WebDriver BiDi for Chromium

CI status

This is an implementation of the WebDriver BiDi protocol with some extensions (BiDi+) for Chromium, implemented as a JavaScript layer translating between BiDi and CDP, running inside a Chrome tab.

Current status can be checked at WPT WebDriver BiDi status.

BiDi+

"BiDi+" is an extension of the WebDriver BiDi protocol. In addition to WebDriver BiDi it has:

Command cdp.sendCommand

1CdpSendCommandCommand = {
2  method: "cdp.sendCommand",
3  params: CdpSendCommandParameters,
4}
5
6CdpSendCommandParameters = {
7   method: text,
8   params: any,
9   session?: text,
10}
11
12CdpSendCommandResult = {
13   result: any,
14   session: text,
15}

The command runs the described CDP command and returns the result.

Command cdp.getSession

1CdpGetSessionCommand = {
2   method: "cdp.getSession",
3   params: CdpGetSessionParameters,
4}
5
6CdpGetSessionParameters = {
7   context: BrowsingContext,
8}
9
10CdpGetSessionResult = {
11   session: text,
12}

The command returns the default CDP session for the selected browsing context.

Command cdp.resolveRealm

1CdpResolveRealmCommand = {
2   method: "cdp.resolveRealm",
3   params: CdpResolveRealmParameters,
4}
5
6CdpResolveRealmParameters = {
7   realm: Script.Realm,
8}
9
10CdpResolveRealmResult = {
11   executionContextId: text,
12}

The command returns resolves a BiDi realm to its CDP execution context ID.

Events cdp

1CdpEventReceivedEvent = {
2   method: "cdp.<CDP Event Name>",
3   params: CdpEventReceivedParameters,
4}
5
6CdpEventReceivedParameters = {
7   event: text,
8   params: any,
9   session: text,
10}

The event contains a CDP event.

Field channel

Each command can be extended with a channel:

1Command = {
2   id: js-uint,
3   channel?: text,
4   CommandData,
5   Extensible,
6}

If provided and non-empty string, the very same channel is added to the response:

1CommandResponse = {
2   id: js-uint,
3   channel?: text,
4   result: ResultData,
5   Extensible,
6}
7
8ErrorResponse = {
9  id: js-uint / null,
10  channel?: text,
11  error: ErrorCode,
12  message: text,
13  ?stacktrace: text,
14  Extensible
15}

When client uses commands session.subscribe and session.unsubscribe with channel, the subscriptions are handled per channel, and the corresponding channel filed is added to the event message:

1Event = {
2  channel?: text,
3  EventData,
4  Extensible,
5}

Dev Setup

npm

This is a Node.js project, so install dependencies as usual:

1npm install

cargo

We use cddlconv to generate our WebDriverBiDi types before building.

1. Install Rust.
2. Run cargo install --git https://github.com/google/cddlconv.git cddlconv

pre-commit.com integration

Refer to the documentation at .pre-commit-config.yaml.

1pre-commit install --hook-type pre-push

Starting WebDriver BiDi Server

This will run the server on port 8080:

1npm run server

Use the PORT= environment variable or --port= argument to run it on another port:

1PORT=8081 npm run server
2npm run server -- --port=8081

Use the DEBUG environment variable to see debug info:

1DEBUG=* npm run server

Use the DEBUG_DEPTH (default: 10) environment variable to see debug deeply nested objects:

1DEBUG_DEPTH=100 DEBUG=* npm run server

Use the CHANNEL=... environment variable with one of the following values to run the specific Chrome channel: stable, beta, canary, dev, local. Default is local. The local channel means the pinned in .browser Chrome version will be downloaded if it is not yet in cache. Otherwise, the requested Chrome version should be installed.

1CHANNEL=dev npm run server

Use the CLI argument --verbose to have CDP events printed to the console. Note: you have to enable debugging output bidi:mapper:debug:* as well.

1DEBUG=bidi:mapper:debug:* npm run server -- --verbose

or

1DEBUG=* npm run server -- --verbose

Starting on Linux and Mac

TODO: verify it works on Windows.

You can also run the server by using npm run server. It will write output to the file log.txt:

1npm run server -- --port=8081 --headless=false

Running with in other project

Sometimes it good to verify that a change will not affect thing downstream for other packages. There is a useful puppeteer label you can add to any PR to run Puppeteer test with your changes. It will bundle chromium-bidi and install it in Puppeteer project then run that package test.

Running

Unit tests

Running:

1npm run unit

E2E tests

The e2e tests serve the following purposes:

1. Brief checks of the scenarios (the detailed check is done in WPT)
2. Test Chromium-specific behavior nuances
3. Add a simple setup for engaging the specific command

The E2E tests are written using Python, in order to more-or-less align with the web-platform-tests.

Installation

Python 3.10+ and some dependencies are required:

1python -m pip install --user pipenv
2pipenv install

Running

The E2E tests require BiDi server running on the same host. By default, tests try to connect to the port 8080. The server can be run from the project root:

1npm run e2e  # alias to to e2e:headless
2npm run e2e:headful
3npm run e2e:headless

This commands will run ./tools/run-e2e.mjs, which will log the PyTest output to console, Additionally the output is also recorded under ./logs/<DATE>.e2e.log, this will contain both the PyTest logs and in the event of FAILED test all the Chromium-BiDi logs.

If you need to see the logs for all test run the command with VERBOSE=true.

Simply pass npm run e2e -- tests/<PathOrFile> and the e2e will run only the selected one. You run a specific test by running npm run e2e -- -k <TestName>.

Use CHROMEDRIVER environment to run tests in chromedriver instead of NodeJS runner:

1CHROMEDRIVER=true npm run e2e

Use the PORT environment variable to connect to another port:

1PORT=8081 npm run e2e

Use the HEADLESS to run the tests in headless (new or old) or headful modes. Values: new, old, false, default: new.

1HEADLESS=new npm run e2e

Updating snapshots

1npm run e2e -- --snapshot-update

See https://github.com/tophat/syrupy for more information.

Local http server

E2E tests use local http server pytest-httpserver, which is run automatically with the tests. However, sometimes it is useful to run the http server outside the test case, for example for manual debugging. This can be done by running:

1pipenv run local_http_server

...or directly:

1python tests/tools/local_http_server.py

Examples

Refer to examples/README.md.

WPT (Web Platform Tests)

WPT is added as a git submodule. To get run WPT tests:

Check out and setup WPT

1. Check out WPT

1git submodule update --init

2. Go to the WPT folder

1cd wpt

3. Set up virtualenv

Follow the System Setup instructions.

4. Setup hosts file

Follow the hosts File Setup instructions.

4.a On Linux, macOS or other UNIX-like system

1./wpt make-hosts-file | sudo tee -a /etc/hosts

4.b On Windows

This must be run in a PowerShell session with Administrator privileges:

1python wpt make-hosts-file | Out-File $env:SystemRoot\System32\drivers\etc\hosts -Encoding ascii -Append

If you are behind a proxy, you also need to make sure the domains above are excluded from your proxy lookups.

5. Set BROWSER_BIN

Set the BROWSER_BIN environment variable to a Chrome, Edge or Chromium binary to launch. For example, on macOS:

1# Chrome
2export BROWSER_BIN="/Applications/Google Chrome Canary.app/Contents/MacOS/Google Chrome Canary"
3export BROWSER_BIN="/Applications/Google Chrome Dev.app/Contents/MacOS/Google Chrome Dev"
4export BROWSER_BIN="/Applications/Google Chrome Beta.app/Contents/MacOS/Google Chrome Beta"
5export BROWSER_BIN="/Applications/Google Chrome.app/Contents/MacOS/Google Chrome"
6export BROWSER_BIN="/Applications/Chromium.app/Contents/MacOS/Chromium"
7
8# Edge
9export BROWSER_BIN="/Applications/Microsoft Edge Canary.app/Contents/MacOS/Microsoft Edge Canary"
10export BROWSER_BIN="/Applications/Microsoft Edge.app/Contents/MacOS/Microsoft Edge"

Run WPT tests

1. Make sure you have Chrome Dev installed

https://www.google.com/chrome/dev/

2. Build Chromedriver BiDi

Oneshot:

1npm run build

Continuously:

1npm run build --watch

3. Run

1npm run wpt -- webdriver/tests/bidi/

Update WPT expectations if needed

1UPDATE_EXPECTATIONS=true npm run wpt -- webdriver/tests/bidi/

How does it work?

The architecture is described in the WebDriver BiDi in Chrome Context implementation plan .

There are 2 main modules:

1. backend WS server in src. It runs webSocket server, and for each ws connection runs an instance of browser with BiDi Mapper.
2. front-end BiDi Mapper in src/bidiMapper. Gets BiDi commands from the backend, and map them to CDP commands.

Contributing

The BiDi commands are processed in the src/bidiMapper/commandProcessor.ts. To add a new command, add it to _processCommand, write and call processor for it.

Publish new npm release

Release branches

chromium-bidi maintains release branches corresponding to Chrome releases. The branches are named using the following pattern: releases/m$MAJOR_VERSION.

The new release branch is created as soon a new major browser version is published by the update-browser-version job:

• the PR created by this job should be marked as a feature and it should cause the major package version to be bumped.
• once the browser version is bumped, the commit preceding the version bump should be used to create a release branch for major version pinned before the bump.

Changes that need to be cherry-picked into the release branch should be marked as patches. Either major or minor version bumps are not allowed on the release branch.

Example workflow:

1gitGraph
2       commit id: "feat: featA"
3       commit id: "release: v0.5.0"
4       branch release/m129
5       checkout main
6       commit id: "feat: roll Chrome to M130 from 129"
7       commit id: "release: v0.6.0"
8       commit id: "fix: for m129"
9       checkout release/m129
10       cherry-pick id: "fix: for m129"
11       commit id: "release: v0.5.1 "

Currently, the releases from release branches are not automated.

Automatic release

We use release-please to automate releases. When a release should be done, check for the release PR in our pull requests and merge it.

Manual release

1. Dry-run

   1npm publish --dry-run

2. Open a PR bumping the chromium-bidi version number in package.json for review:

   1npm version patch -m 'chore: Release v%s' --no-git-tag-version

   Instead of patch, use minor or major as needed.

3. After the PR is reviewed, create a GitHub release specifying the tag name matching the bumped version. Our CI then automatically publishes the new release to npm based on the tag name.

Roll into Chromium

This section assumes you already have a Chromium set-up locally, and knowledge on how to submit changes to the repo. Otherwise submit an issue for a project maintainer.

1. Create a new branch in chromium src/.
2. Update the mapper version:

1third_party/bidimapper/roll_bidmapper

3. Submit a CL with bug 42323268 (link).

4. Regenerate WPT expectations or baselines:

   4.1. Trigger a build and test run:

   1third_party/blink/tools/blink_tool.py rebaseline-cl --build="linux-blink-rel" --verbose

   4.2. Once the test completes on the builder, rerun that command to update the baselines. Update test expectations if there are any crashes or timeouts. Commit the changes (if any), and upload the new patch to the CL.

5. Add appropriate reviewers or comment the CL link on the PR.

Adding new command

Want to add a shiny new command to WebDriver BiDi for Chromium? Here's the playbook:

Prerequisites

Specification

The WebDriver BiDi module, command, or event must be specified either in the WebDriver BiDi specification or as an extension in a separate specification (e.g., the Permissions specification). The specification should include the command's type definitions in valid CDDL format.

WPT wdspec tests

You'll need tests to prove your command works as expected. These tests should be written using WPT wdspec and submitted along with the spec itself. Don't forget to roll the WPT repo into the Mapper (dependabot can help, and you will likely need to tweak some expectations afterward).

CDP implementation

Make sure Chromium already has the CDP methods your command will rely on.

Update CDDL types

1. If your command lives in a separate spec, add a link to that spec in the "Build WebDriverBiDi types" GitHub action (check out the "bluetooth" pull request for an example).
2. Run the "Update WebdriverBiDi types" GitHub action. This will create a pull request with your new types. If you added a command, this PR will have a failing check complaining about a non-exhaustive switch statement:

   error: Switch is not exhaustive. Cases not matched: "{NEW_COMMAND_NAME}" @typescript-eslint/switch-exhaustiveness-check

3. Update the created pull request. Add your new command to CommandProcessor.#processCommand. For now, just have it throw an UnknownErrorException (see the example for how to do this).

1case '{NEW_COMMAND_NAME}':
2  throw new UnknownErrorException(
3    `Method ${command.method} is not implemented.`,
4  );

4. Merge it! Standard PR process: create, review, merge.

Implement the new command

CommandProcessor.#processCommand handles parsing parameters and running your command.

(only if the new command has non-empty parameters) parse command parameters

If your command has parameters, update the BidiCommandParameterParser and implement the parsing logic in BidiNoOpParser, BidiParser and protocol-parser. Look at the example for guidance.

Implement the new command

Write the core logic for your command in the appropriate domain processor. Again, example is your friend.

Call the domain processor's method

Call your new domain processor method from CommandProcessor.#processCommand, passing in the parsed parameters. Example.

Add e2e tests

Write end-to-end tests for your command, including the happy path and any edge cases that might trip things up. Focus on testing the code in the mapper.

Update WPT expectations

Your WPT tests will probably fail now.

Tests with unexpected results: PASS [expected FAIL] ...

Update the expectations in a draft PR with the "update-expectations" label. This will trigger an automated PR "test: update the expectations for PR" that you'll need to merge to your branch.

Merge it!

Mark your PR as ready, get it reviewed, and merge it in.

Roll in ChromeDriver

This bit usually involves the core devs:

1. Release your changes.
2. Roll the changes into ChromeDriver.