IPC interface (interprocess communication) ========================================== Michael Stapelberg July 2012 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. == 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); ------------------------------------------------------------- == 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 <> 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. So, a typical message could look like this: -------------------------------------------------- "i3-ipc" -------------------------------------------------- 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 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). === 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. === 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 } ------------------- === 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" } ] ------------------- === 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 } ------------------- === 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 }, } ] ------------------- === 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 all other containers, the content is not defined (yet). border (string):: Can be either "normal", "none" or "1pixel", dependending on the container’s border style. layout (string):: Can be either "default", "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". 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). 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 } } ] } ] } ] } ------------------------ === MARKS reply The reply consists of a single array of strings for each container that has a mark. The order of that array is undefined. If more than one container has the same mark, it will be represented multiple times in the reply (the array contents are not unique). If no window has a mark the response will be the empty array []. === 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. 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. focused_workspace_text/focused_workspace_bg:: Text color/background color for a workspace button when the workspace has focus. active_workspace_text/active_workspace_bg:: Text color/background 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:: Text color/background 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_bar:: Text color/background color for workspaces which contain at least one window with the urgency hint set. *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, "verbose": false, "colors": { "background": "#c0c0c0", "statusline": "#00ff00", "focused_workspace_text": "#ffffff", "focused_workspace_bg": "#000000" } } -------------- == Events [[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. === 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" ] --------------------------------- === 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"; } -------------------------------------------------------------------- === 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" } --------------------- === 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" } --------------------------- == 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:: http://github.com/badboy/i3-ipc Perl:: http://search.cpan.org/search?query=AnyEvent::I3 Python:: https://github.com/whitelynx/i3ipc https://github.com/ziberna/i3-py (includes higher-level features)