envoyproxy/envoy

make `per_filter_config` specific configs work automatically for filters

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#10,164 opened on Feb 25, 2020

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area/httpenhancementhelp wanted

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Description

Currently filter writers need additional plumbing to allow their filter to do per vhost/route overrides. E.g.:

// Fetch the virtual host specific config.
const VHostSpecificFilterConfig* Filter::getSpecificConfig() const {
  if (!decoder_callbacks_->route() || !decoder_callbacks_->route()->routeEntry()) {
    return nullptr;
  }

  const auto* entry = decoder_callbacks_->route()->routeEntry();
  const auto* settings = entry->virtualHost().perFilterConfig("pinterest.my_filter");

  if (settings != nullptr) {
    auto* vhost_config = dynamic_cast<const VHostSpecificFilterConfig*>(settings);
    return vhost_config;
  }

  return nullptr;
}

and then you have to merge that, with the config object you got from the Filter Factory. It's not that much logic, but it's a bit of hassle to a) do it for every filter and b) remember that you have to do it.

Thoughts on providing some plumbing to avoid repeating the above pattern (or thoughts on the general future of per vhost/route config overrides)?

cc: @mattklein123 @htuch @fishcakez

Contributor guide

Research direction
Examine existing filters that manually implement per virtual host/route config overrides and identify a common pattern. Propose a base class or helper function that automatically merges the per filter config with the generic per filter config from the vhost/route. Implement the solution in one filter as a proof of concept and then refactor others.
Tech stack
cpp
Domain
backend
Issue type
Feature
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.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C++Envoy filter development
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40