mirror of
https://github.com/permissionlesstech/bitchat-android.git
synced 2026-08-08 06:46:11 +00:00
46de1a3623
`BitchatFilePacket.decode` resolved every tag through the four-value
`TLVType` enum and bailed on the first miss:
val t = TLVType.from(data[off].toUByte()) ?: return null
So a file packet carrying one tag this build does not know is not
partially understood — it is discarded whole, media included. The
receiver shows nothing and logs nothing; the sender sees a successful
transfer. Both apps look healthy.
iOS has always skipped unknown tags (`case nil: continue` in its own
`BitchatFilePacket.decode`), so the two implementations disagreed about
what a valid packet is, and the tag list stopped being extensible in
practice: any optional field added by a newer or third-party client
costs every Android peer the whole file rather than just that field.
Unknown tags now advance past the value, exactly as iOS does. Known-tag
handling, the 4-byte CONTENT length, multi-CONTENT concatenation and
every existing rejection are unchanged.
The skip path is deliberately allocation- and log-free per TLV, because
its iteration count is chosen by the sender: a zero-length unknown TLV
costs 3 bytes, so a padded packet would otherwise mean millions of empty
array copies and formatted log lines monopolising the mesh handler. The
count is reported once after the loop instead.
Tests: `decode should skip unknown TLV types instead of dropping the
whole file` (extension before CONTENT), `decode should skip an unknown
TLV that trails the content` (after it), and `decode should handle a
packet padded with many zero-length unknown TLVs` (200k of them). The
first two fail on the old decoder.
bitchat for Android
A decentralized peer-to-peer messaging app with dual transport architecture: local Bluetooth mesh networks for offline communication and internet-based Nostr protocol for global reach. No accounts, no phone numbers, no central servers.
This is the Android implementation of bitchat, fully protocol-compatible with the iOS version for cross-platform mesh communication.
License
This project is released into the public domain. See the LICENSE file for details.
Features
- Dual Transport Architecture: Bluetooth LE mesh for offline messaging, Nostr relays for internet-based messaging
- Location-Based Channels: Geographic chat rooms using geohash coordinates over Nostr relays
- Intelligent Message Routing: Automatically chooses the best transport, with queuing and retry when a peer is unreachable
- End-to-End Encryption: Noise Protocol (XX pattern, X25519 + ChaCha20-Poly1305) for private messages over the mesh
- Decentralized Mesh Network: Automatic peer discovery and multi-hop relay over Bluetooth LE (max 7 hops)
- Wi-Fi Aware Transport: Higher-bandwidth local mesh on supported devices
- Channel Chats: Topic-based group messaging with optional password protection (Argon2id + AES-256-GCM)
- IRC-Style Commands: Familiar
/join,/msg,/whostyle interface - Tor Support: Built-in Tor (Arti) for private internet connectivity
- Emergency Wipe: Triple-tap to instantly clear all data
- Cross-Platform: Binary protocol compatible with bitchat on iOS and macOS
Technical Architecture
Bluetooth Mesh Network (Offline)
- Direct peer-to-peer within Bluetooth range, multi-hop relay through nearby devices
- Noise Protocol sessions with forward secrecy; peer identities derived from static keys
- Compact binary packet format with fragmentation, TTL routing, and deduplication
- Adaptive duty cycling and connection limits for battery efficiency
- Foreground service keeps the mesh alive within Android background execution limits
Nostr Protocol (Internet)
- Global reach via public relays, geohash-based location channels
- Private messages fall back to Nostr for mutual favorites when the mesh is unavailable
- Ephemeral keys per geohash area
Android Stack
- Kotlin, Jetpack Compose (Material 3), MVVM
- Coroutines and Flow for all networking and state
- Core components:
MeshForegroundService(persistent connectivity),BluetoothMeshService/WifiAwareMeshService(transports),UnifiedMeshService(transport selection),NoiseSessionManager(encryption sessions),MessageRouter(mesh/Nostr routing with outbox retry)
Building
Requires Android Studio and the Android SDK (API 26+).
git clone https://github.com/permissionlesstech/bitchat-android.git
cd bitchat-android
./gradlew assembleDebug
Install on a connected device:
adb install -r app/build/outputs/apk/debug/app-debug.apk
The app requests Bluetooth, location (required for BLE scanning), and notification permissions at runtime.
Release APKs and the Android App Bundle can be rebuilt byte-for-byte in the pinned Linux container. Maintainers should follow the Android release guide. See Reproducible builds for the build trust model and public GitHub/Google Play verification procedures.
Testing
# Unit tests
./gradlew test
# Lint
./gradlew lint
# Instrumented tests (requires a device or emulator)
./gradlew connectedAndroidTest
Note that BLE mesh behavior is difficult to emulate; protocol and session logic is covered by unit tests, while radio-level behavior needs real devices.