http: add http.setGlobalProxyFromEnv()

This adds an API to dynamically enable built-in proxy support
for all of fetch() and http.request()/https.request(), so
that users do not have to be aware of them all and configure them
one by one.

PR-URL: https://github.com/nodejs/node/pull/60953
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Tim Perry <pimterry@gmail.com>

lib/http.js

@@ -25,11 +25,12 @@ const {
   ObjectDefineProperty,
 } = primordials;
 
-const { validateInteger } = require('internal/validators');
+const { validateInteger, validateObject } = require('internal/validators');
 const httpAgent = require('_http_agent');
 const { ClientRequest } = require('_http_client');
 const { methods, parsers } = require('_http_common');
 const { IncomingMessage } = require('_http_incoming');
+const { ERR_PROXY_INVALID_CONFIG } = require('internal/errors').codes;
 const {
   validateHeaderName,
   validateHeaderValue,
@@ -41,6 +42,11 @@ const {
   Server,
   ServerResponse,
 } = require('_http_server');
+const {
+  parseProxyUrl,
+  getGlobalAgent,
+} = require('internal/http');
+const { URL } = require('internal/url');
 let maxHeaderSize;
 let undici;
 
@@ -123,6 +129,58 @@ function lazyUndici() {
   return undici ??= require('internal/deps/undici/undici');
 }
 
+function setGlobalProxyFromEnv(env = process.env) {
+  validateObject(env, 'proxyEnv');
+  const httpProxy = parseProxyUrl(env, 'http:');
+  const httpsProxy = parseProxyUrl(env, 'https:');
+  const noProxy = env.no_proxy || env.NO_PROXY;
+
+  if (!httpProxy && !httpsProxy) {
+    return () => {};
+  }
+
+  if (httpProxy && !URL.canParse(httpProxy)) {
+    throw new ERR_PROXY_INVALID_CONFIG(httpProxy);
+  }
+  if (httpsProxy && !URL.canParse(httpsProxy)) {
+    throw new ERR_PROXY_INVALID_CONFIG(httpsProxy);
+  }
+
+  let originalDispatcher, originalHttpsAgent, originalHttpAgent;
+  if (httpProxy || httpsProxy) {
+    // Set it for fetch.
+    const { setGlobalDispatcher, getGlobalDispatcher, EnvHttpProxyAgent } = lazyUndici();
+    const envHttpProxyAgent = new EnvHttpProxyAgent({
+      __proto__: null, httpProxy, httpsProxy, noProxy,
+    });
+    originalDispatcher = getGlobalDispatcher();
+    setGlobalDispatcher(envHttpProxyAgent);
+  }
+
+  if (httpProxy) {
+    originalHttpAgent = module.exports.globalAgent;
+    module.exports.globalAgent = getGlobalAgent(env, httpAgent.Agent);
+  }
+  if (httpsProxy && !!process.versions.openssl) {
+    const https = require('https');
+    originalHttpsAgent = https.globalAgent;
+    https.globalAgent = getGlobalAgent(env, https.Agent);
+  }
+
+  return function restore() {
+    if (originalDispatcher) {
+      const { setGlobalDispatcher } = lazyUndici();
+      setGlobalDispatcher(originalDispatcher);
+    }
+    if (originalHttpAgent) {
+      module.exports.globalAgent = originalHttpAgent;
+    }
+    if (originalHttpsAgent) {
+      require('https').globalAgent = originalHttpsAgent;
+    }
+  };
+}
+
 module.exports = {
   _connectionListener,
   METHODS: methods.toSorted(),
@@ -142,6 +200,7 @@ module.exports = {
     validateInteger(max, 'max', 1);
     parsers.max = max;
   },
+  setGlobalProxyFromEnv,
 };
 
 ObjectDefineProperty(module.exports, 'maxHeaderSize', {