initial simple rate limiting

[BrianGreenhill]

Description

this is a very simple implementation of rate limiting for the imageproxy service.

Motivation

addresses #200

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[codecov[bot]]

Codecov Report

Merging #224 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #224   +/-   ##
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  Coverage   89.16%   89.16%           
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  Files           6        6           
  Lines         674      674           
=======================================
  Hits          601      601           
  Misses         50       50           
  Partials       23       23

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[BrianGreenhill]

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[willnorris]

Hey @BrianGreenhill, I'm finally catching up on outstanding PRs 😕

I'm curious what you think of the alternate approach in #235. Rather than wrapping the handler and limiting all requests like tollbooth does, I'd kind of like to be more surgical and limit just the requests that are likely to consume resources... namely, those that require transformations. If a response is already cached, there's probably not a need to limit it. (Though I guess the counter argument there is that if it's cached, then it's probably going to return very quickly, and won't block other requests for very long. hmm....)

[BrianGreenhill]

Hey @BrianGreenhill, I'm finally catching up on outstanding PRs confused

I'm curious what you think of the alternate approach in #235. Rather than wrapping the handler and limiting all requests like tollbooth does, I'd kind of like to be more surgical and limit just the requests that are likely to consume resources... namely, those that require transformations. If a response is already cached, there's probably not a need to limit it. (Though I guess the counter argument there is that if it's cached, then it's probably going to return very quickly, and won't block other requests for very long. hmm....)

@willnorris if we can be more specific and limit requests that we know will consume more resources then I think that's the better solution. I wonder if a global rate limiting flag as an upper bound for limiting rps may also be desirable for some users? However, this concern can also be handled in other ways and doesn't necessarily have to be the responsibility of the application.

Thanks for responding and please go ahead with the alternative approach here :+1: