--resume-prefix to activate on errors

[AlphaSlayer1964]

Provide us a use case of the feature
Sometimes instagram accounts are marked as being hijacked for using instaloader giving a 400 error ending the download session. --resume-prefix would activate on these types of errors stopping you from having to re-download all the posts again to get to the remaining ones.

Describe the solution you'd like
--resume-prefix saves a json file when you encounter an error and not just when manually aborting the program. (maybe excluding 429 as sometimes you can wait it out)

Describe alternatives you've considered
Unless I’m miss understanding how the resume feature works I don't see a built in alternative.

If the feature request is accepted, would you be willing to submit a pull request?
No. Sorry I only no basic python

Additional context
None

[aandergr]

Instaloader does not abort when it encounters an error. Instead, it retries the request that has been responded with an error code, and when the request repeatedly failed, the corresponding post is skipped and Instaloader goes to the next post in the loop. The resume logic (i.e. saving the iterator file that is used for later resuming) is only triggered when manually aborting the loop, e.g. by hitting Control+C or by sending the SIGINT signal.

So the here-described feature suggestion might be that Instaloader should have a flag (e.g. --abort-on-400) that when a request is responded with the error code 400, the download loop is aborted and the resume logic is triggered.

I think this would be good to have in Instaloader, to alleviate the problems that are caused with the "400 Bad Request" lock that has been reported in #770 and #828, unless of course someone discovers a way to entirely avoid this error.

[aandergr]

Implemented in upcoming/v4.7 (syntax is --abort-on=400).

[AlphaSlayer1964]

Thank you so much for this! Another question maybe you could answer but if I use --resume-prefix and --fast-update will it go to where the resume json says to start then do the typical fast update procedure of stopping once a matched name is found? I'm trying to write a command that has --abort-on=400 --resume-prefix resume --fast-update so when downloading an account if my account gets timed out it will save the position it timed out on but when finished if run again would use the fats update.

[aandergr]

Sure, --fast-update also works when resuming, aborting the download once the first already-downloaded post is encountered.

[AlphaSlayer1964]

ok thanks for letting me know. Also I have noticed on the upcoming 4.7 build while it may still get stuck in a 429 loop and take a while to download stuff the new timing seems to prevent the account from being locked! I currently have three different accounts (on different ips) downloading posts for the last four days and no account locks have occurred. Though it is quite slow to download everything again but updating what's already ben downloaded should be super easy now.