Make HTTP errors cacheable

[robinjmurphy]

• HTTP errors (404, 500 etc.) are now cached as indicated by the cache-control header
• This relies on a change to our underlying cache data format
• We no longer just store the body in the cache
• We now store an object with either a body property or an error property
• The error property contains everything we need to recreate an Error object when we pull it out of the cache
• err.message, err.statusCode, err.body
• The above is required as we can't just JSON stringify Error objects

A valid response is cached as:

{
  "body": {
    "foo": "bar"
  }
}

A HTTP error is cached as:

{
  "error": {
    "message": "An error occurred",
    "statusCode": 503,
    "body": {
      "oh": "no!"
    }
  }
}

[robinjmurphy]

We're storing everything we need to recreate a proper Error object.

[robinjmurphy]

Would be interested in your feedback @nspragg @hjerling @DaMouse404.

[robinjmurphy]

Note that we're free to change the cached object structure in any release because the cache key includes the version number of the library.

[hjerling]

👍
Looks good to me. I had a bit of a dig through to make sure that we don't use the cached error on retries but that is clearly out of harms way.
I like the way it caches any response based on cache-control, regardless of success or error!
🍪

[Mousius]

Looks like a good idea! 👍

[nspragg]

👍