Make apm.captureError() return error uuid

[lenartbezek]

The problem
We pass uuids of internal errors through our client API, so that clients can trace and report them back to us. Because there is currently no way of getting the uuid that the agent assigns to errors, we have to add a tag with another uuid, that we can also pass with the error response.

Preferred solution
Having apm.captureError() return the assigned uuid through callback or directly.

Alternatives considered
Using tags with a different uuid.

[watson]

Great idea 😃 Yes it would make a great addition to expose the uuid in some way.

I think it's best to expose it via the callback as you also suggested and not hijack the return value. That way the function will remain easy to promisify if you want.

[lenartbezek]

The callback has a different purpose though; it is called after errors are successfully sent to APM. It doesn't seem right to have the application wait for the agent to finish sending errors just to get the uuid.

Perhaps a better solution is to just supply your own uuid through opts argument of apm.captureError()? Very trivial to implement as well.

[watson]

That might work as well - as long as it follows the format that we expect. Today that's uuid v4

[Qard]

That's changing in v2 though, and will be stricter, because of the need to inherit from the transaction context.

[watson]

Will the error id also change? I thought it was only transaction/span ids...

[Qard]

Good question. My PR currently replaces the id everywhere with id and traceId from the trace context, which has a different format. 🤔

[Qard]

Looks like the error id does change. https://github.com/elastic/apm-server/blob/v2/docs/spec/errors/v2_error.json#L12