Chromium-based Fuchsia services

This directory contains implementation code for various Fuchsia services living in the Chromium repository. To build Chromium on Fuchsia, check this documentation.

Code organization

Each of the following subdirectories contain code for a specific Fuchsia service:

  • ./engine contains the WebEngine implementation. The WebEngine enables Fuchsia applications to embed Chromium frames for rendering web content.
  • ./runnerscontains implementations of Fuchsia sys.runner.
    • ./runners/cast Enables the Fuchsia system to launch cast applications.
    • ./runners/web Enables the Fuchsia system to launch HTTP or HTTPS URLs.
  • ./media_receiver contains an implementation for an Open Screen receiver.

When writing a new Fuchsia service, it is recommended to create a new subdirectory under //fuchsia or a new subdirectory under //fuchsia/runners depending on the use case.

The ./base subdirectory contains common utilities used by more than one of the aforementioned Fuchsia services.

The ./cipd and ./fidl subdirectories contain CIPD definitions and FIDL interface definitions, respectfully.


Code that is not shared across multiple targets should live in the global namespace. Code that is shared across multiple targets should live in the cr_fuchsia namespace.

Test code

Under the //fuchsia directory , there are 3 major types of tests:

  • Unit tests: Exercises a single class in isolation, allowing full control over the external environment of this class.
  • Browser tests: Spawns a full browser process along child processes. The test code is run inside the browser process, allowing for full access to the browser code, but not other processes.
  • Integration tests: they exercise the published API of a Fuchsia component. For instance, //fuchsia/engine:web_engine_integration_tests make use of the //fuchsia/engine:web_engine component. The test code is run in a separate process in a separate component, allowing only access to the published API of the component under test.

Integration tests are more resource-intensive than browser tests, which are in turn more expensive than unit tests. Therefore, when writing new tests, it is preferred to write unit tests over browser tests over integration tests.

As a general rule, test-only code should live in the same directory as the code under test with an explicit file name, either fake_*, test_*, *, *_ or *

Test code that is shared across components should live in a dedicated test directory, under the cr_fuchsia namespace. For instance, see the //fuchsia/engine/test directory, which contains code shared by all browser tests.

Deploying and running Fuchsia code.

Fuchsia binaries are deployed and executed via scripts that are automatically generated by the fuchsia_package_installer() or fuchsia_run_script_with_packages() GN templates. Details on deploying and running Fuchsia test binaries can be found here


Check this documentation for debugging tips.


Building and deploying the WebRunner service

When you build web_runner, Chromium will automatically generate scripts for you that will automatically provision a device with Fuchsia and then install web_runner and its dependencies.

To build and run web_runner, follow these steps:

  1. (Optional) Ensure that you have a device ready to boot into Fuchsia.

    If you wish to have web_runner manage the OS deployment process, then you should have the device booting into Zedboot.

  2. Build web_runner.

    $ autoninja -C out/fuchsia web_runner
  3. Install web_runner.

    • For devices running Zedboot:

      $ out/fuchsia/bin/install_web_runner -d
    • For devices already booted into Fuchsia:

      You will need to add command line flags specifying the device's IP address and the path to the ssh_config used by the device (located at $FUCHSIA_OUT_DIR/ssh-keys/ssh_config):

      $ out/fuchsia/bin/install_web_runner -d --ssh-config $PATH_TO_SSH_CONFIG
  4. Press Alt-Esc key on your device to switch back to terminal mode or run fx shell from the host.

  5. Launch a webpage.

    $ tiles_ctl add
  6. Press Alt-Esc to switch back to graphical view if needed. The browser window should be displayed and ready to use.

  7. You can deploy and run new versions of Chromium without needing to reboot.

    First kill any running processes:

    $ killall context_provider.cmx; killall web_runner.cmx

    Then repeat steps 1 through 6 from the installation instructions, excluding step #3 (running Tiles).

Closing a webpage

  1. Press the Windows key to return to the terminal.

  2. Instruct tiles_ctl to remove the webpage‘s window tile. The tile’s number is reported by step 6, or it can be found by running tiles_ctl list and noting the ID of the “url” entry.

    $ tiles_ctl remove TILE_NUMBER