Multiple calls to getRandomValues

[quintasda]

What React Native libraries do you use?

React Native without Frameworks, Hermes, RN New Architecture

Are you using sentry.io or on-premise?

sentry.io (SaS)

@sentry/react-native SDK Version

@sentry/react-native": "7.2.0"

How does your development environment look like?

System:
  OS: macOS 15.7.2
  CPU: (16) arm64 Apple M4 Max
  Memory: 795.45 MB / 64.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 24.10.0
    path: ~/.nvm/versions/node/v24.10.0/bin/node
  Yarn:
    version: 4.10.2
    path: ~/.nvm/versions/node/v24.10.0/bin/yarn
  npm:
    version: 11.6.1
    path: ~/.nvm/versions/node/v24.10.0/bin/npm
  Watchman:
    version: 2025.10.27.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.14.3
    path: /.rvm/gems/ruby-3.2.2/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.2
      - iOS 26.2
      - macOS 26.2
      - tvOS 26.2
      - visionOS 26.2
      - watchOS 26.2
  Android SDK: Not Found
IDEs:
  Android Studio: 2025.2 AI-252.25557.131.2521.14344949
  Xcode:
    version: 26.2/17C52
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.17
    path: /usr/bin/javac
  Ruby:
    version: 3.2.2
    path: /.rvm/rubies/ruby-3.2.2/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.0.0
    wanted: 20.0.0
  react:
    installed: 19.1.0
    wanted: 19.1.0
  react-native:
    installed: 0.81.5
    wanted: patch:react-native@npm%3A0.81.5#~/.yarn/patches/react-native-npm-0.81.5-d8232ef145.patch
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: false

info React Native v0.83.0 is now available (your project is running on v0.81.5).

Sentry.init()

Sentry.init({
  dsn: SENTRY_DSN,
  environment:
    __DEV__ || process.env.E2E_MODE === 'true' ? 'development' : 'production',
  release,
  dist,

  // Keep disabled to avoid attaching stacktraces to non-exception events (can affect event titles in UI).
  attachStacktrace: false,

  // Generic targets (no company/app domains).
  tracePropagationTargets: ['localhost'],

  // Keep the same behavior as the original wrapper.
  tracesSampleRate: 1,

  integrations: [
    routingInstrumentation,
    Sentry.hermesProfilingIntegration?.({ platformProfilers: false }),
    Sentry.breadcrumbsIntegration?.({
      dom: false,
      fetch: false,
      history: false,
      sentry: false,
      xhr: false,
      console: false,
    }),
    Sentry.reactNativeTracingIntegration?.({ idleTimeoutMs: 1500 }),
  ].filter(Boolean),

  // denyUrls: [...],
  // ignoreErrors: [...],
  // beforeSend: (event) => event,
  // beforeSendTransaction: (tx) => tx,
  // tracesSampler: (ctx) => 0.1,
  // maxBreadcrumbs: 50,
});

// Initial config needs to be done after Sentry.init is called.
setSentryConfig({
  tracesSampleRate: baseTransactionSampleRate,
  tracesSampleRateByName: {
    // Low importance transactions (generic example).
    'GET /example/low-importance-endpoint': baseTransactionSampleRate / 2,
  },
  sessionRateLimit: {
    maxDuplicatedEvents: process.env.E2E_MODE === 'true' || __DEV__ ? 1 : 10,
    totalMaxEvents: process.env.E2E_MODE === 'true' || __DEV__ ? 10 : 5_000,
  },
  identification: {
    domain: 'example.com',
  },
});

Steps to Reproduce

Making request in the app, found
node_modules/@sentry/core/build/esm/utils/tracing.js

/**
 * Create sentry-trace header from span context values.
 */
function generateSentryTraceHeader(
  traceId = generateTraceId(),
  spanId = generateSpanId(),
  sampled,
) {
  let sampledString = '';
  if (sampled !== undefined) {
    sampledString = sampled ? '-1' : '-0';
  }
  return `${traceId}-${spanId}${sampledString}`;
}

function generateTraceparentHeader(
  traceId = generateTraceId(),
  spanId = generateSpanId(),
  sampled,
) {
  return `00-${traceId}-${spanId}-${sampled ? '01' : '00'}`;
}
the generateTraceId and generateSpanId because are there as default the are being executed always, no matter if you call the function passing values.

Expected Result

calling the function generateSentryTraceHeader and generateTraceparentHeader, shouldn't generate extra calls to getRandomValues when generating a uuid4

Actual Result

calling the function generateSentryTraceHeader and generateTraceparentHeader, generate more than 90 calls to the getRandomValues to generate the uuid4

[linear]

RN-462

[antonis]

Thank you for reporting 🙇

This might be related to #4976, where react-native-get-random-values was missing as a peer dependency. If the polyfill isn't working correctly, it could cause generateTraceId() and generateSpanId() to return undefined, which would trigger the multiple calls. Is react-native-get-random-values listed in your package.json?

Could you share how you detected the 90+ redundant calls to getRandomValues? Understanding your measurement methodology will help us reproduce the issue accurately.

[gedu]

Thanks for the quick response 🙇

To answer your questions:

Dependency check

Yes — we do have react-native-get-random-values installed.
We’re currently using version 2.0.0, and it is correctly listed in our package.json.

How we detected the redundant getRandomValues calls

Here’s the methodology we followed to identify the ~90+ calls:
1. We initially noticed that a hashing function in our app was being called an unexpectedly high number of times.
2. Tracing upward, we found that this hashing function was ultimately triggered by getRandomValues.
3. We then logged request URLs and noticed that these calls happened right after the fetch request was fully constructed, which suggested a request-level concern rather than app logic.
4. From there, we identified that the calls were going through Sentry instrumentation.
5. As a sanity check:
• Disabling Sentry → the extra calls stopped entirely.
• Re-enabling Sentry → the calls immediately came back.
6. Digging deeper, we found that most of the getRandomValues calls were coming from createTraceparentHeader, which generates trace/span IDs.
7. That led us to inspect the implementation in
node_modules/@sentry/core/build/esm/utils/tracing.js.

Root cause we identified

The issue appears to be related to the use of function calls as default parameters, for example:

function generateSentryTraceHeader(
  traceId = generateTraceId(),
  spanId = generateSpanId(),
  sampled,
) {
   // ....
}

function generateTraceparentHeader(
  traceId = generateTraceId(),
  spanId = generateSpanId(),
  sampled,
) {
  // ....
}

Because generateTraceId() and generateSpanId() are used as default values, they are executed every time the function is invoked

Hope that helps, ping me if you need more information

[antonis]

Thank you for iterating on this 🙇
We are still investigating the report but the getRandomValues calls you're seeing might be legitimate UUID generation for spans. Each fetch request creates multiple spans (parent transaction span, http.client span, etc.), and each span needs a unique ID. The question is whether ~90 calls per request is expected or excessive. To verify if this is excessive: Check the Sentry Performance UI for one of these requests. If you see 2-3 spans but ~90 getRandomValues calls, something is wrong.