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 Gets the configuration (as JSON map) of the workspace bar with the
69 given ID. If no ID is provided, an array with all configured bar IDs is
72 So, a typical message could look like this:
73 --------------------------------------------------
74 "i3-ipc" <message length> <message type> <payload>
75 --------------------------------------------------
78 ------------------------------------------------------------------------------
79 00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
80 00000010 69 74 0a |it.|
81 ------------------------------------------------------------------------------
83 To generate and send such a message, you could use the following code in Perl:
84 ------------------------------------------------------------
85 sub format_ipc_command {
88 # Get the real byte count (vs. amount of characters)
89 { use bytes; $len = length($msg); }
90 return "i3-ipc" . pack("LL", $len, 0) . $msg;
93 $sock->write(format_ipc_command("exit"));
94 ------------------------------------------------------------------------------
96 == Receiving replies from i3
98 Replies from i3 usually consist of a simple string (the length of the string
99 is the message_length, so you can consider them length-prefixed) which in turn
100 contain the JSON serialization of a data structure. For example, the
101 GET_WORKSPACES message returns an array of workspaces (each workspace is a map
102 with certain attributes).
106 The reply format is identical to the normal message format. There also is
107 the magic string, then the message length, then the message type and the
110 The following reply types are implemented:
113 Confirmation/Error code for the COMMAND message.
115 Reply to the GET_WORKSPACES message.
117 Confirmation/Error code for the SUBSCRIBE message.
119 Reply to the GET_OUTPUTS message.
121 Reply to the GET_TREE message.
123 Reply to the GET_MARKS message.
125 Reply to the GET_BAR_CONFIG message.
129 The reply consists of a single serialized map. At the moment, the only
130 property is +success (bool)+, but this will be expanded in future versions.
137 === GET_WORKSPACES reply
139 The reply consists of a serialized list of workspaces. Each workspace has the
140 following properties:
143 The logical number of the workspace. Corresponds to the command
144 to switch to this workspace.
146 The name of this workspace (by default num+1), as changed by the
147 user. Encoded in UTF-8.
149 Whether this workspace is currently visible on an output (multiple
150 workspaces can be visible at the same time).
152 Whether this workspace currently has the focus (only one workspace
153 can have the focus at the same time).
155 Whether a window on this workspace has the "urgent" flag set.
157 The rectangle of this workspace (equals the rect of the output it
158 is on), consists of x, y, width, height.
160 The video output this workspace is on (LVDS1, VGA1, …).
198 The reply consists of a single serialized map. The only property is
199 +success (bool)+, indicating whether the subscription was successful (the
200 default) or whether a JSON parse error occurred.
207 === GET_OUTPUTS reply
209 The reply consists of a serialized list of outputs. Each output has the
210 following properties:
213 The name of this output (as seen in +xrandr(1)+). Encoded in UTF-8.
215 Whether this output is currently active (has a valid mode).
216 current_workspace (integer)::
217 The current workspace which is visible on this output. +null+ if the
218 output is not active.
220 The rectangle of this output (equals the rect of the output it
221 is on), consists of x, y, width, height.
229 "current_workspace": 4,
240 "current_workspace": 1,
253 The reply consists of a serialized tree. Each node in the tree (representing
254 one container) has at least the properties listed below. While the nodes might
255 have more properties, please do not use any properties which are not documented
256 here. They are not yet finalized and will probably change!
259 The internal ID (actually a C pointer value) of this container. Do not
260 make any assumptions about it. You can use it to (re-)identify and
261 address containers when talking to i3.
263 The internal name of this container. For all containers which are part
264 of the tree structure down to the workspace contents, this is set to a
265 nice human-readable name of the container.
266 For all other containers, the content is not defined (yet).
268 Can be either "normal", "none" or "1pixel", dependending on the
269 container’s border style.
271 Can be either "default", "stacked", "tabbed", "dockarea" or "output".
272 Other values might be possible in the future, should we add new
274 orientation (string)::
275 Can be either "none" (for non-split containers), "horizontal" or
278 The percentage which this container takes in its parent. A value of
279 +null+ means that the percent property does not make sense for this
280 container, for example for the root container.
282 The absolute display coordinates for this container. Display
283 coordinates means that when you have two 1600x1200 monitors on a single
284 X11 Display (the standard way), the coordinates of the first window on
285 the second monitor are +{ "x": 1600, "y": 0, "width": 1600, "height":
288 The coordinates of the *actual client window* inside its container.
289 These coordinates are relative to the container and do not include the
290 window decoration (which is actually rendered on the parent container).
291 So, when using the +default+ layout, you will have a 2 pixel border on
292 each side, making the window_rect +{ "x": 2, "y": 0, "width": 632,
293 "height": 366 }+ (for example).
295 The original geometry the window specified when i3 mapped it. Used when
296 switching a window to floating mode, for example.
298 Whether this container (window or workspace) has the urgency hint set.
300 Whether this container is currently focused.
302 Please note that in the following example, I have left out some keys/values
303 which are not relevant for the type of the node. Otherwise, the example would
304 be by far too long (it already is quite long, despite showing only 1 window and
307 It is useful to have an overview of the structure before taking a look at the
321 -----------------------
348 "layout": "dockarea",
349 "orientation": "vertical",
372 "orientation": "horizontal",
379 "floating_nodes": [],
403 "name": "bottomdock",
404 "layout": "dockarea",
405 "orientation": "vertical",
432 ------------------------
436 The reply consists of a single array of strings for each container that has a
437 mark. The order of that array is undefined. If more than one container has the
438 same mark, it will be represented multiple times in the reply (the array
439 contents are not unique).
441 If no window has a mark the response will be the empty array [].
443 === GET_BAR_CONFIG reply
445 This can be used by third-party workspace bars (especially i3bar, but others
446 are free to implement compatible alternatives) to get the +bar+ block
447 configuration from i3.
449 Depending on the input, the reply is either:
452 An array of configured bar IDs
454 A JSON map containing the configuration for the specified bar.
456 Each bar configuration has the following properties:
459 The ID for this bar. Included in case you request multiple
460 configurations and want to differentiate the different replies.
462 Either +dock+ (the bar sets the dock window type) or +hide+ (the bar
463 does not show unless a specific key is pressed).
465 Either +bottom+ or +top+ at the moment.
466 status_command (string)::
467 Command which will be run to generate a statusline. Each line on stdout
468 of this command will be displayed in the bar. At the moment, no
469 formatting is supported.
471 The font to use for text on the bar.
472 workspace_buttons (boolean)::
473 Display workspace buttons or not? Defaults to true.
475 Should the bar enable verbose output for debugging? Defaults to false.
477 Contains key/value pairs of colors. Each value is a color code in hex,
478 formatted #rrggbb (like in HTML).
480 The following colors can be configured at the moment:
483 Background color of the bar.
485 Text color to be used for the statusline.
486 focused_workspace_text/focused_workspace_bg::
487 Text color/background color for a workspace button when the workspace
489 active_workspace_text/active_workspace_bg::
490 Text color/background color for a workspace button when the workspace
491 is active (visible) on some output, but the focus is on another one.
492 You can only tell this apart from the focused workspace when you are
493 using multiple monitors.
494 inactive_workspace_text/inactive_workspace_bg::
495 Text color/background color for a workspace button when the workspace
496 does not have focus and is not active (visible) on any output. This
497 will be the case for most workspaces.
498 urgent_workspace_text/urgent_workspace_bar::
499 Text color/background color for workspaces which contain at least one
500 window with the urgency hint set.
503 *Example of configured bars:*
508 *Example of bar configuration:*
513 "position": "bottom",
514 "status_command": "i3status",
515 "font": "-misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1",
516 "workspace_buttons": true,
519 "background": "#c0c0c0",
520 "statusline": "#00ff00",
521 "focused_workspace_text": "#ffffff",
522 "focused_workspace_bg": "#000000"
531 To get informed when certain things happen in i3, clients can subscribe to
532 events. Events consist of a name (like "workspace") and an event reply type
533 (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
534 as replies to specific commands. However, the highest bit of the message type
535 is set to 1 to indicate that this is an event reply instead of a normal reply.
537 Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
538 that the requests to i3 are processed in order. This means, the following
539 situation can happen: You send a GET_WORKSPACES request but you receive a
540 "workspace" event before receiving the reply to GET_WORKSPACES. If your
541 program does not want to cope which such kinds of race conditions (an
542 event based library may not have a problem here), I suggest you create a
543 separate connection to receive events.
545 === Subscribing to events
547 By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
548 you can register to an event.
551 ---------------------------------
553 payload: [ "workspace", "focus" ]
554 ---------------------------------
559 The numbers in parenthesis is the event type (keep in mind that you need to
560 strip the highest bit first).
563 Sent when the user switches to a different workspace, when a new
564 workspace is initialized or when a workspace is removed (because the
565 last client vanished).
567 Sent when RandR issues a change notification (of either screens,
568 outputs, CRTCs or output properties).
571 --------------------------------------------------------------------
572 # the appropriate 4 bytes read from the socket are stored in $input
574 # unpack a 32-bit unsigned integer
575 my $message_type = unpack("L", $input);
577 # check if the highest bit is 1
578 my $is_event = (($message_type >> 31) == 1);
581 my $event_type = ($message_type & 0x7F);
584 say "Received event of type $event_type";
586 --------------------------------------------------------------------
590 This event consists of a single serialized map containing a property
591 +change (string)+ which indicates the type of the change ("focus", "init",
595 ---------------------
596 { "change": "focus" }
597 ---------------------
601 This event consists of a single serialized map containing a property
602 +change (string)+ which indicates the type of the change (currently only
606 ---------------------------
607 { "change": "unspecified" }
608 ---------------------------
612 For some languages, libraries are available (so you don’t have to implement
613 all this on your own). This list names some (if you wrote one, please let me
617 i3 includes a headerfile +i3/ipc.h+ which provides you all constants.
618 However, there is no library yet.
620 http://github.com/badboy/i3-ipc
622 http://search.cpan.org/search?query=AnyEvent::I3
624 http://github.com/thepub/i3ipc