Offline Protocol SDK

Offline-first messaging protocol with intelligent multi-transport switching, mesh networking, and automatic end-to-end encryption

Dual-licensed: use it under AGPL-3.0-only, or buy a commercial license, your call — see the License section for the full breakdown.

Features

• Multi-Transport: Automatically switches between BLE, WiFi Direct, Internet, Reticulum, and Nostr relays
• Mesh Networking: Automatic peer discovery and message relay
• End-to-End Encryption: Automatic MLS encryption with forward secrecy (RFC 9420)
• Group Roles: Admin/member role management with last-admin safety invariants
• DORS: Dynamic Offline Relay Switch for optimal transport selection
• Reliability: ACKs, retries, and deduplication built-in
• Cross-Platform Bindings: React Native for iOS/Android and Python for macOS/Linux/Windows

What you must implement: the Rust crates are I/O-free protocol engines — they queue, route, encrypt, and select transports, but never open a socket or touch a radio. A platform bridge does the actual I/O: it drains each transport's outbound queue, performs the send, reports the outcome, and injects inbound bytes. The React Native binding ships these bridges for iOS and Android (BLE, WiFi Direct, Internet, Nostr, Reticulum), and the Python binding ships BLE and Internet bridges. If you consume the Rust crates directly via cargo add, you write the bridge yourself — the contract is documented in the offline-protocol-transport crate docs.

Quick Start

For React Native Apps

npm install @offline-protocol/mesh-sdk

import { OfflineProtocol, MessagePriority } from '@offline-protocol/mesh-sdk';

const protocol = new OfflineProtocol({
  appId: 'my-app',
  profile: 'user123',
  // Encryption is enabled by default!
});

await protocol.start();

// Initialize MLS encryption (required once)
await protocol.initializeMlsWithSecureStorage();

// Messages are automatically encrypted!
const messageId = await protocol.sendMessage({
  recipient: 'recipient456',
  content: 'Hello!',  // Automatically encrypted
  priority: MessagePriority.Medium,
});

For Python Desktop Apps

The Python binding supports macOS, Linux, and Windows. Build and install it from the repository:

cd bindings/python
bash scripts/build-desktop.sh
pip install -e .

from offline_protocol_sdk import ProtocolManager
from offline_protocol_sdk.offline_protocol import ProtocolConfig, OverflowPolicy

config = ProtocolConfig(
    app_id="my-app",
    profile="user123",
    ble_enabled=False,
    wifi_direct_enabled=False,
    internet_enabled=True,
    reticulum_enabled=False,
    nostr_enabled=False,
    prefer_online=True,
    initial_ttl=8,
    encryption_enabled=True,
    auto_key_exchange=True,
    store_pending=True,
    require_encryption=False,
    max_pending_per_peer=64,
    max_pending_global=4096,
    pending_ttl_ms=1_800_000,  # 30 min — matches the SDK default
    overflow_policy=OverflowPolicy.DROP_OLDEST,
)
protocol = ProtocolManager(
    config,
    # Must be removed by the application uninstaller.
    state_root="/app/install-owned-data/offline-protocol",
)

See the Python binding guide for transport setup, secure storage, and complete lifecycle examples.

Encryption Configuration

Encryption is fail-closed by default: if a message cannot be encrypted (e.g. MLS was never initialized), the send fails with a typed error instead of silently falling back to plaintext. Messages to peers whose secure session is still being established are queued and delivered encrypted once it is ready.

const protocol = new OfflineProtocol({
  appId: 'my-app',
  profile: 'user123',
  encryption: {
    enabled: true,           // Auto-encrypt (default)
    autoKeyExchange: true,   // Exchange keys on peer discovery (default)
    storePending: true,      // Queue messages until session ready (default)
    requireEncryption: true, // Fail closed, never silent plaintext (default)
  },
});

To deliberately operate in plaintext (e.g. an open-broadcast mesh with no provisioned key storage), opt out explicitly with requireEncryption: false — each plaintext send then emits a security_warning event with the PLAINTEXT_SEND reason code (once per peer).

Building the SDK

Prerequisites

• Rust (via rustup)
• uniffi-bindgen: cargo install uniffi --version 0.30.0 --features cli --locked (must match the workspace uniffi = "0.30" pin)
• For Android: the Android NDK (set ANDROID_NDK_HOME); for iOS: Xcode

Build Mobile UniFFI Libraries

cd bindings/react-native

# Build for all platforms
npm run build:uniffi:all

# Or build individually
npm run build:uniffi:ios      # iOS only
npm run build:uniffi:android  # Android only

Regenerate Bindings After a UDL Change

./scripts/generate-bindings.sh

One script generates all three languages — Swift, Kotlin and Python — because they are one artifact set produced from one UDL and carry the FFI checksums of the library they were generated against. Regenerating a subset leaves the rest describing a different ABI, which no build catches; the app fails at the first call instead. npm run generate:bindings and the platform build scripts delegate here, so every path produces the whole set. Commit all three together.

Build Python Desktop Bindings

cd bindings/python
bash scripts/build-desktop.sh

The desktop build produces the native .dylib, .so, or .dll for the host platform and regenerates the bindings (all three languages, via the shared script above).

Architecture

The SDK consists of modular Rust crates:

• offline-protocol-core - Core types and data structures
• offline-protocol-transport - Multi-transport abstraction (BLE, WiFi, Internet, Reticulum, Nostr)
• offline-protocol-router - DORS routing and relay management
• offline-protocol-reliability - ACKs, retries, deduplication
• offline-protocol-mls - End-to-end encryption using MLS (RFC 9420)
• offline-protocol-services - Service discovery and request/response over mesh
• offline-protocol - Main protocol engine with auto-encryption
• offline-protocol-uniffi - UniFFI bindings for Swift/Kotlin

DORS: Dynamic Offline Relay Switch

DORS automatically selects and switches between Internet, BLE Mesh, Wi-Fi Direct, Reticulum, and Nostr based on real-time network conditions. It scores each transport on signal strength, proximity, bandwidth, congestion, energy efficiency, reliability, and available capacity, then applies hysteresis, cooldown, and stability checks to prevent flapping.

For details, see the DORS Deep Dive and DORS Configuration Guide.

Mesh Networking

The SDK implements a cluster-based, self-organizing mesh network. Devices discover peers via BLE advertisements, form clusters with scored peer connections, and bridge separate clusters automatically.

A message addressed to someone out of radio range is carried by the devices in between: each hands it onward to a bounded set of neighbors until it arrives or runs out of hops. Delivery acknowledgements travel back the same way, so a message that crossed several devices is not mistaken for a lost one. Devices only carry traffic when their own battery policy allows it, and every device caps how much it forwards — per second overall and per neighbor — so a crowded room stays usable rather than filling with repeated copies.

For details, see the Mesh Networking Guide.

Documentation

See the docs/ directory for detailed guides:

• Upgrading — read first if you are moving an existing app onto the storage-split release
• Architecture Deep Dive
• API Reference
• Configuration Guide
• Message Delivery — ACK ladder, retries, offline park/push, group delivery reports
• DORS Deep Dive / DORS Configuration
• Mesh Networking Guide
• MLS Encryption Integration
• Transport Architecture
• Service Discovery
• React Native Integration
• Python Desktop Bindings
• Reticulum Transport / Nostr Transport
• Telemetry
• iOS Integration / Android Integration

Reference material for anyone implementing against the protocol or changing its behaviour:

• Protocol Specification, the wire and behaviour contract, independent of this implementation
• Threat Model, including the residual risks stated plainly
• State Machines for delivery, retries, sessions, groups, and transports
• Architecture Decision Records, why the non-obvious choices are what they are
• Bridge Contracts for Swift, Kotlin, Python, and TypeScript

Development

cargo build --workspace            # Build
cargo test --workspace             # Test
cargo clippy --workspace -- -D warnings  # Lint
cargo fmt --all                    # Format

See CONTRIBUTING.md for development guidelines and QUICKSTART.md for platform-specific setup.

License

Copyright © 2025-2026 Offline Protocol, Inc.

The Offline Protocol SDK is dual-licensed:

• GNU Affero General Public License v3.0 (AGPL-3.0-only) — see LICENSE. Free for use in projects that comply with AGPL-3.0, including its network-use source-disclosure requirement (section 13).
• Commercial License — for organizations that cannot or do not wish to comply with the AGPL (e.g., shipping the SDK inside a proprietary mobile app or SaaS without releasing source). See LICENSE-COMMERCIAL.md for terms and contact details.

You may use the SDK under either license; you do not need both. Contributions are accepted under the terms described in CONTRIBUTING.md.

App-store distribution has consequences under the AGPL — see the Licensing FAQ. And this software contains encryption: EXPORT.md describes its export-control status and what app teams must handle themselves.

Neither license grants rights to the "Offline Protocol" name or logo — see TRADEMARKS.md.