Fix EndpointCache

[MarcusSmith]

EndpointCache's get(on: Request) convenience function was calling through directly to download, which was completely bypassing the cache. Updated this function to call through to get(using: Client, on: EventLoop) instead which should check cache correctly.

Before this get merged, anyone else running into this can work around the bug by calling cache.get(using: request.client, on: request.eventLoop) instead of cache.get(on: request)

[gwynne]

At a glance, this does look correct to me, but I'm not fully familiar with this particular logic; @0xTim can you chime in?

In the meantime, @MarcusSmith can you add a test to EndpointCacheTests.swift for this issue?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 76.86%. Comparing base (3a7da19) to head (491091a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3156   +/-   ##
=======================================
  Coverage   76.86%   76.86%           
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  Files         211      211           
  Lines        8119     8119           
=======================================
  Hits         6241     6241           
  Misses       1878     1878           

Files	Coverage Δ
Sources/Vapor/HTTP/EndpointCache.swift	63.07% <0.00%> (ø)

[MarcusSmith]

Is there a recommended way to get ahold of a Request in a test to pass into it?

Best I've been able to come up with is define a new middleware that uses an endpoint cache for something and trigger that multiple times through a get request and assert that it only calls that cache's endpoint once. But I'm unsure of how I'd be able to make those assertions

Just did a live test of our hackaround to use the other init and it fixed our production issue, so I'm pretty confident this was the issue

[0xTim]

@MarcusSmith you can stub out the client with something similar to #2928 to make it possible to make assertions on that (and avoid any network requests)