✨ Pulse open WebSocket vitals on a shared heartbeat by bdibon · Pull Request #5095 · DataDog/browser-sdk

bdibon · 2026-10-01T09:53:15Z

Motivation

A connection held open for an hour is invisible until it closes, and one that dies without a close event reports nothing about the traffic it carried. Open connections now report where they are on a heartbeat.

Part of the WebSocket vitals stack. Every PR targets the previous one; the first one targets the boris.dibon/websocket-vitals integration branch, which is merged into main in one go once the whole stack is approved. #5055 stays open as the reference implementation: the tip of this stack is content-identical to it, rebased on the current main.

🔧 Pin rum-events-format and add WebSocket test utilities #5092 🔧 Pin rum-events-format and add WebSocket test utilities
✨ Collect connecting, open and closed WebSocket vitals #5093 ✨ Collect connecting, open and closed WebSocket vitals
✨ Report the websocket_closing vital #5094 ✨ Report the websocket_closing vital
✨ Pulse open WebSocket vitals on a shared heartbeat #5095 ✨ Pulse open WebSocket vitals on a shared heartbeat 👈 this PR
✨ Report WebSocket silences and send queue depth, and protect WebSocket vitals in beforeSend #5096 ✨ Report WebSocket silences and send queue depth, and protect WebSocket vitals in beforeSend
✨ End WebSocket tracking when the page is discarded #5097 ✨ End WebSocket tracking when the page is discarded

Changes

Commit by commit:

✨ Date open WebSocket vitals at their pulse: recordPulse() dates the next open vital and bumps the snapshot version it rides on. The first open vital is dated at the open event; a pulse outside the open phase is ignored.
✨ Pulse open WebSocket vitals on a shared heartbeat: every WEBSOCKET_HEARTBEAT_INTERVAL (1 min, the rate Chrome throttles hidden tabs' timers to), every connection in phase open emits a new websocket_open vital. One timer serves every connection and only runs while one is open; a closing connection falls silent, so a hung close stops looking alive.
✨ Pulse open WebSocket vitals when the page is hidden, frozen or unloading: on PREPARE_URGENT_FLUSH, so the traffic is sent before the page is frozen or lost. On mobile, hidden is the only signal guaranteed at that point.
✅ Cover the WebSocket heartbeat end to end

Test instructions

Unit: yarn test:unit --spec "packages/browser-rum-core/src/domain/webSocket/*.spec.ts" --spec packages/browser-rum-core/src/browser/webSocketObservable.spec.ts
E2E: yarn test:e2e -g "rum websockets"

Note

check-staging-merge is expected to fail: staging-40 already contains the earlier merge of #5055, which touches the same files. It clears at the next staging bump; the other checks should be green.

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 · 2026-10-01T09:53:26Z

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ℹ️ Info

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🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 80.65%
• Overall Coverage: 77.38% (+0.01%)

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🔗 Commit SHA: e050cd3 | Docs | View more details | Give us feedback!}

cit-pr-commenter-54b7da · 2026-10-01T09:54:57Z

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum Salesforce	N/A	186.81 KiB	N/A	N/A	N/A
Rum	186.30 KiB	186.79 KiB	+501 B	+0.26%	✅
Rum-salesforce Profiler	N/A	8.35 KiB	N/A	N/A	N/A
Rum Profiler	8.35 KiB	8.35 KiB	0 B	0.00%	✅
Rum-salesforce Recorder	N/A	31.94 KiB	N/A	N/A	N/A
Rum Recorder	31.94 KiB	31.94 KiB	0 B	0.00%	✅
Logs	59.00 KiB	59.00 KiB	0 B	0.00%	✅
Rum Slim	144.29 KiB	144.75 KiB	+480 B	+0.32%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅
Rum Shopify	N/A	217.20 KiB	N/A	N/A	N/A
Rum-shopify Profiler	N/A	8.35 KiB	N/A	N/A	N/A
Rum-shopify Recorder	N/A	4.77 KiB	N/A	N/A	N/A

chatgpt-codex-connector · 2026-10-01T12:18:43Z

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-07T16:18:32.129134Z	`e050cd3`	New commits

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bcaudan · 2026-10-06T08:15:21Z

    case 'open':
-      return state.openClocks
+      return state.pulseClocks


💬 suggestion: ‏Looking at that, I guess we could maybe remove the pulse concept.

pulseClocks -> openClocks

recordPulse -> updateOpen

I think we need the openClocks to record the timeToFirstMessage, for example:
connection opens at T0 -> no messages... -> heartbeat pulses, the openClocks would then change -> a message is sent or received -> timeToFirstMessage is computed from openClocks which is actually pulseClocks

I will rename it to reportClocks, to be coherent with your next comments

An open connection can now be reported again at a later pulse: recordPulse dates its next open vital and bumps the snapshot version it rides on. The first open vital is dated at the open event; a pulse outside the open phase is ignored. Co-authored-by: Cursor <cursoragent@cursor.com>

Every WEBSOCKET_HEARTBEAT_INTERVAL (one minute), each connection in phase open reports a new websocket_open vital with the next snapshot version, so a long-lived connection is visible while it is open. One timer serves every connection, and only runs while one is open; a closing connection falls silent. Co-authored-by: Cursor <cursoragent@cursor.com>

…ading A background transition is the only signal mobile browsers guarantee before a page goes away, and a connection may not survive it. Open connections report a pulse on every PREPARE_URGENT_FLUSH, so the traffic they carried is sent before the page is frozen or lost. Co-authored-by: Cursor <cursoragent@cursor.com>

Co-authored-by: Cursor <cursoragent@cursor.com>

bdibon mentioned this pull request Oct 1, 2026

✨ WebSocket vitals (stacked review) #5091

Closed

3 of 5 tasks

bdibon force-pushed the boris.dibon/websocket-vitals-4-pulse branch from 8e9d84a to 1d9542c Compare October 1, 2026 11:59

bdibon added this pull request to stack #5099 October 1, 2026 12:13

bdibon marked this pull request as ready for review October 1, 2026 12:18

bdibon requested a review from a team as a code owner October 1, 2026 12:18

bcaudan reviewed Oct 6, 2026

View reviewed changes

bdibon and others added 7 commits October 7, 2026 15:15

✅ Cover the WebSocket heartbeat end to end

ee95afc

Co-authored-by: Cursor <cursoragent@cursor.com>

👌 Extract heartbeat cleanup to a dedicated function

2274827

👌 Update language from "heartbeat" to "periodic report"

7913e49

👌 Update language from "pulse" -> "report"

2b63be9

bdibon force-pushed the boris.dibon/websocket-vitals-4-pulse branch from 1d9542c to 2b63be9 Compare October 7, 2026 14:28

bdibon requested a review from bcaudan October 7, 2026 15:04

bcaudan reviewed Oct 7, 2026

View reviewed changes

Comment thread packages/browser-rum-core/src/domain/webSocket/webSocketCollection.ts Outdated

Comment thread packages/browser-rum-core/src/domain/webSocket/trackedConnection.ts Outdated

Comment thread packages/browser-rum-core/src/domain/webSocket/webSocketCollection.ts Outdated

bcaudan approved these changes Oct 7, 2026

View reviewed changes

bdibon added 2 commits October 7, 2026 17:41

📝 Clean up comments

004f25f

👌 Split reportOpenConnectionsPeriodically

e050cd3

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✨ Pulse open WebSocket vitals on a shared heartbeat - #5095

✨ Pulse open WebSocket vitals on a shared heartbeat#5095
bdibon wants to merge 9 commits into
boris.dibon/websocket-vitals-3-closingfrom
boris.dibon/websocket-vitals-4-pulse

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