envoyproxy/envoy

[ExtProc] Content-Length Header Mutation in FULL_DUPLEX_STREAMED body processing mode

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#39,035 opened on Apr 7, 2025

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enhancementext-prochelp wanted

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Description

Title: [ExtProc] Content-Length Header Mutation in FULL_DUPLEX_STREAMED body processing mode

Description: Should ExtProc in FULL_DUPLEX_STREAMED body processing mode switch to chunked encoded transfer even if a content length is provided as part of a header mutation? The following comment in https://github.com/envoyproxy/envoy/blob/737efd331cce18b172a2f0241638d810ee73d604/source/extensions/filters/http/ext_proc/processor_state.h#L190 states otherwise

ext_proc filter can not guarantee to set the content length correctly if body is mutated by external processor later.

But, I am not sure if this is correct for duplex streamed processing, where to my understanding the extproc filter is in full control over what is delivered down or upstream.

I guess the situation is more complicated. Can any one shed some light on the topic.

Thank you very much.

Andre

Contributor guide

Research direction
Investigate the referenced code in processor state.h and the behavior of FULL DUPLEX STREAMED mode regarding Content Length header mutation. Trace the code path for header mutations in that mode to determine if switching to chunked encoding is necessary or correct.
Tech stack
cpp
Domain
backendinfrastructure
Issue type
Research
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.
Half day
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
Envoy internalsHTTP/1.1 semanticsExtProc filter
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30