea",
343 "orientation": "vertical",
366 "orientation": "horizontal",
373 "floating_nodes": [],
397 "name": "bottomdock",
398 "layout": "dockarea",
399 "orientation": "vertical",
430 The reply consists of a single array of strings for each container that has a
431 mark. The order of that array is undefined. If more than one container has the
432 same mark, it will be represented multiple times in the reply (the array
433 contents are not unique).
435 If no window has a mark the response will be the empty array [].
436 ------------------------
443 To get informed when certain things happen in i3, clients can subscribe to
444 events. Events consist of a name (like "workspace") and an event reply type
445 (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
446 as replies to specific commands. However, the highest bit of the message type
447 is set to 1 to indicate that this is an event reply instead of a normal reply.
449 Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
450 that the requests to i3 are processed in order. This means, the following
451 situation can happen: You send a GET_WORKSPACES request but you receive a
452 "workspace" event before receiving the reply to GET_WORKSPACES. If your
453 program does not want to cope which such kinds of race conditions (an
454 event based library may not have a problem here), I suggest you create a
455 separate connection to receive events.
457 === Subscribing to events
459 By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
460 you can register to an event.
463 ---------------------------------
465 payload: [ "workspace", "focus" ]
466 ---------------------------------
471 The numbers in parenthesis is the event type (keep in mind that you need to
472 strip the highest bit first).
475 Sent when the user switches to a different workspace, when a new
476 workspace is initialized or when a workspace is removed (because the
477 last client vanished).
479 Sent when RandR issues a change notification (of either screens,
480 outputs, CRTCs or output properties).
483 --------------------------------------------------------------------
484 # the appropriate 4 bytes read from the socket are stored in $input
486 # unpack a 32-bit unsigned integer
487 my $message_type = unpack("L", $input);
489 # check if the highest bit is 1
490 my $is_event = (($message_type >> 31) == 1);
493 my $event_type = ($message_type & 0x7F);
496 say "Received event of type $event_type";
498 --------------------------------------------------------------------
502 This event consists of a single serialized map containing a property
503 +change (string)+ which indicates the type of the change ("focus", "init",
507 ---------------------
508 { "change": "focus" }
509 ---------------------
513 This event consists of a single serialized map containing a property
514 +change (string)+ which indicates the type of the change (currently only
518 ---------------------------
519 { "change": "unspecified" }
520 ---------------------------
524 For some languages, libraries are available (so you don’t have to implement
525 all this on your own). This list names some (if you wrote one, please let me
529 i3 includes a headerfile +i3/ipc.h+ which provides you all constants.
530 However, there is no library yet.
532 http://github.com/badboy/i3-ipc
534 http://search.cpan.org/search?query=AnyEvent::I3
536 http://github.com/thepub/i3ipc
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