Support saving/loading the cooke store as JSON

[scottschroeder]

This is inspired by some of the code & discussion from #1009

I'm looking for feedback, I don't think this is ready as-is.

API Changes

• Add a save_cookies_json to the Client
• Add a load_cookies_json to the ClientBuilder

This sort-of exposes the json format as part of the API. Changes to cookie_store could result in old JSON files being unreadable. Given that this would just be an error, and not an API breakage, I'm not sure if that's a concern.

Questions

1) Do we make reqwest::cookie::CookieStore pub?

• This would make building simpler, because the caller would be responsible for instantiation & error handling.
• Unfortunately the underlying cookie_store::CookieStore does not support .clone(). Do we care that load_cookies_json would be done on a CookieStore, but save_cookies_json would be done directly on a Client?

2) Error handling?

• The cookie_store crate raises either Box<dyn Error> or its own CookieError enum. This PR managed to dodge the issue by having save_cookies_json create an io::Error, and load_cookies_json used the Kind::Builder enum.
• Are we okay with this strategy? Should we add Kind::Cookie? Other ideas?

3) Arguments for save_cookies_json

• Right now there are two bool flags for persistent and expired. I think the "right" thing is to only save persistent non-expired cookies, but there are reasons to want more options:
  • for debugging purposes, you might want all cookies
  • for my personal usecase, I need to save the non-persistent cookies to be used later, so I would guess there are many similar APIs where cookies are not tagged properly

[meh]

Any update on this?

[seanmonstar]

With #1203 merged, adding the CookieStore trait, it's now possible to create any kind of cookie store, such that you can load or save cookies anywhere, and then provide them to a ClientBuilder. Thus, I think this can be closed.

[meh]

Oh, absolutely, didn't know that happened, thanks!

[ShayBox]

Smells like we need a serde-cookie-store crate or something now.