[remark-images-download] Do not throw error when HTTP status code is 301

[StaloneLab]

Thanks for this PR, unfortunately I do not think it can be merged as is. When a 301 or 302 code is returned to the Node http agent, it doesn't follow the redirection. Hence, with your changes, no error is thrown but the image inserted in the resulting content is invalid (with an empty file downloaded I think). In fact, it seems the default http module doesn't support following redirects by default, so if you want to fix it, you'll likely need to:

• implement a way to follow redirects, for instance by using the follow-redirect package from NPM;
• add a test to make sure everything works as expected (301 are redirected and the image. In fact, this can be quite tricky for this module: firstly, you need to add a way to generate 301 in the mock server. Secondly, add a test in the corresponding file;
• I'm also thinking of a potential infinite redirects problem (looping on 301), that will need careful attention. If you feel inspired, a test might also be added for it;
• finally, but that should be a formality, run npm run build -- --scope=remark-images-download to run Babel on your changes.

Hope I'm not forgetting anything, you'll likely encounter problems I haven't even thought of anyway. Feel free if you have any questions, you're not restricted to empty messages :upside_down_face: .

[artragis]

Warning, any "follow-redirect" implementation MUST define a max-hop attribute to avoid redirection bombing. For us it should be set to 1 as we mainly want to follow http -> https.

[StaloneLab]

Yes, I think what you are referring to was what I meant by "potential infinite redirects problem" ;)

[Situphen]

I first thought this would be an easy fix but it clearly isn't. I will see if I can work to fix this or if it's easier to fix the content themselves.

[StaloneLab]

Closing for inactivity. Do not hesitate to reopen either this PR or a new issue for the problem.