test: deflake test-http-keep-alive-empty-line

- Do not call `client.end()` to ensure that the socket is closed by the
  server.
- Remove the timer and the send the empty line when the response is
  received.

Fixes: #59577

Author: lpinca

test/parallel/test-http-keep-alive-empty-line.mjs

@@ -3,6 +3,10 @@ import assert from 'node:assert';
 import { createServer } from 'node:http';
 import { connect } from 'node:net';
 
+// This test ensures that data like an empty line (`\r\n`) recevied by the
+// server after a request, does not reset the keep-alive timeout. See
+// https://github.com/nodejs/node/issues/58140.
+
 const server = createServer({
   connectionsCheckingInterval: 100,
   headersTimeout: 100,
@@ -28,23 +32,24 @@ server.listen(0, () => {
           '\r\n'
     );
 
-    setTimeout(() => {
-      client.write('\r\n');
-    }, 100);
-
-    let responseBuffer = '';
+    let response = '';
+    let responseReceived = false;
 
+    client.setEncoding('utf-8');
     client.on('data', (chunk) => {
-      responseBuffer += chunk.toString();
+      response += chunk;
 
       // Check if we've received the full header (ending with \r\n\r\n)
-      if (responseBuffer.includes('\r\n\r\n')) {
-        const statusLine = responseBuffer.split('\r\n')[0];
+      if (response.includes('\r\n\r\n')) {
+        responseReceived = true;
+        const statusLine = response.split('\r\n')[0];
         const status = statusLine.split(' ')[1];
         assert.strictEqual(status, '404');
-        client.end();
+        client.write('\r\n');
       }
     });
-    client.on('end', common.mustCall());
+    client.on('end', common.mustCall(() => {
+      assert.ok(responseReceived);
+    }));
   });
 });