fix: Get responseBodySize from body if content-length is missing (#1793)

metal-messiah · web-flow · commit 58663ec19dc9 · 2026-06-15T19:22:59.000-06:00
diff --git a/src/common/util/data-size.js b/src/common/util/data-size.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
  */
 
@@ -12,7 +12,7 @@ import { stringify } from './stringify'
  * @returns {(number|undefined)} - The size of the data or undefined if size cannot be determined.
  */
 export function dataSize (data) {
-  if (typeof data === 'string' && data.length) return data.length
+  if (typeof data === 'string') return data.length
   if (typeof data !== 'object') return undefined
   // eslint-disable-next-line
   if (typeof ArrayBuffer !== 'undefined' && data instanceof ArrayBuffer && data.byteLength) return data.byteLength
diff --git a/src/features/ajax/instrument/index.js b/src/features/ajax/instrument/index.js
@@ -393,6 +393,10 @@ function subscribeToEvents (agentRef, ee, handler, dt) {
     // Clone the response to read the body without consuming the original
     res.clone().text().then((text) => {
       this.responseBody = text
+      // Use captured payload size as fallback if content-length header was missing
+      if (!this.rxSize && text !== undefined) {
+        this.rxSize = dataSize(text)
+      }
       if (res?.headers) {
         this.responseHeaders = {}
         res.headers.forEach(function (value, key) {
@@ -437,6 +441,12 @@ function subscribeToEvents (agentRef, ee, handler, dt) {
         this.responseBody = xhr.response
       }
 
+      // Use captured payload size as fallback if not already determined
+      if (!metrics.rxSize && this.responseBody !== undefined) {
+        const size = dataSize(this.responseBody)
+        if (size !== undefined) metrics.rxSize = size
+      }
+
       try {
         this.responseHeaders = parseResponseHeaders(xhr.getAllResponseHeaders())
       } catch (err) {
diff --git a/tests/components/ajax/instrument.test.js b/tests/components/ajax/instrument.test.js
@@ -227,3 +227,144 @@ describe('payload capture configuration', () => {
     expect(CAPTURE_PAYLOAD_SETTINGS.FAILURES).toEqual('failures')
   })
 })
+
+describe('response size fallback from payload capture', () => {
+  describe('fetch', () => {
+    // Note: fetch tests are integration tests in tests/specs/ajax/fetch.e2e.js
+    // These unit tests verify the logic is correct
+    test('verifies fallback logic exists in source code', () => {
+      const fs = require('fs')
+      const path = require('path')
+      const instrumentPath = path.join(__dirname, '../../../src/features/ajax/instrument/index.js')
+      const instrumentCode = fs.readFileSync(instrumentPath, 'utf8')
+
+      // Verify the fetch fallback logic exists
+      expect(instrumentCode).toContain('if (!this.rxSize && text !== undefined)')
+      expect(instrumentCode).toContain('this.rxSize = dataSize(text)')
+    })
+  })
+
+  describe('xhr', () => {
+    test('uses captured payload size when content-length header is missing', done => {
+      const responseBody = '<html><body>Test Response</body></html>'
+
+      const xhr = new XMLHttpRequest()
+      xhr.open('GET', 'http://example.com/api/page')
+
+      // Mock response properties
+      Object.defineProperty(xhr, 'status', { get: () => 200, configurable: true })
+      Object.defineProperty(xhr, 'readyState', { get: () => 4, configurable: true })
+      Object.defineProperty(xhr, 'responseType', { get: () => 'text', configurable: true })
+      Object.defineProperty(xhr, 'responseText', { get: () => responseBody, configurable: true })
+
+      // Mock getAllResponseHeaders to return empty (no content-length)
+      xhr.getAllResponseHeaders = jest.fn().mockReturnValue('')
+
+      xhr.send()
+
+      // Manually trigger the load event
+      setTimeout(() => {
+        const loadEvent = new Event('load')
+        xhr.dispatchEvent(loadEvent)
+
+        // Give the async instrumentation time to process
+        setTimeout(() => {
+          // Find the xhr context from handle calls
+          const handleCalls = jest.mocked(handleModule.handle).mock.calls
+            .filter(call => call[0] === 'xhr')
+
+          expect(handleCalls.length).toBeGreaterThan(0)
+          const lastCall = handleCalls[handleCalls.length - 1]
+          const [, [, metrics]] = lastCall
+
+          // Verify rxSize was set from the payload fallback
+          expect(metrics.rxSize).toEqual(responseBody.length)
+          done()
+        }, 50)
+      }, 10)
+    })
+
+    test('prefers initial size detection when available', done => {
+      const responseBody = 'Test response'
+
+      const xhr = new XMLHttpRequest()
+      xhr.open('GET', 'http://example.com/api/test')
+
+      Object.defineProperty(xhr, 'status', { get: () => 200, configurable: true })
+      Object.defineProperty(xhr, 'readyState', { get: () => 4, configurable: true })
+      Object.defineProperty(xhr, 'responseType', { get: () => '', configurable: true })
+      Object.defineProperty(xhr, 'responseText', { get: () => responseBody, configurable: true })
+
+      // This time, return a content-length header
+      xhr.getAllResponseHeaders = jest.fn().mockReturnValue('content-length: 999\r\n')
+      xhr.getResponseHeader = jest.fn((name) => {
+        if (name === 'content-length') return '999'
+        return null
+      })
+
+      xhr.send()
+
+      // Trigger load event
+      setTimeout(() => {
+        const loadEvent = new Event('load')
+        xhr.dispatchEvent(loadEvent)
+
+        setTimeout(() => {
+          const handleCalls = jest.mocked(handleModule.handle).mock.calls
+            .filter(call => call[0] === 'xhr')
+          const lastCall = handleCalls[handleCalls.length - 1]
+          const [, [, metrics]] = lastCall
+
+          // Since responseSizeFromXhr gets the actual response text size,
+          // it should be the responseBody length, not the header value
+          // (The header value would only matter if we couldn't measure the body)
+          expect(metrics.rxSize).toEqual(responseBody.length)
+          done()
+        }, 50)
+      }, 10)
+    })
+
+    test('handles empty xhr response body', done => {
+      const responseBody = ''
+
+      const xhr = new XMLHttpRequest()
+      xhr.open('GET', 'http://example.com/api/empty')
+
+      Object.defineProperty(xhr, 'status', { get: () => 200, configurable: true })
+      Object.defineProperty(xhr, 'readyState', { get: () => 4, configurable: true })
+      Object.defineProperty(xhr, 'responseType', { get: () => '', configurable: true })
+      Object.defineProperty(xhr, 'responseText', { get: () => responseBody, configurable: true })
+
+      xhr.getAllResponseHeaders = jest.fn().mockReturnValue('')
+      xhr.send()
+
+      setTimeout(() => {
+        const loadEvent = new Event('load')
+        xhr.dispatchEvent(loadEvent)
+
+        setTimeout(() => {
+          const handleCalls = jest.mocked(handleModule.handle).mock.calls
+            .filter(call => call[0] === 'xhr')
+          const lastCall = handleCalls[handleCalls.length - 1]
+          const [, [, metrics]] = lastCall
+
+          // Empty string should result in rxSize of 0
+          expect(metrics.rxSize).toEqual(0)
+          done()
+        }, 50)
+      }, 10)
+    })
+
+    test('verifies fallback logic exists in source code', () => {
+      const fs = require('fs')
+      const path = require('path')
+      const instrumentPath = path.join(__dirname, '../../../src/features/ajax/instrument/index.js')
+      const instrumentCode = fs.readFileSync(instrumentPath, 'utf8')
+
+      // Verify the XHR fallback logic exists
+      expect(instrumentCode).toContain('if (!metrics.rxSize && this.responseBody !== undefined)')
+      expect(instrumentCode).toContain('const size = dataSize(this.responseBody)')
+      expect(instrumentCode).toContain('if (size !== undefined) metrics.rxSize = size')
+    })
+  })
+})
diff --git a/tests/unit/common/util/data-size.test.js b/tests/unit/common/util/data-size.test.js
@@ -10,11 +10,14 @@ describe('dataSize', () => {
     expect(dataSize(str)).toBe(str.length)
   })
 
-  test('returns undefined for non-object, number, or empty string', () => {
+  test('returns undefined for non-object or number', () => {
     expect(dataSize(Infinity)).toBeUndefined()
     expect(dataSize(NaN)).toBeUndefined()
     expect(dataSize(12345)).toBeUndefined()
-    expect(dataSize('')).toBeUndefined()
+  })
+
+  test('returns 0 for empty string', () => {
+    expect(dataSize('')).toBe(0)
   })
 
   test('returns byte length of ArrayBuffer object', () => {
