# IPC interface (interprocess communication)

Michael Stapelberg
`<michael@i3wm.org>`
October 2014

This document describes how to interface with i3 from a separate process. This is useful for example to remote-control i3 (to write test cases for example) or to get various information like the current workspaces to implement an external workspace bar.

The method of choice for IPC in our case is a unix socket because it has very little overhead on both sides and is usually available without headaches in most languages. In the default configuration file, the ipc-socket gets created in `/tmp/i3-%u.XXXXXX/ipc-socket.%p` where `%u` is your UNIX username, `%p` is the PID of i3 and XXXXXX is a string of random characters from the portable filename character set (see mkdtemp(3)). You can get the socketpath from i3 by calling `i3 --get-socketpath`.

All i3 utilities, like `i3-msg` and `i3-input` will read the `I3_SOCKET_PATH` X11 property, stored on the X11 root window.

Warning | Use an existing library! There are existing libraries for many languages. You can have a look at [libraries] or search the web if your language of choice is not mentioned. Usually, it is not necessary to implement low-level communication with i3 directly.

## 1. Establishing a connection

To establish a connection, simply open the IPC socket. The following code snippet illustrates this in Perl:

    use IO::Socket::UNIX;
    chomp(my $path = qx(i3 --get-socketpath));
    my $sock = IO::Socket::UNIX->new(Peer => $path);

## 2. Sending messages to i3

To send a message to i3, you have to format in the binary message format which i3 expects. This format specifies a magic string in the beginning to ensure the integrity of messages (to prevent follow-up errors). Following the magic string comes the length of the payload of the message as 32-bit integer, and the type of the message as 32-bit integer (the integers are not converted, so they are in native byte order).

The magic string currently is "i3-ipc" and will only be changed when a change in the IPC API is done which breaks compatibility (we hope that we don’t need to do that).

Currently implemented message types are the following:

COMMAND (0)

  The payload of the message is a command for i3 (like the commands you can bind to keys in the configuration file) and will be executed directly after receiving it.

GET_WORKSPACES (1)

  Gets the current workspaces. The reply will be a JSON-encoded list of workspaces (see the reply section).

SUBSCRIBE (2)

  Subscribes your connection to certain events. See [events] for a description of this message and the concept of events.

GET_OUTPUTS (3)

  Gets the current outputs. The reply will be a JSON-encoded list of outputs (see the reply section).

GET_TREE (4)

  Gets the layout tree. i3 uses a tree as data structure which includes every container. The reply will be the JSON-encoded tree (see the reply section).

GET_MARKS (5)

  Gets a list of marks (identifiers for containers to easily jump to them later). The reply will be a JSON-encoded list of window marks (see reply section).

GET_BAR_CONFIG (6)

  Gets the configuration (as JSON map) of the workspace bar with the given ID. If no ID is provided, an array with all configured bar IDs is returned instead.

GET_VERSION (7)

  Gets the version of i3. The reply will be a JSON-encoded dictionary with the major, minor, patch and human-readable version.

So, a typical message could look like this:

    "i3-ipc" <message length> <message type> <payload>

Or, as a hexdump:

    00000000  69 33 2d 69 70 63 04 00  00 00 00 00 00 00 65 78  |i3-ipc........ex|
    00000010  69 74                                             |it|

To generate and send such a message, you could use the following code in Perl:

    sub format_ipc_command {
        my ($msg) = @_;
        my $len;
        # Get the real byte count (vs. amount of characters)
        { use bytes; $len = length($msg); }
        return "i3-ipc" . pack("LL", $len, 0) . $msg;
    }

    $sock->write(format_ipc_command("exit"));

## 3. Receiving replies from i3

Replies from i3 usually consist of a simple string (the length of the string is the message_length, so you can consider them length-prefixed) which in turn contain the JSON serialization of a data structure. For example, the GET_WORKSPACES message returns an array of workspaces (each workspace is a map with certain attributes).

### 3.1. Reply format

The reply format is identical to the normal message format. There also is the magic string, then the message length, then the message type and the payload.

The following reply types are implemented:

COMMAND (0)

  Confirmation/Error code for the COMMAND message.

WORKSPACES (1)

  Reply to the GET_WORKSPACES message.

SUBSCRIBE (2)

  Confirmation/Error code for the SUBSCRIBE message.

OUTPUTS (3)

  Reply to the GET_OUTPUTS message.

TREE (4)

  Reply to the GET_TREE message.

MARKS (5)

  Reply to the GET_MARKS message.

BAR_CONFIG (6)

  Reply to the GET_BAR_CONFIG message.

VERSION (7)

  Reply to the GET_VERSION message.

### 3.2. COMMAND reply

The reply consists of a list of serialized maps for each command that was parsed. Each has the property `success (bool)` and may also include a human-readable error message in the property `error (string)`.

Example:

    [{ "success": true }]

### 3.3. WORKSPACES reply

The reply consists of a serialized list of workspaces. Each workspace has the following properties:

num (integer)

  The logical number of the workspace. Corresponds to the command to switch to this workspace. For named workspaces, this will be -1.

name (string)

  The name of this workspace (by default num+1), as changed by the user. Encoded in UTF-8.

visible (boolean)

  Whether this workspace is currently visible on an output (multiple workspaces can be visible at the same time).

focused (boolean)

  Whether this workspace currently has the focus (only one workspace can have the focus at the same time).

urgent (boolean)

  Whether a window on this workspace has the "urgent" flag set.

rect (map)

  The rectangle of this workspace (equals the rect of the output it is on), consists of x, y, width, height.

output (string)

  The video output this workspace is on (LVDS1, VGA1, …).

Example:

    [
     {
      "num": 0,
      "name": "1",
      "visible": true,
      "focused": true,
      "urgent": false,
      "rect": {
       "x": 0,
       "y": 0,
       "width": 1280,
       "height": 800
      },
      "output": "LVDS1"
     },
     {
      "num": 1,
      "name": "2",
      "visible": false,
      "focused": false,
      "urgent": false,
      "rect": {
       "x": 0,
       "y": 0,
       "width": 1280,
       "height": 800
      },
      "output": "LVDS1"
     }
    ]

### 3.4. SUBSCRIBE reply

The reply consists of a single serialized map. The only property is `success (bool)`, indicating whether the subscription was successful (the default) or whether a JSON parse error occurred.

Example:

    { "success": true }

### 3.5. OUTPUTS reply

The reply consists of a serialized list of outputs. Each output has the following properties:

name (string)

  The name of this output (as seen in `xrandr(1)`). Encoded in UTF-8.

active (boolean)

  Whether this output is currently active (has a valid mode).

current_workspace (string)

  The name of the current workspace that is visible on this output. `null` if the output is not active.

rect (map)

  The rectangle of this output (equals the rect of the output it is on), consists of x, y, width, height.

Example:

    [
     {
      "name": "LVDS1",
      "active": true,
      "current_workspace": "4",
      "rect": {
       "x": 0,
       "y": 0,
       "width": 1280,
       "height": 800
      }
     },
     {
      "name": "VGA1",
      "active": true,
      "current_workspace": "1",
      "rect": {
       "x": 1280,
       "y": 0,
       "width": 1280,
       "height": 1024
      },
     }
    ]

### 3.6. TREE reply

The reply consists of a serialized tree. Each node in the tree (representing one container) has at least the properties listed below. While the nodes might have more properties, please do not use any properties which are not documented here. They are not yet finalized and will probably change!

id (integer)

  The internal ID (actually a C pointer value) of this container. Do not make any assumptions about it. You can use it to (re-)identify and address containers when talking to i3.

name (string)

  The internal name of this container. For all containers which are part of the tree structure down to the workspace contents, this is set to a nice human-readable name of the container. For containers that have an X11 window, the content is the title (_NET_WM_NAME property) of that window. For all other containers, the content is not defined (yet).

type (string)

  Type of this container. Can be one of "root", "output", "con", "floating_con", "workspace" or "dockarea".

border (string)

  Can be either "normal", "none" or "1pixel", dependending on the container’s border style.

current_border_width (integer)

  Number of pixels of the border width.

layout (string)

  Can be either "splith", "splitv", "stacked", "tabbed", "dockarea" or "output". Other values might be possible in the future, should we add new layouts.

orientation (string)

  Can be either "none" (for non-split containers), "horizontal" or "vertical". THIS FIELD IS OBSOLETE. It is still present, but your code should not use it. Instead, rely on the layout field.

percent (float)

  The percentage which this container takes in its parent. A value of `null` means that the percent property does not make sense for this container, for example for the root container.

rect (map)

  The absolute display coordinates for this container. Display coordinates means that when you have two 1600x1200 monitors on a single X11 Display (the standard way), the coordinates of the first window on the second monitor are `{ "x": 1600, "y": 0, "width": 1600, "height": 1200 }`.

window_rect (map)

  The coordinates of the actual client window inside its container. These coordinates are relative to the container and do not include the window decoration (which is actually rendered on the parent container). So, when using the `default` layout, you will have a 2 pixel border on each side, making the window_rect `{ "x": 2, "y": 0, "width": 632, "height": 366 }` (for example).

deco_rect (map)

  The coordinates of the window decoration inside its container. These coordinates are relative to the container and do not include the actual client window.

geometry (map)

  The original geometry the window specified when i3 mapped it. Used when switching a window to floating mode, for example.

window (integer)

  The X11 window ID of the actual client window inside this container. This field is set to null for split containers or otherwise empty containers. This ID corresponds to what xwininfo(1) and other X11-related tools display (usually in hex).

urgent (bool)

  Whether this container (window or workspace) has the urgency hint set.

focused (bool)

  Whether this container is currently focused.

Please note that in the following example, I have left out some keys/values which are not relevant for the type of the node. Otherwise, the example would be by far too long (it already is quite long, despite showing only 1 window and one dock window).

It is useful to have an overview of the structure before taking a look at the JSON dump:

- root

  - LVDS1

    - topdock

    - content

      - workspace 1

        - window 1

    - bottomdock

      - dock window 1

  - VGA1

Example:

    {
     "id": 6875648,
     "name": "root",
     "rect": {
       "x": 0,
       "y": 0,
       "width": 1280,
       "height": 800
     },
     "nodes": [

       {
        "id": 6878320,
        "name": "LVDS1",
        "layout": "output",
        "rect": {
          "x": 0,
          "y": 0,
          "width": 1280,
          "height": 800
        },
        "nodes": [

          {
           "id": 6878784,
           "name": "topdock",
           "layout": "dockarea",
           "orientation": "vertical",
           "rect": {
             "x": 0,
             "y": 0,
             "width": 1280,
             "height": 0
           },
          },

          {
           "id": 6879344,
           "name": "content",
           "rect": {
             "x": 0,
             "y": 0,
             "width": 1280,
             "height": 782
           },
           "nodes": [

             {
              "id": 6880464,
              "name": "1",
              "orientation": "horizontal",
              "rect": {
                "x": 0,
                "y": 0,
                "width": 1280,
                "height": 782
              },
              "floating_nodes": [],
              "nodes": [

                {
                 "id": 6929968,
                 "name": "#aa0000",
                 "border": "normal",
                 "percent": 1,
                 "rect": {
                   "x": 0,
                   "y": 18,
                   "width": 1280,
                   "height": 782
                 }
                }

              ]
             }

           ]
          },

          {
           "id": 6880208,
           "name": "bottomdock",
           "layout": "dockarea",
           "orientation": "vertical",
           "rect": {
             "x": 0,
             "y": 782,
             "width": 1280,
             "height": 18
           },
           "nodes": [

             {
              "id": 6931312,
              "name": "#00aa00",
              "percent": 1,
              "rect": {
                "x": 0,
                "y": 782,
                "width": 1280,
                "height": 18
              }
             }

           ]
          }
        ]
       }
     ]
    }

### 3.7. MARKS reply

The reply consists of a single array of strings for each container that has a mark. A mark can only be set on one container, so the array is unique. The order of that array is undefined.

If no window has a mark the response will be the empty array [].

### 3.8. BAR_CONFIG reply

This can be used by third-party workspace bars (especially i3bar, but others are free to implement compatible alternatives) to get the `bar` block configuration from i3.

Depending on the input, the reply is either:

empty input

  An array of configured bar IDs

Bar ID

  A JSON map containing the configuration for the specified bar.

Each bar configuration has the following properties:

id (string)

  The ID for this bar. Included in case you request multiple configurations and want to differentiate the different replies.

mode (string)

  Either `dock` (the bar sets the dock window type) or `hide` (the bar does not show unless a specific key is pressed).

position (string)

  Either `bottom` or `top` at the moment.

status_command (string)

  Command which will be run to generate a statusline. Each line on stdout of this command will be displayed in the bar. At the moment, no formatting is supported.

font (string)

  The font to use for text on the bar.

workspace_buttons (boolean)

  Display workspace buttons or not? Defaults to true.

binding_mode_indicator (boolean)

  Display the mode indicator or not? Defaults to true.

verbose (boolean)

  Should the bar enable verbose output for debugging? Defaults to false.

colors (map)

  Contains key/value pairs of colors. Each value is a color code in hex, formatted #rrggbb (like in HTML).

The following colors can be configured at the moment:

background

  Background color of the bar.

statusline

  Text color to be used for the statusline.

separator

  Text color to be used for the separator.

focused_background

  Background color of the bar on the currently focused monitor output.

focused_statusline

  Text color to be used for the statusline on the currently focused monitor output.

focused_separator

  Text color to be used for the separator on the currently focused monitor output.

focused_workspace_text/focused_workspace_bg/focused_workspace_border

  Text/background/border color for a workspace button when the workspace has focus.

active_workspace_text/active_workspace_bg/active_workspace_border

  Text/background/border color for a workspace button when the workspace is active (visible) on some output, but the focus is on another one. You can only tell this apart from the focused workspace when you are using multiple monitors.

inactive_workspace_text/inactive_workspace_bg/inactive_workspace_border

  Text/background/border color for a workspace button when the workspace does not have focus and is not active (visible) on any output. This will be the case for most workspaces.

urgent_workspace_text/urgent_workspace_bg/urgent_workspace_border

  Text/background/border color for workspaces which contain at least one window with the urgency hint set.

binding_mode_text/binding_mode_bg/binding_mode_border

  Text/background/border color for the binding mode indicator.

Example of configured bars:

    ["bar-bxuqzf"]

Example of bar configuration:

    {
     "id": "bar-bxuqzf",
     "mode": "dock",
     "position": "bottom",
     "status_command": "i3status",
     "font": "-misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1",
     "workspace_buttons": true,
     "binding_mode_indicator": true,
     "verbose": false,
     "colors": {
       "background": "#c0c0c0",
       "statusline": "#00ff00",
       "focused_workspace_text": "#ffffff",
       "focused_workspace_bg": "#000000"
     }
    }

### 3.9. VERSION reply

The reply consists of a single JSON dictionary with the following keys:

major (integer)

  The major version of i3, such as `4`.

minor (integer)

  The minor version of i3, such as `2`. Changes in the IPC interface (new features) will only occur with new minor (or major) releases. However, bugfixes might be introduced in patch releases, too.

patch (integer)

  The patch version of i3, such as `1` (when the complete version is `4.2.1`). For versions such as `4.2`, patch will be set to `0`.

human_readable (string)

  A human-readable version of i3 containing the precise git version, build date and branch name. When you need to display the i3 version to your users, use the human-readable version whenever possible (since this is what `i3 --version` displays, too).

loaded_config_file_name (string)

  The current config path.

Example:

    {
       "human_readable" : "4.2-169-gf80b877 (2012-08-05, branch \"next\")",
       "loaded_config_file_name" : "/home/hwangcc23/.i3/config",
       "minor" : 2,
       "patch" : 0,
       "major" : 4
    }

## 4. Events

To get informed when certain things happen in i3, clients can subscribe to events. Events consist of a name (like "workspace") and an event reply type (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format as replies to specific commands. However, the highest bit of the message type is set to 1 to indicate that this is an event reply instead of a normal reply.

Caveat: As soon as you subscribe to an event, it is not guaranteed any longer that the requests to i3 are processed in order. This means, the following situation can happen: You send a GET_WORKSPACES request but you receive a "workspace" event before receiving the reply to GET_WORKSPACES. If your program does not want to cope which such kinds of race conditions (an event based library may not have a problem here), I suggest you create a separate connection to receive events.

### 4.1. Subscribing to events

By sending a message of type SUBSCRIBE with a JSON-encoded array as payload you can register to an event.

Example:

    type: SUBSCRIBE
    payload: [ "workspace", "output" ]

### 4.2. Available events

The numbers in parenthesis is the event type (keep in mind that you need to strip the highest bit first).

workspace (0)

  Sent when the user switches to a different workspace, when a new workspace is initialized or when a workspace is removed (because the last client vanished).

output (1)

  Sent when RandR issues a change notification (of either screens, outputs, CRTCs or output properties).

mode (2)

  Sent whenever i3 changes its binding mode.

window (3)

  Sent when a client’s window is successfully reparented (that is when i3 has finished fitting it into a container), when a window received input focus or when certain properties of the window have changed.

barconfig_update (4)

  Sent when the hidden_state or mode field in the barconfig of any bar instance was updated and when the config is reloaded.

binding (5)

  Sent when a configured command binding is triggered with the keyboard or mouse

Example:

    # the appropriate 4 bytes read from the socket are stored in $input

    # unpack a 32-bit unsigned integer
    my $message_type = unpack("L", $input);

    # check if the highest bit is 1
    my $is_event = (($message_type >> 31) == 1);

    # use the other bits
    my $event_type = ($message_type & 0x7F);

    if ($is_event) {
      say "Received event of type $event_type";
    }

### 4.3. workspace event

This event consists of a single serialized map containing a property `change (string)` which indicates the type of the change ("focus", "init", "empty", "urgent"). A `current (object)` property will be present with the affected workspace whenever the type of event affects a workspace (otherwise, it will be +null).

When the change is "focus", an `old (object)` property will be present with the previous workspace. When the first switch occurs (when i3 focuses the workspace visible at the beginning) there is no previous workspace, and the `old` property will be set to `null`. Also note that if the previous is empty it will get destroyed when switching, but will still be present in the "old" property.

Example:

    {
     "change": "focus",
     "current": {
      "id": 28489712,
      "type": "workspace",
      ...
     }
     "old": {
      "id": 28489715,
      "type": "workspace",
      ...
     }
    }

### 4.4. output event

This event consists of a single serialized map containing a property `change (string)` which indicates the type of the change (currently only "unspecified").

Example:

    { "change": "unspecified" }

### 4.5. mode event

This event consists of a single serialized map containing a property `change (string)` which holds the name of current mode in use. The name is the same as specified in config when creating a mode. The default mode is simply named default. It contains a second property, `pango_markup`, which defines whether pango markup shall be used for displaying this mode.

Example:

    {
      "change": "default",
      "pango_markup": true
    }

### 4.6. window event

This event consists of a single serialized map containing a property `change (string)` which indicates the type of the change

- `new` - the window has become managed by i3

- `close` - the window has closed

- `focus` - the window has received input focus

- `title` - the window’s title has changed

- `fullscreen_mode` - the window has entered or exited fullscreen mode

- `move` - the window has changed its position in the tree

- `floating` - the window has transitioned to or from floating

- `urgent` - the window has become urgent or lost its urgent status

Additionally a `container (object)` field will be present, which consists of the window’s parent container. Be aware that for the "new" event, the container will hold the initial name of the newly reparented window (e.g. if you run urxvt with a shell that changes the title, you will still at this point get the window title as "urxvt").

Example:

    {
     "change": "new",
     "container": {
      "id": 35569536,
      "type": "con",
      ...
     }
    }

### 4.7. barconfig_update event

This event consists of a single serialized map reporting on options from the barconfig of the specified bar_id that were updated in i3. This event is the same as a `GET_BAR_CONFIG` reply for the bar with the given id.

### 4.8. binding event

This event consists of a single serialized map reporting on the details of a binding that ran a command because of user input. The `change (sring)` field indicates what sort of binding event was triggered (right now it will always be `"run"` but may be expanded in the future).

The `binding (object)` field contains details about the binding that was run:

command (string)

  The i3 command that is configured to run for this binding.

event_state_mask (array of strings)

  The group and modifier keys that were configured with this binding.

input_code (integer)

  If the binding was configured with `bindcode`, this will be the key code that was given for the binding. If the binding is a mouse binding, it will be the number of the mouse button that was pressed. Otherwise it will be 0.

symbol (string or null)

  If this is a keyboard binding that was configured with `bindsym`, this field will contain the given symbol. Otherwise it will be `null`.

input_type (string)

  This will be `"keyboard"` or `"mouse"` depending on whether or not this was a keyboard or a mouse binding.

Example:

    {
     "change": "run",
     "binding": {
      "command": "nop",
      "event_state_mask": [
        "shift",
        "ctrl"
      ],
      "input_code": 0,
      "symbol": "t",
      "input_type": "keyboard"
     }
    }

## 5. See also (existing libraries)

For some languages, libraries are available (so you don’t have to implement all this on your own). This list names some (if you wrote one, please let me know):

C

  - i3 includes a headerfile `i3/ipc.h` which provides you all constants.

  - https://github.com/acrisci/i3ipc-glib

C++

  - https://github.com/drmgc/i3ipcpp

Go

  - https://github.com/proxypoke/i3ipc

JavaScript

  - https://github.com/acrisci/i3ipc-gjs

Lua

  - https://github.com/acrisci/i3ipc-lua

Perl

  - https://metacpan.org/module/AnyEvent::I3

Python

  - https://github.com/acrisci/i3ipc-python

  - https://github.com/whitelynx/i3ipc (not maintained)

  - https://github.com/ziberna/i3-py (not maintained)

Ruby

  - https://github.com/veelenga/i3ipc-ruby

  - https://github.com/badboy/i3-ipc (not maintained)

Rust

  - https://github.com/tmerr/i3ipc-rs