Structure of Layered Components and iOS Code 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
***\[On hold:** Due to the significant flux with componentization and
upstreaming, it's not yet clear which code will actually need consumer APIs,
so for now this is not enforced and does not need to be built out
further.\]*

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