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, no ipc-socket path is specified and thus no socket is created. The standard path (which i3-msg and i3-input use) is ~/.i3/ipc.sock.
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; my $sock = IO::Socket::UNIX->new(Peer => '~/.i3/ipc.sock');
2. Sending messages to i3
To send a message to i3, you have to format in the binary message format which i3 expects. This format specifies a magic string in the beginning to ensure the integrity of messages (to prevent follow-up errors). Following the magic string comes the length of the payload of the message as 32-bit integer, and the type of the message as 32-bit integer (the integers are not converted, so they are in native byte order).
The magic string currently is "i3-ipc" and will only be changed when a change in the IPC API is done which breaks compatibility (we hope that we don’t need to do that).
Currently implemented message types are the following:
- COMMAND (0)
-
The payload of the message is a command for i3 (like the commands you can bind to keys in the configuration file) and will be executed directly after receiving it. There is no reply to this message.
- GET_WORKSPACES (1)
-
Gets the current workspaces. The reply will be a JSON-encoded list of workspaces (see the reply section).
- SUBSCRIBE (2)
-
Subscribes your connection to certain events. See [events] for a description of this message and the concept of events.
- GET_OUTPUTS (3)
-
Gets the current outputs. The reply will be a JSON-encoded list of outputs (see the reply section).
So, a typical message could look like this:
"i3-ipc" <message length> <message type> <payload>
Or, as a hexdump:
00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex| 00000010 69 74 0a |it.|
To generate and send such a message, you could use the following code in Perl:
sub format_ipc_command {
my ($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.
- GET_WORKSPACES (1)
-
Reply to the GET_WORKSPACES message.
- SUBSCRIBE (2)
-
Confirmation/Error code for the SUBSCRIBE message.
- GET_OUTPUTS (3)
-
Reply to the GET_OUTPUTS message.
3.2. COMMAND reply
The reply consists of a single serialized map. At the moment, the only property is success (bool), but this will be expanded in future versions.
Example:
{ "success": true }
3.3. GET_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.
- 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. GET_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 (integer)
-
The current workspace which 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
},
}
]
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", "focus" ]
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).
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").
Example:
{ "change": "focus" }
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" }
5. See also
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. However, there is no library yet.
- Ruby
- Perl
- Python