webdriver library

The webdriver crate is a library implementation of the wire protocol for the W3C WebDriver standard written in Rust. WebDriver is a remote control interface that enables introspection and control of user agents. It provides a platform- and language-neutral wire protocol as a way for out-of-process programs to remotely instruct the behaviour of web browsers.

The webdriver library provides the formal types, error codes, type and bounds checks, and JSON marshaling conventions for correctly parsing and emitting the WebDriver protocol. It also provides an HTTP server where endpoints are mapped to the different WebDriver commands.

As of right now, this is an implementation for the server side of the WebDriver API in Rust, not the client side.


The library is built using the usual Rust conventions:

% cargo build

To run the tests:

% cargo test


To start an HTTP server that handles incoming command requests, a request handler needs to be implemented. It takes an incoming WebDriverMessage and emits a WebDriverResponse:

impl WebDriverHandler for MyHandler {
    fn handle_command(
        &mut self,
        _: &Option<Session>,
        msg: WebDriverMessage,
    ) -> WebDriverResult<WebDriverResponse> {

    fn delete_session(&mut self, _: &Option<Session>) {

let addr = SocketAddr::new("localhost", 4444);
let handler = MyHandler {};
let server = webdriver::server::start(addr, handler, vec![])?;
info!("Listening on {}", server.socket);

It is also possible to provide so called extension commands by providing a vector of known extension routes, for which each new route needs to implement the WebDriverExtensionRoute trait. Each route needs to map to a WebDriverExtensionCommand:

pub enum MyExtensionRoute { HelloWorld }
pub enum MyExtensionCommand { HelloWorld }

impl WebDriverExtensionRoute for MyExtensionRoute {
    fn command(
        captures: &Captures,
        body: &Json,
    ) -> WebDriverResult<WebDriverCommand<MyExtensionCommand>> {

let extension_routes = vec![
    (Method::Get, "/session/{sessionId}/moz/hello", MyExtensions::HelloWorld)


let server = webdriver::server::start(addr, handler, extension_routes[..])?;


The mailing list for webdriver discussion is tools-marionette@lists.mozilla.org (subscribe, archive).

There is also an IRC channel to talk about using and developing webdriver in #ateam on irc.mozilla.org.