OFFChat: Resilient Offline Mesh Messaging for Infrastructure-Free Communication

Today's communication platforms rely on internet connectivity, cellular networks, Wi-Fi infrastructure, and centralised servers. During natural disasters, network outages, internet shutdowns, large public events, remote expeditions, or infrastructure failures, these services may become unavailable, overloaded, or unreliable. This affects families, emergency responders, volunteers, travellers, and local communities who need to exchange critical information, coordinate assistance, or communicate with nearby people. Even when users are physically close, conventional messaging applications cannot function without an active network connection. Existing offline messaging solutions generally support only direct device-to-device communication. Once two users move beyond Bluetooth or local wireless range, communication stops. This limitation makes traditional peer-to-peer systems unsuitable for large-scale emergency communication. A resilient solution is needed that can connect nearby devices, relay messages through intermediate users, and maintain communication without relying on internet access, mobile networks, or centralised infrastructure.

OFFChat is an Android-based offline mesh messaging application that enables nearby devices to communicate without internet access, cellular service, or a centralised server. Each participating smartphone acts as both a user device and a network node. Devices automatically discover nearby peers, establish direct peer-to-peer connections, exchange routing information, and forward messages for other users. This creates a local mesh network in which messages can travel across multiple devices. For example, if Device A cannot directly communicate with Device C, but both can communicate with Device B, Device B automatically relays messages between them. This multi-hop communication extends the network beyond the wireless range of a single device. OFFChat uses heartbeat and presence messages to maintain up-to-date routing information. When a device disconnects or moves out of range, invalid routes are removed automatically, and network reachability is recalculated. Messages and important application data are stored locally, allowing the system to preserve communication history and recover after application restarts. The current prototype demonstrates: - Device discovery - Direct peer-to-peer messaging - Multi-hop message relaying - Dynamic route propagation - Presence sharing - Approximate distance estimation - Local message persistence - Offline communication across relay devices Future versions will introduce end-to-end encryption, message authentication, delivery acknowledgements, group chats, file sharing, battery-aware routing, store-and-forward message delivery, and an offline Lost & Found system for emergency reporting and community assistance.

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