gri3-wm/docs/ipc

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2010-03-12 03:06:40 +01:00
IPC interface (interprocess communication)
==========================================
Michael Stapelberg <michael+i3@stapelberg.de>
March 2010
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 +/tmp/i3-ipc.sock+.
== 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 $sock = IO::Socket::UNIX->new(Peer => '/tmp/i3-ipc.sock');
-------------------------------------------------------------
== Sending messages to i3
To send a message to i3, you have to format in the binary message format which
i3 expects. This format specifies a magic string in the beginning to ensure
the integrity of messages (to prevent follow-up errors). Afterwards follows
the length of the payload of the message as 32-bit integer and the type of
the message as 32-bit integer (the integers are not converted, so they are
in native byte order).
The magic string currently is "i3-ipc" and will only be changed when a change
in the IPC API is done which breaks compatibility (we hope that we dont need
to do that).
Currently implemented message types are the following:
0 (COMMAND)::
The payload of the message is a command for i3 (like the commands you
can bind to keys in the configuration file) and will be executed
directly after receiving it. There is no reply to this message.
1 (GET_WORKSPACES)::
Gets the current workspaces. The reply will be a JSON-encoded list of
workspaces (see the reply section).
So, a typical message could look like this:
--------------------------------------------------
"i3-ipc" <message length> <message type> <payload>
--------------------------------------------------
Or, as a hexdump:
------------------------------------------------------------------------------
00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
00000010 69 74 0a |it.|
------------------------------------------------------------------------------
To generate and send such a message, you could use the following code in Perl:
------------------------------------------------------------
sub format_ipc_command {
my ($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"));
------------------------------------------------------------
== Receiving replies from i3
Replies of 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).
=== 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:
1 (GET_WORKSPACES)::
Reply to the GET_WORKSPACES message.
=== GET_WORKSPACES reply
The reply consists of a serialized list of workspaces. Each workspace has the
following properties:
num (integer)::
The internal 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).
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,
"rect": {
"x": 0,
"y": 0,
"width": 1280,
"height": 800
},
"output": "LVDS1"
},
{
"num": 1,
"name": "2",
"visible": false,
"focused": false,
"rect": {
"x": 0,
"y": 0,
"width": 1280,
"height": 800
},
"output": "LVDS1"
}
]
-------------------