eb_kwargs for errback

[Shleif91]

Since version 2.0 cb_kwargs has appeared which I use to transfer data to callback.

Now need to handle errors in errback. How to forward data there (logically there should be eb_kwargs, but there is none)?

[elacuesta]

The original PR (#3563) briefly mentions this. We decided there was no need, since the original request is available in the errback's failure, so the callback arguments can be accessed through failure.request.cb_kwargs

[Shleif91]

Thanks for the answer. Did as you showed. Perhaps you need to mention this in the documentation?

[Gallaecio]

I guess it makes sense to be more specific about this in https://docs.scrapy.org/en/latest/topics/request-response.html#scrapy.http.Request.cb_kwargs

[dsandeep0138]

@Gallaecio I have updated the docs. Can you please review the pull request and provide feedback? Thanks.