Recording Mainframe Screen Sessions with the Loki Recorder

Starting from OpenLegacy Core 5.1.12, OpenLegacy has integrated the OpenLegacy Loki recorder directly into the OL Screens connector.

Previously the Loki recorder was a separate capability. With this integration, recording and mocking a mainframe green screen session is available out of the box in the Screens connector — no additional component is required.

What the Loki Recorder Does

The Loki recorder captures the traffic exchanged between the OpenLegacy API and the mainframe during a green screen (3270/5250-style) session. The captured session can then be:

• Recorded — saved to a file for later inspection.
• Mocked — replayed without a live connection to the mainframe.

This is particularly useful when you need to reproduce the exact behavior of a session without depending on the availability of the host system.

When to Use It

The most common use case is debugging and reproducing an issue. When a problem occurs against a live mainframe, recording the session lets you:

• Capture the precise sequence of screens and traffic that led to the problem.
• Reproduce the issue reliably, away from the live host.
• Share the recording so the behavior can be investigated and replayed by others.

How to Enable Recording

To record a session, add the following property to the module connection configuration:

"recordingFile": "{FILE NAME}.json"

Replace {FILE NAME} with the name you want for the recording file.

Once this property is set, the OpenLegacy API will save the recorded mainframe traffic into the specified .json file as the session runs.

Example

"recordingFile": "session-debug.json"

With this configuration, the traffic for the session is written to session-debug.json.