http: support HTTP[S]_PROXY environment variables

lib/internal/process/pre_execution.js

@@ -119,6 +119,7 @@ function prepareExecution(options) {
   initializeConfigFileSupport();
 
   require('internal/dns/utils').initializeDns();
+  setupHttpProxy();
 
   if (isMainThread) {
     assert(internalBinding('worker').isMainThread);
@@ -154,6 +155,17 @@ function prepareExecution(options) {
   return mainEntry;
 }
 
+function setupHttpProxy() {
+  if (process.env.NODE_USE_ENV_PROXY &&
+      (process.env.HTTP_PROXY || process.env.HTTPS_PROXY)) {
+    const { setGlobalDispatcher, EnvHttpProxyAgent } = require('internal/deps/undici/undici');
+    const envHttpProxyAgent = new EnvHttpProxyAgent();
+    setGlobalDispatcher(envHttpProxyAgent);
+    // TODO(joyeecheung): handle http/https global agents and perhaps Agent constructor
+    // behaviors.
+  }
+}
+
 function setupUserModules(forceDefaultLoader = false) {
   initializeCJSLoader();
   initializeESMLoader(forceDefaultLoader);

test/fixtures/fetch-and-log.mjs

@@ -0,0 +1,4 @@
+const address = process.env.SERVER_ADDRESS;
+const response = await fetch(address);
+const body = await response.text();
+console.log(body);

test/fixtures/proxy-handler.js

@@ -0,0 +1,22 @@
+const net = require('net');
+
+exports.onConnect = function (req, clientSocket, head) {
+  const [hostname, port] = req.url.split(':');
+
+  const serverSocket = net.connect(port, hostname, () => {
+    clientSocket.write(
+      'HTTP/1.1 200 Connection Established\r\n' +
+      'Proxy-agent: Node.js-Proxy\r\n' +
+      '\r\n'
+    );
+    serverSocket.write(head);
+    clientSocket.pipe(serverSocket);
+    serverSocket.pipe(clientSocket);
+  });
+
+  serverSocket.on('error', (err) => {
+    console.error('Error on CONNECT tunnel:', err.message);
+    clientSocket.write('HTTP/1.1 500 Connection Error\r\n\r\n');
+    clientSocket.end();
+  });
+};

test/parallel/test-http-proxy-fetch.js

@@ -0,0 +1,64 @@
+'use strict';
+
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const assert = require('assert');
+const { spawn } = require('child_process');
+const http = require('http');
+const { onConnect } = require('../fixtures/proxy-handler');
+
+// Start a server to process the final request.
+const server = http.createServer((req, res) => {
+  res.end('Hello world');
+});
+server.on('error', (err) => { console.log('Server error', err); });
+
+server.listen(0, common.mustCall(() => {
+  // Start a proxy server to tunnel the request.
+  const proxy = http.createServer();
+  // If the request does not go through the proxy server, common.mustCall fails.
+  proxy.on('connect', common.mustCall((req, clientSocket, head) => {
+    console.log('Proxying CONNECT', req.url, req.headers);
+    assert.strictEqual(req.url, `localhost:${server.address().port}`);
+    onConnect(req, clientSocket, head);
+  }));
+  proxy.on('error', (err) => { console.log('Proxy error', err); });
+
+  proxy.listen(0, common.mustCall(() => {
+    const proxyAddress = `http://localhost:${proxy.address().port}`;
+    const serverAddress = `http://localhost:${server.address().port}`;
+    const child = spawn(process.execPath,
+                        [fixtures.path('fetch-and-log.mjs')],
+                        {
+                          env: {
+                            ...process.env,
+                            HTTP_PROXY: proxyAddress,
+                            NODE_USE_ENV_PROXY: true,
+                            SERVER_ADDRESS: serverAddress,
+                          },
+                        });
+
+    const stderr = [];
+    const stdout = [];
+    child.stderr.on('data', (chunk) => {
+      stderr.push(chunk);
+    });
+    child.stdout.on('data', (chunk) => {
+      stdout.push(chunk);
+    });
+
+    child.on('exit', common.mustCall(function(code, signal) {
+      proxy.close();
+      server.close();
+
+      console.log('--- stderr ---');
+      console.log(Buffer.concat(stderr).toString());
+      console.log('--- stdout ---');
+      const stdoutStr = Buffer.concat(stdout).toString();
+      console.log(stdoutStr);
+      assert.strictEqual(stdoutStr.trim(), 'Hello world');
+      assert.strictEqual(code, 0);
+      assert.strictEqual(signal, null);
+    }));
+  }));
+}));