feat: Add support for breadcrumb filtering.

packages/telemetry/browser-telemetry/__tests__/BrowserTelemetryImpl.test.ts

@@ -22,6 +22,7 @@ const defaultOptions: ParsedOptions = {
     },
     evaluations: true,
     flagChange: true,
+    filters: [],
   },
   stack: {
     source: {
@@ -208,3 +209,153 @@ it('unregisters collectors on close', () => {
 
   expect(mockCollector.unregister).toHaveBeenCalled();
 });
+
+it('filters breadcrumbs using provided filters', () => {
+  const options: ParsedOptions = {
+    ...defaultOptions,
+    breadcrumbs: {
+      ...defaultOptions.breadcrumbs,
+      click: false,
+      evaluations: false,
+      flagChange: false,
+      http: { instrumentFetch: false, instrumentXhr: false },
+      keyboardInput: false,
+      filters: [
+        // Filter to remove breadcrumbs with id:2
+        (breadcrumb) => {
+          if (breadcrumb.type === 'custom' && breadcrumb.data?.id === 2) {
+            return undefined;
+          }
+          return breadcrumb;
+        },
+        // Filter to transform breadcrumbs with id:3
+        (breadcrumb) => {
+          if (breadcrumb.type === 'custom' && breadcrumb.data?.id === 3) {
+            return {
+              ...breadcrumb,
+              data: { id: 'filtered-3' },
+            };
+          }
+          return breadcrumb;
+        },
+      ],
+    },
+  };
+  const telemetry = new BrowserTelemetryImpl(options);
+
+  telemetry.addBreadcrumb({
+    type: 'custom',
+    data: { id: 1 },
+    timestamp: Date.now(),
+    class: 'custom',
+    level: 'info',
+  });
+
+  telemetry.addBreadcrumb({
+    type: 'custom',
+    data: { id: 2 },
+    timestamp: Date.now(),
+    class: 'custom',
+    level: 'info',
+  });
+
+  telemetry.addBreadcrumb({
+    type: 'custom',
+    data: { id: 3 },
+    timestamp: Date.now(),
+    class: 'custom',
+    level: 'info',
+  });
+
+  const error = new Error('Test error');
+  telemetry.captureError(error);
+  telemetry.register(mockClient);
+
+  expect(mockClient.track).toHaveBeenCalledWith(
+    '$ld:telemetry:error',
+    expect.objectContaining({
+      breadcrumbs: expect.arrayContaining([
+        expect.objectContaining({ data: { id: 1 } }),
+        expect.objectContaining({ data: { id: 'filtered-3' } }),
+      ]),
+    }),
+  );
+
+  // Verify breadcrumb with id:2 was filtered out
+  expect(mockClient.track).toHaveBeenCalledWith(
+    '$ld:telemetry:error',
+    expect.objectContaining({
+      breadcrumbs: expect.not.arrayContaining([expect.objectContaining({ data: { id: 2 } })]),
+    }),
+  );
+});
+
+it('omits breadcrumb when a filter throws an exception', () => {
+  const breadSpy = jest.fn((breadcrumb) => breadcrumb);
+  const options: ParsedOptions = {
+    ...defaultOptions,
+    breadcrumbs: {
+      ...defaultOptions.breadcrumbs,
+      filters: [
+        () => {
+          throw new Error('Filter error');
+        },
+        // This filter should never run
+        breadSpy,
+      ],
+    },
+  };
+  const telemetry = new BrowserTelemetryImpl(options);
+
+  telemetry.addBreadcrumb({
+    type: 'custom',
+    data: { id: 1 },
+    timestamp: Date.now(),
+    class: 'custom',
+    level: 'info',
+  });
+
+  const error = new Error('Test error');
+  telemetry.captureError(error);
+  telemetry.register(mockClient);
+
+  expect(mockClient.track).toHaveBeenCalledWith(
+    '$ld:telemetry:error',
+    expect.objectContaining({
+      breadcrumbs: [],
+    }),
+  );
+
+  expect(breadSpy).not.toHaveBeenCalled();
+});
+
+it('omits breadcrumbs when a filter is not a function', () => {
+  const options: ParsedOptions = {
+    ...defaultOptions,
+    breadcrumbs: {
+      ...defaultOptions.breadcrumbs,
+      // @ts-ignore
+      filters: ['potato'],
+    },
+  };
+  const telemetry = new BrowserTelemetryImpl(options);
+
+  telemetry.addBreadcrumb({
+    type: 'custom',
+    data: { id: 1 },
+    timestamp: Date.now(),
+    class: 'custom',
+    level: 'info',
+  });
+
+  const error = new Error('Test error');
+  telemetry.captureError(error);
+  telemetry.register(mockClient);
+
+  expect(mockClient.track).toHaveBeenCalledWith(
+    '$ld:telemetry:error',
+    expect.objectContaining({
+      breadcrumbs: [],
+    }),
+  );
+});

packages/telemetry/browser-telemetry/__tests__/options.test.ts

@@ -22,6 +22,7 @@ it('can set all options at once', () => {
       click: false,
       evaluations: false,
       flagChange: false,
+      filters: [(breadcrumb) => breadcrumb],
     },
     collectors: [new ErrorCollector(), new ErrorCollector()],
   });
@@ -38,6 +39,7 @@ it('can set all options at once', () => {
         instrumentFetch: true,
         instrumentXhr: true,
       },
+      filters: expect.any(Array),
     },
     stack: {
       source: {
@@ -420,3 +422,19 @@ it('warns when breadcrumbs.http.customUrlFilter is not a function', () => {
     'The "breadcrumbs.http.customUrlFilter" must be a function. Received string',
   );
 });
+
+it('warns when filters is not an array', () => {
+  const outOptions = parse(
+    {
+      breadcrumbs: {
+        // @ts-ignore
+        filters: 'not an array',
+      },
+    },
+    mockLogger,
+  );
+  expect(outOptions.breadcrumbs.filters).toEqual([]);
+  expect(mockLogger.warn).toHaveBeenCalledWith(
+    'Config option "breadcrumbs.filters" should be of type array, got string, using default value',
+  );
+});

packages/telemetry/browser-telemetry/src/BrowserTelemetryImpl.ts

@@ -5,7 +5,7 @@
  */
 import type { LDContext, LDEvaluationDetail, LDInspection } from '@launchdarkly/js-client-sdk';
 
-import { LDClientTracking } from './api';
+import { BreadcrumbFilter, LDClientTracking } from './api';
 import { Breadcrumb, FeatureManagementBreadcrumb } from './api/Breadcrumb';
 import { BrowserTelemetry } from './api/BrowserTelemetry';
 import { Collector } from './api/Collector';
@@ -52,6 +52,28 @@ function safeValue(u: unknown): string | boolean | number | undefined {
   }
 }
 
+function applyBreadcrumbFilter(
+  breadcrumb: Breadcrumb | undefined,
+  filter: BreadcrumbFilter,
+): Breadcrumb | undefined {
+  return breadcrumb === undefined ? undefined : filter(breadcrumb);
+}
+
+function applyBreadcrumbFilters(
+  breadcrumb: Breadcrumb,
+  filters: BreadcrumbFilter[],
+): Breadcrumb | undefined {
+  try {
+    return filters.reduce(
+      (breadcrumbToFilter: Breadcrumb | undefined, filter: BreadcrumbFilter) =>
+        applyBreadcrumbFilter(breadcrumbToFilter, filter),
+      breadcrumb,
+    );
+  } catch (e) {
+    return undefined;
+  }
+}
+
 function configureTraceKit(options: ParsedStackOptions) {
   const TraceKit = getTraceKit();
   // Include before + after + source line.
@@ -191,9 +213,12 @@ export default class BrowserTelemetryImpl implements BrowserTelemetry {
   }
 
   addBreadcrumb(breadcrumb: Breadcrumb): void {
-    this._breadcrumbs.push(breadcrumb);
-    if (this._breadcrumbs.length > this._maxBreadcrumbs) {
-      this._breadcrumbs.shift();
+    const filtered = applyBreadcrumbFilters(breadcrumb, this._options.breadcrumbs.filters);
+    if (filtered !== undefined) {
+      this._breadcrumbs.push(filtered);
+      if (this._breadcrumbs.length > this._maxBreadcrumbs) {
+        this._breadcrumbs.shift();
+      }
     }
   }
 

packages/telemetry/browser-telemetry/src/api/Options.ts

@@ -1,3 +1,4 @@
+import { Breadcrumb } from './Breadcrumb';
 import { Collector } from './Collector';
 
 /**
@@ -22,7 +23,17 @@ export interface UrlFilter {
   (url: string): string;
 }
 
-export interface HttpBreadCrumbOptions {
+/**
+ * Interface for breadcrumb filters.
+ *
+ * Given a breadcrumb the filter may return a modified breadcrumb or undefined to
+ * exclude the breadcrumb.
+ */
+export interface BreadcrumbFilter {
+  (breadcrumb: Breadcrumb): Breadcrumb | undefined;
+}
+
+export interface HttpBreadcrumbOptions {
   /**
    * If fetch should be instrumented and breadcrumbs included for fetch requests.
    *
@@ -131,7 +142,38 @@ export interface Options {
      * http: false
      * ```
      */
-    http?: HttpBreadCrumbOptions | false;
+    http?: HttpBreadcrumbOptions | false;
+
+    /**
+     * Custom breadcrumb filters.
+     *
+     * Can be used to redact or modify breadcrumbs.
+     *
+     * Example:
+     * ```
+     * // We want to redact any click events that include the message 'sneaky-button'
+     * filters: [
+     *   (breadcrumb) => {
+     *     if(
+     *       breadcrumb.class === 'ui' &&
+     *       breadcrumb.type === 'click' &&
+     *       breadcrumb.message?.includes('sneaky-button')
+     *     ) {
+     *       return;
+     *     }
+     *    return breadcrumb;
+     *   }
+     * ]
+     * ```
+     *
+     * If you want to redact or modify URLs in breadcrumbs, then a urlFilter should be used.
+     *
+     * If any breadcrumb filters throw an exception while processing a breadcrumb, then that breadcrumb will be excluded.
+     *
+     * If any breadcrumbFilter cannot be executed, for example because it is not a function, then all breadcrumbs will
+     * be excluded.
+     */
+    filters?: BreadcrumbFilter[];
   };
 
   /**

packages/telemetry/browser-telemetry/src/collectors/http/fetchDecorator.ts

@@ -77,7 +77,8 @@ export default function decorateFetch(callback: (breadcrumb: HttpBreadcrumb) =>
       return response;
     });
   }
-  wrapper.prototype = originalFetch.prototype;
+
+  wrapper.prototype = originalFetch?.prototype;
 
   try {
     // Use defineProperty to prevent this value from being enumerable.

packages/telemetry/browser-telemetry/src/options.ts

@@ -1,5 +1,11 @@
 import { Collector } from './api/Collector';
-import { HttpBreadCrumbOptions, Options, StackOptions, UrlFilter } from './api/Options';
+import {
+  BreadcrumbFilter,
+  HttpBreadcrumbOptions,
+  Options,
+  StackOptions,
+  UrlFilter,
+} from './api/Options';
 import { MinLogger } from './MinLogger';
 
 export function defaultOptions(): ParsedOptions {
@@ -14,6 +20,7 @@ export function defaultOptions(): ParsedOptions {
         instrumentFetch: true,
         instrumentXhr: true,
       },
+      filters: [],
     },
     stack: {
       source: {
@@ -55,7 +62,7 @@ function itemOrDefault<T>(item: T | undefined, defaultValue: T, checker?: (item:
 }
 
 function parseHttp(
-  options: HttpBreadCrumbOptions | false | undefined,
+  options: HttpBreadcrumbOptions | false | undefined,
   defaults: ParsedHttpOptions,
   logger?: MinLogger,
 ): ParsedHttpOptions {
@@ -163,6 +170,11 @@ export default function parse(options: Options, logger?: MinLogger): ParsedOptio
         checkBasic('boolean', 'breadcrumbs.keyboardInput', logger),
       ),
       http: parseHttp(options.breadcrumbs?.http, defaults.breadcrumbs.http, logger),
+      filters: itemOrDefault(
+        options.breadcrumbs?.filters,
+        defaults.breadcrumbs.filters,
+        checkBasic('array', 'breadcrumbs.filters', logger),
+      ),
     },
     stack: parseStack(options.stack, defaults.stack),
     maxPendingEvents: itemOrDefault(
@@ -271,6 +283,11 @@ export interface ParsedOptions {
      * Settings for http instrumentation and breadcrumbs.
      */
     http: ParsedHttpOptions;
+
+    /**
+     * Custom breadcrumb filters.
+     */
+    filters: BreadcrumbFilter[];
   };
 
   /**