envoyproxy/envoy

CacheFilter: Parse and handle precondition request headers

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#9,855 opened on Jan 28, 2020

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area/cachehelp wanted

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Description

CacheFilter (#7198) must fully parse and handle precondition request headers (RFC7232): if-match, if-none-match, if-modified-since, if-unmodified-since, and if-range.

This must be fixed before CacheFilter can be appropriate for production deployment.

We currently ignore these headers, which is incorrect, and will result in serving wrong content from cache. As a temporary shortcut, it would be acceptable to instead bypass caching for requests with precondition header. This would reduce cache effectiveness and give clients an easy way to bypass cache, but would never cause incorrect results. With the shortcut, this issue would no longer block production deployment of CacheFilter.

Contributor guide

Research direction
Study the CacheFilter code in source/extensions/filters/http/cache to understand current header handling. Implement parsing of if match, if none match, if modified since, if unmodified since, and if range headers, then evaluate conditions against cache entry metadata. Alternatively, add logic to bypass cache for requests containing these headers.
Tech stack
None
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
C++HTTP
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65