fix: Calculate browser_stack_hash from truncated stack trace

src/features/jserrors/aggregate/format-stack-trace.js

@@ -1,5 +1,5 @@
 /**
- * Copyright 2020-2025 New Relic, Inc. All rights reserved.
+ * Copyright 2020-2026 New Relic, Inc. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -10,7 +10,7 @@ export function formatStackTrace (stackLines) {
   return truncateStackLines(stackLines).replace(stripNewlinesRegex, '')
 }
 
-// takes array of stack lines and returns string with top 50 and buttom 50 lines
+// takes array of stack lines and returns string with top 50 and bottom 50 lines
 function truncateStackLines (stackLines) {
   var stackString
   if (stackLines.length > 100) {
@@ -26,5 +26,5 @@ function truncateStackLines (stackLines) {
 
 // truncates stack string to limit what is sent to backend
 export function truncateSize (stackString) {
-  return (stackString.length > MAX_STACK_TRACE_LENGTH) ? stackString.substr(0, MAX_STACK_TRACE_LENGTH) : stackString
+  return stackString.length > MAX_STACK_TRACE_LENGTH ? stackString.substr(0, MAX_STACK_TRACE_LENGTH) : stackString
 }

src/features/jserrors/aggregate/index.js

@@ -267,7 +267,7 @@ export class Aggregate extends AggregateBase {
       params.stack_trace = truncateSize(stackInfo.stackString)
       this.observedAt[bucketHash] = Math.floor(this.agentRef.runtime.timeKeeper.correctRelativeTimestamp(time))
     } else {
-      params.browser_stack_hash = stringHashCode(stackInfo.stackString)
+      params.browser_stack_hash = stringHashCode(truncateSize(stackInfo.stackString))
     }
     params.releaseIds = stringify(this.agentRef.runtime.releaseIds)
 

tests/components/jserrors/browser-stack-hash.test.js

@@ -0,0 +1,61 @@
+import { stringHashCode } from '../../../src/features/jserrors/aggregate/string-hash-code'
+import { Instrument as JsErrors } from '../../../src/features/jserrors/instrument'
+import { resetAgent, setupAgent } from '../setup-agent'
+
+let mainAgent
+beforeAll(() => {
+  mainAgent = setupAgent({
+    init: {
+      jserrors: { enabled: true }
+    }
+  })
+})
+
+let jserrorsAggregate
+beforeEach(async () => {
+  const jserrorsInstrument = new JsErrors(mainAgent)
+  await Promise.all([jserrorsInstrument.onAggregateImported])
+  jserrorsAggregate = jserrorsInstrument.featAggregate
+
+  jserrorsAggregate.ee.emit('rumresp', [{ err: 1 }]) // register rumresp event to activate and drain error buffer
+  await new Promise(process.nextTick)
+})
+afterEach(() => {
+  resetAgent(mainAgent)
+})
+
+// This function will generate an error with a stack trace that is larger than the maximum size allowed for the stack trace string
+const generateTestError = (errorName) => {
+  const maxSize = 65530
+  const error = new Error(errorName)
+  const stackHeader = error.stack.split('\n')[0]
+  const stackLines = [stackHeader]
+  let i = 0
+  while (stackLines.join('\n').length < maxSize + 100) {
+    stackLines.push(`    at generated${'F'.repeat(maxSize / 100)}rame (https://example.com/app.js:1:${i})`)
+    i++
+  }
+
+  error.stack = stackLines.join('\n')
+  return error
+}
+
+test('in error params, string hash code of max-sized stack trace equals browser stack hash', async () => {
+  let harvestedData
+
+  await new Promise(process.nextTick)
+  jserrorsAggregate.processError(generateTestError('test message'), 100) // emit an error with max-sized stack trace
+
+  harvestedData = jserrorsAggregate.events.get(jserrorsAggregate.harvestOpts)
+  const stack_trace = harvestedData.err[0].params.stack_trace // get the stack trace
+
+  jserrorsAggregate.events.clear() // pretend that we drained the data by clearing the buffer; needed to get browser stack hash
+
+  await new Promise(process.nextTick)
+  jserrorsAggregate.processError(generateTestError('test message'), 101) // emit the same error again
+
+  harvestedData = jserrorsAggregate.events.get(jserrorsAggregate.harvestOpts)
+  const browser_stack_hash = harvestedData.err[0].params.browser_stack_hash // get the browser stack hash
+
+  expect(stringHashCode(stack_trace)).toEqual(browser_stack_hash) // string hashed stack_trace must equal browser_stack_hash
+})