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Collecting Page Details

The first step in the Autofill process is to collect what are referred to as the "Page Details" in the codebase. The Page Details are an array of metadata about the page source of the current browser tab.

Because it needs access to the DOM of the tab, the collection of the Page Details must be performed by a content script. The Bitwarden browser extension performs this through the CollectAutofillContentService that is initialized in the autofill-init.ts content script. The logic in this class is responsible for parsing the page DOM and returning a data structure that represents the Page Details of the current tab.

Page Details

For in-depth knowledge of what is contained in the Page Details, the AutofillPageDetails TypeScript class is documented to explain the properties and their purposes.

Requesting page detail collection

Page detail collection can be requested from other content scripts or from the extension itself.

Requesting page details in the background

Page detail collection is requested from content script in two cases:

  • The notificationBar.js content script detects that the page DOM or URL has changed, or
  • The user has Autofill on Page Load turned on, so autofiller.js requests autofill on page load

In both of these cases, page detail collection is handled as follows:

  1. The requesting content script sends the bgCollectPageDetails command to communicate the request to the runtime.background.ts background page.
  2. The runtime.background.ts page calls the collectPageDetailsForContentScript method on main.background.ts.
  3. The collectPageDetailsForContentScript method sends a message with command collectPageDetails to the autofill-init.ts content script.
  4. The autofill-init.ts content script generates the page details and broadcasts a collectPageDetailsResponse message with a sender of either autofiller or notificationBar.
  5. The runtime.background.js and notification.background.js are listening for these two messages, respectively, and will act upon them.

These flows are diagrammed below:

Autofill on Page Load


Notification Bar


Requesting page details from context menu

Bitwarden extension users have the ability to trigger Autofill from the context menu by right-clicking on the page and selecting "Bitwarden / Autofill", then picking a vault item from the items matching the current page URI.

When the user selects an item on the context menu, the browser contextMenu.OnClicked() event is fired. This event is handled by the contextMenus.background.js background page. The page issues a collectPageDetails command with a contextMenus sender. The autofill-init.ts content script catches this request and issues a collectPageDetailsResponse with a sender of contextMenus when complete, which is handled by the runtime.background.js background page.


Requesting page details on keyboard shortcut

The keyboard shortcut for the Bitwarden Autofill is configured in the manifest.json and manifest.v3.json files, for Manifest v2 and v3, respectively. The command is defined in the manifest files as autofill_login. When the user initiates that key combination, the browser command is broadcast to all listeners. This behavior is detailed here.

Manifest v2

In a browser extension running Manifest v2, the commands.background.ts background page is listening for the autofill_login command. This background page executes the collectPageDetailsForContentScript() method on main.background.js, which broadcasts the collectPageDetails message to the autofill-init.ts content script.

After generating the page details, the autofill-init.ts content script broadcasts a collectPageDetailsResponse message with an autofill_cmd sender. The runtime.background.js background page is listening for this message and receives it.


Manifest v3

For browser extensions running Manifest v3, the background pages are replaced with the commandListener. The commandListener is listening for the autofill_login command, and it responds by broadcasting the collectPageDetailsImmediately command.

The collectPageDetailsImmediately is different from the collectPageDetails command, in that the response is not another message broadcast through the browser command API. Instead, the autofill-init.ts content script performs the page details generation and returns the response asynchronously through a Promise.


Requesting page details from the extension UI

There are two ways that a user can request an autofill from the Bitwarden browser extension UI:

  • Clicking the Autofill button when viewing an item in their vault (view.component.ts), or
  • Clicking on a vault item on the Current Tab view (current-tab.component.ts)

In both of these cases, the component issues a collectPageDetails command with the extension instance's unique BroadcasterSubscriptionId as the sender. The autofill-init.ts content script generates the page details and responds with a collectPageDetailsResponse message with the same sender, ensuring that the message is received properly by the correct sender.


Performing the collection of the page details

In all the scenarios above, the autofill-init.ts content script receives a request to collect page details. When this occurs, the collection of the page details takes place through the getPageDetails() method of the CollectAutofillContentService.

The getPageDetails() method parses the page DOM and creates an instance of the AutofillPageDetails class.

This class contains arrays of AutofillField and AutofillForm objects, each of which represents a potentially fillable field on the page source. The properties on the objects are used in the next step of the Autofill process, 'Generating the Fill Scripts'.