http: match subdomains for plain NO_PROXY entries

doc/api/http.md

@@ -4615,7 +4615,7 @@ Proxy URLs can use either HTTP or HTTPS protocols:
 The `NO_PROXY` environment variable supports several formats:
 
 * `*` - Bypass proxy for all hosts
-* `example.com` - Exact host name match
+* `example.com` - Host and subdomain match (matches `sub.example.com`)
 * `.example.com` - Domain suffix match (matches `sub.example.com`)
 * `*.example.com` - Wildcard domain match
 * `192.168.1.100` - Exact IP address match

lib/internal/http.js

@@ -163,9 +163,10 @@ class ProxyConfig {
       if (entry === '*') return false;  // * bypasses all hosts.
       if (entry === host || entry === hostWithPort) return false;  // Matching host and host:port
 
-      // Follow curl's behavior: strip leading dot before matching suffixes.
-      if (entry[0] === '.') {
-        const suffix = entry.substring(1);
+      // Strip a leading "." if present, then match as a suffix with a
+      // label boundary. "*.example.com" is handled below (subdomains only).
+      if (!entry.startsWith('*.')) {
+        const suffix = entry[0] === '.' ? entry.substring(1) : entry;
         if (host === suffix || (host.endsWith(suffix) && host[host.length - suffix.length - 1] === '.')) return false;
       }
 

test/client-proxy/test-http-proxy-request-no-proxy-domain.mjs

@@ -10,7 +10,7 @@ import { runProxiedRequest } from '../common/proxy-server.js';
 const server = http.createServer(common.mustCall((req, res) => {
   res.writeHead(200, { 'Content-Type': 'text/plain' });
   res.end('Hello World\n');
-}, 5));
+}, 7));
 server.on('error', common.mustNotCall((err) => { console.error('Server error', err); }));
 server.listen(0, '127.0.0.1');
 await once(server, 'listening');
@@ -78,6 +78,43 @@ await once(proxy, 'listening');
   assert.strictEqual(signal, null);
 }
 
+{
+  // Test NO_PROXY with a plain domain also matching subdomains.
+  const { code, signal, stderr, stdout } = await runProxiedRequest({
+    NODE_USE_ENV_PROXY: 1,
+    REQUEST_URL: `http://test.example.com:${server.address().port}/test`,
+    HTTP_PROXY: `http://localhost:${proxy.address().port}`,
+    RESOLVE_TO_LOCALHOST: 'test.example.com',
+    NO_PROXY: 'example.com',
+  });
+
+  // The request should succeed and bypass proxy.
+  assert.match(stdout, /Status Code: 200/);
+  assert.match(stdout, /Hello World/);
+  assert.match(stdout, /Resolving lookup for test\.example\.com/);
+  assert.strictEqual(stderr.trim(), '');
+  assert.strictEqual(code, 0);
+  assert.strictEqual(signal, null);
+}
+
+{
+  // Test NO_PROXY with a plain domain should NOT match partial domain names.
+  const { code, signal, stderr, stdout } = await runProxiedRequest({
+    NODE_USE_ENV_PROXY: 1,
+    REQUEST_URL: `http://badexample.com:${server.address().port}/test`,
+    HTTP_PROXY: `http://localhost:${server.address().port}`,
+    RESOLVE_TO_LOCALHOST: 'badexample.com',
+    NO_PROXY: 'example.com',
+  });
+
+  // The request should go through the proxy (not bypass it),
+  // because badexample.com is not a subdomain of example.com.
+  assert.match(stdout, /Status Code: 200/);
+  assert.strictEqual(stderr.trim(), '');
+  assert.strictEqual(code, 0);
+  assert.strictEqual(signal, null);
+}
+
 // Test NO_PROXY with leading-dot entry should NOT match partial domain names.
 // Regression test: .example.com must not match notexample.com or badexample.com.
 {