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 So, a typical message could look like this:
64 --------------------------------------------------
65 "i3-ipc" <message length> <message type> <payload>
66 --------------------------------------------------
69 ------------------------------------------------------------------------------
70 00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
71 00000010 69 74 0a |it.|
72 ------------------------------------------------------------------------------
74 To generate and send such a message, you could use the following code in Perl:
75 ------------------------------------------------------------
76 sub format_ipc_command {
79 # Get the real byte count (vs. amount of characters)
80 { use bytes; $len = length($msg); }
81 return "i3-ipc" . pack("LL", $len, 0) . $msg;
84 $sock->write(format_ipc_command("exit"));
85 ------------------------------------------------------------------------------
87 == Receiving replies from i3
89 Replies from i3 usually consist of a simple string (the length of the string
90 is the message_length, so you can consider them length-prefixed) which in turn
91 contain the JSON serialization of a data structure. For example, the
92 GET_WORKSPACES message returns an array of workspaces (each workspace is a map
93 with certain attributes).
97 The reply format is identical to the normal message format. There also is
98 the magic string, then the message length, then the message type and the
101 The following reply types are implemented:
104 Confirmation/Error code for the COMMAND message.
106 Reply to the GET_WORKSPACES message.
108 Confirmation/Error code for the SUBSCRIBE message.
110 Reply to the GET_OUTPUTS message.
112 Reply to the GET_TREE message.
116 The reply consists of a single serialized map. At the moment, the only
117 property is +success (bool)+, but this will be expanded in future versions.
124 === GET_WORKSPACES reply
126 The reply consists of a serialized list of workspaces. Each workspace has the
127 following properties:
130 The logical number of the workspace. Corresponds to the command
131 to switch to this workspace.
133 The name of this workspace (by default num+1), as changed by the
134 user. Encoded in UTF-8.
136 Whether this workspace is currently visible on an output (multiple
137 workspaces can be visible at the same time).
139 Whether this workspace currently has the focus (only one workspace
140 can have the focus at the same time).
142 Whether a window on this workspace has the "urgent" flag set.
144 The rectangle of this workspace (equals the rect of the output it
145 is on), consists of x, y, width, height.
147 The video output this workspace is on (LVDS1, VGA1, …).
185 The reply consists of a single serialized map. The only property is
186 +success (bool)+, indicating whether the subscription was successful (the
187 default) or whether a JSON parse error occurred.
194 === GET_OUTPUTS reply
196 The reply consists of a serialized list of outputs. Each output has the
197 following properties:
200 The name of this output (as seen in +xrandr(1)+). Encoded in UTF-8.
202 Whether this output is currently active (has a valid mode).
203 current_workspace (integer)::
204 The current workspace which is visible on this output. +null+ if the
205 output is not active.
207 The rectangle of this output (equals the rect of the output it
208 is on), consists of x, y, width, height.
216 "current_workspace": 4,
227 "current_workspace": 1,
240 The reply consists of a serialized tree. Each node in the tree (representing
241 one container) has at least the properties listed below. While the nodes might
242 have more properties, please do not use any properties which are not documented
243 here. They are not yet finalized and will probably change!
246 The internal ID (actually a C pointer value) of this container. Do not
247 make any assumptions about it. You can use it to (re-)identify and
248 address containers when talking to i3.
250 The internal name of this container. For all containers which are part
251 of the tree structure down to the workspace contents, this is set to a
252 nice human-readable name of the container.
253 For all other containers, the content is not defined (yet).
255 Can be either "normal", "none" or "1pixel", dependending on the
256 container’s border style.
258 Can be either "default", "stacked", "tabbed", "dockarea" or "output".
259 Other values might be possible in the future, should we add new
261 orientation (string)::
262 Can be either "none" (for non-split containers), "horizontal" or
265 The percentage which this container takes in its parent. A value of
266 +null+ means that the percent property does not make sense for this
267 container, for example for the root container.
269 The absolute display coordinates for this container. Display
270 coordinates means that when you have two 1600x1200 monitors on a single
271 X11 Display (the standard way), the coordinates of the first window on
272 the second monitor are +{ "x": 1600, "y": 0, "width": 1600, "height":
275 The coordinates of the *actual client window* inside its container.
276 These coordinates are relative to the container and do not include the
277 window decoration (which is actually rendered on the parent container).
278 So, when using the +default+ layout, you will have a 2 pixel border on
279 each side, making the window_rect +{ "x": 2, "y": 0, "width": 632,
280 "height": 366 }+ (for example).
282 The original geometry the window specified when i3 mapped it. Used when
283 switching a window to floating mode, for example.
285 Whether this container (window or workspace) has the urgency hint set.
287 Whether this container is currently focused.
289 Please note that in the following example, I have left out some keys/values
290 which are not relevant for the type of the node. Otherwise, the example would
291 be by far too long (it already is quite long, despite showing only 1 window and
294 It is useful to have an overview of the structure before taking a look at the
308 -----------------------
335 "layout": "dockarea",
336 "orientation": "vertical",
359 "orientation": "horizontal",
366 "floating_nodes": [],
390 "name": "bottomdock",
391 "layout": "dockarea",
392 "orientation": "vertical",
419 ------------------------
426 To get informed when certain things happen in i3, clients can subscribe to
427 events. Events consist of a name (like "workspace") and an event reply type
428 (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
429 as replies to specific commands. However, the highest bit of the message type
430 is set to 1 to indicate that this is an event reply instead of a normal reply.
432 Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
433 that the requests to i3 are processed in order. This means, the following
434 situation can happen: You send a GET_WORKSPACES request but you receive a
435 "workspace" event before receiving the reply to GET_WORKSPACES. If your
436 program does not want to cope which such kinds of race conditions (an
437 event based library may not have a problem here), I suggest you create a
438 separate connection to receive events.
440 === Subscribing to events
442 By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
443 you can register to an event.
446 ---------------------------------
448 payload: [ "workspace", "focus" ]
449 ---------------------------------
454 The numbers in parenthesis is the event type (keep in mind that you need to
455 strip the highest bit first).
458 Sent when the user switches to a different workspace, when a new
459 workspace is initialized or when a workspace is removed (because the
460 last client vanished).
462 Sent when RandR issues a change notification (of either screens,
463 outputs, CRTCs or output properties).
466 --------------------------------------------------------------------
467 # the appropriate 4 bytes read from the socket are stored in $input
469 # unpack a 32-bit unsigned integer
470 my $message_type = unpack("L", $input);
472 # check if the highest bit is 1
473 my $is_event = (($message_type >> 31) == 1);
476 my $event_type = ($message_type & 0x7F);
479 say "Received event of type $event_type";
481 --------------------------------------------------------------------
485 This event consists of a single serialized map containing a property
486 +change (string)+ which indicates the type of the change ("focus", "init",
490 ---------------------
491 { "change": "focus" }
492 ---------------------
496 This event consists of a single serialized map containing a property
497 +change (string)+ which indicates the type of the change (currently only
501 ---------------------------
502 { "change": "unspecified" }
503 ---------------------------
507 For some languages, libraries are available (so you don’t have to implement
508 all this on your own). This list names some (if you wrote one, please let me
512 i3 includes a headerfile +i3/ipc.h+ which provides you all constants.
513 However, there is no library yet.
515 http://github.com/badboy/i3-ipc
517 http://search.cpan.org/search?query=AnyEvent::I3
519 http://github.com/thepub/i3ipc