introduce test

test/jdk/java/nio/channels/Selector/FailedConnect.java

@@ -0,0 +1,121 @@
+/*
+ * Copyright (c) 2026, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.io.IOException;
+import java.net.ConnectException;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.nio.channels.SelectionKey;
+import java.nio.channels.Selector;
+import java.nio.channels.SocketChannel;
+import java.time.Duration;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/*
+ * @test
+ * @summary Verify that when a SocketChannel is registered with a Selector
+ *          with an interest in CONNECT operation, then SocketChannel.finishConnect()
+ *          throws the correct exception message, if the connect() fails
+ * @run junit ${test.main.class}
+ */
+class FailedConnect {
+
+    /*
+     * On a non-blocking SocketChannel, registered with a Selector, this test method
+     * attempts a SocketChannel.connect() against an address that is expected to return
+     * Connection refused. The test then calls SocketChannel.finishConnect() when the
+     * Selector makes available the ready key for this connect operation and expects
+     * that finishConnect() throws a ConnectException with the expected exception message.
+     */
+    @Test
+    void testFinishConnect() throws Exception {
+        // find a suitable address against which the connect() attempt
+        // will result in a Connection refused exception
+        final InetSocketAddress destAddr = findSuitableRefusedAddress();
+        // we don't want to skip the test, because we expect at least one port
+        // which would result in a connection refused
+        assertNotNull(destAddr, "couldn't find a suitable port which will generate" +
+                " a connection refused error");
+        try (Selector selector = Selector.open();
+             SocketChannel sc = SocketChannel.open()) {
+
+            // non-blocking
+            sc.configureBlocking(false);
+            sc.register(selector, SelectionKey.OP_CONNECT);
+
+            System.err.println("establishing connection to " + destAddr);
+            boolean connected = sc.connect(destAddr);
+            assertFalse(connected, "unexpectedly connected to " + destAddr);
+            // wait for ready ops
+            int numReady = selector.select(Duration.ofMinutes(10).toMillis());
+            System.err.println("Num ready keys = " + numReady);
+            for (SelectionKey readyKey : selector.selectedKeys()) {
+                System.err.println("ready key: " + readyKey);
+                assertTrue(readyKey.isConnectable(), "unexpected key, readyOps = "
+                        + readyKey.readyOps());
+                readyKey.cancel();
+
+                AtomicBoolean success = new AtomicBoolean();
+                // expect SocketChannel.finishConnect() to throw a ConnectException
+                ConnectException ce = assertThrows(ConnectException.class, () -> {
+                    success.set(sc.finishConnect());
+                }, "finishConnect() was expected to fail but didn't, connected = "
+                        + success.get());
+                System.err.println("got expected exception - " + ce);
+                // verify exception message
+                assertEquals("Connection refused", ce.getMessage());
+            }
+        }
+    }
+
+    // Try to find a suitable port to provoke a "Connection Refused" error.
+    private static InetSocketAddress findSuitableRefusedAddress() throws IOException {
+        final InetAddress loopbackAddr = InetAddress.getLoopbackAddress();
+        // port 47 is reserved - there should be nothing listening on it
+        InetSocketAddress destAddr = new InetSocketAddress(loopbackAddr, 47);
+        try (SocketChannel sc1 = SocketChannel.open(destAddr)) {
+            // If we manage to connect, let's try to use some other
+            // port.
+            // port 51 is reserved too - there should be nothing there.
+            destAddr = new InetSocketAddress(loopbackAddr, 51);
+            try (SocketChannel sc2 = SocketChannel.open(destAddr)) {
+            }
+            // OK, last attempt...
+            // port 61 is reserved too - there should be nothing there.
+            destAddr = new InetSocketAddress(loopbackAddr, 61);
+            try (SocketChannel sc3 = SocketChannel.open(destAddr)) {
+            }
+            return null;
+        } catch (ConnectException x) {
+        }
+        // the address which will generate a connection refused, when a connection is attempted
+        return destAddr;
+    }
+}