XMPP Real-Time Messaging Client

A high-performance, offline-first iOS XMPP chat client built from scratch using Swift Concurrency, SwiftUI, and SwiftData. Features a custom TCP socket layer bypassing legacy dependencies.

This project demonstrates a production-ready real-time messaging architecture, completely bypassing heavy legacy Objective-C dependencies like XMPPFramework. It features a custom NWConnection socket layer, a lightweight raw XML stream parser, end-to-end message encryption, and an offline-first sync engine.

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🚀 Key Features

• Custom XMPP Engine: Built purely in Swift using Network.framework (TCP sockets) and custom XMLParser handler. Manages full XMPP handshake including TLS upgrades (STARTTLS), SASL authentication (Plain), and resource binding.
• End-to-End Encryption (E2EE): Zero-trust message encryption using Apple's CryptoKit. P-256 Elliptic Curve Diffie-Hellman (ECDH) key agreement, HKDF-SHA256 key derivation, and AES-GCM-256 payload sealing with dynamic public key exchange via presence stanzas (<e2ee-pubkey>).
• Secure Enclave Storage: Hardware-backed private key generation (kSecAttrAccessibleWhenUnlockedThisDeviceOnly) with Keychain fallback for iOS Simulators.
• Offline-First Architecture: Powered by SwiftData. Messages and roster contacts are persisted locally before transmission, ensuring zero data loss during network disconnects. The UI reads exclusively from the local cache.
• Real-Time Presence & Status: Live bidirectional presence tracking (Available, Away, Offline) with automated roster subscription handling and typing indicators.
• Media & Image Sharing: Built-in XEP-0363 HTTP File Upload support for sending images over TLS with async upload progress indicators.
• Modern Concurrency & Architecture: Built with Swift Concurrency (async/await, Task, Sendable, @Observable), decoupled clean MVVM pattern, and dependency injection.

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🛠 Tech Stack & Standards

• UI & UX: SwiftUI (iOS 17+), custom dark-mode glassmorphic design system.
• Concurrency: Swift 5.10 / 6 ready Concurrency (async/await, Task, MainActor, Sendable).
• Cryptography & Security: CryptoKit, Security.framework (Keychain), Secure Enclave.
• Persistence: SwiftData (ModelContainer, @Model).
• Networking: Network.framework (NWConnection), custom XML stream parser.
• XMPP & XEP Specifications:
  • RFC 6120: XMPP Core (Stream management, TLS, SASL)
  • RFC 6121: XMPP Instant Messaging & Presence (Roster management)
  • XEP-0363: HTTP File Upload (Media attachment delivery)
  • E2EE Extension: Custom <e2ee-pubkey> and <e2ee> stanza payload extension.

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📱 Screenshots

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🧠 Architecture Highlights

1. The Real-Time Engine (XMPPManager)

Maintains a persistent background TCP socket via Network.framework. Incoming XML fragments are streamed through an event-driven parser. When <iq>, <presence>, or <message> stanzas arrive, they are parsed into strongly-typed Swift models and handled asynchronously without blocking the UI.

2. End-to-End Encryption Engine (CryptoService)

Upon authenticating, the client advertises its ECDH P-256 public key over XMPP presence. When sending a chat message, CryptoService derives an ephemeral symmetric key via HKDF SHA-256 from the recipient's public key and encrypts the plaintext payload using AES-GCM-256.

3. Data Synchronization (MessageStore & RosterStore)

Local-first strategy. Messages are immediately saved to SwiftData and rendered in the view, while background tasks manage XMPP network delivery. If network connectivity drops, outbound updates queue gracefully.

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🧪 Testing & Quality Assurance

The codebase includes an automated unit test suite covering critical layers:

• CryptoServiceTests: Validates ECDH key agreement, public key derivation, and AES-GCM encryption/decryption round-trips.
• XMPPStanzaTests: Verifies XML serialization/parsing for core stanzas, presence updates, and <e2ee> encrypted payloads.
• XMPPStreamParserTests: Validates chunked TCP data buffering and XML stream parsing edge cases.
• AuthViewModelTests & ConversationListViewModelTests: Tests authentication validation and view model state handling.
• MessageStoreTests: Tests SwiftData query filtering and message history persistence.

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🚀 Getting Started

1. Clone the repository:

   git clone https://github.com/username/XMPPDemo.git
   cd XMPPDemo

2. Run a local XMPP Server (ejabberd):

   brew install ejabberd
   ejabberdctl start
   ejabberdctl register alice localhost password123
   ejabberdctl register bob localhost password123

3. Build & Run: Open XMPPDemo.xcodeproj in Xcode 15+ and run on two iOS 17+ Simulators.

4. Login & Chat: Sign in as alice@localhost on Simulator 1 and bob@localhost on Simulator 2 to experience real-time messaging, presence sync, and E2EE encryption.

Local Image Upload Setup (XEP-0363)

To test HTTP image uploads locally with ejabberd:

openssl req -x509 -newkey rsa:2048 -nodes \
  -keyout /opt/homebrew/etc/ejabberd/localhost.pem \
  -out /opt/homebrew/etc/ejabberd/localhost.pem \
  -days 3650 -subj "/CN=localhost" \
  -addext "subjectAltName=DNS:localhost,DNS:upload.localhost,IP:127.0.0.1,IP:::1"

Add the certificate path to your ejabberd.yml:

certfiles:
  - /opt/homebrew/etc/ejabberd/localhost.pem

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📝 License

This project is created for demonstration and portfolio purposes.