node-fetch: agent can be a boolean

The `agent` option is (after checking to see if it's a function, and if
so replacing itself with the return value of calling it) passed directly
to `http.request` (or `https.request`) so we should be able to pass any
type supported there. Notably, `agent: false` is distinct from `agent:
undefined`.

A PR making essentially the same change was merged upstream (the
upstream repo maintains their own types for v3 but not for v2):
node-fetch/node-fetch#1502

types/node-fetch/index.d.ts

@@ -16,7 +16,7 @@
 /// <reference types="node" />
 
 import FormData = require('form-data');
-import { Agent } from "http";
+import { RequestOptions } from "http";
 import { URLSearchParams, URL } from "url";
 import { AbortSignal } from "./externals";
 
@@ -31,7 +31,7 @@ export class Request extends Body {
     url: string;
 
     // node-fetch extensions to the whatwg/fetch spec
-    agent?: Agent | ((parsedUrl: URL) => Agent) | undefined;
+    agent?: RequestOptions['agent'] | ((parsedUrl: URL) => RequestOptions['agent']);
     compress: boolean;
     counter: number;
     follow: number;
@@ -51,7 +51,7 @@ export interface RequestInit {
     signal?: AbortSignal | null | undefined;
 
     // node-fetch extensions
-    agent?: Agent | ((parsedUrl: URL) => Agent) | undefined; // =null http.Agent instance, allows custom proxy, certificate etc.
+    agent?: RequestOptions['agent'] | ((parsedUrl: URL) => RequestOptions['agent']); // =null http.Agent instance, allows custom proxy, certificate etc.
     compress?: boolean | undefined; // =true support gzip/deflate content encoding. false to disable
     follow?: number | undefined; // =20 maximum redirect count. 0 to not follow redirect
     size?: number | undefined; // =0 maximum response body size in bytes. 0 to disable

types/node-fetch/node-fetch-tests.ts

@@ -19,7 +19,8 @@ function test_fetchUrlWithOptions() {
         method: "POST",
         redirect: "manual",
         size: 100,
-        timeout: 5000
+        timeout: 5000,
+        agent: false,
     };
     handlePromise(
         fetch("http://www.andlabs.net/html5/uCOR.php", requestOptions)
@@ -75,7 +76,7 @@ function test_fetchUrlWithRequestObject() {
     );
     const timeout: number = request.timeout;
     const size: number = request.size;
-    const agent: Agent | ((parsedUrl: URL) => Agent) | undefined = request.agent;
+    const agent: Agent | ((parsedUrl: URL) => boolean | Agent | undefined) | boolean | undefined = request.agent;
     const protocol: string = request.protocol;
 
     handlePromise(fetch(request));
@@ -127,7 +128,7 @@ function test_fetchUrlObjectWithRequestObject() {
     );
     const timeout: number = request.timeout;
     const size: number = request.size;
-    const agent: Agent | ((parsedUrl: URL) => Agent) | undefined = request.agent;
+    const agent: Agent | ((parsedUrl: URL) => boolean | Agent | undefined) | boolean | undefined = request.agent;
     const protocol: string = request.protocol;
 
     handlePromise(fetch(request));