Add fetcher option to transportOptions (#195)

Author: robertcepa

packages/toucan-js/README.md

@@ -26,6 +26,17 @@ This SDK provides all options and methods of [Hub](https://github.com/getsentry/
 | request            | Request            | If set, the SDK will send information about incoming requests to Sentry. By default, only the request method and request origin + pathname are sent. If you want to include more data, you need to use `requestDataOptions` option.                                                                                                                                                                                                                                                                                      |
 | requestDataOptions | RequestDataOptions | Object containing allowlist for specific parts of request. Refer to sensitive data section below.                                                                                                                                                                                                                                                                                                                                                                                                                        |
 
+### Constructor options overrides
+
+#### Transport options
+
+On top of base `transportOptions` you can pass additional configuration:
+
+| Option  | Type                   | Description                                                                                                                                                                                    |
+| ------- | ---------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| headers | Record<string, string> | Custom headers passed to fetch.                                                                                                                                                                |
+| fetcher | typeof fetch           | Custom fetch function. This can be useful for tests or when the global `fetch` used by `toucan-js` doesn't satisfy your use-cases. Note that custom fetcher must conform to `fetch` interface. |
+
 ### Additional methods
 
 - `Toucan.setEnabled(enabled: boolean): void`: Can be used to disable and again enable the SDK later in your code.

packages/toucan-js/src/transports/fetch.ts

@@ -15,7 +15,8 @@ export function makeFetchTransport(options: FetchTransportOptions): Transport {
     body,
   }: TransportRequest): PromiseLike<TransportMakeRequestResponse> {
     try {
-      const request = fetch(options.url, {
+      const fetchFn = options.fetcher ?? fetch;
+      const request = fetchFn(options.url, {
         method: 'POST',
         headers: options.headers,
         body,

packages/toucan-js/src/transports/types.ts

@@ -2,7 +2,18 @@ import type { BaseTransportOptions } from '@sentry/types';
 import type { Context } from '../types';
 
 export type FetchTransportOptions = BaseTransportOptions & {
+  /**
+   * Custom headers passed to fetch.
+   */
   headers?: Record<string, string>;
 
+  /**
+   * Cloudflare Workers context.
+   */
   context?: Context;
+
+  /**
+   * Custom fetch function.
+   */
+  fetcher?: typeof fetch;
 };

packages/toucan-js/test/helpers.ts

@@ -4,6 +4,10 @@ const realMathRandom = Math.random;
 let mathRandomReturnValues: number[] = [];
 let mathRandomReturnValuesCurrentIndex = -1;
 
+export const mockFetch = () => {
+  return jest.fn(async () => new Response());
+};
+
 export const mockMathRandom = (returnValues: number[]) => {
   if (returnValues.length === 0)
     jest.fn(() => {

packages/toucan-js/test/index.spec.ts

@@ -2,6 +2,7 @@ import type { Event, EventProcessor, Integration } from '@sentry/types';
 import { Toucan } from 'toucan-js';
 import {
   mockConsole,
+  mockFetch,
   mockMathRandom,
   resetConsole,
   resetMathRandom,
@@ -309,6 +310,24 @@ describe('Toucan', () => {
       expect(requests[0].headers['x-custom-header']).toEqual('1');
     });
 
+    test('custom fetcher', async () => {
+      const fetcher = mockFetch();
+      const toucan = new Toucan({
+        dsn: VALID_DSN,
+        transportOptions: {
+          fetcher,
+        },
+        context,
+      });
+      toucan.captureMessage('test');
+
+      const waitUntilResults = await getMiniflareWaitUntil(context);
+
+      expect(waitUntilResults.length).toBe(1);
+      expect(requests.length).toBe(0);
+      expect(fetcher.mock.calls.length).toBe(1);
+    });
+
     test('unhandled exception in SDK options does not explode the worker', async () => {
       const toucan = new Toucan({
         dsn: VALID_DSN,