Gnome Shell extension code for grabbing key events from X

keys.js

const GLib = imports.gi.GLib;
const Gio = imports.gi.Gio;

let initialized = false;

let keymap = {}, xinputPids = [], xinputs = [];

function trackKeys(callback, out_reader, res) {
  if (!initialized) initialize();

  const [out, length] = out_reader.read_upto_finish(res);
  if (length > 0) {
    if (/key *press *(\d+)/.test(out)) {
      callback((keymap[RegExp.$1] || "unknown key") + ';' + new Date());
    }

    out_reader.read_upto_async("", 0, 0, null, trackKeys.bind(null, callback), "");
  }
}

let nonAsciiWordRegex = /(grave|acute|circumflex|tilde|diaeresis|ring|E|cedilla|caron|ogonek|breve|abovedot|stroke|doubleacute|macron|slash)/;
let nonLatinLanguageRegex = /(hebrew|thai)/;

function initialize() {
  const [ret, stdout, stderr, stat] = GLib.spawn_sync(null, ['/usr/bin/xmodmap', '-pke'], null, 0, null);
  (stdout+'').split('\n').forEach((line) => {
    if (/keycode *(\d+) = (\w+)/.test(line)) {
      const scancode = RegExp.$1,
            symbol   = RegExp.$2;
      let type;
      if (symbol.startsWith("XF86")) type = 'media';
      else if (/^F\d+$/.test(symbol)) type = 'function';
      // TODO make this list more complete and inclusive of non-western-europian languages
      // (current generated by hand from /usr/include/X11/keysymdef.h)
      else if (/^\w$/.test(symbol.replace(nonAsciiWordRegex, '')) || nonLatinLanguageRegex.test(line)) type = 'alphanum';
      else type = symbol;
      keymap[scancode] = type;
    }
  });

  initialized = true;
}

const xinput = {
  poll: pollXinputs,
  respawn: respawnXinputs,
  spawn: spawnXinputs,
  kill: killXinputs
};

function pollXinputs(callback) {
  // TODO, don't compare lengths, compare actual contents
  if (xinputs.length !== listXinputs().length) {
    respawnXinputs(callback);
  }
}

function respawnXinputs(callback) {
  killXinputs();
  spawnXinputs(callback);
}

function spawnXinputs(callback) {
  // TODO handle xinput not existing
  xinputs = listXinputs();
  xinputs.forEach((xinput) => {
    const [res, pid, in_fd, out_fd, err_fd]  = GLib.spawn_async_with_pipes(null, ['/usr/bin/xinput', 'test', xinput.id], null, 0, null);
    xinputPids.push(pid);
    const out_reader = new Gio.DataInputStream({
      base_stream: new Gio.UnixInputStream({fd: out_fd})
    });

    out_reader.read_upto_async(
      "", 0, 0, null,
      trackKeys.bind(null, (line) => callback(line + ';' + xinput.name + ';' + xinput.id)), '');
  });
}

function killXinputs() {
  xinputPids.forEach((xinputPid) => {
    GLib.spawn_close_pid(xinputPid);
    // TODO: is there a safer way to kill xinput?
  });
  GLib.spawn_command_line_sync('killall xinput');
  xinputPids = [];
}

function listXinputs() {
  const [ret, stdout, stderr, stat] = GLib.spawn_sync(null, ['/usr/bin/xinput', 'list'], null, 0, null);
  return (stdout+'')
    .split('\n')
    .map((line) => {
      if (/↳ (.*)\tid=(\d+)/.test(line)) {
        return {
          'name': RegExp.$1.trim(),
          'id': RegExp.$2
        };
      } else {
        return null;
      }
    })
    .filter((x) => !!x);
}