add x-envoy-original-host to keep original host

[wbpcode]

Commit Message: add x-envoy-original-host to keep original host
Additional Description:

This PR added a x-envoy-original-host to keep original host value if the host rewriting happens.

Risk Level: low.
Testing: n/a.
Docs Changes: n/a.
Release Notes: n/a.
Platform Specific Features: n/a.

[repokitteh-read-only]

CC @envoyproxy/api-shepherds: Your approval is needed for changes made to (api/envoy/|docs/root/api-docs/).
envoyproxy/api-shepherds assignee is @mattklein123
CC @envoyproxy/api-watchers: FYI only for changes made to (api/envoy/|docs/root/api-docs/).

🐱

Caused by: #39617 was opened by wbpcode.

see: more, trace.

[wbpcode]

This header is used to ensure that, when recreateStream happens, we can use the original host and path to re-match route and re-traverse the filter.

I am not sure if this could acceptable to community, so I created this PR first and get some response from the community.

[mattklein123]

This seems fine if it's only written when the host header is rewritten, but you should add to the docs where we explain all the other headers that are set as well as the release notes.

/wait

[wbpcode]

This seems fine if it's only written when the host header is rewritten, but you should add to the docs where we explain all the other headers that are set as well as the release notes.

/wait

Got it, I will add related docs and release note, thanks!

[wbpcode]

Moving finalizeRequestHeaders here could avoid to expose the getRequestHostValue method and could avoid possible multiple host calculating/string copy/heap allocations, etc.

Another side effect is we could use this to effect upstream lb selection now (like the override host lb could select a specified host based on headers values). Although this can't be guaranteed because we have no constraint on the order of headers mutations and other operations in the router filter.

[Copilot]

Pull Request Overview

This PR introduces support for preserving the original host header via a new header (x‑envoy‑original‑host) before any host rewriting takes place. Key changes include updates to header finalization logic (in functions such as Utility::updateAuthority and RouteEntryImplBase::finalizeRequestHeaders), modifications to tests to assert the presence and correctness of the new header, and corresponding API and documentation updates.

Reviewed Changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/mocks/router/mocks.cc	Removed the mocking of getRequestHostValue to align with the new changes.
test/common/router/router_test.cc	Added tests to verify that the original host is correctly preserved.
test/common/router/config_impl_test.cc	Updated tests to assert x‑envoy‑original‑host values under different scenarios.
test/common/http/utility_test.cc	Modified test cases for updateAuthority; one test loop uses a premature return.
source/common/router/upstream_request.cc	Updated the call to updateAuthority with the new flag for suppressing envoy headers.
source/common/router/router.cc	Adjusted header finalization and attempt count handling to support the new header logic.
source/common/router/delegating_route_impl.{h,cc}	Removed the deprecated getRequestHostValue function.
source/common/router/config_impl.{h,cc}	Changed the signature and behavior of header finalization functions.
source/common/http/utility.{h,cc}	Updated updateAuthority to set x‑envoy‑original‑host and handle forwarded host appropriately.
source/common/http/conn_manager_utility.cc	Ensured removal of the original host header from downstream requests.
envoy/router/router.h & envoy/http/header_map.h	Updated API definitions to reflect the removal of getRequestHostValue and addition of the new header.
docs/root/configuration/http/http_filters/router_filter.rst	Updated documentation for the new x‑envoy‑original‑host configuration.
changelogs/current.yaml & api/envoy/config/route/v3/route_components.proto	Documented the feature addition and updated API references accordingly.

[wbpcode]

/retest