ProfessionalCommunity Edition

Filtering the WebSockets history with Bambdas

• Last updated: December 19, 2024

• Read time: 3 Minutes

You can apply Java-based Bambdas to create powerful custom filters for your WebSockets history. You can do this in two ways:

• Load existing Bambdas - Load Bambdas from your Bambda library.

• Create new Bambdas - Write and apply Bambdas directly in the WebSockets history filter window.

Keyboard shortcuts

To speed up your workflow when creating or loading Bambdas, you can use the following keyboard shortcuts:

• Save - Ctrl + S or Cmd + S

• Save as - Ctrl + Shift + S or Cmd + Shift + S

• Create new Bambda - Ctrl + N or Cmd + N

• Load recent Bambda - Ctrl + O or Cmd + O

Loading Bambdas from your library

You can load and apply Bambdas that are stored in your library to filter the WebSockets history.

To load a Bambda from your library:

1. In Proxy > WebSockets history, click the filter bar to open the WebSockets history filter window.

2. In the WebSockets history filter window, click Bambda mode.

3. Click Load.

4. Select a recent Bambda from the list.

5. [Optional] If required, edit the Bambda:

   1. Make your changes.

   2. Click Apply to compile and test the Bambda. Fix any errors shown in the Compilation errors panel. For more information, see Troubleshooting Bambdas.

   3. Save your changes:

      • To overwrite the existing Bambda, click Save > Save.

      • To save a new version, click Save > Save as.

6. Click Apply & close.

Burp compiles your Bambda and applies it to every item already logged in your WebSockets history, as well as any future WebSocket traffic generated in this project.

Creating custom Bambdas

You can write your own Bambdas directly in the WebSockets history filter window.

Converting filter settings to Bambdas

You can convert filter settings to a Bambda as a starting point for further customization:

1. In Proxy > WebSockets history, click the filter bar to open the WebSockets history filter window.

2. Make changes to the filter settings as necessary.

3. At the bottom of the WebSocket history filter window, click Convert to Bambda.

Your filter is converted into a Bambda, enabling you to customize it further using Java.

Creating your Bambda

Two objects of the Montoya API are available to help you write your Bambda:

• ProxyWebSocketMessage

• Utilities

To create a Bambda to filter your WebSockets history:

1. In Proxy > WebSockets history, click the filter bar to open the WebSockets history filter window.

2. In the WebSockets history filter window, click Bambda mode.

3. Write your Bambda using Java.

4. Click Apply to compile and test the Bambda. Fix any errors shown in the Compilation errors panel. For more information, see Troubleshooting Bambdas.

5. [Optional] Click Save > Save. The Bambda is saved to your Bambda library for future use across Burp.

6. Click Apply & close.

Burp compiles your Bambda and applies it to every item already logged in your WebSockets history, as well as any future WebSockets traffic generated in this project.

Example Bambda

This example Bambda filters the WebSockets history to show only items that meet the following criteria:

• The message must be sent from the server.

• The message payload length must be greater than 300 characters.

In this example, our Bambda is:

return message.payload().length() > 300 && message.direction() == Direction.SERVER_TO_CLIENT;