How to inspect WebSocket messages

Chat apps, live dashboards and development servers keep a WebSocket open and send messages over it. Browser developer tools can show a browser's WebSockets, but VioLens shows them for any app that goes through it, decompressed and as they arrive.

1. Capture the connection

Start VioLens, then open the app or page. A WebSocket connection shows in the session list as the request that opened it, with status 101. To find it quickly, type status:101 in the filter box.

2. Open the WebSocket tab

Select the session and open the WebSocket tab. Each message has a row:

↑ is a message the client sent, and ↓ one it received.
Each row shows when it was sent, its type (text, binary, close, ping or pong), its size and the start of its data.
Select a row to see the whole message. JSON is indented, and binary data is shown as hex.

The list keeps growing while the connection is open. Check Hide pings and pongs to hide keep-alive messages.

3. Search and save

Find (Ctrl+F) searches text messages too. To keep the messages, use File > Export HAR: WebSocket messages are saved in HAR files, but not in SAZ files yet.

Compressed messages (permessage-deflate) are decompressed for you, and messages sent in several pieces are put back together.