test: add ALS test using http agent keep alive

Add a tests to verify AsyncLocalStore functionality for HTTP using a
keep alive agent.

AsyncLocalStore moves away from using async_hooks therefore relying on
async_hooks tests alone is not longer valid.

Author: Flarna

test/parallel/test-async-local-storage-http-agent.js

@@ -0,0 +1,82 @@
+'use strict';
+const common = require('../common');
+const assert = require('node:assert');
+const { AsyncLocalStorage } = require('node:async_hooks');
+const http = require('node:http');
+
+// Similar as test-async-hooks-http-agent but verifies AsyncLocalStorage
+// functionality instead async_hooks
+
+const cls = new AsyncLocalStorage();
+
+// Make sure a single socket is transparently reused for 2 requests.
+const agent = new http.Agent({
+  keepAlive: true,
+  keepAliveMsecs: Infinity,
+  maxSockets: 1
+});
+
+const server = http.createServer(common.mustCall((req, res) => {
+  req.once('data', common.mustCallAtLeast(() => {
+    res.writeHead(200, { 'Content-Type': 'text/plain' });
+    res.write('foo');
+  }));
+  req.on('end', common.mustCall(() => {
+    res.end('bar');
+  }));
+}, 2)).listen(0, common.mustCall(() => {
+  const port = server.address().port;
+  const payload = 'hello world';
+
+  // First request. This is useless except for adding a socket to the
+  // agent’s pool for reuse.
+  cls.run('first', common.mustCall(() => {
+    assert.strictEqual(cls.getStore(), 'first');
+    const r1 = http.request({
+      agent, port, method: 'POST'
+    }, common.mustCall((res) => {
+      assert.strictEqual(cls.getStore(), 'first');
+      res.on('data', common.mustCallAtLeast(() => {
+        assert.strictEqual(cls.getStore(), 'first');
+      }));
+      res.on('end', common.mustCall(() => {
+        assert.strictEqual(cls.getStore(), 'first');
+        // setImmediate() to give the agent time to register the freed socket.
+        setImmediate(common.mustCall(() => {
+          assert.strictEqual(cls.getStore(), 'first');
+
+          cls.run('second', common.mustCall(() => {
+            // Second request. To re-create the exact conditions from the
+            // referenced issue, we use a POST request without chunked encoding
+            // (hence the Content-Length header) and call .end() after the
+            // response header has already been received.
+            const r2 = http.request({
+              agent, port, method: 'POST', headers: {
+                'Content-Length': payload.length
+              }
+            }, common.mustCall((res) => {
+              assert.strictEqual(cls.getStore(), 'second');
+              // Empty payload, to hit the “right” code path.
+              r2.end('');
+
+              res.on('data', common.mustCallAtLeast(() => {
+                assert.strictEqual(cls.getStore(), 'second');
+              }));
+              res.on('end', common.mustCall(() => {
+                assert.strictEqual(cls.getStore(), 'second');
+                // Clean up to let the event loop stop.
+                server.close();
+                agent.destroy();
+              }));
+            }));
+
+            // Schedule a payload to be written immediately, but do not end the
+            // request just yet.
+            r2.write(payload);
+          }));
+        }));
+      }));
+    }));
+    r1.end(payload);
+  }));
+}));