Allow custom fetch function to be provided

[iammminzzy]

What does this PR do?

This PR allows a custom fetch function to be provided. This makes it a lot easier to add proxy support without having to copy the implementation (and remember to keep it up-to-date) of IsomorphicFetchHttpLibrary along with all of its dependencies:

datadog-api-client-typescript/packages/datadog-api-client-common/http/isomorphic-fetch.ts

Lines 1 to 11 in 16cf2b7

	import {
	HttpLibrary,
	RequestContext,
	ResponseContext,
	ZstdCompressorCallback,
	} from "./http";
	import { fetch as crossFetch } from "cross-fetch";
	import pako from "pako";
	import bufferFrom from "buffer-from";
	import { isBrowser, isNode } from "../util";
	import { logger } from "../../../logger";

Example usage:

import { ProxyAgent, fetch } from 'undici';

const configuration = client.createConfiguration({
  fetch: (input, init) =>
    fetch(input, { ...init, dispatcher: new ProxyAgent('...') })
});

Additional Notes

Review checklist

Please check relevant items below:

• This PR includes all newly recorded cassettes for any modified tests.

• This PR does not rely on API client schema changes.

  • The CI should be fully passing.

• Or, this PR relies on API schema changes and this is a Draft PR to include tests for that new functionality.

  • Note: CI shouldn't be run on this Draft PR, as its expected to fail without the corresponding schema changes.

[iammminzzy]

I'm not sure whether this is the right type or I should just use any (for example https://github.com/octokit/request.js allows you to pass a custom fetch function but types it as any: https://github.com/octokit/types.ts/blob/b21cc042affd15918abdc0636cb017e3751bbadc/src/Fetch.ts) because the Node fetch and browser fetch types aren't fully compatible: nodejs/undici#1943

[jack-edmonds-dd]

In my opinion, any sounds a little safer to me.

[NMinhNguyen]

Agreed! Feel free to push edits to this PR directly if you have edit rights

[NMinhNguyen]

@skarimo, @HantingZhang2, apologies for the direct ping but could you review this PR when you get a chance please?

[NMinhNguyen]

cc @therve

[skarimo]

@NMinhNguyen 👋 We will review this soon and follow up.

[NMinhNguyen]

@jack-edmonds-dd thanks a lot for the updates and merging the PR! Roughly when can we expect a new release to be published?

[jack-edmonds-dd]

@jack-edmonds-dd thanks a lot for the updates and merging the PR! Roughly when can we expect a new release to be published?

Probably early next week.