balena-labs-projects/browser

Provides a hardware accelerated web browser to present internal and external URLs on a connected display. The browser block is a docker image that runs a Chromium browser via X11, optimized for balenaOS. The block provides an API for dynamic configuration, and also exposes the Chromium Remote Debug port.

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Features

• Chromium browser optimized for device arch
• Hardware video acceleration (if enabled)
• Optional KIOSK mode
• Remotely configurable launch URL
• Automatically displays local HTTP (port 80 or 8080) or HTTPS (443) service endpoints.
• API for remote configuration and management
• Chromium remote debugging port

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Usage

docker-compose file

To use this image, create a container in your docker-compose.yml file as shown below:

version: '2'

volumes:
  settings:                          # Only required if using PERSISTENT flag (see below)

services:

  browser:
    image: bh.cr/balenalabs/browser-<arch> # where <arch> is one of aarch64, arm32 or amd64
    privileged: true # required for UDEV to find plugged in peripherals such as a USB mouse
    ports:
        - '5011' # management API (optional)
        - '35173' # Chromium debugging port (optional)
    volumes:
      - 'settings:/data' # Only required if using PERSISTENT flag (see below)

To pin to a specific version of this block use:

services:
  browser:
    image: bh.cr/balenalabs/browser-<arch>/<version>
    privileged: true # required for UDEV to find plugged in peripherals such as a USB mouse
    ports:
        - '5011' # management API (optional)
        - '35173' # Chromium debugging port (optional)
    volumes:
      - 'settings:/data' # Only required if using PERSISTENT flag (see below)

See here for more details about how to use blocks hosted in balenaCloud.

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Customization

Extend image configuration

By default the browser block uses the first local display (i.e. DISPLAY=:0) which would typically be a connected monitor, TV or a Pi Display. However for custom configurations you can overload the CMD directive, as such:

dockerfile.template

FROM bh.cr/balenalabs/browser-%%BALENA_ARCH%%

CMD ["export DISPLAY=:1"]

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Environment variables

The following environment variables allow configuration of the browser block:

Environment variable	Options	Default	Description
LAUNCH_URL	http or https URL	N\A	Web page to display
DISPLAY_NUM	n	0	Display number to use
LOCAL_HTTP_DELAY	Number (seconds)	0	Number of seconds to wait for a local HTTP service to start before trying to detect it
KIOSK	0, 1	0	Run in kiosk mode with no menus or status bars. 0 = off, 1 = on
SHOW_CURSOR	0, 1	0	Enables/disables the cursor when in kiosk mode 0 = off, 1 = on
FLAGS	many!	N/A	Replaces the flags chromium is started with. Enter a space (' ') separated list of flags (e.g. --noerrdialogs --disable-session-crashed-bubble) Use with caution!
EXTRA_FLAGS	many!	N/A	Adds additional flags chromium is started with. Enter a space (' ') separated list of flags (e.g. --audio-buffer-size=2048 --audio-output-channels=8)
PERSISTENT	0, 1	0	Enables/disables user profile data being stored on the device. Note: you'll need to create a settings volume. See example above 0 = off, 1 = on
ROTATE_DISPLAY	normal, left, right, inverted	normal	Rotates the display
ROTATE_DELAY	n	3	Add an artificial delay (in seconds) before applying display rotation
TOUCHSCREEN	string	N\A	Name of Touch Input to rotate
ENABLE_GPU	0, 1	0	Enables the GPU rendering. Necessary for Pi3B+ to display YouTube videos. 0 = off, 1 = on
WINDOW_SIZE	x,y	Detected screen resolution	Sets the browser window size, such as 800,600. Note: Reverse the dimensions if you also rotate the display to left or right
WINDOW_POSITION	x,y	0,0	Specifies the browser window position on the screen
API_PORT	port number	5011	Specifies the port number the API runs on
REMOTE_DEBUG_PORT	port number	35173	Specifies the port number the chrome remote debugger runs on

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Choosing what to display

If you want the browser to display a website, you can set the LAUNCH_URL as noted above. However, you can also drop the browser into a multicontainer app, and use it to display the (HTTP, port 80 or 8080, or HTTPS port 443) output of another service, such as a Grafana dashboard. The browser will automatically detect that a service is running a HTTP server and display that. Just make sure that you don't set a LAUNCH_URL environment variable, as they take precedence. Example:

docker-compose.yml

version: '2.1'
volumes:
  settings:
services:
  browser:
    restart: always
    image: bh.cr/balenalabs/browser-<arch>
    privileged: true
    volumes:
      - 'settings:/data'
  grafana:
    restart: always
    build: ./grafana
    ports:
      - "80"

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Choosing audio output device

By default the browser block will output audio via HDMI. If you want to route audio through a different interface you can do it with the help of the audio block. The browser block is pre-configured to use it if present so you only need to add it to your docker-compose.yml file and then use AUDIO_OUTPUT environment variable to select the desired output. Check out the audio block documentation to learn more about it.

In this example we add the audio block and route the browser audio to the Raspberry Pi headphone jack:

services:
  browser:
    image: bh.cr/balenalabs/browser-<arch>
  audio:
    image: bh.cr/balenalabs/audio-<arch>
    privileged: true
    ports:
      - 4317:4317
    environment:
      AUDIO_OUTPUT: RPI_HEADPHONES

Note: The browser block expects the audio block to be named as such. If you change it's service name you'll need to override the PULSE_SERVER environment variable value to match it in the browser dockerfile. For example add ENV PULSE_SERVER=tcp:not-audio:4317.

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API

The browser block exposes an HTTP API running on port 5011. The following endpoints are available:

GET /ping

Returns HTTP 200 if the browser block is ready

POST /refresh

Refreshes the currently displayed page

POST /autorefresh/{interval}

Automatically refreshes the browser window

Value	Description
0	disable
1-60	refresh every interval seconds

POST /scan

Re-scans the device to find local HTTP or HTTPS services to display. This can be used by the HTTP/S service to notify the browser block that it is ready to be displayed, should there be a startup race.

note: the LAUNCH_URL must not be set for local services to be detected.

GET /url

Returns the URL currently being displayed

PUT /url

Sets the URL to be displayed. The URL is set in the request body. Example:

curl --data "url=www.balena.io" http://localhost:5011/url

You can also pre-set the kiosk and GPU settings as part of a URL put request. Example:

curl --data "url=www.balena.io&gpu=0&kiosk=1" http://localhost:5011/url

GET /gpu

Returns the status of the GPU:

Return Value	Description
0	disabled
1	enabled

PUT /gpu/{value}

Enables or disables the GPU

Value	Description
0	disable
1	enable

GET /kiosk

Returns whether the device is running kiosk mode or not:

Return Value	Description
0	disabled
1	enabled

PUT /kiosk/{value}

Enables or disables kiosk mode

Value	Description
0	disable
1	enable

GET /flags

Returns the flags Chromium was started with

GET /version

Returns the version of Chromium that browser is running

GET /screenshot

Uses scrot to take a screenshot of the chromium window. The screenshot will be saved as a temporary file in the container.

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Supported devices

The browser block has been tested to work on the following devices:

Device Type	Status
Raspberry Pi 3b+	✔
Raspberry Pi 3b+ (64-bit OS)	✔
balena Fin	✔
Raspberry Pi 4	✔
Intel NUC	✔
Generic AMD64	✔

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Troubleshooting

This section provides some guidance for common issues encountered:

Black border on HDMI display

Thanks to 1980's CRT televisions, manufacturers had to invent a method for cutting off the edges of a picture to ensure the "important" bits were displayed nicely on the screen. This is called overscan and there's a good article on it here. If, when you plug one of the supported devices into your HDMI screen, you find black borders around the picture, you need to disable overscan. For the device this can be achieved by setting a Device Configuration variable called BALENA_HOST_CONFIG_disable_overscan and setting the value to 1:

You may also need to turn it off on the screen itself (check your device instructions for details).

Partial/strange display output

Occasionally users report weird things are happening with their display output like:

• Only a portion of the browser screen appears on their display
• The screen is displaying skewed or fragmented
• Colors have changed dramatically

Here are some things to try:

• Setting the WINDOW_SIZE manually to your display's resolution (e.g. 1980,1080) - the display may be mis-reporting it's resolution to the device
• Increase the memory being allocated to the GPU with the Device Configuration tab on the dashboard, or via configuration variable - for large displays the device may need to allocate more memory to displaying the output