Developing a browser app that uses an alternative browser engine

At a glance

Project structure

Source bundle/
└── BrowserExample/
    ├── BrowserApp/
    │   ├── AlertManager.swift
    │   ├── BrowserApp.swift
    │   ├── BrowserPageViewModel.swift
    │   ├── TabViewModel.swift
    │   └── BrowserPage.swift
    ├── NetworkingExtension/
    │   └── NetworkingExtension.swift
    ├── RenderingExtension/
    │   └── RenderingExtension.swift
    ├── WebContentExtension/
    │   └── WebContentExtension.swift
    └── CustomBrowserEngine/
        ├── UIProcess/
        │   ├── WebView.swift
        │   └── WebContentView.swift
        ├── XPC/
        │   └── XPCCodable.swift
        └── NetworkProcess/
            └── NetworkSession.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C/Objective-C header, Objective-C, Swift.
• The verified tree contains 14 project/configuration file(s) and 64 source declaration(s).

Overall architecture

flowchart LR
    N1["AlertManager"]
    N2["ContentView"]
    N3["BrowserPageViewModel"]
    N4["ServiceProvider"]
    N5["BrowserEngineKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

BrowserExample/BrowserApp/AlertManager.swift:48 — architecture anchor

 @main

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into BrowserEngineKit.

Ownership and state

classDiagram
    Alert *-- UUID : id
    Alert *-- String : title
    Alert *-- String : message
    Alert *-- Array : buttons

Ownership evidence

BrowserExample/BrowserApp/AlertManager.swift:13 — stored dependency or nearest verified ownership anchor

public struct Alert: Identifiable {
    // ...
  public var id = UUID()
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Class and protocol design

BrowserExample/CustomBrowserEngine/UIProcess/WebView.swift:23 — representative type boundary

public protocol WebViewUIDelegate: AnyObject {
  func webViewDidStartLoading(_ webView: WebView)
  func webViewDidStopLoading(_ webView: WebView)
}

The source explicitly defines local protocol relationships: BrowserExtensionTask → XPCCodable, WebContentExtensionTask → XPCCodable, WebContentExtensionBootstrapCommand → XPCCodable, HostingHandleMessage → XPCCodable, IOSurfaceMessage → XPCCodable, NetworkExtensionTask → XPCCodable.

Access control

Reference code

BrowserExample/BrowserApp/ActivityViewButton.swift:12 — representative boundary

private let log = Logger(subsystem: Constants.logSubsystem, category: String(describing: ActivityViewController.self))

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: App: BrowserApp, MyApp; Command: WebContentExtensionBootstrapCommand; Controller: ActivityViewController; Delegate: WebViewUIDelegate; Manager: AlertManager; Provider: ServiceProvider; Session: NetworkSession; View: ContentView, TabContentView, WebContentView, WebView.
• Protocols: WebViewUIDelegate, ServiceProvider, WebViewNavigationNelegate, XPCCodable, XPCEncodable, XPCDecodable.
• Methods: present, dismissCurrentAlert, body, makeActions, makeMessage, presentingAlerts, open, handle.
• Files: BrowserExample/BrowserApp/AlertManager.swift, BrowserExample/BrowserApp/BrowserApp.swift, BrowserExample/BrowserApp/BrowserPageViewModel.swift, BrowserExample/BrowserApp/TabViewModel.swift, BrowserExample/CustomBrowserEngine/UIProcess/WebView.swift, BrowserExample/BrowserApp/BrowserPage.swift.

Architecture takeaways

• AlertManager is the main source-visible entry or composition anchor for this sample.
• Framework work reaches XPC, BrowserEngineKit, CustomBrowserEngine, SwiftUI through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation