Bug: Parallel Batch Requests do not return correct order or requestId

[wesbos]

Operating System Info

Other

Other OS

Mac OS 15

OBS Studio Version

Other

OBS Studio Version (Other)

31

obs-websocket Version

5.1.0

OBS Studio Log URL

12:02:52.339: [obs-websocket] [WebSocketServer::onOpen] New WebSocket client has connected from [::ffff:127.0.0.1]:59723

OBS Studio Crash Log URL

No response

Expected Behavior

parallel batch requests return data in order of the requests

Current Behavior

CleanShot.2025-09-12.at.12.10.16.mp4

when performing a parallel batch request for GetSourceScreenshot, the data is not returned in order, and optional requestIds are not attached to the correct response data.

I am using the OBS websocket JS package, but this seems to be a lower level problem with the OBS Websocket implementation. I have a list of source names, and I am requesting screenshots of them all:

const sourceNames = ['Desktop', 'cam-only', 'Termina', 'Desk View']; 
            const request: RequestBatchRequest[] = sourceNames.map((sourceName) => ({
              requestType: 'GetSourceScreenshot',
              requestId: sourceName, // This is so we can line them up with the source names in the response
              requestData: {
                sourceName,
                imageFormat: 'png',
                imageWidth: Math.floor(1920 / 8),
                imageHeight: Math.floor(1080 / 8)
              }
            }));
            const previews = await obs.callBatch(request, {
              executionType: 2 // Parallel
            });

I am using parallel execution here, and the order at which the items return are random.

I tried to fix this by attaching a requestId to the request, so I can re-order them once the data comes back, however the requestIds do come back in the correct order, but the responseData attached to it is not the correct source.

If I remove parallel execution, it works correctly.

Steps to Reproduce

see above

Anything else we should know?

No response

[wesbos]

To add - this behaviour also exists on other calls - not just screenshots. I tried it with GetSourceFilterList and they were returned out-of-order