✨ [RUM-16985] Capture wasm module build_ids and enrich error events by ImaneLargou · Pull Request #4920 · DataDog/browser-sdk

ImaneLargou · 2026-07-27T13:03:25Z

Motivation

Browser WebAssembly runtime errors currently lack the module metadata required for WASM symbolication.

This change identifies errors containing WebAssembly stack frames and reports the loaded WASM module URL and build ID. This allows the error-processing pipeline to distinguish ordinary browser errors from errors that should use WASM/DWARF symbolication.

Related upstream schema change: DataDog/rum-events-format#427

Changes

Track WebAssembly modules loaded through:
- WebAssembly.instantiate
- WebAssembly.instantiateStreaming
- WebAssembly.compile
- WebAssembly.compileStreaming
Extract module build IDs from the build_id custom section, with external_debug_info as a fallback.
Detect WASM errors by checking the complete error stack for WASM-specific frames.
Report the following metadata on WASM errors:
- error.source_type: "browser+wasm"
- error.wasm_modules, containing the module URL and build ID
Add support to both RUM and Browser Logs.
Keep ordinary JavaScript errors unchanged. In particular, .js frames do not qualify an error as WASM.
Update the generated RUM event types from the corresponding rum-events-format schema change.

Test instructions

Run the relevant unit tests:

packages/browser-core/src/domain/wasmModules/wasmBinaryParser.spec.ts
packages/browser-core/src/domain/wasmModules/wasmModuleTracking.spec.ts
packages/browser-rum-core/src/domain/error/errorCollection.spec.ts
packages/browser-logs/src/domain/createErrorFieldFromRawError.spec.ts

Run the E2E scenario:

yarn test:e2e -g "send WebAssembly runtime errors with module metadata"

The E2E test loads a real .wasm module using WebAssembly.instantiateStreaming, triggers a runtime error, and verifies that both RUM and Logs events contain:

  {
    "source_type": "browser+wasm",
    "wasm_modules": [
      {
        "url": "<test module URL>",
        "build_id": "abcd"
      }
    ]
  }

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

Intercepts WebAssembly.instantiate / instantiateStreaming at SDK script-load time to record (url, build_id) per loaded module, including lazily-loaded modules. On error capture, attaches error.wasm_modules[] and sets source_type='browser+wasm' so the backend can dispatch wasm symbolication. - New wasmModules/wasmModuleTracking.ts: hooks all four WebAssembly entry points; reads build_id via a minimal custom-section parser; registry stays live for lazy module loads - New wasmModules/wasmBinaryParser.ts: walks wasm binary sections, extracts build_id custom section or falls back to external_debug_info - errorCollection: populates error.wasm_modules[] and flips source_type to 'browser+wasm' when any module is registered - rawRumEvent.types: adds wasm_modules?: Array<{url, build_id}> to RawRumErrorEvent - main.ts: installs tracking synchronously at script-load time to close the race window before DD_RUM.init()'s deferred microtask Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

github-actions · 2026-07-27T13:03:37Z

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

datadog-official · 2026-07-27T13:03:41Z

✨ Unblock PR with BitsAI

⚠️ Warnings

❌ Your PR has failed checks. Please review the issues below and take necessary action before merging.

🚦 2 Pipeline jobs failed

DataDog/browser-sdk | build-and-lint — 🔧 Needs a code fix, caused by this PR

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ℹ️ Info

No other issues found (see more)

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 80.77%
• Overall Coverage: 77.03% (+0.02%)

Useful? React with 👍 / 👎

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

🔗 Commit SHA: 58d9927 | Docs | View more details | Give us feedback!}

…-experiment

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cit-pr-commenter-54b7da · 2026-08-11T09:59:53Z

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	182.00 KiB	182.06 KiB	+69 B	+0.04%	✅
Rum Profiler	8.43 KiB	8.43 KiB	0 B	0.00%	✅
Rum Recorder	25.32 KiB	25.32 KiB	0 B	0.00%	✅
Logs	57.93 KiB	58.55 KiB	+631 B	+1.06%	✅
Rum Salesforce	N/A	140.10 KiB	N/A	N/A	N/A
Rum Slim	140.05 KiB	140.10 KiB	+49 B	+0.03%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅
Rum Shopify	N/A	206.86 KiB	N/A	N/A	N/A
Rum-shopify Profiler	N/A	8.43 KiB	N/A	N/A	N/A
Rum-shopify Recorder	N/A	3.74 KiB	N/A	N/A	N/A

ImaneLargou · 2026-08-11T15:57:51Z

I have read the CLA Document and I hereby sign the CLA

…-experiment

mormubis · 2026-08-21T13:44:18Z

+// wrapper only resolves once both are done. This guarantees that an error
+// thrown immediately by an exported function can reference the loaded module.
+function captureFromResponse(response: Response): Promise<void> {
+  const url = response.url || '<wasm-instantiate-streaming-no-url>'


❓ question: ‏How could the URL be empty? Is this just because of the types?

It can be empty when the response is created manually with new Response(wasmBytes) instead of coming from fetch(). This is probably uncommon, but the fallback handles that edge case. I can remove the fallback if we don’t want to send a synthetic URL.

mormubis · 2026-08-21T13:45:07Z

+  trackingClients += 1
+  if (!stopTracking) {
+    stopTracking = installWasmModuleTracking()
+  }
+
+  let stopped = false
+  return () => {
+    if (stopped) {
+      return
+    }
+    stopped = true
+    trackingClients -= 1
+    if (trackingClients === 0) {
+      stopTracking?.()
+      stopTracking = undefined
+      registry.clear()
+    }
+  }


❓ question: ‏How many clients could we expect tracking WebAssembly?

Once the module calls are removed, we expect at most two clients: RUM and Logs.

mormubis · 2026-08-21T13:53:13Z

 import { makeLogsPublicApi } from '../boot/logsPublicApi'

+// Install WebAssembly hooks before deferred Logs initialization so eagerly loaded modules are captured.
+startWasmModuleTracking()


🔨 warning: ‏The philosophy of the SDK is not to override any APIs unless we are allowed to track the user.

This should be deferred until SDK initialization.

mormubis · 2026-08-21T13:54:31Z

+  // reads it to set source_type='browser+wasm' and error.wasm_modules.
+  // Must start before any wasm load — RUM is initialised before the page's
+  // wasm fetch in typical setups.
+  const stopWasmModuleTracking = startWasmModuleTracking()


❓ question: ‏Are we not initializing this in different places?

Yes, this was part of my first tests at wasm module tracking but modules loaded before startRum runs were missed. Forgot to remove it 😅. I'll delete it.

mormubis · 2026-08-21T13:56:33Z

+// wasm modules — by the time the deferred wrap installs, instantiateStreaming
+// may have already been called. Installing here (before any deferral) closes
+// that race.
+startWasmModuleTracking()


🔨 warning: ‏Mentioned before.

mormubis · 2026-08-21T13:56:51Z

 import { makeProfilerApiStub } from '../boot/stubProfilerApi'

+// Install WebAssembly hooks before deferred RUM initialization so eagerly loaded modules are captured.
+startWasmModuleTracking()


🔨 warning: ‏Keeping track of all the places where this is automatically tracked.

…-experiment # Conflicts: # package.json # packages/browser-core/src/domain/telemetry/telemetryEvent.types.ts # yarn.lock

…-experiment # Conflicts: # package.json # packages/browser-logs/src/domain/runtimeError/runtimeErrorCollection.spec.ts # packages/browser-logs/src/rawLogsEvent.types.ts # yarn.lock

BenoitZugmeyer · 2026-09-01T14:18:10Z

      trackingConsentState.onGrantedOnce(() => {
        startTrackingConsentContext(hooks, trackingConsentState)
        mockable(startTelemetry)(TelemetryService.LOGS, configuration, hooks.assembleTelemetry, sdkName)
+        stopWasmModuleTracking = mockable(startWasmModuleTracking)()


question: why do we start module tracking here?

It starts after consent but before the asynchronous session-manager startup to avoid missing modules loaded during that wait. When I was testing with rum, it seemed like modules were missing if we start later than this.

BenoitZugmeyer · 2026-09-01T14:34:28Z

+  // Hook 1: instantiate(bytes | module, imports). For raw bytes, we can read
+  // build_id directly; for an already-compiled WebAssembly.Module we have no
+  // URL or bytes to inspect — register a placeholder.
+  WebAssembly.instantiate = function (this: typeof WebAssembly, source: any, importObject?: any) {


suggestion: use instrumentMethod to instrument all methods.

Changed to instrumentMethod

BenoitZugmeyer · 2026-09-01T14:37:30Z

+// Streaming compilation and metadata extraction happen in parallel, but the
+// wrapper only resolves once both are done. This guarantees that an error
+// thrown immediately by an exported function can reference the loaded module.
+function captureFromResponse(response: Response): Promise<void> {


nitpick: this might be better written as an async function

This function has been removed. We now extract the build ID directly from the compiled WebAssembly.Module, so we no longer clone or read the response body.

BenoitZugmeyer · 2026-09-01T14:54:32Z

+    WebAssembly.compileStreaming = function (source) {
+      return Promise.resolve(source).then((response: Response) => {
+        const capturePromise = captureFromResponse(response)
+        return Promise.all([origCompileStreaming.call(this, response), capturePromise]).then(([module]) => module)


issue: using instrumentMethod here would make sure all received argument are passed to the original compileStreaming method (mdn shows that it supports a compileOptions object)

Changed it to use instrumentMethod!

BenoitZugmeyer · 2026-09-01T14:58:36Z

+  try {
+    return response
+      .clone()
+      .arrayBuffer()


issue: you are downloading the whole response in memory -- that will have an impact on large wasm files. Would it be possible to read only a limited amount of bytes instead?

Updated the PR so now we extract the build ID directly from the compiled WebAssembly.Module, and we no longer clone or read the response body.

BenoitZugmeyer · 2026-09-01T15:12:03Z

+      await page.evaluate(async () => {
+        const { instance } = await WebAssembly.instantiateStreaming(fetch('/test-module.wasm'))
+
+        setTimeout(() => (instance.exports.run as () => void)())


question: why do we need this setTimeout?

The setTimeout makes the WASM trap occur as an uncaught browser error. If we call run() directly inside page.evaluate(), the exception is reported as an evaluation failure instead.

BenoitZugmeyer · 2026-09-01T15:14:03Z

    })

+  createTest('send WebAssembly runtime errors with module metadata')
+    .withRum()


suggestion: don't add a rum test in logs.scenario. Move the test in a common scenario file, or add split the test (one for rum, one for logs)

Tests are split into one for logs and one for rum now.

ImaneLargou changed the title ~~✨ [RUM-WASM] Capture wasm module build_ids and enrich error events~~ [WASM] Capture wasm module build_ids and enrich error events Jul 27, 2026

Merge remote-tracking branch 'origin/main' into imane.largou/wasm-sdk…

4d8b227

…-experiment

ImaneLargou marked this pull request as ready for review August 11, 2026 09:47

ImaneLargou requested a review from a team as a code owner August 11, 2026 09:47

🔧 [RUM-WASM] Remove stale fallback comment from wasmBinaryParser

193a2da

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ImaneLargou marked this pull request as draft August 11, 2026 10:10

✨ [RUM-WASM] Report WASM errors from Browser Logs

0070e34

ImaneLargou changed the title ~~[WASM] Capture wasm module build_ids and enrich error events~~ ✨ [RUM-16985] Capture wasm module build_ids and enrich error events Aug 11, 2026

✅ [RUM-16985] Test WASM error reporting

aded8c6

ImaneLargou mentioned this pull request Aug 12, 2026

[RUM-16985] Add browser WASM error metadata DataDog/rum-events-format#427

Merged

ImaneLargou added 4 commits August 12, 2026 13:54

🐛 [RUM-16985] Stabilize WASM error metadata

8f16b67

✅ [RUM-16985] Support browsers without streaming WASM

5f43474

✅ [RUM-16985] Scope WASM runtime E2E by browser

511f810

Merge remote-tracking branch 'origin/main' into imane.largou/wasm-sdk…

420fdee

…-experiment

mormubis reviewed Aug 21, 2026

View reviewed changes

ImaneLargou added 4 commits August 26, 2026 13:40

♻️ [RUM-16985] Initialize WASM tracking after consent

15057b4

Merge remote-tracking branch 'origin/main' into imane.largou/wasm-sdk…

1a861b9

…-experiment # Conflicts: # package.json # packages/browser-core/src/domain/telemetry/telemetryEvent.types.ts # yarn.lock

✅ [RUM-16985] Prevent WASM tracking leaks in tests

03c3b8a

Merge remote-tracking branch 'origin/main' into imane.largou/wasm-sdk…

ec098b1

…-experiment # Conflicts: # package.json # packages/browser-logs/src/domain/runtimeError/runtimeErrorCollection.spec.ts # packages/browser-logs/src/rawLogsEvent.types.ts # yarn.lock

ImaneLargou marked this pull request as ready for review August 31, 2026 11:23

BenoitZugmeyer reviewed Sep 1, 2026

View reviewed changes

ImaneLargou added 4 commits September 2, 2026 18:06

✨ Add WebAssembly error tracking plugin

7f749a4

🐛 Preserve complete WebAssembly build IDs

2554af5

Merge origin/main into imane.largou/wasm-sdk-experiment

06cf8d9

🐛 Fix WebAssembly plugin package checks

ac41674

🐛 Expose logger errors to Logs plugins before assembly

58d9927

This was referenced Sep 4, 2026

♻️ introduce Logs plugin API and assemble hook enrichment #5014

Open

♻️ Merge message context into raw logs event at collection time #5009

Open

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