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Wails v3 iOS Architecture

Executive Summary

This document provides a comprehensive technical architecture for iOS support in Wails v3. The implementation enables Go applications to run natively on iOS with a WKWebView frontend, maintaining the Wails philosophy of using web technologies for UI while leveraging Go for business logic.

Table of Contents

  1. Architecture Overview
  2. Core Components
  3. Layer Architecture
  4. Implementation Details
  5. Battery Optimization
  6. Build System
  7. Security Considerations
  8. API Reference

Architecture Overview

Design Principles

  1. Battery Efficiency First: All architectural decisions prioritize battery life
  2. No Network Ports: Asset serving happens in-process via native APIs
  3. Minimal WebView Instances: Maximum 2 concurrent WebViews (1 primary, 1 for transitions)
  4. Native Integration: Deep iOS integration using Objective-C runtime
  5. Wails v3 Compatibility: Maintain API compatibility with existing Wails v3 applications

High-Level Architecture

┌─────────────────────────────────────────────────────────────┐
│                     iOS Application                          │
├─────────────────────────────────────────────────────────────┤
│                    UIKit Framework                           │
│  ┌─────────────────────────────────────────────────────┐   │
│  │              WailsViewController                     │   │
│  │  ┌───────────────────────────────────────────────┐  │   │
│  │  │            WKWebView Instance                  │  │   │
│  │  │  ┌─────────────────────────────────────────┐  │  │   │
│  │  │  │         Web Application (HTML/JS)        │  │  │   │
│  │  │  └─────────────────────────────────────────┘  │  │   │
│  │  └───────────────────────────────────────────────┘  │   │
│  └─────────────────────────────────────────────────────┘   │
├─────────────────────────────────────────────────────────────┤
│                  Bridge Layer (CGO)                          │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐     │
│  │URL Handler   │  │JS Bridge     │  │Message Handler│     │
│  └──────────────┘  └──────────────┘  └──────────────┘     │
├─────────────────────────────────────────────────────────────┤
│                    Go Runtime                                │
│  ┌──────────────────────────────────────────────────────┐  │
│  │                 Wails Application                     │  │
│  │  ┌──────────┐  ┌──────────┐  ┌──────────────────┐  │  │
│  │  │App Logic │  │Services  │  │Asset Server      │  │  │
│  │  └──────────┘  └──────────┘  └──────────────────┘  │  │
│  └──────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────┘

Core Components

1. Platform Layer (application_ios.go)

Purpose: Go interface for iOS platform operations

Key Functions:

  • platformRun(): Initialize and run the iOS application
  • platformQuit(): Gracefully shutdown the application
  • isDarkMode(): Detect iOS dark mode state
  • ExecuteJavaScript(windowID uint, js string): Execute JS in WebView

Exported Go Functions (Called from Objective-C):

  • ServeAssetRequest(windowID C.uint, urlStr *C.char, callbackID C.uint)
  • HandleJSMessage(windowID C.uint, message *C.char)

2. Native iOS Layer (application_ios.m)

Components:

WailsSchemeHandler

@interface WailsSchemeHandler : NSObject <WKURLSchemeHandler>
  • Implements WKURLSchemeHandler protocol
  • Intercepts wails:// URL requests
  • Bridges to Go for asset serving
  • Manages pending requests with callback IDs

Methods:

  • startURLSchemeTask:: Intercept request, call Go handler
  • stopURLSchemeTask:: Cancel pending request
  • completeRequest:withData:mimeType:: Complete request with data from Go

WailsMessageHandler

@interface WailsMessageHandler : NSObject <WKScriptMessageHandler>
  • Implements JavaScript to Go communication
  • Handles window.webkit.messageHandlers.external.postMessage()
  • Serializes messages to JSON for Go processing

Methods:

  • userContentController:didReceiveScriptMessage:: Process JS messages

WailsViewController

@interface WailsViewController : UIViewController
  • Main view controller containing WKWebView
  • Manages WebView lifecycle
  • Handles JavaScript execution requests

Properties:

  • webView: WKWebView instance
  • schemeHandler: Custom URL scheme handler
  • messageHandler: JS message handler
  • windowID: Unique window identifier

Methods:

  • viewDidLoad: Initialize WebView with configuration
  • executeJavaScript:: Run JS code in WebView

3. Bridge Layer (CGO)

C Interface Functions:

void ios_app_init(void);                    // Initialize iOS app
void ios_app_run(void);                     // Run main loop
void ios_app_quit(void);                    // Quit application
bool ios_is_dark_mode(void);                // Check dark mode
unsigned int ios_create_webview(void);      // Create WebView
void ios_execute_javascript(unsigned int windowID, const char* js);
void ios_complete_request(unsigned int callbackID, const char* data, const char* mimeType);

Layer Architecture

Layer 1: Presentation Layer (WebView)

Responsibilities:

  • Render HTML/CSS/JavaScript UI
  • Handle user interactions
  • Communicate with native layer

Key Features:

  • WKWebView for modern web standards
  • Hardware-accelerated rendering
  • Efficient memory management

Layer 2: Communication Layer

Request Interception:

WebView Request → WKURLSchemeHandler → Go ServeAssetRequest → AssetServer → Response

JavaScript Bridge:

JS postMessage → WKScriptMessageHandler → Go HandleJSMessage → Process → ExecuteJavaScript

Layer 3: Application Layer (Go)

Components:

  • Application lifecycle management
  • Service binding and method calls
  • Asset serving from embedded fs.FS
  • Business logic execution

Layer 4: Platform Integration Layer

iOS-Specific Features:

  • Dark mode detection
  • System appearance integration
  • iOS-specific optimizations

Implementation Details

Request Handling Flow

  1. WebView makes request to wails://localhost/path
  2. WKURLSchemeHandler intercepts request
  3. Creates callback ID and stores WKURLSchemeTask
  4. Calls Go function ServeAssetRequest with URL and callback ID
  5. Go processes request through AssetServer
  6. Go calls ios_complete_request with response data
  7. Objective-C completes the WKURLSchemeTask with response

JavaScript Execution Flow

  1. Go calls ios_execute_javascript with JS code
  2. Bridge dispatches to main thread
  3. WKWebView evaluates JavaScript
  4. Completion handler logs any errors

Message Passing Flow

  1. JavaScript calls window.webkit.messageHandlers.wails.postMessage(data)
  2. WKScriptMessageHandler receives message
  3. Serializes to JSON and passes to Go
  4. Go processes message in HandleJSMessage
  5. Go can respond via ExecuteJavaScript

Battery Optimization

WebView Configuration

// Disable unnecessary features
config.suppressesIncrementalRendering = NO;
config.allowsInlineMediaPlayback = YES;
config.mediaTypesRequiringUserActionForPlayback = WKAudiovisualMediaTypeNone;

Memory Management

  1. Single WebView Instance: Reuse instead of creating new instances
  2. Automatic Reference Counting: Use ARC for Objective-C objects
  3. Lazy Loading: Initialize components only when needed
  4. Resource Cleanup: Properly release resources when done

Request Optimization

  1. In-Process Serving: No network overhead
  2. Direct Memory Transfer: Pass data directly without serialization
  3. Efficient Caching: Leverage WKWebView's built-in cache
  4. Minimal Wake Locks: No background network activity

Build System

Build Tags

//go:build ios

CGO Configuration

#cgo CFLAGS: -x objective-c -fobjc-arc
#cgo LDFLAGS: -framework Foundation -framework UIKit -framework WebKit

Build Script (build_ios.sh)

Steps:

  1. Check dependencies (go, xcodebuild, xcrun)
  2. Set up iOS cross-compilation environment
  3. Build Go binary with iOS tags
  4. Create app bundle structure
  5. Generate Info.plist
  6. Sign for simulator
  7. Create launch script

Environment Variables:

export CGO_ENABLED=1
export GOOS=ios
export GOARCH=arm64
export SDK_PATH=$(xcrun --sdk iphonesimulator --show-sdk-path)

Simulator Deployment

xcrun simctl install "$DEVICE_ID" "WailsIOSDemo.app"
xcrun simctl launch "$DEVICE_ID" "com.wails.iosdemo"

Security Considerations

URL Scheme Security

  1. Custom Scheme: Use wails:// to avoid conflicts
  2. Origin Validation: Only serve to authorized WebViews
  3. No External Access: Scheme handler only responds to app's WebView

JavaScript Execution

  1. Input Validation: Sanitize JS code before execution
  2. Sandboxed Execution: WKWebView provides isolation
  3. No eval(): Avoid dynamic code evaluation

Data Protection

  1. In-Memory Only: No temporary files on disk
  2. ATS Compliance: App Transport Security enabled
  3. Secure Communication: All data stays within app process

API Reference

Go API

Application Functions

// Create new iOS application
app := application.New(application.Options{
    Name: "App Name",
    Description: "App Description",
})

// Run the application
app.Run()

// Execute JavaScript
app.ExecuteJavaScript(windowID, "console.log('Hello')")

Service Binding

type MyService struct{}

func (s *MyService) Greet(name string) string {
    return fmt.Sprintf("Hello, %s!", name)
}

app := application.New(application.Options{
    Services: []application.Service{
        application.NewService(&MyService{}),
    },
})

JavaScript API

Send Message to Go

window.webkit.messageHandlers.wails.postMessage({
    type: 'methodCall',
    service: 'MyService',
    method: 'Greet',
    args: ['World']
});

Receive from Go

window.wailsCallback = function(data) {
    console.log('Received:', data);
};

Objective-C Bridge API

From Go to Objective-C

// Execute JavaScript
ios_execute_javascript(windowID, "alert('Hello')");

// Complete asset request
ios_complete_request(callbackID, htmlData, "text/html");

From Objective-C to Go

// Serve asset request
ServeAssetRequest(windowID, urlString, callbackID);

// Handle JavaScript message
HandleJSMessage(windowID, jsonMessage);

Performance Metrics

Target Metrics

  • WebView Creation: < 100ms
  • Asset Request: < 10ms for cached, < 50ms for first load
  • JS Execution: < 5ms for simple scripts
  • Message Passing: < 2ms round trip
  • Memory Usage: < 50MB baseline
  • Battery Impact: < 2% per hour active use

Monitoring

  1. Xcode Instruments: CPU, Memory, Energy profiling
  2. WebView Inspector: JavaScript performance
  3. Go Profiling: pprof for Go code analysis

Future Enhancements

Phase 1: Core Stability

  • Production-ready error handling
  • Comprehensive test suite
  • Performance optimization

Phase 2: Feature Parity

  • Multiple window support
  • System tray integration
  • Native menu implementation

Phase 3: iOS-Specific Features

  • Widget extension support
  • App Clip support
  • ShareSheet integration
  • Siri Shortcuts

Phase 4: Advanced Features

  • Background task support
  • Push notifications
  • CloudKit integration
  • Apple Watch companion app

Conclusion

This architecture provides a solid foundation for iOS support in Wails v3. The design prioritizes battery efficiency, native performance, and seamless integration with the existing Wails ecosystem. The proof of concept demonstrates all four required capabilities:

  1. ✅ WebView Creation: Native WKWebView with optimized configuration
  2. ✅ Request Interception: Custom scheme handler without network ports
  3. ✅ JavaScript Execution: Bidirectional communication bridge
  4. ✅ iOS Simulator Support: Complete build and deployment pipeline

The architecture is designed to scale from this proof of concept to a full production implementation while maintaining the simplicity and elegance that Wails developers expect.