feat: AudioContext baseLatency entropy source (#1004)

src/sources/audio_base_latency.test.ts

@@ -0,0 +1,38 @@
+import { getBrowserVersion, isGecko, isWebKit } from '../../tests/utils'
+import getAudioBaseLatency from './audio_base_latency'
+
+describe('Sources', () => {
+  describe('audioBaseLatency', () => {
+    it("doesn't fail", () => {
+      const result = getAudioBaseLatency()
+      if (!hasBaseLatencySupport()) {
+        expect(result).toBe(undefined)
+        return
+      }
+
+      if (isGecko()) {
+        expect(result).toBe(0)
+      } else {
+        expect(result).toBeGreaterThan(0)
+      }
+    })
+
+    it('returns a stable value', () => {
+      const first = getAudioBaseLatency()
+      const second = getAudioBaseLatency()
+      expect(second).toBe(first)
+    })
+  })
+})
+
+function hasBaseLatencySupport() {
+  if (isWebKit()) {
+    const { major, minor } = getBrowserVersion() || { major: 0, minor: 0 }
+    if (major < 14) {
+      return false
+    } else if (major == 14) {
+      return minor >= 1
+    }
+  }
+  return true
+}

src/sources/audio_base_latency.ts

@@ -0,0 +1,7 @@
+export default function getAudioContextBaseLatency(): number | undefined {
+  if (!window.AudioContext) {
+    return undefined
+  }
+
+  return new AudioContext().baseLatency
+}

src/sources/index.ts

@@ -37,6 +37,7 @@ import getArchitecture from './architecture'
 import getApplePayState from './apple_pay'
 import getPrivateClickMeasurement from './private_click_measurement'
 import { getWebGlBasics, getWebGlExtensions } from './webgl'
+import getAudioContextBaseLatency from './audio_base_latency'
 
 /**
  * The list of entropy sources used to make visitor identifiers.
@@ -92,6 +93,7 @@ export const sources = {
   architecture: getArchitecture,
   applePay: getApplePayState,
   privateClickMeasurement: getPrivateClickMeasurement,
+  audioBaseLatency: getAudioContextBaseLatency,
 
   // Some sources can affect other sources (e.g. WebGL can affect canvas), so it's important to run these sources
   // after other sources.