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* BLE background presence: pending-connect wake-on-proximity + wake-window maintenance (#1395) iOS cancels nothing for us: pending CBCentralManager connects never expire, complete whenever the peer reappears in range, and relaunch the app via the existing state-restoration path. Use that as the wake-on-proximity mechanism: - BLERecentPeripheralCache: retains handles to recently seen/dropped peripherals (LRU 16, 15 min max age to respect BLE address rotation) - On backgrounding, arm indefinite pending connects to cached peripherals within a slot budget (2 of 6 central slots reserved for live background discovery); armed entries carry lastConnectionAttempt == nil so a quick background/foreground bounce can't strand them as connecting - The 8s app-level connect timeout defers while backgrounded so discovery-driven background connects also stay pending - Foreground return cancels stale pending connects (including connecting entries rebuilt by state restoration after a relaunch) and hands control back to the scanner/scheduler - A link dropped while backgrounded re-arms after the disconnect-settle window, so a peer walking away and returning wakes us again - Packet ingress while backgrounded triggers a catch-up maintenance pass (announce/flush/drain) since the maintenance timer is suspended with the app; rate-limited to the normal 5s cadence Battery cost ~0: pending connects live in the controller's allowlist (no scanning, no app CPU), and the catch-up pass only runs inside wake windows the radio already granted. Co-authored-by: jack <jackjackbits@users.noreply.github.com> Co-authored-by: Claude Fable 5 <noreply@anthropic.com> * Restore: seed wake-on-proximity cache and resume service discovery Field finding from on-device testing: after a state-restoration relaunch, the recent-peripheral cache starts empty, so backgrounding shortly after a restore armed no pending connects. Seed the cache from the restored peripherals — they are the freshest proximity candidates we have. Also resume service discovery for peripherals restored as connected with no characteristic: the CBCharacteristic reference dies with the old process, and without rediscovery the link sits connected-but-unusable until the peer drops it. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Defer restored-link service rediscovery until poweredOn Field finding: CBPeripheral.discoverServices issued inside willRestoreState fires before the central manager reaches poweredOn — CoreBluetooth drops the command with an API MISUSE warning, leaving restored-connected links characteristic-less after all. Move the rediscovery to centralManagerDidUpdateState(.poweredOn), which restoration guarantees runs afterwards. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> * Let disconnect re-arms use the freed slot (Codex P2 on #1396) The background-entry arm reserves 2 of 6 central slots for live discovery, but the disconnect re-arm path shared that budget: with 4+ links remaining the budget hit zero and the just-dropped peer was never armed — defeating walk-away/walk-back re-arming in dense meshes. The disconnect path now arms with no reserve, consuming the slot the disconnect itself freed. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> --------- Co-authored-by: jack <jackjackbits@users.noreply.github.com> Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
bitchat
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. It's the side-groupchat.
License
This project is released into the public domain. See the LICENSE file for details.
Features
- Dual Transport Architecture: Bluetooth mesh for offline + Nostr protocol for internet-based messaging
- Location-Based Channels: Geographic chat rooms using geohash coordinates over global Nostr relays
- Intelligent Message Routing: Automatically chooses best transport (Bluetooth → Nostr fallback)
- Decentralized Mesh Network: Automatic peer discovery and multi-hop message relay over Bluetooth LE
- Privacy First: No accounts, no phone numbers, no persistent identifiers
- Private Message End-to-End Encryption: Noise Protocol for mesh, NIP-17 for Nostr
- IRC-Style Commands: Familiar
/slap,/msg,/whostyle interface - Universal App: Native support for iOS and macOS
- Emergency Wipe: Triple-tap to instantly clear all data
- Performance Optimizations: LZ4 message compression, adaptive battery modes, and optimized networking
Technical Architecture
BitChat uses a hybrid messaging architecture with two complementary transport layers:
Bluetooth Mesh Network (Offline)
- Local Communication: Direct peer-to-peer within Bluetooth range
- Multi-hop Relay: Messages route through nearby devices (max 7 hops)
- No Internet Required: Works completely offline in disaster scenarios
- Noise Protocol Encryption: End-to-end encryption with forward secrecy
- Binary Protocol: Compact packet format optimized for Bluetooth LE constraints
- Automatic Discovery: Peer discovery and connection management
- Adaptive Power: Battery-optimized duty cycling
Nostr Protocol (Internet)
- Global Reach: Connect with users worldwide via internet relays
- Location Channels: Geographic chat rooms using geohash coordinates
- 290+ Relay Network: Distributed across the globe for reliability
- NIP-17 Encryption: Gift-wrapped private messages for internet privacy
- Ephemeral Keys: Fresh cryptographic identity per geohash area
Channel Types
mesh #bluetooth
- Transport: Bluetooth Low Energy mesh network
- Scope: Local devices within multi-hop range
- Internet: Not required
- Use Case: Offline communication, protests, disasters, remote areas
Location Channels (block #dr5rsj7, neighborhood #dr5rs, country #dr)
- Transport: Nostr protocol over internet
- Scope: Geographic areas defined by geohash precision
block(7 chars): City block levelneighborhood(6 chars): District/neighborhoodcity(5 chars): City levelprovince(4 chars): State/provinceregion(2 chars): Country/large region
- Internet: Required (connects to Nostr relays)
- Use Case: Location-based community chat, local events, regional discussions
Direct Message Routing
Private messages use intelligent transport selection:
-
Bluetooth First (preferred when available)
- Direct connection with established Noise session
- Fastest and most private option
-
Nostr Fallback (when Bluetooth unavailable)
- Uses recipient's Nostr public key
- NIP-17 gift-wrapping for privacy
- Routes through global relay network
-
Smart Queuing (when neither available)
- Messages queued until transport becomes available
- Automatic delivery when connection established
For detailed protocol documentation, see the Technical Whitepaper.
Setup
Option 1: Using Xcode
cd bitchat
open bitchat.xcodeproj
To run on a device there're a few steps to prepare the code:
- Clone the local configs:
cp Configs/Local.xcconfig.example Configs/Local.xcconfig - Add your Developer Team ID into the newly created
Configs/Local.xcconfig- Bundle ID would be set to
chat.bitchat.<team_id>(unless you set to something else)
- Bundle ID would be set to
- Entitlements need to be updated manually (TODO: Automate):
- Search and replace
group.chat.bitchatwithgroup.<your_bundle_id>(e.g.group.chat.bitchat.ABC123)
- Search and replace
Option 2: Using just
brew install just
Want to try this on macos: just run will set it up and run from source.
Run just clean afterwards to restore things to original state for mobile app building and development.
Localization
- Base app resources live under
bitchat/Localization/Base.lproj/. Add new copy toLocalizable.stringsand plural rules toLocalizable.stringsdict. - Share extension strings are separate in
bitchatShareExtension/Localization/Base.lproj/Localizable.strings. - Prefer keys that describe intent (
app_info.features.offline.title) and reuse existing ones where possible. - Run
xcodebuild -project bitchat.xcodeproj -scheme "bitchat (macOS)" -configuration Debug CODE_SIGNING_ALLOWED=NO buildto compile-check any localization updates.