Offline Chat

A peer-to-peer chat app that works without the internet. Devices on the same local network discover each other with Android's Network Service Discovery (NSD/mDNS), then one device hosts a chat room over a raw TCP socket while the others join it. Recent rooms are remembered locally with Room, so you can find them again quickly.

Features

• No server required — chat runs over your LAN via mDNS discovery + TCP sockets.
• Host a room or join one from the discovered devices list.
• Real-time message feed with a simple send/receive client and server.
• Device list persisted locally with Room.
• MVVM architecture with Hilt dependency injection and Jetpack Navigation.

Screenshots

Architecture

The reusable parts live in the :offlinechat-core library module, while :app is a thin demo application on top of it:

offlinechat-core/                    # reusable library (:offlinechat-core)
└── src/main/java/org/turkiye/offlinechat/
    ├── data/
    │   ├── entity/      # Room entities
    │   ├── local/       # Room database, DAOs, type converters
    │   ├── model/       # network/UI models
    │   └── remote/      # Retrofit API (optional REST layer)
    ├── di/              # Hilt modules (Api, App, Database)
    ├── interfaces/      # discovery / room / click listeners
    ├── repository/      # UsersRepository
    └── util/            # constants, extensions, IP helpers

app/                                 # demo application (:app)
└── src/main/java/org/turkiye/offlinechat/
    ├── App.kt
    └── ui/
        ├── activitys/   # MainActivity
        ├── adapters/    # RecyclerView / Array adapters
        ├── dialogs/     # join dialog
        └── fragments/   # main / client / server fragments + view models

The app follows MVVM: fragments observe LiveData exposed by @HiltViewModel view models, which delegate to repositories backed by Room and the network layer.

Tech stack

• Kotlin + Coroutines / Flow
• Hilt (Dagger) for dependency injection
• Room for local persistence (schema exported to offlinechat-core/schemas)
• Retrofit + OkHttp for the optional REST layer
• Jetpack Navigation for in-app navigation
• ViewBinding for type-safe view access

Permissions

The app requests WiFi/network permissions so that mDNS discovery and the local socket server can operate:

INTERNET, ACCESS_NETWORK_STATE, ACCESS_WIFI_STATE, CHANGE_WIFI_STATE, CHANGE_WIFI_MULTICAST_STATE, NEARBY_WIFI_DEVICES.

All devices must be on the same network.

Requirements

Tool	Version
minSdk	24
compileSdk / targetSdk	36
Gradle	8.14.5
Android Gradle Plugin	8.13.2
Kotlin	2.2.21
JDK	17

Building

./gradlew assembleDebug      # debug APK
./gradlew assembleRelease    # release APK

Library module

The data, repository and dependency-injection layers are packaged as the :offlinechat-core Android library (com.ferhatozcelik:offlinechat-core). Publish it to your local Maven repository and consume it from another project:

./gradlew :offlinechat-core:publishToMavenLocal -PVERSION_NAME=1.0.0

repositories {
    mavenLocal()
}

dependencies {
    implementation("com.ferhatozcelik:offlinechat-core:1.0.0")
}

Author

Ferhat OZCELIK

• GitHub: @ferhatozcelik
• LinkedIn: ferhatozcelik

License

Apache License 2.0 — see LICENSE. If this project helped you, give it a ⭐️.