331 lines
9.9 KiB
Plaintext
331 lines
9.9 KiB
Plaintext
IPC interface (interprocess communication)
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==========================================
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Michael Stapelberg <michael+i3@stapelberg.de>
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March 2010
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This document describes how to interface with i3 from a separate process. This
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is useful for example to remote-control i3 (to write test cases for example) or
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to get various information like the current workspaces to implement an external
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workspace bar.
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The method of choice for IPC in our case is a unix socket because it has very
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little overhead on both sides and is usually available without headaches in
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most languages. In the default configuration file, no ipc-socket path is
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specified and thus no socket is created. Alternatively you can set the
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environment-variable +I3SOCK+. Setting a path in the configfile will override
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+I3SOCK+.
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+i3-msg+ and +i3-input+ will use +I3SOCK+ to connect to i3, unless -s is passed.
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If neither is given, they will default to +/tmp/i3-ipc.sock+.
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== Establishing a connection
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To establish a connection, simply open the IPC socket. The following code
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snippet illustrates this in Perl:
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-------------------------------------------------------------
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use IO::Socket::UNIX;
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my $sock = IO::Socket::UNIX->new(Peer => '/tmp/i3-ipc.sock');
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-------------------------------------------------------------
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== Sending messages to i3
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To send a message to i3, you have to format in the binary message format which
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i3 expects. This format specifies a magic string in the beginning to ensure
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the integrity of messages (to prevent follow-up errors). Following the magic
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string comes the length of the payload of the message as 32-bit integer, and
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the type of the message as 32-bit integer (the integers are not converted, so
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they are in native byte order).
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The magic string currently is "i3-ipc" and will only be changed when a change
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in the IPC API is done which breaks compatibility (we hope that we don’t need
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to do that).
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Currently implemented message types are the following:
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COMMAND (0)::
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The payload of the message is a command for i3 (like the commands you
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can bind to keys in the configuration file) and will be executed
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directly after receiving it. There is no reply to this message.
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GET_WORKSPACES (1)::
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Gets the current workspaces. The reply will be a JSON-encoded list of
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workspaces (see the reply section).
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SUBSCRIBE (2)::
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Subscribes your connection to certain events. See <<events>> for a
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description of this message and the concept of events.
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GET_OUTPUTS (3)::
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Gets the current outputs. The reply will be a JSON-encoded list of outputs
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(see the reply section).
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So, a typical message could look like this:
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--------------------------------------------------
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"i3-ipc" <message length> <message type> <payload>
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--------------------------------------------------
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Or, as a hexdump:
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------------------------------------------------------------------------------
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00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
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00000010 69 74 0a |it.|
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------------------------------------------------------------------------------
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To generate and send such a message, you could use the following code in Perl:
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------------------------------------------------------------
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sub format_ipc_command {
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my ($msg) = @_;
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my $len;
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# Get the real byte count (vs. amount of characters)
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{ use bytes; $len = length($msg); }
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return "i3-ipc" . pack("LL", $len, 0) . $msg;
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}
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$sock->write(format_ipc_command("exit"));
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------------------------------------------------------------------------------
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== Receiving replies from i3
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Replies from i3 usually consist of a simple string (the length of the string
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is the message_length, so you can consider them length-prefixed) which in turn
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contain the JSON serialization of a data structure. For example, the
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GET_WORKSPACES message returns an array of workspaces (each workspace is a map
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with certain attributes).
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=== Reply format
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The reply format is identical to the normal message format. There also is
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the magic string, then the message length, then the message type and the
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payload.
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The following reply types are implemented:
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COMMAND (0)::
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Confirmation/Error code for the COMMAND message.
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GET_WORKSPACES (1)::
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Reply to the GET_WORKSPACES message.
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SUBSCRIBE (2)::
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Confirmation/Error code for the SUBSCRIBE message.
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GET_OUTPUTS (3)::
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Reply to the GET_OUTPUTS message.
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=== COMMAND reply
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The reply consists of a single serialized map. At the moment, the only
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property is +success (bool)+, but this will be expanded in future versions.
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*Example:*
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-------------------
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{ "success": true }
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-------------------
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=== GET_WORKSPACES reply
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The reply consists of a serialized list of workspaces. Each workspace has the
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following properties:
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num (integer)::
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The logical number of the workspace. Corresponds to the command
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to switch to this workspace.
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name (string)::
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The name of this workspace (by default num+1), as changed by the
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user. Encoded in UTF-8.
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visible (boolean)::
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Whether this workspace is currently visible on an output (multiple
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workspaces can be visible at the same time).
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focused (boolean)::
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Whether this workspace currently has the focus (only one workspace
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can have the focus at the same time).
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urgent (boolean)::
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Whether a window on this workspace has the "urgent" flag set.
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rect (map)::
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The rectangle of this workspace (equals the rect of the output it
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is on), consists of x, y, width, height.
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output (string)::
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The video output this workspace is on (LVDS1, VGA1, …).
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*Example:*
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-------------------
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[
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{
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"num": 0,
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"name": "1",
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"visible": true,
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"focused": true,
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"urgent": false,
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"rect": {
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"x": 0,
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"y": 0,
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"width": 1280,
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"height": 800
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},
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"output": "LVDS1"
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},
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{
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"num": 1,
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"name": "2",
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"visible": false,
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"focused": false,
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"urgent": false,
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"rect": {
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"x": 0,
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"y": 0,
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"width": 1280,
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"height": 800
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},
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"output": "LVDS1"
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}
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]
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-------------------
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=== SUBSCRIBE reply
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The reply consists of a single serialized map. The only property is
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+success (bool)+, indicating whether the subscription was successful (the
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default) or whether a JSON parse error occurred.
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*Example:*
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-------------------
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{ "success": true }
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-------------------
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=== GET_OUTPUTS reply
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The reply consists of a serialized list of outputs. Each output has the
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following properties:
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name (string)::
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The name of this output (as seen in +xrandr(1)+). Encoded in UTF-8.
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active (boolean)::
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Whether this output is currently active (has a valid mode).
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current_workspace (integer)::
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The current workspace which is visible on this output. +null+ if the
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output is not active.
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rect (map)::
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The rectangle of this output (equals the rect of the output it
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is on), consists of x, y, width, height.
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*Example:*
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-------------------
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[
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{
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"name": "LVDS1",
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"active": true,
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"current_workspace": 4,
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"rect": {
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"x": 0,
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"y": 0,
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"width": 1280,
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"height": 800
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}
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},
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{
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"name": "VGA1",
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"active": true,
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"current_workspace": 1,
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"rect": {
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"x": 1280,
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"y": 0,
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"width": 1280,
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"height": 1024
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},
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}
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]
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-------------------
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== Events
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[[events]]
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To get informed when certain things happen in i3, clients can subscribe to
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events. Events consist of a name (like "workspace") and an event reply type
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(like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
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as replies to specific commands. However, the highest bit of the message type
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is set to 1 to indicate that this is an event reply instead of a normal reply.
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Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
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that the requests to i3 are processed in order. This means, the following
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situation can happen: You send a GET_WORKSPACES request but you receive a
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"workspace" event before receiving the reply to GET_WORKSPACES. If your
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program does not want to cope which such kinds of race conditions (an
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event based library may not have a problem here), I suggest you create a
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separate connection to receive events.
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=== Subscribing to events
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By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
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you can register to an event.
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*Example:*
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---------------------------------
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type: SUBSCRIBE
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payload: [ "workspace", "focus" ]
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---------------------------------
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=== Available events
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The numbers in parenthesis is the event type (keep in mind that you need to
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strip the highest bit first).
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workspace (0)::
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Sent when the user switches to a different workspace, when a new
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workspace is initialized or when a workspace is removed (because the
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last client vanished).
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output (1)::
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Sent when RandR issues a change notification (of either screens,
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outputs, CRTCs or output properties).
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*Example:*
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--------------------------------------------------------------------
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# the appropriate 4 bytes read from the socket are stored in $input
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# unpack a 32-bit unsigned integer
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my $message_type = unpack("L", $input);
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# check if the highest bit is 1
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my $is_event = (($message_type >> 31) == 1);
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# use the other bits
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my $event_type = ($message_type & 0x7F);
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if ($is_event) {
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say "Received event of type $event_type";
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}
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--------------------------------------------------------------------
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=== workspace event
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This event consists of a single serialized map containing a property
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+change (string)+ which indicates the type of the change ("focus", "init",
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"empty", "urgent").
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*Example:*
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---------------------
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{ "change": "focus" }
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---------------------
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=== output event
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This event consists of a single serialized map containing a property
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+change (string)+ which indicates the type of the change (currently only
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"unspecified").
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*Example:*
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---------------------------
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{ "change": "unspecified" }
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---------------------------
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== See also
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For some languages, libraries are available (so you don’t have to implement
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all this on your own). This list names some (if you wrote one, please let me
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know):
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C::
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i3 includes a headerfile +i3/ipc.h+ which provides you all constants.
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However, there is no library yet.
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Ruby::
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http://github.com/badboy/i3-ipc
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Perl::
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http://search.cpan.org/search?query=AnyEvent::I3
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Python::
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http://github.com/thepub/i3ipc
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