envoyproxy/envoy

FR: nested network filter chains

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#18,035 opened on Sep 9, 2021

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area/listenerdesign proposalhelp wanted

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Description

Currently, listener inspectors and transport sockets are forced to reside at one-level: first inspect, then match, then use a transport socket. This is quite inflexible, and leads to situations where a whole expensive listener is needed (e.g. https://github.com/envoyproxy/envoy/issues/4076). The proposal is to add a oneof that allows (inspectors + filter chains) to reside within the filter chains next to filters. The semantics is that processing is staged where once a filter chain is selected, transport socket is applied, and then inspector + filter chain matching restart.

This solves a bunch of issues:

  1. Proxy protocol can be placed within TLS on server-side.
  2. TLS-within-TLS can be matched provided outer TLS is prior knowledge.
  3. HTTP-within-TLS can be sniffed provided outer TLS is prior knowledge.

Contributor guide

Research direction
Study the existing filter chain implementation in Envoy, especially the listener filter and network filter chain matching logic. Understand how transport sockets are applied and how nested chains would require recursive processing. Look at the referenced issue #4076 and the discussion in this issue for context.
Tech stack
cpp
Domain
backendnetworking
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Over 1 week
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.
Clear
Prerequisites
C++Networking
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20