# CLAUDE.md

Guidance for Claude Code when working in this repository.

## Project

**ProxyApp** — on-device iOS HTTP/HTTPS proxy with MITM decryption, inspired by Proxyman/Charles. Runs a SwiftNIO proxy inside a `NEPacketTunnelProvider` so the app can intercept its own device's traffic without a computer.

- Min iOS: 17.0
- Swift: 6.0 (PacketTunnel target is Swift 5 — NEPacketTunnelProvider Sendable issues)
- Strict concurrency: complete
- Device families: iPhone + iPad

## Build

The Xcode project is generated by **xcodegen** from `project.yml`. Do not hand-edit `ProxyApp.xcodeproj/project.pbxproj`.

```sh
xcodegen generate          # regenerate project after editing project.yml or adding files
xcodebuild -scheme ProxyApp -destination 'generic/platform=iOS Simulator' build
```

Scheme: `ProxyApp` (builds ProxyApp + PacketTunnel + ProxyCore).

## Targets

| Target | Type | Notes |
|--------|------|-------|
| `ProxyApp` | iOS app | SwiftUI UI, hosts the PacketTunnel extension |
| `PacketTunnel` | App extension | `NEPacketTunnelProvider` — sets up proxy network settings, runs ProxyServer |
| `ProxyCore` | Static framework (`MACH_O_TYPE: staticlib`) | Shared code used by app + extension |

Both processes share `group.com.treyt.proxyapp` App Group for the SQLite DB, CA material, and IPC.

## Layout

```
App/                         ProxyApp target (SwiftUI entry + app state)
  ContentView.swift          Adaptive: TabView on iPhone, NavigationSplitView on iPad
  AppState.swift             VPN control, lock state, top-level observable
PacketTunnel/                Packet tunnel extension (just wires up ProxyServer)
ProxyCore/Sources/
  ProxyEngine/               SwiftNIO pipeline
    ProxyServer.swift        ServerBootstrap on 127.0.0.1, HTTP/CONNECT parser
    ConnectHandler.swift     CONNECT tunnel + plain HTTP forwarding + auto-pin fallback
    MITMHandler.swift        SNI sniff → leaf cert → NIOSSLServerHandler → decrypted pipeline
    HTTPCaptureHandler.swift Parses decrypted HTTP, writes to TrafficRepository
    GlueHandler.swift        Bidirectional channel glue (local <-> remote)
    CertificateManager.swift Root CA + leaf cert generation/LRU cache
    RulesEngine.swift        Block / SSL-proxy / map-local / DNS spoof / breakpoint matching
  DataLayer/
    Database/DatabaseManager.swift  GRDB pool in App Group container
    Repositories/*Repository.swift  All DB access goes through these
    Models/*.swift                  GRDB record structs
  Shared/
    IPCManager.swift                Darwin notifications between app & extension
    NotificationThrottle.swift      Rate-limits Darwin notifications (0.5s floor)
    AppGroupPaths.swift             Centralized container URLs
    ProxyLogger.swift               os.Logger per subsystem (tunnel/proxy/mitm/cert/db/ipc/ui…)
    HTTPBodyDecoder.swift           gzip/br body decoding
    CURLParser.swift, WildcardMatcher.swift, SystemTrafficFilter.swift
UI/
  Home/                      Live traffic list (GRDB ValueObservation + Darwin refresh)
  Pin/                       Pinned domains view
  Compose/                   Request composer (curl import, editor, history)
  More/                      Cert install, rule lists, settings, setup guide
  SharedComponents/          JSONTreeView, HexView, FilterChipsView, badges, etc.
```

## How the proxy works

1. User enables VPN → `PacketTunnelProvider.startTunnel` is called.
2. Provider sets `NEProxySettings` to route all traffic to `127.0.0.1:<port>`. **No DNS settings** — adding DNS breaks the tunnel.
3. Provider spins up `ProxyServer` (SwiftNIO `ServerBootstrap`) on that port.
4. Each incoming connection goes through:
   - HTTP parser → plain HTTP: forward via `ConnectHandler`, capture via `HTTPCaptureHandler`
   - CONNECT → check rules: passthrough (tunnel bytes) or MITM (decrypt)
5. MITM path: sniff SNI from ClientHello → `CertificateManager.tlsServerContext(for:)` → `NIOSSLServerHandler` → decrypted HTTP parser → `HTTPCaptureHandler` → upstream via a second NIO client with `NIOSSLClientHandler`.
6. **Auto-pinning**: If TLS handshake fails on a domain being MITM'd, `TLSErrorLogger` (inside `MITMHandler`) records the domain in `pinned_domains` and next time it goes to passthrough. This is how SSL-pinned apps stop breaking.

## Certificate install flow

`CertificateView` runs a tiny `Network.framework` `NWListener` on localhost serving the root CA as `application/x-x509-ca-cert`, then opens Safari to `http://localhost:PORT/ProxyCA.cer`. This triggers the iOS profile installation flow. The CA lives in the App Group container, not Keychain.

## Data flow / IPC

- App and extension both open the same GRDB pool at `AppGroupPaths.databaseURL`.
- Extension writes traffic → `IPCManager.shared.post(.newTrafficCaptured)` (throttled) → app's `HomeView` observes via `IPCManager.observe(...)` and refreshes its GRDB `ValueObservation`.
- Config changes from the app (rules, SSL list, block list) → post `.configurationChanged` → extension reloads `RulesEngine` snapshot.
- **Wrap all Darwin notification callbacks in `DispatchQueue.main.async`** before touching `@State`. Not doing this crashes the app.

## Logging

Use `ProxyLogger` (os.Logger wrapper) — never `print`. Pick the right subsystem:

```swift
ProxyLogger.tunnel.info("...")  // PacketTunnelProvider
ProxyLogger.proxy.info("...")   // ProxyServer setup
ProxyLogger.connect.info("...") // ConnectHandler
ProxyLogger.mitm.info("...")    // MITMHandler
ProxyLogger.capture.info("...") // HTTPCaptureHandler
ProxyLogger.cert.info("...")    // CertificateManager
ProxyLogger.rules.info("...")   // RulesEngine
ProxyLogger.db.info("...")      // DB layer
ProxyLogger.ipc.info("...")     // IPC
ProxyLogger.ui.info("...")      // SwiftUI
```

View extension logs: `/axiom:console` (xclog) or Console.app filtering on subsystem `com.treyt.proxyapp`.

## Conventions

- **All DB access goes through a repository.** No `dbPool.read` in UI code.
- **Never `try!` / `!` force-unwrap** in proxy pipeline code — crashes the extension and kills the whole VPN.
- **Use `Color.accentColor` / `Color.primary`**, not `.accentColor` (ShapeStyle ambiguity errors).
- **iPad adaptation**: check `horizontalSizeClass == .regular` in `ContentView` — do not create iPad-only views, adapt existing ones.
- **No force-adding features without being asked.** This codebase already has half-stubbed features (breakpoints, WebSocket capture, image preview toggle) — leave them alone unless the request is about them.
- **No print/NSLog.** Use `ProxyLogger`.
- **No new files unless needed.** Prefer extending existing repositories/views.

## When adding a source file

Add it under the appropriate target's source directory and regenerate:
```sh
xcodegen generate
```
`project.yml` uses directory globs — you don't edit it, you just drop the file in `App/`, `UI/`, `ProxyCore/Sources/...`, or `PacketTunnel/`.

## Gotchas

- **Clean builds fail with "No such module NIOCore"** → derived data is stale. Delete `~/Library/Developer/Xcode/DerivedData/ProxyApp-*` and rebuild.
- **dyld "Library not loaded: ProxyCore.framework"** → ProxyCore must stay `staticlib`; if you change `MACH_O_TYPE`, update the app/extension embed settings.
- **VPN starts but no traffic** → check for DNS settings in `PacketTunnelProvider`. There should be none.
- **Swift 6 concurrency errors in PacketTunnel** → that target is pinned to Swift 5 on purpose. Don't "upgrade" it.
- **`xcuserstate` modified in every commit** → it's now gitignored; if it shows up again, re-add the pattern.

## Airline research project

There is a separate project at `~/Desktop/code/flights` that uses Frida hooks to capture airline API traffic. It is **not** part of this repo. The proxy app is the user-facing version of the same idea (MITM instead of Frida).