NexusBridge

A complete SMS Bridge system that connects an Sonim Dumb phone to a web-based messaging UI via a WebSocket relay server.

Roadmap:

1. Make connection screen dpad compatible also.
2. Add option to start a new conversation directly from the index.html
3. Add media sending options.

Tested Devices:

1. Sonim XP3800

Get Started

No hosted builder available yet. You will need to selfhost builder.

Self-Hosting the Builder

To run the builder on linux.

git clone https://github.com/JMTDI/nexussmsbridge
cd NexusSMSbridge
pip install -r requirements.txt
python builder.py

Open http://localhost:8000 in your browser.

The builder will walk you through three steps:

1. Deploy your server — click the "Deploy to Railway" button to spin up a free server in one click

2. Enter your server URL — paste the Railway URL you get after deploying

3. Build your app — the builder generates and downloads a zip containing:

   • nexusbridge.apk — ready-to-install Android app
   • index.html — web messaging UI, pre-configured for your server

4. Run the follow command to grant permission.

 adb shell pm grant com.nexusbridge.smsbridge android.permission.READ_PHONE_STATE

No coding required.

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Architecture

Android App (phone) ──WebSocket──▶ server.py ──WebSocket──▶ index.html (browser)
                                       │
                                  REST API
                                  /new-session
                                  /session-status/{token}

Components

1. server.py — Python Bridge Server

Runs on port 8000 (HTTP + WebSocket on the same port).

Setup:

pip install -r requirements.txt
python server.py

Endpoints:

• GET / → serves index.html
• GET /new-session → creates a new session, returns { sessionToken, pin, qrData }
• GET /session-status/{token} → returns phone connection status
• GET /health → health check
• wss://host/ws/{token}?role=phone|client → WebSocket bridge

2. index.html — Web Client

Single-file, no build step required. Open directly in a browser or via https://yourserver.com/.

Features:

• Pairing screen with QR code + 6-digit PIN
• Full conversation list + thread view
• Real-time messaging via WebSocket
• Dark theme, fully responsive
• Session saved in localStorage for reconnection

3. Android App (android/)

Package: com.nexusbridge.smsbridge

Features:

• D-pad navigable numpad for PIN entry
• ZXing QR code scanner
• Foreground service maintaining persistent WebSocket connection
• Reads SMS/MMS via ContentProvider
• Sends SMS via SmsManager
• BroadcastReceiver for incoming SMS
• Exponential backoff reconnection

Build: Open android/ folder in Android Studio and run on device.

Required Permissions: READ_SMS, SEND_SMS, RECEIVE_SMS, READ_CONTACTS, INTERNET, FOREGROUND_SERVICE, POST_NOTIFICATIONS, CAMERA

Message Protocol

All WebSocket messages are JSON:

{ "type": "...", "payload": { ... } }

Type	Direction	Description
sms_list	phone → client	Full conversation list
sms_thread	client → phone, phone → client	Request/response for thread messages
sms_send	client → phone	Send SMS { to, body }
sms_incoming	phone → client	New inbound SMS notification
read_receipt	client → phone	Mark thread as read
typing_indicator	client → phone	Typing notification
mms_attachment	phone → client	Base64 MMS attachment
contacts_list	phone → client	Contact directory
ping / pong	both	30-second keepalive
phone_connected	server → client	Phone joined the session
phone_disconnected	server → client	Phone disconnected
connection_status	server → client	Current phone connection state

Session Flow

1. Web client calls GET /new-session → gets sessionToken + pin + qrData
2. Web client connects WebSocket as role=client
3. Web client polls GET /session-status/{token} every 2 seconds
4. Android app scans QR or enters PIN → connects WebSocket as role=phone
5. Server links phone ↔ client, notifies client via phone_connected
6. All messages relay bidirectionally in real time