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Evdev Lua module

A Lua 5.2 and 5.3 module for interacting with input devices on Linux. You can read events with a Device object, or create a virtual input device with a Uinput object.

The evdev.constants module contains most of the relevant constants from linux/input.h (EV_KEY, BTN_0, KEY_A, ABS_X, etc), and is used as an __index for the evdev module itself for convenience.

Example: Reading events from /dev/input/event* nodes:

local evdev = require "evdev"
-- (assuming event0 is the keyboard, which in practice easily varies)
local keyboard = evdev.Device "/dev/input/event0"
while true do
    local timestamp, eventType, eventCode, value = keyboard:read()
    if eventType == evdev.EV_KEY then
		if eventCode == evdev.KEY_ESC then
			break
		end
		if value == 0 then
			print("Key Released:", eventCode)
		else
			print("Key Pressed:", eventCode)
		end
    end
end

Example: Creating a fake mouse:

local e = require "evdev"
local fakeMouse = e.Uinput "/dev/uinput"
-- register supported events
fakeMouse:useEvent(e.EV_KEY)
fakeMouse:useEvent(e.EV_REL)
fakeMouse:useKey(e.BTN_0)
fakeMouse:useKey(e.BTN_1)
fakeMouse:useRelAxis(e.REL_X,-100,100)
fakeMouse:useRelAxis(e.REL_Y,-100,100)
fakeMouse:init()
-- inject a few events; mouse move, button press, button release
fakeMouse:write(e.EV_REL, e.REL_X, -50)
fakeMouse:write(e.EV_REL, e.REL_Y, 0)
fakeMouse:write(e.EV_SYN, e.SYN_REPORT, 0)
fakeMouse:write(e.EV_KEY, e.BTN_0, 1)
fakeMouse:write(e.EV_SYN, e.SYN_REPORT, 0)
fakeMouse:write(e.EV_KEY, e.BTN_0, 0)
fakeMouse:write(e.EV_SYN, e.SYN_REPORT, 0)
-- dispose
fakeMouse:close()

API

Device - read input events

evdev.Device(path[, writeMode]) - open the device event node at path, returning a Device object. File permissions to read path are necessary, and if writeMode is true, an attempt to open for writing will be made to support Device:write().

(Note! lua-evdev 1.3 would always try to open for writing; in keeping with the principle of least priviledge, lua-evdev 2.0 requires explictly specifying that you want to open for writing.)

Device:read() - read a single event, returning 4 values:

  1. the floating-point timestamp of the event
  2. the general type of event (EV_SYN, EV_KEY, EV_REL, EV_ABS, etc.)
  3. the event code (KEY_A, REL_X, ABS_Y, etc.)
  4. the event value (axis value, or 0/1 for button state)

The read will block if no events are available, and throw an error if the device reaches EOF (such as if unplugged).

Device:tryRead() - like Device:read(), but returns nil on EOF.

Device:grab([enable]) - if the argument is true or not given, grab the device, ensuring all input events for it are exclusively delivered to this handle. Returns true if the grab suceeded.

If the argument is false, release any existing grab.

Device:write(type, code, value) - send an event back to the input device. For example, an EV_LED event to control keyboard lights. Only works if the device was successfully opened for writing.

Device:close() - close the file descriptor; further reads will be errors. Device objects are automatically closed on garbage-collection.

Device:pollfd() - return the numeric fd, which can be used with external event loops or polling libraries to avoid blocking.

Device.events - "r"; provided to allow a Device object to be compatable with cqueues.poll(), if you use the cqueues library.

Uinput - submit virtual input events

evdev.Uinput(path) - open the uinput device node at path, returning a Uinput object. File permissions to read path are necessary. If path is not given, a default of "/dev/uinput" is used.

Uinput:useEvent(type) - declare that this virtual device will emit events of the given type (such as EV_KEY, EV_REL, EV_ABS, etc.); must be called before :init()

Uinput:useKey(code) - declare that this virtual device can emit key events of the given keycode (such as KEY_A, KEY_ESC, KEY_LEFT, etc.); must be called before :init(); the EV_KEY event should be declared.

Uinput:useAbsAxis(axis, min, max), Uinput:useRelAxis(axis, min, max) - declare that this virtual device can emit absolute or relative axis events on the given axis (such as ABS_X, REL_Y, REL_WHEEL, ABS_PRESSURE, etc.); must be called before :init(); the EV_ABS or EV_REL event should be declared.

Uinput:init(title) - create the virtual device. title will be used for the human-friendly name visible to the system if given.

Uinput:write(type, code, value) - feed the given event to the input system via this virtual device; must be called after :init(). Note that you need to write an (EV_SYN, SYN_REPORT, 0) event immediately after each batch of events; listeners to the virtual device won't see an event until you send the associated SYN.

Uinput:close() - close the file descriptor; further writes will be errors. Uinput objects are automatically closed on garbage-collection.