How do I get real-time streaming updates from PI Web API?

PI Web API supports real-time data through channels (WebSocket-based) and SignalR, allowing you to receive updates without polling.

Using Channels (WebSocket)

Channels provide server-sent updates over a persistent WebSocket connection:

// Browser JavaScript example
const webId = "P0HkAB...";
const ws = new WebSocket(
  `wss://your-pi-server/piwebapi/streams/${webId}/channel`
);

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);
  data.Items.forEach(item => {
    console.log(`Value: ${item.Value}, Time: ${item.Timestamp}`);
  });
};

ws.onclose = () => console.log('Channel closed');

Polling as Fallback

If WebSockets aren't available, poll the snapshot endpoint:

import time
import requests

while True:
    response = requests.get(
        f"{base_url}/streams/{web_id}/value",
        auth=auth, verify=False
    )
    value = response.json()
    print(f"{value['Value']} at {value['Timestamp']}")
    time.sleep(5)

Best Practices

• Use channels for true real-time needs (operator displays, dashboards).
• Use polling for simple integrations or when WebSocket support is limited.
• Set appropriate update rates — don't request faster than your scan class.
• Handle reconnection logic for WebSocket disconnects.
• Consider PI Web API's updateRate parameter to throttle channel updates.