Launch and control a fullscreen web browser from Elixir. This is intended for kiosks running Nerves but can be used anywhere you need to show a user a local web-based UI.
Here's an example run:
iex> {:ok, kiosk} = WebengineKiosk.start_link(fullscreen: false)
iex> WebengineKiosk.go_to_url(kiosk, "https://elixir-lang.org/")
iex> WebengineKiosk.run_javascript(kiosk, "window.alert('Hello, Elixir!')")
iex> WebengineKiosk.stop(kiosk)It can also be linked into your application's supervision tree:
# Example childspecs
[
{WebengineKiosk, {[homepage: "https://somewhere.com", background: "black"], name: Display}}
]
# Somewhere else in your code
WebengineKiosk.run_javascript(Display, "window.alert('Hello, Elixir!')")The kiosk starts fullscreen and goes to a default local web page. To change this, set one or more options:
background_color: color- specify a background color as #RRGGBB or by nameblank_image: path- specify a path to an image for when the screen is blankeddata_dir: path- specify a writable path for data filesdebug_keys: boolean- enable key combinations useful for debuggingfullscreen: boolean- show fullscreengid: gid- run the browser with this group idhomepage: url- load this page first. For local files, specifyfile:///path/to/index.htmlhttp_accept_language: string- overrides the default Accept-Language stringhttp_user_agent: string- overrides the default UserAgent stringmonitor: index- select the monitor for the web browser (0, 1, etc.)opengl: "gl" | "gles" | "software" | "auto"- specify the OpenGL backend. This is only a hint.progress: boolean- show a progress bar when loading pagesrun_as_root: boolean- set to true if you really want to run Chromium as rootsounds: boolean- play sounds on clicksuid: uid- run the browser as this user
See lib/webengine_kiosk.ex for some untested options.
Process can subscribe to receive events from WebengineKiosk. Subscribe using register function like this from another process:
WebengineKiosk.register(Display, self())If the subscribing process is GenServer you can handle events like this:
def handle_info({:webengine_kiosk, {:channel_message, message}}, state) do
# Do something with event ...
{:noreply, state}
endYou can send data from Javascript back to elixir using QtWebChannel.
First you need to load appropriate javascript library:
Place this somewhere in <head>
<script type="text/javascript" src="qrc:///qtwebchannel/qwebchannel.js"></script>Than in your javascript code initialize QtWebChannel:
new QWebChannel(qt.webChannelTransport, function (channel) {
var JSobject = channel.objects.elixirJsChannel;
window.elixirJsChannel = JSobject;
});than anywhere in your javascript code you can call following function to send messages:
window.elixirJsChannel.send("Hello world!");The message will appear as :channel_message event. Only text can be sent, but if you want so send objects, you can serialize the to JSON and send them as such.
WebengineKiosk requires Qt version 5.10 or later (it may
work on earlier versions, but we haven't tested it). It is likely that your
package manager already has a Qt package.
On Debian or Ubuntu:
sudo apt install qtwebengine5-dev qtmultimedia5-dev qt5-defaultOn OSX:
brew install qt
# Homebrew doesn't automatically add `qmake` to your path, so run this when
# building or add it to your .bashrc, .zshrc, etc.
export PATH="/usr/local/opt/qt/bin:$PATH"If you are installing Qt manually, then the first time that you run mix,
you'll need to point to the installation location. If you don't, you'll either
get an error that qmake isn't found or you'll being using your system's
version of Qt. Here's an example commandline:
QMAKE=~/Qt/5.11.1/gcc_64/bin/qmake mix compileFinally, if you're using Nerves, you'll need a Nerves system that includes Qt. Take a look at kiosk_system_rpi3 for an example.
Once you've done all that, go ahead and add webengine_kiosk to your mix.exs
dependencies like normal:
def deps do
[
{:webengine_kiosk, "~> 0.2"}
]
endWebengineKiosk will refuse to run as the root user. You may specify a name or
number using the :uid and :gid parameters to WebengineKiosk.start_link/2.
If unspecified and running as root, WebengineKiosk will try to drop to a
kiosk user and kiosk group by default. If dropping privileges, then you also
need to ensure that QtWebEngine has a writable data directory. Use the
:data_dir option do do this.
The next set of permissions to check are platform-specific. Qt and Chromium
directly access videos drivers and input devices. Usually the device files
associated with those have group permissions and adding the user to the
appropriate groups makes everything work. For example, on the Raspberry Pi,
you'll need the kiosk user to be part of the video and input groups. You may
also need to update the permissions and group ownership on /dev/vchiq if
running on Nerves since it doesn't yet do that by default.
If the kiosk binary exits immediately then something basic is wrong.
Unfortunately, errors often get printed to the terminal and don't end up in
Elixir logs. If this happens to you, try running the kiosk binary by itself:
iex> path = Application.app_dir(:webengine_kiosk, "priv/kiosk")
"/srv/erlang/lib/webengine_kiosk-0.1.0/priv/kiosk"
iex> System.cmd(path, [])