HTTP Cache

HTTP Cache Generator

Generate a production HTTP caching layer that integrates with your existing networking code. Supports Cache-Control directives, ETag/Last-Modified conditional requests, stale-while-revalidate, and offline fallback.

When This Skill Activates

Use this skill when the user:

• Asks to "add HTTP caching" or "cache API responses"
• Wants "offline support" or "offline fallback"
• Mentions "reduce API calls" or "cache network responses"
• Asks about "ETag" or "conditional requests" or "304 Not Modified"
• Wants "stale-while-revalidate" behavior

Pre-Generation Checks

1. Project Context Detection

• Check Swift version (requires Swift 5.9+)
• Check deployment target (iOS 16+ / macOS 13+)
• Search for existing caching implementations
• Identify source file locations

2. Networking Layer Detection

Search for existing networking code:

Glob: **/*API*.swift, **/*Client*.swift, **/*Network*.swift
Grep: "APIClient" or "URLSession" or "HTTPURLResponse"

If networking-layer generator was used, detect the APIClient protocol and generate a decorator that wraps it.

3. Conflict Detection

Search for existing caching:

Glob: **/*Cache*.swift
Grep: "URLCache" or "ResponseCache" or "CachePolicy"

If found, ask user whether to replace or extend.

Configuration Questions

Ask user via AskUserQuestion:

1. Cache storage sizes?

   • Small (10 MB memory / 50 MB disk)
   • Medium (25 MB memory / 100 MB disk) — recommended
   • Large (50 MB memory / 250 MB disk)

2. Caching strategy?

   • Respect server Cache-Control headers (standard)
   • Cache-first with background revalidation (stale-while-revalidate)
   • Manual per-endpoint policies

3. Offline support?

   • Yes — serve stale cache when network unavailable
   • No — only cache while online

4. Integration style?

   • Decorator wrapping existing APIClient (recommended if networking-layer exists)
   • Standalone cache you call directly

Generation Process

Step 1: Read Templates

Read http-cache-patterns.md for architecture guidance. Read templates.md for production Swift code.

Step 2: Create Core Files

Generate these files:

1. HTTPCacheConfiguration.swift — Memory/disk sizes, default policy
2. CachePolicy.swift — Per-endpoint enum (default, noCache, forceCache, cacheFirst)
3. CacheControlHeader.swift — Cache-Control header parser
4. ConditionalRequestHandler.swift — ETag/Last-Modified/304 handling
5. HTTPResponseCache.swift — Protocol + disk-backed response store

Step 3: Create Integration Files

Based on configuration:

• CachingAPIClient.swift — Decorator wrapping existing APIClient (if decorator style)
• NetworkReachability.swift — NWPathMonitor wrapper (if offline support selected)

Step 4: Determine File Location

Check project structure:

• If Sources/Networking/ exists → Sources/Networking/Cache/
• If App/Networking/ exists → App/Networking/Cache/
• If Networking/ exists → Networking/Cache/
• Otherwise → Cache/

Output Format

After generation, provide:

Files Created

Networking/Cache/
├── HTTPCacheConfiguration.swift    # Memory/disk sizes, default policy
├── CachePolicy.swift               # Per-endpoint caching enum
├── CacheControlHeader.swift        # Cache-Control header parser
├── ConditionalRequestHandler.swift # ETag/Last-Modified/304
├── HTTPResponseCache.swift         # Protocol + disk implementation
├── CachingAPIClient.swift          # Decorator for existing APIClient
└── NetworkReachability.swift       # NWPathMonitor (optional)

Integration Steps

Wrap your existing client:

let baseClient = URLSessionAPIClient(configuration: .production)
let cachingClient = CachingAPIClient(
    wrapping: baseClient,
    cache: DiskHTTPResponseCache(),
    configuration: .default
)

// Use cachingClient everywhere you used baseClient
let users = try await cachingClient.request(UsersEndpoint())

Per-endpoint cache policy:

struct UsersEndpoint: APIEndpoint, CacheConfigurable {
    var cachePolicy: CachePolicy { .cacheFirst(maxAge: 300) }
}

struct OrdersEndpoint: APIEndpoint, CacheConfigurable {
    var cachePolicy: CachePolicy { .noCache }
}

With SwiftUI:

struct UsersView: View {
    @Environment(\.apiClient) private var apiClient

    var body: some View {
        List(users) { user in
            Text(user.name)
        }
        .task {
            // Automatically uses cache if available
            users = try await apiClient.request(UsersEndpoint())
        }
    }
}

Testing

@Test
func cachedResponseReturnedOnSecondRequest() async throws {
    let mockClient = MockAPIClient()
    let cache = InMemoryHTTPResponseCache()
    let cachingClient = CachingAPIClient(wrapping: mockClient, cache: cache)

    mockClient.mockResponse(for: UsersEndpoint.self, response: [.mock])

    // First request hits network
    let first = try await cachingClient.request(UsersEndpoint())
    #expect(mockClient.requestCount == 1)

    // Second request comes from cache
    let second = try await cachingClient.request(UsersEndpoint())
    #expect(mockClient.requestCount == 1) // No additional network call
    #expect(first == second)
}

References

• http-cache-patterns.md — Cache-Control directives, ETag flow, stale-while-revalidate
• templates.md — All production Swift templates
• Related: generators/networking-layer — Base networking layer this decorates