Support for conditional requests

[netomi]

This PR adds support for conditional requests.

I extracted the relevant code in a separate method so that I can check in a test whether it was called with mocking.
However, it would be great if httpbin would support an endpoint to changes its etag over time. Will look into that and provide a patch there so we can use it here as well if accepted.

This fixes #79 .

Code cov needs to be improved though.

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (8ed3214) 97.21% compared to head (69c2b49) 96.32%.
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #188      +/-   ##
==========================================
- Coverage   97.21%   96.32%   -0.90%     
==========================================
  Files          10       10              
  Lines         934      979      +45     
  Branches      171      181      +10     
==========================================
+ Hits          908      943      +35     
- Misses         15       23       +8     
- Partials       11       13       +2     

Files	Coverage Δ
aiohttp_client_cache/backends/base.py	96.77% <ø> (ø)
aiohttp_client_cache/cache_control.py	98.43% <100.00%> (+0.16%)	⬆️
aiohttp_client_cache/session.py	84.72% <67.74%> (-13.16%)	⬇️

... and 2 files with indirect coverage changes

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[JWCook]

Thank you for putting this together. I appreciate it!

[netomi]

I still work on improving code coverage in the test, need a proper endpoint I can use during the tests. httpbin does not support that and is basically a dead project. It probably makes sense to create a fork supporting something like that.

I have a pretty good idea how this could be done, e.g. a /cache/10 endpoint that updates the etag every 10s.

The etag would be generated from the current time in an interval based on the parameter.

There is a function available that can do that: https://gist.github.com/mscheper/9c39091e12f2ca8addb3d5eef7a40480

Then you could write a test that calls /cache/1, waits 2s and make a conditional request with the etag from before. Now the etag has changed and the server should respond with a 200 with the new content.

[JWCook]

@netomi I believe I handled this in requests-cache with mock responses instead of real requests + httpbin. I used the requests-mock library there, and aioresponses is a similar one available for aiohttp.

If you want to test with a real endpoint, I think it would be simpler to make a separate test app rather than forking httpbin. Here's an example with Flask that does what you describe:

from datetime import datetime
from hashlib import md5
from flask import Flask, request

app = Flask(__name__)


@app.route("/cache/<int:interval>")
def cache(interval):
    """Cacheable endpoint that uses an ETag that resets every `interval` seconds"""
    now = datetime.now()
    server_etag = md5(str(now.second // interval).encode()).hexdigest()
    request_etag = request.headers.get("If-None-Match")
    if request_etag == server_etag:
        return ("NOT MODIFIED", 304)
    else:
        return ("OK", 200, {"ETag": server_etag})

[netomi]

that is really nice will work on a PR

[JWCook]

These changes are now available in v0.10. Thank you again for your help!

Just fyi, at some point in the future I may merge some of this logic into the CacheActions class (similar to the current layout in requests-cache, to separate general HTTP cache logic from the aiohttp-specific parts).

[netomi]

great, so I can update my app to use that version and remove my workaround. Putting the logic into the CacheActions class certainly makes sense!

btw. could you also make a release from the 0.10.0 tag? The latest release is still 0.9.

[JWCook]

Yes, I'll add that shortly.