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.
  • ./http contains an implementation for the Fuchsia HTTP service.
  • ./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.

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_runner() GN target. fuchsia_package_runner() targets exist for all tests and a number of frequently used standalone executables like "content_shell_fuchsia"'. The scripts can deploy to either emulators started by the runner script, an existing emulator instance, or a physical device.

For the sake of this example, we will be using base_unittests as the package we wish to install and/or execute.

Hermetic emulation

$ out/fuchsia/bin/run_base_unittests

Run on an physical device running Zedboot. Note the -d flag, which is an alias for --device.

$ out/fuchsia/bin/run_base_unittests -d

Run on a device paved with Fuchsia built from source.

$ out/fuchsia/bin/run_base_unittests -d

Install on a device running Fuchsia built from source.

$ out/fuchsia/bin/install_base_unittests

You will need to run the package manually on your device. In this case, run the following from your Fuchsia directory:

$ fx shell run fuchsia-pkg://

If you are frequently deploying to Fuchsia built from source, you might want to add the following entry to your

default_fuchsia_build_dir_for_installation = "/path/to/fuchsia/outdir"

With this flag in place, the --fuchsia-out-dir flag will automatically be used whenever you run_ or install_ Fuchsia packages, making your command lines much shorter:

$ out/fuchsia/bin/run_base_unittests -d

Make sure that the CPU architecture of your Chromium output directory matches the architecture of the Fuchsia output directory (x64==x64, arm64==arm64, etc.).


  1. (From Chromium) Install your package(s) and its symbols onto the device.

    $ out/fuchsia/bin/install_base_unittests
  2. (From Fuchsia source tree) Run the debugger.

$ fx debug
  1. Set up the debugger to attach to the process.
[zxdb] attach base_unittests.cmx
  1. Configure breakpoint(s).
[zxdb] break base::GetDefaultJob
  1. (In another terminal, from Fuchsia source tree) Run the test package.
$ fx shell run fuchsia-pkg://
  1. At this point, you should hit a breakpoint in zxdb.
[zxdb] f
▶ 0 base::GetDefaultJob() •
  1 base::$anon::LaunchChildTestProcessWithOptions(…) •
  2 base::$anon::DoLaunchChildTestProcess(…) •
  3 base::TestLauncher::LaunchChildGTestProcess(…) •
  1. Enjoy debugging! Steps 2 through 6 will also work for things like services which aren't run directly from the command line, such as WebEngine. Run help inside ZXDB to see what debugger commands are available.


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 chromium.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