# React Native

Once you've started receiving data from a [device](https://app.gitbook.com/s/eJJpVMsUARUJq9lYmL6t/streaming-api/core-concepts#device) into your app, you can start sending this data to Terra's websocket server.

{% hint style="info" %}

#### Prerequisite

Before following the steps below, make sure you've followed the guide to [stream data from a wearable device to your app](https://docs.tryterra.co/streaming-api/connect-wearable-to-sdk/react-native)
{% endhint %}

## Streaming to Terra's Server

You'll have previously set up a local stream using `startRealtime` without a token. To also send data to Terra's server, pass a **streaming token** as the third argument:

```tsx
import { getUserId, startRealtime, Connections, DataTypes } from 'react-native-terra-rt-react';

const startServerStreaming = async () => {
  // 1. Get the Terra user ID
  const { userId } = await getUserId();
  if (!userId) return;

  // 2. Get a streaming token from your backend
  const tokenResponse = await fetch('YOUR_BACKEND_URL/streaming-token', {
    method: 'POST',
    body: JSON.stringify({ userId }),
  });
  const { token } = await tokenResponse.json();

  // 3. Start streaming with the token — data goes to BOTH your app and Terra's server
  const dataTypes = [DataTypes.HEART_RATE, DataTypes.STEPS];
  await startRealtime(Connections.BLE, dataTypes, token);
};
```

The `token` parameter is the only difference from local-only streaming. When provided, the SDK opens a websocket connection to Terra and relays data in real time.

Listen for websocket connection status via the `ConnectionUpdate` event:

```tsx
import { NativeEventEmitter, NativeModules } from 'react-native';

const connectionEmitter = new NativeEventEmitter(NativeModules.ConnectionHandler);
connectionEmitter.addListener('ConnectionUpdate', (connected: boolean) => {
  console.log('Websocket connected:', connected);
});
```

Your backend should generate the streaming token by calling:

{% openapi src="<https://raw.githubusercontent.com/tryterra/openapi/refs/heads/master/rt.yml>" path="/auth/user" method="post" %}
<https://raw.githubusercontent.com/tryterra/openapi/refs/heads/master/rt.yml>
{% endopenapi %}