✨ Support `{ includeDefaults: true }` in trackResourceHeaders by bdibon · Pull Request #4825 · DataDog/browser-sdk

bdibon · 2026-06-26T14:37:14Z

Motivation

Enabling trackResourceHeaders with custom matchers while still collecting the built-in defaults previously required spreading DEFAULT_TRACKED_RESOURCE_HEADERS manually:

trackResourceHeaders: [
  ...DEFAULT_TRACKED_RESOURCE_HEADERS.map((name) => ({ name })),
  { name: 'x-request-id' },
]

This is verbose and forces customers to import (NPM) or reference (CDN) the DEFAULT_TRACKED_RESOURCE_HEADERS constant. This change adds an ergonomic sentinel so the defaults can be pulled in inline.

Changes

Validation (configuration.ts): validateAndBuildTrackResourceHeaders now expands a { includeDefaults: true } array entry into DEFAULT_TRACKED_RESOURCE_HEADERS in place, preserving array order so it can be combined with custom matchers. A typed shouldIncludeDefaultHeaders predicate keeps the union narrowing intact.
TSDoc: documented the new { includeDefaults: true } entry and updated the example to use it.
Deprecation: marked the DEFAULT_TRACKED_RESOURCE_HEADERS field on the DD_RUM public API as @deprecated in favor of the new sentinel. The field/value is kept to avoid a breaking change.
Tests: added cases for the sentinel alone and combined with a custom matcher.

New usage:

trackResourceHeaders: [{ includeDefaults: true }, { name: 'x-request-id' }]

Test instructions

Automated

yarn test:unit --spec packages/browser-rum-core/src/domain/configuration/configuration.spec.ts
yarn typecheck
yarn lint

All trackResourceHeaders tests pass (89/89), typecheck and lint are clean.

Manual (end-to-end)

Start the dev server and create a temporary sandbox page that combines the sentinel with a custom matcher:

yarn dev-server start

cat > sandbox/test-include-defaults.html << 'HTML'
<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>Test includeDefaults</title>
    <script src="/datadog-rum.js"></script>
    <script>
      DD_RUM.init({
        clientToken: 'xxx',
        applicationId: 'xxx',
        proxy: '/proxy',
        trackResources: true,
        trackResourceHeaders: [{ includeDefaults: true }, { name: 'x-custom-header' }],
      })
      function makeRequest() {
        fetch('/datadog-rum.js', { headers: { 'x-custom-header': 'hello' } })
      }
    </script>
  </head>
  <body>
    <button id="fetch-btn" onclick="makeRequest()">Fetch</button>
  </body>
</html>
HTML

Then exercise it (dev-server URL from yarn dev-server status):

yarn dev-server intake clear
agent-browser open http://localhost:8081/test-include-defaults.html
agent-browser click '#fetch-btn'
# wait for the fetch's PerformanceResourceTiming, then flush
agent-browser reload
yarn dev-server intake rum-resources \
  | jq -c 'select(.resource.type=="fetch") | {request_headers: .resource.request.headers, response_headers: .resource.response.headers}'

Expected output — the custom matcher (x-custom-header) is captured on the request and the expanded defaults (content-type, content-length, …) are captured on the response:

{"request_headers":{"x-custom-header":"hello"},"response_headers":{"content-type":"text/javascript; charset=utf-8","content-length":"2429864"}}

Cleanup:

yarn dev-server stop
rm sandbox/test-include-defaults.html

Checklist

Tested locally
Tested on staging
Added unit tests for this change.
Added e2e/integration tests for this change.
Updated documentation and/or relevant AGENTS.md file

datadog-datadog-prod-us1-2 · 2026-06-26T14:38:22Z

Tests

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 50.00%
• Overall Coverage: 77.19% (-0.01%)

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: 0cd0389 | Docs | Datadog PR Page | Give us feedback!}

Allow including the default tracked resource headers within a custom trackResourceHeaders array via a `{ includeDefaults: true }` entry, removing the need to spread DEFAULT_TRACKED_RESOURCE_HEADERS manually. Deprecate the DEFAULT_TRACKED_RESOURCE_HEADERS field on the DD_RUM public API in favor of the new sentinel (kept to avoid a breaking change). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cit-pr-commenter-54b7da · 2026-06-26T14:47:24Z

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	172.75 KiB	172.84 KiB	+91 B	+0.05%	✅
Rum Profiler	8.22 KiB	8.22 KiB	0 B	0.00%	✅
Rum Recorder	21.14 KiB	21.14 KiB	0 B	0.00%	✅
Logs	54.44 KiB	54.44 KiB	0 B	0.00%	✅
Rum Slim	130.27 KiB	130.35 KiB	+85 B	+0.06%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅

BenoitZugmeyer · 2026-06-29T07:43:26Z

   * trackResourceHeaders: [{ url: /\/api\//, name: 'server-timing', extractor: /dur=(\d+)/, location: 'response' }]
   */
-  trackResourceHeaders?: boolean | MatchHeader[] | undefined
+  trackResourceHeaders?: boolean | Array<MatchHeader | { includeDefaults: true }> | undefined


suggestion: make includeDefaults a MatchHeader option?

I don't think it's a good idea, if we want to do this we either have to:

A)

Add includeDefaults field on type MatchHeader, then we may end up with non-sensical entries such as { name: 'x-my-header', includeDefaults: true}, we could make name optional, but we will have to handle possibly undefined matchHeader.name

What's nice in the current design is that validateAndBuildTrackResourceHeaders always resolves entries of the configuration option to a MatchHeader, which the rest of the SDK uses.

B)

We do something like type MatchHeader = HeaderMatcher | IncludeDefaultsOption, SDK uses internally the HeaderMatcher type. It adds a type whose name will be hard to not be confusing.

I like the optional MatchHeader.name because:

it is more powerful, i.e. the user can include default headers for a specific URL only, or specific "location". Solution B only allows to include the default headers on all URLs and locations

it doesn't add a new data model/concept into the mix

What's nice in the current design is that validateAndBuildTrackResourceHeaders always resolves entries of the configuration option to a MatchHeader, which the rest of the SDK uses.

Having an optional name is trivial to handle, I would argue that it makes things even simpler. See this commit for illustration.

bdibon force-pushed the boris.dibon/track-resource-headers-include-defaults branch from 2e08107 to 0cd0389 Compare June 26, 2026 14:45

BenoitZugmeyer reviewed Jun 29, 2026

View reviewed changes

bdibon marked this pull request as ready for review June 30, 2026 07:09

bdibon requested a review from a team as a code owner June 30, 2026 07:09

bdibon requested a review from BenoitZugmeyer June 30, 2026 07:10

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

✨ Support `{ includeDefaults: true }` in trackResourceHeaders#4825

✨ Support `{ includeDefaults: true }` in trackResourceHeaders#4825
bdibon wants to merge 1 commit into
mainfrom
boris.dibon/track-resource-headers-include-defaults

bdibon commented Jun 26, 2026 •

edited

Loading

Uh oh!

datadog-datadog-prod-us1-2 Bot commented Jun 26, 2026 •

edited by datadog-prod-us1-5 Bot

Loading

Uh oh!

cit-pr-commenter-54b7da Bot commented Jun 26, 2026

Uh oh!

BenoitZugmeyer Jun 29, 2026

Uh oh!

bdibon Jun 29, 2026

Uh oh!

BenoitZugmeyer Jul 1, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

Conversation

bdibon commented Jun 26, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Motivation

Changes

Test instructions

Automated

Manual (end-to-end)

Checklist

Uh oh!

datadog-datadog-prod-us1-2 Bot commented Jun 26, 2026 • edited by datadog-prod-us1-5 Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

cit-pr-commenter-54b7da Bot commented Jun 26, 2026

Bundles Sizes Evolution

Uh oh!

BenoitZugmeyer Jun 29, 2026

Choose a reason for hiding this comment

Uh oh!

bdibon Jun 29, 2026

Choose a reason for hiding this comment

Uh oh!

BenoitZugmeyer Jul 1, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

bdibon commented Jun 26, 2026 •

edited

Loading

datadog-datadog-prod-us1-2 Bot commented Jun 26, 2026 •

edited by datadog-prod-us1-5 Bot

Loading