envoyproxy/envoy

hcm: Allow filter to control on emitting trailers (e.g. to skip encoding trailers when empty)

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#12,374 opened on Jul 30, 2020

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area/httpenhancementhelp wanted

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Description

Context: Some of the filters, e.g. gRPC Web requires to skip encoding trailers due to https://github.com/envoyproxy/envoy/issues/10514.

i.e. currently, we have the following "problematic" response frames.

[  5.036] recv DATA frame <length=28, flags=0x00, stream_id=13>
[  5.040] recv DATA frame <length=52, flags=0x00, stream_id=13>
[  5.053] recv HEADERS frame <length=0, flags=0x05, stream_id=13>
          ; END_STREAM | END_HEADERS

What we want is something like:

[  5.036] recv DATA frame <length=28, flags=0x00, stream_id=13>
[  5.040] recv DATA frame <length=52, flags=0x00, stream_id=13>
          ; END_STREAM

We have the current data frames since we always encode trailers. The proposed solution will be to have control from the filter side.

A couple of options:

  1. introduce a new return enum to FilterTrailersStatus, to indicate that trailers should not be emitted.
  2. add end_stream flags to addEncodedData, end stream there and encodeTrailers return StopIteration

From the discussion here, the second of the options above is preferable and when doing that we should do a parallel fix in addDecodedData too.

Contributor guide

Research direction
Review the linked PR discussion (#12178) to understand the preferred approach (option 2: add end stream flags to addEncodedData). Then, implement the changes in the filter manager to allow filters to control whether trailers are emitted, ensuring consistency for both encoded and decoded data paths.
Tech stack
c
Domain
backendinfrastructure
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.
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 pipeline
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20