feat: support https_proxy

Based on nodejs/node#43187 (comment)

index.cjs

@@ -1,5 +1,12 @@
-const { fetch } = require("undici");
+const { fetch, setGlobalDispatcher, ProxyAgent } = require("undici");
+
+const proxyServer =
+process.env['https_proxy'] || process.env['HTTPS_PROXY'];
+if (proxyServer) {
+  setGlobalDispatcher(new ProxyAgent(proxyServer));
+}
 
 if (!Object.keys(global).includes("fetch")) {
   Object.defineProperty(global, "fetch", { value: fetch });
 }
+

index.mjs

@@ -1,4 +1,9 @@
-import { fetch } from "undici";
+import { fetch, setGlobalDispatcher, ProxyAgent } from "undici";
+
+const proxyServer = process.env["https_proxy"] || process.env["HTTPS_PROXY"];
+if (proxyServer) {
+  setGlobalDispatcher(new ProxyAgent(proxyServer));
+}
 
 if (!Object.keys(global).includes("fetch")) {
   Object.defineProperty(global, "fetch", { value: fetch });

package.json

@@ -11,7 +11,7 @@
     "index.*"
   ],
   "scripts": {
-    "test": "node tests/with-polyfill.mjs && node tests/without-polyfill.mjs"
+    "test": "node tests/index.mjs"
   },
   "repository": {
     "type": "git",

tests/index.mjs

@@ -0,0 +1,11 @@
+import { run } from "node:test";
+import { resolve, dirname } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+const files = ["with-proxy.mjs", "with-polyfill.mjs", "without-polyfill.mjs"].map(
+  (testFile) => resolve(__dirname, testFile)
+);
+
+run({ files }).pipe(process.stdout);

tests/with-polyfill.mjs

@@ -1,7 +1,15 @@
-import "fetch-undici-polyfill";
 import { test } from "node:test";
 import assert from "node:assert";
+import { getGlobalDispatcher, ProxyAgent } from "undici";
 
+// Act
+await import("fetch-undici-polyfill");
+
+// Assert
 test("fetch exists", () => {
   assert(typeof fetch !== "undefined");
 });
+
+test("proxy is not set", () => {
+  assert(!(getGlobalDispatcher() instanceof ProxyAgent));
+});

tests/with-proxy.mjs

@@ -0,0 +1,18 @@
+import { test } from "node:test";
+import assert from "node:assert";
+import { getGlobalDispatcher, ProxyAgent } from "undici";
+
+// Arrange
+process.env["HTTPS_PROXY"] = "https://foo.com";
+
+// Act
+await import("fetch-undici-polyfill");
+
+// Assert
+test("fetch exists", () => {
+  assert(typeof fetch !== "undefined");
+});
+
+test("proxy is set", () => {
+  assert(getGlobalDispatcher() instanceof ProxyAgent);
+});