Helper function to bind same random port multiple times in Netty

coap-mbedtls/src/test/java/org/opencoap/transport/mbedtls/MbedtlsNettyTest.java

@@ -237,7 +237,7 @@ protected void initChannel(DatagramChannel ch) {
     private Bootstrap createClientBootstrap(InetSocketAddress destinationAddress) {
         return new Bootstrap()
                 .group(eventLoopGroup)
-                .localAddress(0)
+                .remoteAddress(destinationAddress)
                 .channel(NioDatagramChannel.class)
                 .handler(new ChannelInitializer<DatagramChannel>() {
                     @Override

coap-mbedtls/src/test/java/org/opencoap/transport/mbedtls/MultithreadedMbedtlsNettyTest.java

@@ -41,7 +41,6 @@
 import java.net.InetSocketAddress;
 import java.time.Duration;
 import java.util.HashSet;
-import java.util.Random;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import org.junit.jupiter.api.AfterAll;
@@ -61,27 +60,14 @@
 @EnabledOnOs(OS.LINUX)
 public class MultithreadedMbedtlsNettyTest {
     private final int threads = 4;
-    private final int serverPort = new Random().nextInt(32000) + 32000;
     private final EventLoopGroup eventLoopGroup = new EpollEventLoopGroup(threads, new DefaultThreadFactory("pool", true));
 
     private final SslConfig clientConf = SslConfig.client(new PskAuth("test", of("secret").getBytes()));
     private final SslConfig serverConf = SslConfig.server(new PskAuth("test", of("secret").getBytes()));
 
-    private final Bootstrap clientBootstrap = new Bootstrap()
-            .group(eventLoopGroup)
-            .localAddress(0)
-            .channel(EpollDatagramChannel.class)
-            .handler(new ChannelInitializer<DatagramChannel>() {
-                @Override
-                protected void initChannel(DatagramChannel ch) {
-                    InetSocketAddress destinationAddress = localhost(serverPort);
-                    ch.pipeline().addFirst("DTLS", new DtlsClientHandshakeChannelHandler(clientConf.newContext(destinationAddress), destinationAddress, SessionWriter.NO_OPS));
-                }
-            });
-
     private final Bootstrap serverBootstrap = new Bootstrap()
             .group(eventLoopGroup)
-            .localAddress(serverPort)
+            .localAddress(0)
             .channel(EpollDatagramChannel.class)
             .option(UnixChannelOption.SO_REUSEPORT, true)
             .handler(new ChannelInitializer<DatagramChannel>() {
@@ -120,10 +106,22 @@ void multi_thread_server() throws Exception {
     }
 
     private String connectAndReadCurrentThreadName() throws IOException, CoapException {
+        InetSocketAddress serverAddress = localhost(((InetSocketAddress) serverBootstrap.config().localAddress()).getPort());
+        Bootstrap clientBootstrap = new Bootstrap()
+                .group(eventLoopGroup)
+                .remoteAddress(serverAddress)
+                .channel(EpollDatagramChannel.class)
+                .handler(new ChannelInitializer<DatagramChannel>() {
+                    @Override
+                    protected void initChannel(DatagramChannel ch) {
+                        ch.pipeline().addFirst("DTLS", new DtlsClientHandshakeChannelHandler(clientConf.newContext(serverAddress), serverAddress, SessionWriter.NO_OPS));
+                    }
+                });
+
         CoapClient client = CoapServer.builder()
                 .executor(eventLoopGroup)
                 .transport(new NettyCoapTransport(clientBootstrap, EMPTY_RESOLVER))
-                .buildClient(localhost(serverPort));
+                .buildClient(serverAddress);
 
         String threadName = client.sendSync(get("/currentThread")).getPayloadString();
         client.close();

coap-netty/src/main/java/org/opencoap/coap/netty/NettyCoapTransport.java

@@ -26,6 +26,7 @@
 import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.ChannelPromise;
 import io.netty.channel.socket.DatagramPacket;
+import io.netty.channel.unix.UnixChannelOption;
 import java.net.InetSocketAddress;
 import java.util.concurrent.CompletableFuture;
 import java.util.function.BiFunction;
@@ -51,7 +52,24 @@ public NettyCoapTransport(Bootstrap bootstrap, Function<DatagramPacket, Transpor
 
     @Override
     public void start() {
-        init(bootstrap.bind().syncUninterruptibly().channel());
+        if (bootstrap.config().remoteAddress() != null) {
+            init(bootstrap.connect().syncUninterruptibly().channel());
+        } else {
+            init(bootstrap.bind().syncUninterruptibly().channel());
+
+            // for random port update bootstrap with actual port but only if SO_REUSEPORT is enabled
+            if (bindToRandomPort() && reusePortIsEnabled()) {
+                bootstrap.localAddress(channel.localAddress());
+            }
+        }
+    }
+
+    private Boolean reusePortIsEnabled() {
+        return (Boolean) bootstrap.config().options().getOrDefault(UnixChannelOption.SO_REUSEPORT, Boolean.FALSE);
+    }
+
+    private boolean bindToRandomPort() {
+        return ((InetSocketAddress) bootstrap.config().localAddress()).getPort() == 0;
     }
 
     void init(Channel channel) {

coap-netty/src/test/java/org/opencoap/coap/netty/MultiChannelNettyTest.java

@@ -117,7 +117,7 @@ private Bootstrap createEpollBootstrap() {
         return new Bootstrap()
                 .group(eventLoopGroup)
                 .option(UnixChannelOption.SO_REUSEPORT, true)
-                .localAddress(65001) // bind multiple times on single port
+                .localAddress(0) // bind multiple times on single port
                 .channel(EpollDatagramChannel.class)
                 .handler(new ChannelInitializer<DatagramChannel>() {
                     @Override

coap-netty/src/test/java/org/opencoap/coap/netty/NettyTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2022-2023 java-coap contributors (https://github.com/open-coap/java-coap)
+ * Copyright (C) 2022-2024 java-coap contributors (https://github.com/open-coap/java-coap)
  * SPDX-License-Identifier: Apache-2.0
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,6 +33,7 @@
 import io.netty.channel.socket.nio.NioDatagramChannel;
 import io.netty.util.concurrent.DefaultThreadFactory;
 import java.io.IOException;
+import java.net.InetSocketAddress;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.ExecutionException;
@@ -83,13 +84,14 @@ void should_exchange_messages() throws Exception {
     @Test
     void should_exchange_messages_with_multiple_clients() throws Exception {
         // given
+        InetSocketAddress serverAddress = localhost(server.getLocalSocketAddress().getPort());
         List<CoapClient> clients = new ArrayList(10);
         for (int i = 0; i < 10; i++) {
             clients.add(
                     CoapServer.builder()
-                            .transport(new NettyCoapTransport(createBootstrap(0), EMPTY_RESOLVER))
+                            .transport(new NettyCoapTransport(createBootstrap(0).remoteAddress(serverAddress), EMPTY_RESOLVER))
                             .executor(eventLoopGroup)
-                            .buildClient(localhost(server.getLocalSocketAddress().getPort()))
+                            .buildClient(serverAddress)
             );
         }