Add ZeroMqChannel test with Curve Auth

Related to https://stackoverflow.com/questions/67214907/zeromq-with-spring-spring-integration-zeromq

* Fix typos in `ZeroMqChannel` JavaDocs

spring-integration-zeromq/src/main/java/org/springframework/integration/zeromq/channel/ZeroMqChannel.java

@@ -48,7 +48,7 @@ import reactor.core.scheduler.Schedulers;
  * It can work in two messaging models:
  * - {@code push-pull}, where sent messages are distributed to subscribers in a round-robin manner
  * according a respective ZeroMQ {@link SocketType#PUSH} and {@link SocketType#PULL} socket types logic;
- * - {@code pub-sub}, where sent messages are distributed to all subscribers;
+ * - {@code pub-sub}, where sent messages are distributed to all subscribers.
  * <p>
  * This message channel can work in local mode, when a pair of ZeroMQ sockets of {@link SocketType#PAIR} type
  * are connected between publisher (send operation) and subscriber using inter-thread transport binding.
@@ -63,7 +63,7 @@ import reactor.core.scheduler.Schedulers;
  * This way sending and receiving operations on this channel are similar to interaction over a messaging broker.
  * <p>
  * An internal logic of this message channel implementation is based on the project Reactor using its
- * {@link Mono}, {@link Flux} and {@link Scheduler} API for better thead model and flow control to avoid
+ * {@link Mono}, {@link Flux} and {@link Scheduler} API for better thread model and flow control to avoid
  * concurrency primitives for multi-publisher(subscriber) communication within the same application.
  *
  * @author Artem Bilan
@@ -278,6 +278,7 @@ public class ZeroMqChannel extends AbstractMessageChannel implements Subscribabl
 
 	/**
 	 * The {@link Consumer} callback to configure a publishing socket.
+	 * The send socket is connected to the frontend socket of ZeroMQ proxy (if any).
 	 * @param sendSocketConfigurer the {@link Consumer} to use.
 	 */
 	public void setSendSocketConfigurer(Consumer<ZMQ.Socket> sendSocketConfigurer) {
@@ -287,6 +288,7 @@ public class ZeroMqChannel extends AbstractMessageChannel implements Subscribabl
 
 	/**
 	 * The {@link Consumer} callback to configure a consuming socket.
+	 * The subscribe socket is connected to the backend socket of ZeroMQ proxy (if any).
 	 * @param subscribeSocketConfigurer the {@link Consumer} to use.
 	 */
 	public void setSubscribeSocketConfigurer(Consumer<ZMQ.Socket> subscribeSocketConfigurer) {

spring-integration-zeromq/src/test/java/org/springframework/integration/zeromq/channel/ZeroMqChannelTests.java

@@ -29,6 +29,8 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.Test;
 import org.zeromq.SocketType;
+import org.zeromq.ZAuth;
+import org.zeromq.ZCert;
 import org.zeromq.ZContext;
 import org.zeromq.ZMQ;
 
@@ -222,4 +224,69 @@ public class ZeroMqChannelTests {
 		proxy.stop();
 	}
 
+	@Test
+	void testPubSubWithCurve() throws InterruptedException {
+		new ZAuth(CONTEXT).configureCurve(ZAuth.CURVE_ALLOW_ANY);
+
+		ZMQ.Curve.KeyPair frontendKeyPair = ZMQ.Curve.generateKeyPair();
+		ZMQ.Curve.KeyPair backendKeyPair = ZMQ.Curve.generateKeyPair();
+
+		ZeroMqProxy proxy = new ZeroMqProxy(CONTEXT, ZeroMqProxy.Type.SUB_PUB);
+		proxy.setBeanName("subPubCurveProxy");
+		proxy.setFrontendSocketConfigurer(socket -> {
+			socket.setZAPDomain("global".getBytes());
+			socket.setCurveServer(true);
+			socket.setCurvePublicKey(frontendKeyPair.publicKey.getBytes());
+			socket.setCurveSecretKey(frontendKeyPair.secretKey.getBytes());
+		});
+		proxy.setBackendSocketConfigurer(socket -> {
+			socket.setZAPDomain("global".getBytes());
+			socket.setCurveServer(true);
+			socket.setCurvePublicKey(backendKeyPair.publicKey.getBytes());
+			socket.setCurveSecretKey(backendKeyPair.secretKey.getBytes());
+		});
+		proxy.afterPropertiesSet();
+		proxy.start();
+
+		ZeroMqChannel channel = new ZeroMqChannel(CONTEXT, true);
+		channel.setZeroMqProxy(proxy);
+		channel.setBeanName("testChannelWithCurve");
+		channel.setSendSocketConfigurer(socket -> {
+			ZCert clientCert = new ZCert();
+			socket.setCurvePublicKey(clientCert.getPublicKey());
+			socket.setCurveSecretKey(clientCert.getSecretKey());
+			socket.setCurveServerKey(frontendKeyPair.publicKey.getBytes());
+		});
+		channel.setSubscribeSocketConfigurer(socket -> {
+					ZCert clientCert = new ZCert();
+					socket.setCurvePublicKey(clientCert.getPublicKey());
+					socket.setCurveSecretKey(clientCert.getSecretKey());
+					socket.setCurveServerKey(backendKeyPair.publicKey.getBytes());
+				}
+		);
+		channel.setConsumeDelay(Duration.ofMillis(10));
+		channel.afterPropertiesSet();
+
+		BlockingQueue<Message<?>> received = new LinkedBlockingQueue<>();
+
+		channel.subscribe(received::offer);
+		channel.subscribe(received::offer);
+
+		await().until(() -> proxy.getBackendPort() > 0);
+
+		// Give it some time to connect and subscribe
+		Thread.sleep(1000);
+
+		GenericMessage<String> testMessage = new GenericMessage<>("test1");
+		assertThat(channel.send(testMessage)).isTrue();
+
+		Message<?> message = received.poll(10, TimeUnit.SECONDS);
+		assertThat(message).isNotNull().isEqualTo(testMessage);
+		message = received.poll(10, TimeUnit.SECONDS);
+		assertThat(message).isNotNull().isEqualTo(testMessage);
+
+		channel.destroy();
+		proxy.stop();
+	}
+
 }