chrome-remote-interface

Remote Debugging Protocol interface that helps to instrument Chrome by providing a simple abstraction of the two main objects exposed by the protocol in a Node.js fashion: commands and notifications.

chrome-remote-interface is listed among third-party Chrome debugging protocol clients.

Installation

npm install chrome-remote-interface

Chrome setup

Chrome needs to be started with the --remote-debugging-port=<port> option to enable the Remote Debugging Protocol, for example:

google-chrome --remote-debugging-port=9222

Sample API usage

The following snippet loads https://github.com and dumps every request made.

var Chrome = require('chrome-remote-interface');
Chrome(function (chrome) {
    with (chrome) {
        Network.requestWillBeSent(function (params) {
            console.log(params.request.url);
        });
        Page.loadEventFired(close);
        Network.enable();
        Page.enable();
        once('ready', function () {
            Page.navigate({'url': 'https://github.com'});
        });
    }
}).on('error', function () {
    console.error('Cannot connect to Chrome');
});

REPL interface and embedded documentation

This module comes with a REPL interface that can be used to interactively control Chrome (run with --help to display the list of available options). It supports command execution and event binding, see the documentation for chrome.<domain>.<method>([params], [callback]) and chrome.<domain>.<event>(callback). Here's a sample session:

chrome> Network.enable()
chrome> Network.requestWillBeSent(console.log)
chrome> Page.navigate({url: 'https://github.com'})

Using the provided help field it's possible to obtain information on the events and methods available through the Remote Debugging Protocol. For example to learn how to call Page.navigate type:

chrome> Page.navigate.help
{ type: 'command',
  name: 'navigate',
  parameters:
   [ { name: 'url',
       type: 'string',
       description: 'URL to navigate the page to.' } ],
  returns:
   [ { name: 'frameId',
       '$ref': 'FrameId',
       hidden: true,
       description: 'Frame id that will be navigated.' } ],
  description: 'Navigates current page to the given URL.',
  handlers: [ 'browser', 'renderer' ] }

The type field determines whether this member is a command or an event.

For what concerns the types instead (they usually start with an upper case letter), just type its name:

chrome> Network.Timestamp
{ id: 'Timestamp',
  type: 'number',
  description: 'Number of seconds since epoch.' }

Remote Debugging Protocol versions

Currently it is not possible to fetch the protocol descriptor (protocol.json) directly from the instrumented Chrome instance (see #10); that file is fetched from time to time from the Blink repo and pushed to this repository. To use some of the bleeding edge features that still does not appear in the provided protocol.json, there are basically two options:

update the local copy with make update-protocol;
use the raw version of the commands and events interface.

API

module([options], [callback])

Connects to a remote instance of Chrome using the Remote Debugging Protocol.

options is an object with the following optional properties:

host: Remote Debugging Protocol host. Defaults to localhost;
port: Remote Debugging Protocol port. Defaults to 9222;
chooseTab: callback used to determine which remote tab attach to. Takes the array returned by http://host:port/json containing the tab list and must return the numeric index of a tab. Defaults to a function which returns the currently active tab (function (tabs) { return 0; }).

callback is a listener automatically added to the connect event of the returned EventEmitter.

Returns an EventEmitter that supports the following events:

Event: 'connect'

function (chrome) {}

Emitted when the connection to Chrome is established.

chrome is an instance of the Chrome class.

Event: 'error'

function (err) {}

Emitted if http://host:port/json can't be reached or if it's not possible to connect to Chrome's remote debugging WebSocket.

err is an instance of Error.

module.listTabs([options], callback)

Request the list of the available open tabs of the remote Chrome instance.

options is an object with the following optional properties:

host: Remote Debugging Protocol host. Defaults to localhost;
port: Remote Debugging Protocol port. Defaults to 9222.

callback is executed when the list is correctly received, it gets the following arguments:

err: a Error object indicating the success status;
tabs: the array returned by http://host:port/json containing the tab list.

For example:

var Chrome = require('chrome-remote-interface');
Chrome.listTabs(function (err, tabs) {
    if (!err) {
        console.log(tabs);
    }
});

Class: Chrome

Event: 'event'

function (message) {}

Emitted when Chrome sends a notification through the WebSocket.

message is the object received, it has the following properties:

method: a string describing the notification (e.g., 'Network.requestWillBeSent').
params: an object containing the payload.

Refer to the Remote Debugging Protocol specifications for more information.

For example:

on('event', function (message) {
    if (message.method === 'Network.requestWillBeSent') {
        console.log(message.params);
    }
});

Event: '`<method>`'

function (params) {}

Emitted when Chrome sends a notification for <method> through the WebSocket.

params is an object containing the payload.

This is just a utility event which allows to easily listen for specific notifications (see the above event), for example:

chrome.on('Network.requestWillBeSent', console.log);

Event: 'ready'

function () {}

Emitted every time that there are no more pending commands waiting for a response from Chrome. Note that the interaction with Chrome is asynchronous so the only way to serialize a sequence of commands is to use the callback provided by the chrome.send method. This event acts as a barrier and it is useful to avoid the callback hell in certain simple situations.

For example to load a URL only after having enabled the notifications of both Network and Page domains:

Network.enable();
Page.enable();
once('ready', function() {
    Page.navigate({'url': 'https://github.com'});
});

In this particular case, not enforcing this kind of serialization may cause that Chrome doesn't properly deliver the desired notifications the client.

chrome.send(method, [params], [callback])

Issue a command to Chrome.

method is a string describing the command.

params is an object containing the payload.

callback is executed when Chrome sends a response to this command, it gets the following arguments:

error: a boolean value indicating the success status, as reported by Chrome;
response: an object containing either the response sent from Chrome (result field, if error === false) or the indication of the error (error field, if error === true).

Note that the field id mentioned in the Remote Debugging Protocol specifications is managed internally and it's not exposed to the user.

For example:

chrome.send('Page.navigate', {'url': 'https://github.com'}, console.log);

chrome.`<domain>`.`<method>`([params], [callback])

Just a shorthand for:

chrome.send('<domain>.<method>', params, callback);

For example:

chrome.Page.navigate({'url': 'https://github.com'}, console.log);

chrome.`<domain>`.`<event>`(callback)

Just a shorthand for:

chrome.on('<domain>.<event>', callback);

For example:

chrome.Network.requestWillBeSent(console.log);

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