envoyproxy/envoy

Support custom formatters in custom request/response headers

Open

#25,571 opened on Feb 15, 2023

View on GitHub
 (7 comments) (0 reactions) (0 assignees)C++ (5,373 forks)batch import
area/httpenhancementhelp wanted

Repository metrics

Stars
 (27,997 stars)
PR merge metrics
 (Avg merge 8d) (378 merged PRs in 30d)

Description

Envoy's standard command operators can be used in the value for custom request/response headers. Please also support custom formatters (or custom command operators?) in addition to the built-in formatters.

Custom formatters are already supported in the access log configuration (see "formatters" in config.core.v3.SubstitutionFormatString), so maybe this can be implemented in a similar way.

Example:

route_config:
  name: local_route
  request_headers_to_add:
  - header:
    key: "x-my-header"
    value: "%MY_CUSTOM_COMMAND_OPERATOR%"

Contributor guide

Research direction
Extend the custom header formatter approach to support custom command operators by leveraging the existing SubstitutionFormatString abstraction used in access logs. Investigate how custom formatters are registered and applied in access log context, then adapt that mechanism for request/response headers.
Tech stack
cpp
Domain
backendapi
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.
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.
Mostly clear
Prerequisites
C++Envoy proxy internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30