Provide ability to persist and restore cookie jar

[gmg137]

Hello, can you increase the local storage and loading of cookies?
Curl-like cookies_jar and cookies_file methods

[sagebind]

Thanks for the question! This is currently not available, but would be a welcome improvement! Cookies are only held in memory at the moment.

Currently the cookies subsystem does not involve libcurl at all -- the primary reason for this is performance. Access to persistent cookies (on disk) would require synchronous I/O which would block our event loop, or a thread pool which would be a lot of overhead if not opted into.

To implement this, we would probably want to provide access to the contents of the cookie jar and leave it up to the user how to persist it. We could implement Serialize and Deserialize from Serde, and optionally provide our own serializer that can convert to and from bytes. To restore saved cookies, we could provide another API that allows you to set the contents of the cookie jar, which could be deserialized from some source like a file.

[sagebind]

Removing this from the 1.0 milestone, which is cluttered as it is. Persisting or allowing serialization of the cookie jar means we need to pick a particular persistence format and make that part of our public API guarantees. Since the cookie API itself isn't even fully available yet, I am not ready to commit to a particular storage format yet.

The tricky part here is that we need to expose several "implementation details" about the cookie jar, including:

• The resolved domain based on the request URI that set the cookie.
• The resolved path based on the request URI that set the cookie.
• Whether or not the cookie should be resolved using "host-only" logic.