net: surface errors from setKeepAlive handle calls

lib/net.js

@@ -885,7 +885,10 @@ Socket.prototype.setKeepAlive = function(enable, initialDelayMsecs,
     this[kSetKeepAliveInitialDelay] = initialDelay;
     this[kSetKeepAliveInterval] = interval;
     this[kSetKeepAliveCount] = count;
-    this._handle.setKeepAlive(enable, initialDelay, interval, count);
+    const err = this._handle.setKeepAlive(enable, initialDelay, interval, count);
+    if (err && !isWindows) {
+      throw new ErrnoException(err, 'setKeepAlive');
+    }
   }
 
   return this;

test/parallel/test-net-setkeepalive-error.js

@@ -0,0 +1,39 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+
+// Regression: setKeepAlive() silently ignored errors returned by the
+// underlying handle (https://github.com/nodejs/node/issues/65529).
+// It should throw like setTypeOfService() does, instead of reporting
+// success when the operation failed.
+if (common.isWindows) {
+  common.skip('keep-alive errors are treated as best-effort on Windows');
+} else {
+  const server = net.createServer(common.mustCall((socket) => {
+    socket.end();
+  }));
+
+  server.listen(0, common.mustCall(() => {
+    const client = net.connect(server.address().port, common.mustCall(() => {
+      // Make the handle report an error (EINVAL) for the keep-alive call.
+      const originalSetKeepAlive = client._handle.setKeepAlive;
+      client._handle.setKeepAlive = () => -22; // UV_EINVAL
+      try {
+        assert.throws(
+          () => client.setKeepAlive(true, 1000),
+          (err) => {
+            assert.strictEqual(err.code, 'EINVAL');
+            assert.strictEqual(err.syscall, 'setKeepAlive');
+            return true;
+          },
+        );
+      } finally {
+        client._handle.setKeepAlive = originalSetKeepAlive;
+      }
+      client.end();
+      server.close();
+    }));
+  }));
+}