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Structure of Layered Components Within the Chromium Codebase

The purpose of this document is to describe the structure of layered components and iOS code within the Chromium source tree. This document assumes the context of the accompanying high-level design and technical strategy documents.

Overview


There will be a new top-level directory, ios/. This directory will contain the following:

  • web/: iOS’s src/content/ equivalent

  • chrome/: iOS’s src/chrome equivalent

  • provider/: the API via which Chromium code will call downstream iOS code

  • consumer/: the API via which downstream iOS code will call Chromium code


Each layered component will be divided as follows:

  • core/: shared code that is src/content/- and src/ios/-free.

  • content/: Content-based driver for the component.

  • ios/: Driver for the component based on src/ios/web/ and src/ios/embed/web/.


For components that are multi-process (i.e., currently have browser/, renderer/, etc. subdirectories), the process division will move to be under the content/ driver (since Chrome for iOS is single-process and almost never uses Chromium code that is not browser-process code).

Detailed Example/Discussion of DEPS Rules

Autofill-Focused Example


The below example indicates a structure for form autofill wherein:

  • content- or ios-specific code detects that a form is being rendered

  • core code determines whether there is data with which to fill the form

  • content- or ios-specific code renders the data


Additionally, we assume that key components of the iOS flow (its WebContents-like object and the object that renders autofill data) are implemented downstream and exposed to upstream code via the embed layer, which will indeed be the case for some amount of time.


Structure under components/autofill/:


  • core/

    • AutofillManager interface/impl

    • AutofillDriver interface

  • content/

    • browser/

      • AutofillDriverImpl

        • Listens for IPC from the renderer to know when a form is rendered and call into AutofillManager

        • Receives OnFormDataFilled calls from AutofillManager and sends IPC, which is caught by the renderer

    • renderer/

  • ios/

    • AutofillDriverIOS

      • Observes WebState to know when a form is rendered and call into AutofillManager

      • Receives OnFormDataFilled calls from AutofillManager and asks AutofillDriverBridge to render the data


Structure under ios/:


  • web/ (upstream impl code of the web layer)

  • chrome/ (startup, glue code, etc.)

  • provider/

    • web/ (interfaces that downstream code provides to the web layer)

      • WebState interface (WebContents-like object)

    • components/

      • autofill/

        • AutofillDriverBridge interface

          • RenderDataForForm()

  • consumer/

    • components/

      • autofill/ (Wrapper API for downstream code to call into autofill)

DEPS Rules


  • ios/foo can depend on ios/provider/foo

    • Purpose of ios/provider/foo is for foo (and higher layers) to use it

  • ios/provider/foo can depend only on lower-layer consumer/ targets

    • Might need lower-level consumer API to pass parameters to downstream code

  • ios/consumer/foo will depend on ios/foo (which can’t depend on ios/consumer/foo)

  • components/foo/ios can depend only on ios/web, ios/provider/web, and lower layers

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