Add Alt-Svc header support to advertise HTTP/3 availability by reta · Pull Request #20434 · opensearch-project/OpenSearch

reta · 2026-01-18T19:24:56Z

Description

It is impossible to determine, in advance, whether a target server supports HTTP/3. It is also impossible to upgrade an existing HTTP/1.1 or HTTP/2 connection to an HTTP/3 connection, since HTTP/1.1 and HTTP/2 are built on top of TCP streams while HTTP/3's QUIC is built on top of UDP datagrams.

By default, if enabled, HTTP/3 transport is available on the same port as HTTP/1.1 and HTTP/2 transports. The Alt-Svc header (see please [1]) is the standard way to advertise alternative services (HTTP/2 or HTTP/3).

Examples:

when HTTP/2 is used

< HTTP/2 200
< alt-svc: h3=":9200"; ma=3600
< x-opensearch-version: OpenSearch/3.5.0-SNAPSHOT (opensearch)
< content-type: application/json; charset=UTF-8
< content-length: 572

when HTTP/3 is used

< HTTP/3 200
< alt-svc: h2=":9200"; ma=3600
< x-opensearch-version: OpenSearch/3.5.0-SNAPSHOT (opensearch)
< content-type: application/json; charset=UTF-8
< content-length: 572

[1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Alt-Svc

Related Issues

Closes #20433

Check List

Functionality includes testing.
API changes companion pull request created, if applicable.
Public documentation issue/PR created, if applicable.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

coderabbitai · 2026-01-18T19:25:22Z

Important

Review skipped

Auto incremental reviews are disabled on this repository.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

📝 Walkthrough

Walkthrough

This PR implements Alt-Svc header support to advertise HTTP/3 availability on OpenSearch servers. It introduces a factory-based system to generate version-specific response headers, threads this factory through the Netty HTTP request/response handling pipeline, and adds integration tests validating HTTP/2 and HTTP/3 advertising behavior.

Changes

Cohort / File(s)	Summary
Interface and Factory for Alt-Svc Headers `modules/transport-netty4/src/main/java/org/opensearch/http/netty4/HttpResponseHeadersFactory.java`, `modules/transport-netty4/src/main/java/org/opensearch/http/netty4/HttpResponseHeadersFactories.java`	Introduces a new `HttpResponseHeadersFactory` interface with a single method `headers(HttpVersion version)` for producing protocol-specific response headers. `HttpResponseHeadersFactories` provides factory methods: `newHttp2Aware()` and `newHttp3Aware()` (with HTTP/3 availability checks and settings-driven feature flags), plus `newDefault()` for no-op behavior.
Request Creator Updates `modules/transport-netty4/src/main/java/org/opensearch/http/netty4/Netty4Http3RequestCreator.java`, `modules/transport-netty4/src/main/java/org/opensearch/http/netty4/Netty4HttpRequestCreator.java`	Both request creators now accept and store an `HttpResponseHeadersFactory` parameter, propagating it into constructed `Netty4HttpRequest` objects across normal and error paths.
Request and Response Handling `modules/transport-netty4/src/main/java/org/opensearch/http/netty4/Netty4HttpRequest.java`	Constructor signatures extended to accept `HttpResponseHeadersFactory`. New private field stores the factory; `createResponse()` now applies headers from the factory to the produced response based on HTTP protocol version. Headers are preserved through copy and transform operations.
Transport Layer Integration `modules/transport-netty4/src/main/java/org/opensearch/http/netty4/Netty4HttpServerTransport.java`, `modules/transport-netty4/src/main/java/org/opensearch/http/netty4/Netty4Http3ServerTransport.java`, `modules/transport-netty4/src/main/java/org/opensearch/http/netty4/ssl/SecureNetty4HttpServerTransport.java`	`HttpChannelHandler` now accepts a new `HttpResponseHeadersFactory` parameter. HTTP/3 transport passes `Http2Aware` factory; secure transport passes `Http3Aware` factory. Factory is threaded into request creator initialization.
Integration Test `modules/transport-netty4/src/internalClusterTest/java/org/opensearch/http/netty4/Netty4Http3IT.java`	New integration test with a nested `SecureSettingsPlugin` that provides TLS/SSL configuration for HTTP/2 and HTTP/3. Tests validate Alt-Svc headers and opaque IDs for GET and POST requests; includes HTTP/3 availability checks and per-node secure settings provisioning.
Test Updates `modules/transport-netty4/src/test/java/org/opensearch/http/netty4/Netty4HttpPipeliningHandlerTests.java`, `modules/transport-netty4/src/test/java/org/opensearch/http/netty4/Netty4HttpServerPipeliningTests.java`	Updated to pass `HttpResponseHeadersFactories.newDefault()` when constructing `Netty4HttpRequest` and `HttpChannelHandler` in test contexts.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

#20017: Implements core HTTP/3 server-side transport support; this PR builds on top by adding Alt-Svc header advertisement for HTTP/3 availability.

Suggested labels

enhancement

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 8.16% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The pull request title accurately describes the main change: adding Alt-Svc header support to advertise HTTP/3 availability, which is the primary objective.
Linked Issues check	✅ Passed	The code changes implement Alt-Svc header support across HTTP transport classes: new HttpResponseHeadersFactory interface and HttpResponseHeadersFactories utilities create Alt-Svc headers with h2/h3 protocols, integration tests validate HTTP/2 and HTTP/3 behavior with Alt-Svc headers, and HTTP transport classes propagate the factory through request/response cycles.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing Alt-Svc header support for HTTP/3 advertising. Constructor signature updates to propagate HttpResponseHeadersFactory and test updates to pass the factory are in scope.
Description check	✅ Passed	The PR description comprehensively covers the purpose, includes related issues, and follows the template structure with all required sections completed.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

github-actions · 2026-01-18T20:04:44Z

❌ Gradle check result for 627e5f8: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-18T21:31:49Z

❌ Gradle check result for 0e8b051: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-18T23:06:22Z

❌ Gradle check result for 0e8b051: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-19T00:34:18Z

❌ Gradle check result for 0e8b051: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-19T02:36:36Z

✅ Gradle check result for 7556129: SUCCESS

codecov · 2026-01-19T02:36:56Z

Codecov Report

❌ Patch coverage is 64.21053% with 34 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.30%. Comparing base (dbb6d2e) to head (1ebdcbc).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
...p/reactor/netty4/HttpResponseHeadersFactories.java	30.43%	13 Missing and 3 partials ⚠️
...arch/http/netty4/HttpResponseHeadersFactories.java	52.00%	11 Missing and 1 partial ⚠️
.../org/opensearch/http/netty4/Netty4HttpRequest.java	77.77%	2 Missing ⚠️
...tty4/ReactorNetty4NonStreamingRequestConsumer.java	66.66%	1 Missing and 1 partial ⚠️
...nsearch/http/netty4/Netty4Http3RequestCreator.java	80.00%	1 Missing ⚠️
.../http/reactor/netty4/ReactorNetty4HttpRequest.java	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main   #20434   +/-   ##
=========================================
  Coverage     73.29%   73.30%           
- Complexity    71990    71996    +6     
=========================================
  Files          5793     5795    +2     
  Lines        329110   329181   +71     
  Branches      47402    47405    +3     
=========================================
+ Hits         241236   241291   +55     
+ Misses        68634    68579   -55     
- Partials      19240    19311   +71

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

github-actions · 2026-01-19T15:23:42Z

❌ Gradle check result for d3dad7b: ABORTED

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-19T16:41:52Z

❌ Gradle check result for d3dad7b: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-19T18:34:23Z

✅ Gradle check result for d3dad7b: SUCCESS

reta · 2026-01-19T21:08:53Z

@cwperks @andrross would appreciate if you folks find the time to take a look, closes the gap on HTTP/3 experimental support, thank you!

...ty4/src/internalClusterTest/java/org/opensearch/http/reactor/netty4/ReactorNetty4HttpIT.java

...or-netty4/src/main/java/org/opensearch/http/reactor/netty4/HttpResponseHeadersFactories.java

Signed-off-by: Andriy Redko <drreta@gmail.com>

.../transport-netty4/src/internalClusterTest/java/org/opensearch/http/netty4/Netty4Http3IT.java

github-actions · 2026-01-20T21:44:37Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-20T23:02:59Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T00:58:37Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T02:27:54Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T03:09:54Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T04:25:52Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T13:37:17Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T16:09:34Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T16:45:56Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T18:34:39Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T20:23:51Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-21T22:41:40Z

❌ Gradle check result for 1ebdcbc: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

github-actions · 2026-01-22T01:22:03Z

✅ Gradle check result for 1ebdcbc: SUCCESS

…ch-project#20434) * Add Alt-Svc header support to advertise HTTP/3 availability Signed-off-by: Andriy Redko <drreta@gmail.com> * Address code review comments Signed-off-by: Andriy Redko <drreta@gmail.com> --------- Signed-off-by: Andriy Redko <drreta@gmail.com>

reta requested review from a team and peternied as code owners January 18, 2026 19:24

reta added the skip-changelog label Jan 18, 2026

github-actions bot added enhancement Enhancement or improvement to existing feature or request Other v3.5.0 Issues and PRs related to version 3.5.0 labels Jan 18, 2026

reta added the distributed framework label Jan 18, 2026

reta force-pushed the issue-20433 branch from 627e5f8 to 0e8b051 Compare January 18, 2026 20:05

reta removed the skip-changelog label Jan 18, 2026

reta force-pushed the issue-20433 branch from 0e8b051 to 7556129 Compare January 19, 2026 01:10

reta force-pushed the issue-20433 branch from 7556129 to d3dad7b Compare January 19, 2026 13:20

cwperks reviewed Jan 20, 2026

View reviewed changes

...ty4/src/internalClusterTest/java/org/opensearch/http/reactor/netty4/ReactorNetty4HttpIT.java Outdated Show resolved Hide resolved

cwperks reviewed Jan 20, 2026

View reviewed changes

...or-netty4/src/main/java/org/opensearch/http/reactor/netty4/HttpResponseHeadersFactories.java Show resolved Hide resolved

reta added 2 commits January 20, 2026 15:31

Add Alt-Svc header support to advertise HTTP/3 availability

23a06b2

Signed-off-by: Andriy Redko <drreta@gmail.com>

Address code review comments

1ebdcbc

Signed-off-by: Andriy Redko <drreta@gmail.com>

reta force-pushed the issue-20433 branch from d3dad7b to 1ebdcbc Compare January 20, 2026 20:31

reta commented Jan 20, 2026

View reviewed changes

.../transport-netty4/src/internalClusterTest/java/org/opensearch/http/netty4/Netty4Http3IT.java Show resolved Hide resolved

cwperks approved these changes Jan 20, 2026

View reviewed changes

reta mentioned this pull request Jan 21, 2026

Introduce new libs/netty4 module to share common implementation between netty-based plugins and modules (transport-netty4, transport-reactor-netty4) #20447

Merged

3 tasks

reta merged commit af61c36 into opensearch-project:main Jan 22, 2026
49 of 76 checks passed

Conversation

reta commented Jan 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Description

Related Issues

Check List

Uh oh!

coderabbitai bot commented Jan 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Review skipped

Walkthrough

Changes

Estimated code review effort

Possibly related PRs

Suggested labels

Uh oh!

github-actions bot commented Jan 18, 2026

Uh oh!

github-actions bot commented Jan 18, 2026

Uh oh!

github-actions bot commented Jan 18, 2026

Uh oh!

github-actions bot commented Jan 19, 2026

Uh oh!

github-actions bot commented Jan 19, 2026

Uh oh!

codecov bot commented Jan 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

github-actions bot commented Jan 19, 2026

Uh oh!

github-actions bot commented Jan 19, 2026

Uh oh!

github-actions bot commented Jan 19, 2026

Uh oh!

reta commented Jan 19, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

github-actions bot commented Jan 20, 2026

Uh oh!

github-actions bot commented Jan 20, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 21, 2026

Uh oh!

github-actions bot commented Jan 22, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

reta commented Jan 18, 2026 •

edited

Loading

coderabbitai bot commented Jan 18, 2026 •

edited

Loading

codecov bot commented Jan 19, 2026 •

edited

Loading