# useTransportStatus

The `useTransportStatus` hook reports whether the transport has seen a discontinuity, and the latest error it reported that has no caller to reject. A discontinuity is a channel state change after which messages may have been missed.

<Code>

#### Javascript

```
import { useTransportStatus } from '@ably/ai-transport/react';

function Status() {
  const { discontinuity, error } = useTransportStatus();

  if (error) return <p>Something went wrong: {error.message}</p>;
  if (discontinuity) return <p>Reconnected. Catching up.</p>;
  return null;
}
```
</Code>

This hook must be used within a [`TransportProvider`](https://ably.com/docs/ai-transport/api/react/transport-provider.md).

To read whether the channel is attached, use `useChannelStateListener` from `ably/react`, which works inside the provider.

`discontinuity` stays `true` once it is set. To recover after every discontinuity, listen with `transport.on('discontinuity')` and subscribe again from the serial of the last message you received, as the [example](#example) shows.

## Parameters 

<Table id='UseTransportStatusParameters'>

| Parameter | Required | Description | Type |
| --- | --- | --- | --- |
| channelName | optional | The channel name of the provider to read. Omit it to read the nearest provider. | String |

</Table>

The hook throws an [`ErrorInfo`](https://ably.com/docs/ai-transport/api/errors.md#errorinfo) with `InvalidArgument` when no matching `TransportProvider` encloses the component.

## Returns 

<Table id='UseTransportStatusReturns'>

| Property | Description | Type |
| --- | --- | --- |
| discontinuity | `true` once the transport has reported a discontinuity. It resets when the provider creates a new transport. | Boolean |
| error | The latest error the transport reported with no caller to reject, such as a failed attach or a codec that threw while decoding, or `undefined`. | [`ErrorInfo`](https://ably.com/docs/ai-transport/api/errors.md#errorinfo) or `undefined` |

</Table>

## Example 

A component replays the conversation from the stored serial when it loads. After each discontinuity, it subscribes again from the serial of the last message it received.

<Code>

### Javascript

```
import { useEffect, useRef } from 'react';
import { fromSerial } from '@ably/ai-transport';
import { useTransport, useTransportStatus } from '@ably/ai-transport/react';

function Conversation({ storedSerial, render }) {
  const { transport } = useTransport();
  const { discontinuity } = useTransportStatus();
  const lastSeen = useRef(storedSerial);

  useEffect(() => {
    if (!transport) return;
    const apply = (delivery) => {
      render(delivery);
      if (delivery.message.serial > lastSeen.current) lastSeen.current = delivery.message.serial;
    };
    const subscribeFrom = (serial) => transport.subscribe(apply, serial ? { history: { replay: fromSerial(serial) } } : undefined);

    let unsubscribe = subscribeFrom(lastSeen.current);
    const off = transport.on('discontinuity', () => {
      unsubscribe();
      unsubscribe = subscribeFrom(lastSeen.current);
    });
    return () => {
      off();
      unsubscribe();
    };
  }, [transport, render]);

  return discontinuity ? <p>Reconnected.</p> : null;
}
```
</Code>

## Related Topics

- [TransportProvider](https://ably.com/docs/ai-transport/api/react/transport-provider.md): API reference for the AI Transport TransportProvider: create a transport for a channel and make it available to React components.
- [useTransport](https://ably.com/docs/ai-transport/api/react/use-transport.md): API reference for the AI Transport useTransport hook: read the transport from the nearest or a named TransportProvider.
- [useDeliveries](https://ably.com/docs/ai-transport/api/react/use-deliveries.md): API reference for the AI Transport useDeliveries hook: receive every delivery on the transport's channel while a component is mounted.
- [useHistory](https://ably.com/docs/ai-transport/api/react/use-history.md): API reference for the AI Transport useHistory hook: read the channel's history one page at a time, oldest first.

## Documentation Index

To discover additional Ably documentation:

1. Fetch [llms.txt](https://ably.com/llms.txt) for the canonical list of available pages.
2. Identify relevant URLs from that index.
3. Fetch target pages as needed.

Avoid using assumed or outdated documentation paths.