refactoring, describing with JavaDocs

build.gradle

@@ -15,6 +15,12 @@ dependencies {
     // https://mvnrepository.com/artifact/org.slf4j/slf4j-api
     implementation group: 'org.slf4j', name: 'slf4j-api', version: '1.7.35'
 
+    // https://mvnrepository.com/artifact/commons-io/commons-io
+    implementation group: 'commons-io', name: 'commons-io', version: '2.11.0'
+
+    // https://mvnrepository.com/artifact/org.apache.commons/commons-lang3
+    implementation group: 'org.apache.commons', name: 'commons-lang3', version: '3.12.0'
+
     testImplementation 'ch.qos.logback:logback-classic:1.2.10'
 
     testImplementation 'org.junit.jupiter:junit-jupiter-api:5.8.1'

src/main/java/me/bvn13/sewy/AbstractClientListener.java

@@ -1,5 +1,5 @@
 /*
-   Copyright 2020 Vyacheslav Boyko
+   Copyright 2022 Vyacheslav Boyko
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -18,49 +18,114 @@ package me.bvn13.sewy;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.BufferedReader;
 import java.io.IOException;
-import java.io.InputStreamReader;
-import java.io.PrintWriter;
+import java.io.InputStream;
+import java.io.OutputStream;
 import java.net.Socket;
+import java.util.ArrayList;
+import java.util.List;
 
+import static me.bvn13.sewy.Sewy.SEPARATOR;
+
+/**
+ * TCP Client listener.
+ * This class provides methods to manage communications between {@link Server} and {@link Client}.
+ * Inherit this class to implement your own communication type.
+ */
 public abstract class AbstractClientListener implements Runnable {
 
-    protected static final Logger log = LoggerFactory.getLogger(AbstractClientListener.class);
+    protected final Logger log = LoggerFactory.getLogger(this.getClass());
 
     protected final Socket socket;
-    protected PrintWriter out;
-    protected BufferedReader in;
+    protected OutputStream out;
+    protected InputStream in;
 
     protected AbstractClientListener(Socket socket) {
+        log.debug("Initializing client listener");
         this.socket = socket;
         try {
-            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
-        } catch (IOException e) {
-            throw new RuntimeException(e);
-        }
-        try {
-            out = new PrintWriter(socket.getOutputStream(), true);
+            this.in = socket.getInputStream();
+            log.debug("BufferedReader successfully created");
+            log.debug("PrintWriter successfully created");
+            out = socket.getOutputStream();
+            log.debug("OutputStream successfully created");
         } catch (IOException e) {
             throw new RuntimeException(e);
         }
     }
 
+    /**
+     * Thread runner.
+     * Override it according the needs
+     */
+    @Override
+    public abstract void run();
+
+    /**
+     * Reads line (separated with '\n') from socket
+     * @return the line read from socket
+     */
     public String readLine() {
+        final byte[] bytes = readBytes(SEPARATOR);
+        final StringBuilder sb = new StringBuilder();
+        for (byte aByte : bytes) {
+            sb.append((char) aByte);
+        }
+        final String string = sb.toString();
+        if (log.isTraceEnabled()) log.trace("Received: " + string);
+        return string;
+    }
+
+    /**
+     * Reads data from socket until {@code separator} is encountered
+     * @param separator byte to separate data portions
+     * @return array of bytes read from socket
+     */
+    public byte[] readBytes(byte separator) {
+        final List<Byte> data = new ArrayList<>(256);
         try {
-            return in.readLine();
+            while (socket.isConnected()) {
+                byte[] portion = in.readNBytes(1);
+                if (portion == null || portion.length == 0 || portion[0] == separator) {
+                    break;
+                }
+                data.add(portion[0]);
+            }
+            final byte[] bytes = new byte[data.size()];
+            int i = 0;
+            for (Byte aByte : data) {
+                bytes[i++] = aByte;
+            }
+            if (log.isTraceEnabled()) log.trace("Received: " + new String(bytes));
+            return bytes;
         } catch (IOException e) {
             throw new RuntimeException(e);
         }
     }
 
+    /**
+     * Writes line into socket ending with default separator '\n'.
+     * Flushes after writing.
+     * @param data data to be sent into socket
+     */
     public void writeLine(String data) {
-        out.println(data);
+        if (log.isTraceEnabled()) log.trace("Sending: " + data);
+        try {
+            out.write(data.getBytes());
+            out.write(SEPARATOR);
+            out.flush();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
     }
 
-    void stop() {
-        out.close();
+    /**
+     * Stops client listener gracefully
+     */
+    public void stop() {
+        log.debug("Stopping");
         try {
+            out.close();
             in.close();
         } catch (IOException e) {
             log.warn("Unable to close IN client buffer");

src/main/java/me/bvn13/sewy/AbstractCommandExecutor.java

@@ -0,0 +1,22 @@
+package me.bvn13.sewy;
+
+import me.bvn13.sewy.command.AbstractCommand;
+
+/**
+ * Interface to describe command executor.
+ * Every command encountered by {@link CommandClientListener}
+ * will be sent into such executor provided
+ * in {@link Client#Client(java.lang.String, int, java.lang.Class)}
+ * or {@link Server#Server(java.lang.String, int, java.lang.Class)}
+ * while instantiating Client and Server
+ * @param <T>
+ */
+@FunctionalInterface
+public interface AbstractCommandExecutor<T extends AbstractCommand> {
+    /**
+     * Command handler
+     * @param command incoming command
+     * @return response on incoming command is another command for corresponding side
+     */
+    AbstractCommand onCommand(T command);
+}

src/main/java/me/bvn13/sewy/Client.java

@@ -1,5 +1,5 @@
 /*
-   Copyright 2020 Vyacheslav Boyko
+   Copyright 2022 Vyacheslav Boyko
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -18,81 +18,111 @@ package me.bvn13.sewy;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.BufferedReader;
 import java.io.IOException;
-import java.io.InputStreamReader;
-import java.io.PrintWriter;
 import java.net.Socket;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.function.Function;
 
 import static java.lang.String.format;
+import static me.bvn13.sewy.ClientListenerFactory.createClientListenerConstructor;
 
-public class Client {
-
-    private static final Logger log = LoggerFactory.getLogger(Client.class);
+/**
+ * TCP Client.
+ * Create the instance of this class to connect to {@link Server}
+ */
+public class Client<T extends AbstractClientListener> {
+    protected final Logger log = LoggerFactory.getLogger(this.getClass());
 
     private final ExecutorService executor = Executors.newCachedThreadPool();
+    protected T client;
 
-    private Socket socket;
-    private PrintWriter out;
-    private BufferedReader in;
+    protected Socket socket;
 
+    /**
+     * Default constructor is to delay connecting to server
+     */
     public Client() {
     }
 
-    public Client(String host, int port) {
-        connect(host, port);
+    /**
+     * Connects to server immediately
+     * @param host host to connect to
+     * @param port port to be used while connecting
+     * @param clientListenerClass client listener class describing protocol of communications
+     */
+    public Client(String host, int port, Class clientListenerClass) {
+        this(host, port, createClientListenerConstructor(clientListenerClass));
     }
 
-    public void stop() {
-        out.close();
-        try {
-            in.close();
-        } catch (IOException e) {
-            log.warn("Unable to close IN client buffer");
-        }
-        try {
-            socket.close();
-        } catch (IOException e) {
-            throw new RuntimeException(e);
-        }
+    /**
+     * Connects to server immediately
+     * @param host host to connect to
+     * @param port port to be used while connecting
+     * @param clientListenerConstructor to provide constructor for client listener (see {@link me.bvn13.sewy.Client#Client(java.lang.String, int, java.lang.Class)})
+     */
+    public Client(String host, int port, Function<Socket, T> clientListenerConstructor) {
+        log.debug("Creating client");
+        connect(host, port, clientListenerConstructor);
     }
 
-    public void connect(String host, int port) {
+    /**
+     * Connects to {@link Server}
+     * @param host host to connect to
+     * @param port port to be used while connecting
+     * @param clientListenerConstructor to provide constructor for client listener (see {@link me.bvn13.sewy.Client#Client(java.lang.String, int, java.lang.Class)})
+     */
+    public void connect(String host, int port, Function<Socket, T> clientListenerConstructor) {
         try {
+            log.debug(format("Connecting to %s:%d", host, port));
             socket = new Socket(host, port);
+            client = clientListenerConstructor.apply(socket);
+            executor.execute(client);
         } catch (IOException e) {
             log.error(format("Error while conversation with %s:%d", host, port), e);
             stop();
-            return;
-        }
-        try {
-            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
-        } catch (IOException e) {
-            throw new RuntimeException(e);
-        }
-        try {
-            out = new PrintWriter(socket.getOutputStream(), true);
-        } catch (IOException e) {
-            throw new RuntimeException(e);
         }
     }
 
+    /**
+     * Stops client gracefully
+     */
+    public void stop() {
+        log.debug("Stopping client");
+        client.stop();
+        executor.shutdown();
+    }
+
+    /**
+     * To check whether socket is online
+     * @return
+     */
+    public boolean isConnected() {
+        return socket != null && socket.isConnected();
+    }
+
+    /**
+     * Reads one line from socket
+     * @return the line read from socket
+     */
     public String readLine() {
-        try {
-            return in.readLine();
-        } catch (IOException e) {
-            throw new RuntimeException(e);
-        }
+        return client.readLine();
     }
 
+    /**
+     * Reads data from socket until {@code separator} is encountered
+     * @param separator
+     * @return
+     */
+    public byte[] readBytes(byte separator) {
+        return client.readBytes(separator);
+    }
+
+    /**
+     * Writes line into socket ending with default separator '\n'.
+     * @param data data to be sent into socket
+     */
     public void writeLine(String data) {
-        out.println(data);
+        client.writeLine(data);
     }
-
-    boolean isConnected() {
-        return socket.isConnected();
-    }
-
 }

src/main/java/me/bvn13/sewy/ClientListenerFactory.java

@@ -0,0 +1,52 @@
+/*
+   Copyright 2022 Vyacheslav Boyko
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+ */
+package me.bvn13.sewy;
+
+import java.lang.reflect.Constructor;
+import java.net.Socket;
+import java.util.function.Function;
+
+/**
+ * Factory constructing client listeners
+ */
+class ClientListenerFactory {
+
+    /**
+     * Creates client listener constructor
+     * @param clientListenerClass class to be used as client listener
+     * @param <T> generic type
+     * @return lambda method to create client listener
+     */
+    @SuppressWarnings("unchecked")
+    static <T extends AbstractClientListener> Function<Socket, T> createClientListenerConstructor(Class clientListenerClass) {
+
+        if (clientListenerClass.getGenericSuperclass() == null
+                /*|| !clientListenerClass.getGenericSuperclass().equals(T.class)*/) {
+            throw new IllegalArgumentException("Wrong client listener of type: "+clientListenerClass.getName());
+        }
+
+        return (client) -> {
+            try {
+                final Constructor<CommandClientListener> constructor = clientListenerClass.getDeclaredConstructor(Socket.class);
+                constructor.setAccessible(true);
+                return (T) constructor.newInstance(client);
+            } catch (Exception e) {
+                throw new RuntimeException(e);
+            }
+        };
+    }
+
+}

src/main/java/me/bvn13/sewy/CommandClient.java

@@ -0,0 +1,81 @@
+/*
+   Copyright 2022 Vyacheslav Boyko
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+ */
+package me.bvn13.sewy;
+
+import me.bvn13.sewy.command.AbstractCommand;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.net.Socket;
+import java.util.function.Function;
+
+import static java.lang.String.format;
+import static me.bvn13.sewy.ClientListenerFactory.createClientListenerConstructor;
+
+/**
+ * TCP Client.
+ * Works with command protocol.
+ * Create the instance of this class to connect to {@link Server}
+ */
+public class CommandClient extends Client<CommandClientListener> {
+    private final Logger log = LoggerFactory.getLogger(this.getClass());
+
+    /**
+     * Default constructor is to delay connecting to Server
+     */
+    public CommandClient() {
+    }
+
+    /**
+     * Starts to connect to server immediately
+     * @param host host to connect to
+     * @param port port to be used while connecting
+     */
+    public CommandClient(String host, int port) {
+        this(host, port, CommandClientListener.class);
+    }
+
+    /**
+     * Starts to connect to server immediately
+     * @param host host to connect to
+     * @param port port to be used while connecting
+     * @param clientListenerClass client listener class describing protocol of communications
+     */
+    public CommandClient(String host, int port, Class clientListenerClass) {
+        this(host, port, createClientListenerConstructor(clientListenerClass));
+    }
+
+    /**
+     * Connects to server immediately
+     * @param host host to connect to
+     * @param port port to be used while connecting
+     * @param clientListenerConstructor to provide constructor for client listener (see {@link me.bvn13.sewy.Client#Client(java.lang.String, int, java.lang.Class)})
+     */
+    public CommandClient(String host, int port, Function<Socket, CommandClientListener> clientListenerConstructor) {
+        log.debug("Creating client");
+        connect(host, port, clientListenerConstructor);
+    }
+
+    /**
+     * Sends command to server
+     * @param command command to be sent
+     * @param <T> generic type
+     */
+    public <T extends AbstractCommand> void send(T command) {
+        log.debug("Start to send command: " + command);
+        client.send(command);
+    }
+}

src/main/java/me/bvn13/sewy/CommandClientListener.java

@@ -0,0 +1,102 @@
+/*
+   Copyright 2022 Vyacheslav Boyko
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+ */
+package me.bvn13.sewy;
+
+import me.bvn13.sewy.command.AbstractCommand;
+import org.apache.commons.lang3.SerializationUtils;
+
+import java.io.IOException;
+import java.io.Serializable;
+import java.net.Socket;
+
+import static java.lang.String.format;
+import static me.bvn13.sewy.Sewy.SEPARATOR;
+
+/**
+ * Client listener describing protocol-oriented communication
+ */
+public class CommandClientListener extends AbstractClientListener implements AbstractCommandExecutor {
+    public CommandClientListener(Socket socket) {
+        super(socket);
+    }
+
+    /**
+     * Thread runner
+     */
+    @Override
+    public void run() {
+        for (Thread.yield(); !socket.isConnected() && !socket.isClosed(); Thread.yield()) {
+        }
+        while (socket.isConnected()) {
+            Thread.yield();
+            byte[] line = readBytes(SEPARATOR);
+            if (line == null || line.length == 0) {
+                continue;
+            }
+            final Object command = SerializationUtils.deserialize(line);
+            if (command == null) {
+                continue;
+            }
+            if (!Sewy.getRegisteredDataTypes().contains(command.getClass())) {
+                log.error("Unexpected command received");
+                continue;
+            }
+            log.debug("Command received: " + command);
+            if (!(command instanceof AbstractCommand)) {
+                log.warn("Incorrect command received: " + command);
+                continue;
+            }
+            final Serializable response = onCommand((AbstractCommand) command);
+            log.debug(format("Response for %s is: %s", command, response));
+            try {
+                out.write(SerializationUtils.serialize(response));
+                out.write(SEPARATOR);
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+
+
+    /**
+     * Method to receive the data command-by-command incoming from clients
+     * You need to override it
+     *
+     * @param command serialized command to be checked by using
+     *                <p>{@code instanceof ConcreteCommandClass}</p>
+     * @return server answer on client command
+     */
+    public AbstractCommand onCommand(AbstractCommand command) {
+        return null;
+    }
+
+    /**
+     * Sends command to opposite side
+     * @param command command to be sent
+     * @param <T> generic type
+     */
+    public <T extends AbstractCommand> void send(T command) {
+        log.debug("Start to send command: " + command);
+        try {
+            out.write(SerializationUtils.serialize(command));
+            out.write(SEPARATOR);
+            out.flush();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+}

src/main/java/me/bvn13/sewy/DefaultClientListener.java

@@ -1,14 +0,0 @@
-package me.bvn13.sewy;
-
-import java.net.Socket;
-
-public class DefaultClientListener extends AbstractClientListener {
-    public DefaultClientListener(Socket socket) {
-        super(socket);
-    }
-
-    @Override
-    public void run() {
-
-    }
-}

src/main/java/me/bvn13/sewy/Server.java

@@ -1,5 +1,5 @@
 /*
-   Copyright 2020 Vyacheslav Boyko
+   Copyright 2022 Vyacheslav Boyko
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -19,7 +19,6 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
-import java.lang.reflect.Constructor;
 import java.net.InetAddress;
 import java.net.ServerSocket;
 import java.net.Socket;
@@ -32,28 +31,47 @@ import java.util.concurrent.Executors;
 import java.util.function.Function;
 
 import static java.lang.String.format;
+import static me.bvn13.sewy.ClientListenerFactory.createClientListenerConstructor;
 
+/**
+ * TCP Server.
+ * Create the instance of this class to connect to {@link Client}
+ */
 public class Server {
 
-    private static final Logger log = LoggerFactory.getLogger(Server.class);
+    private final Logger log = LoggerFactory.getLogger(this.getClass());
 
     private final ExecutorService executor = Executors.newCachedThreadPool();
-    final List<AbstractClientListener> clients = Collections.synchronizedList(new ArrayList<>());
+    private final List<AbstractClientListener> clients = Collections.synchronizedList(new ArrayList<>());
 
     private ServerSocket socket;
 
+    /**
+     * @param host host to bind in order to start listen to clients
+     * @param port port to start listen to
+     */
     public Server(String host, int port) {
-        this(host, port, DefaultClientListener.class);
+        this(host, port, CommandClientListener.class);
     }
 
-    @SuppressWarnings("unchecked")
+    /**
+     * @param host host to bind in order to start listen to clients
+     * @param port port to start listen to
+     * @param clientListenerClass client listen class to be used for communication
+     */
     public Server(String host, int port, Class clientListenerClass) {
-        this(host, port, defaultClientListenerConstructor(clientListenerClass));
+        this(host, port, createClientListenerConstructor(clientListenerClass));
     }
 
+    /**
+     *
+     * @param host host to bind in order to start listen to clients
+     * @param port port to start listen to
+     * @param clientListenerConstructor to provide constructor for client listener (see {@link me.bvn13.sewy.Server#Server(java.lang.String, int, java.lang.Class)})
+     */
     @SuppressWarnings("unchecked")
-    public Server(String host, int port, Function<Socket, AbstractClientListener> clientListenerConstructor) {
-
+    public Server(String host, int port, Function<Socket, CommandClientListener> clientListenerConstructor) {
+        log.debug("Starting server");
         executor.execute(() -> {
             try (final ServerSocket server = new ServerSocket(port, 0, InetAddress.getByName(host))) {
 
@@ -73,7 +91,12 @@ public class Server {
 
     }
 
+    /**
+     * Stops server gracefully
+     * Disconnects from every client
+     */
     public void stop() {
+        log.debug("Stopping server");
         final Iterator<AbstractClientListener> iterator = clients.iterator();
         while (iterator.hasNext()) {
             final AbstractClientListener client = iterator.next();
@@ -83,28 +106,12 @@ public class Server {
         executor.shutdown();
     }
 
-    boolean isListening() {
+    /**
+     * To check whether the server is ready for new connections
+     * @return
+     */
+    public boolean isListening() {
         return socket != null && socket.isBound();
     }
 
-    @SuppressWarnings("unchecked")
-    private static Function<Socket, AbstractClientListener> defaultClientListenerConstructor(Class clientListenerClass) {
-
-        if (clientListenerClass.getGenericSuperclass() == null
-                || !clientListenerClass.getGenericSuperclass().equals(AbstractClientListener.class)) {
-            throw new IllegalArgumentException("Wrong client listener of type: "+clientListenerClass.getName());
-        }
-
-        return (client) -> {
-            try {
-                final Constructor<AbstractClientListener> constructor = clientListenerClass.getDeclaredConstructor(Socket.class);
-                constructor.setAccessible(true);
-                return constructor.newInstance(client);
-            } catch (Exception e) {
-                throw new RuntimeException(e);
-            }
-        };
-
-    }
-
 }

src/main/java/me/bvn13/sewy/Sewy.java

@@ -1,5 +1,5 @@
 /*
-   Copyright 2020 Vyacheslav Boyko
+   Copyright 2022 Vyacheslav Boyko
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -15,23 +15,56 @@
  */
 package me.bvn13.sewy;
 
-import java.io.Serializable;
+import me.bvn13.sewy.command.AbstractCommand;
+
+import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.locks.ReentrantLock;
 
+/**
+ * Supporting class providing protocol restrictions
+ */
 public final class Sewy {
 
+    static final byte SEPARATOR = '\n';
+
     private static Sewy INSTANCE;
     private static final ReentrantLock LOCK = new ReentrantLock();
 
-    private final List<Serializable> registeredDataTypes = new CopyOnWriteArrayList<>();
+    private final List<Class<?>> registeredDataTypes = new CopyOnWriteArrayList<>();
 
-    public static void register(Serializable clazz) {
+    /**
+     * Registers command in white list for further communications
+     * @param clazz command class
+     * @param <T> generic type
+     */
+    public static <T extends AbstractCommand> void register(Class<T> clazz) {
         getInstance().registeredDataTypes.add(clazz);
     }
 
-    private Sewy() {}
+    /**
+     * Registers commands in white list for further communications
+     * @param classes array of command classes
+     * @param <T> generic type
+     */
+    public static <T extends AbstractCommand> void register(Class<T>[] classes) {
+        for (Class<T> clazz: classes) {
+            register(clazz);
+        }
+    }
+
+    private Sewy() {
+    }
+
+    @SuppressWarnings("unchecked")
+    static List<Class<AbstractCommand>> getRegisteredDataTypes() {
+        final List<Class<AbstractCommand>> dataTypes = new ArrayList<>();
+        for (Class<?> registeredDataType : INSTANCE.registeredDataTypes) {
+            dataTypes.add((Class<AbstractCommand>) registeredDataType);
+        }
+        return dataTypes;
+    }
 
     private static Sewy getInstance() {
         try {

src/main/java/me/bvn13/sewy/SimpleClientListener.java

@@ -0,0 +1,36 @@
+/*
+   Copyright 2022 Vyacheslav Boyko
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+ */
+package me.bvn13.sewy;
+
+import java.net.Socket;
+
+/**
+ * Simple client listener is to disable automatic receiving and sending data.
+ * Override {@link SimpleClientListener#run()} to implement business logic of communicating
+ */
+public class SimpleClientListener extends AbstractClientListener {
+    protected SimpleClientListener(Socket socket) {
+        super(socket);
+    }
+
+    /**
+     * Thread runner
+     */
+    @Override
+    public void run() {
+
+    }
+}

src/main/java/me/bvn13/sewy/command/AbstractCommand.java

@@ -0,0 +1,25 @@
+/*
+   Copyright 2022 Vyacheslav Boyko
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+ */
+package me.bvn13.sewy.command;
+
+import java.io.Serializable;
+
+/**
+ * The very parent class every command should be inherited from
+ */
+public class AbstractCommand implements Serializable {
+
+}

src/main/java/me/bvn13/sewy/command/PingCommand.java

@@ -0,0 +1,22 @@
+package me.bvn13.sewy.command;
+
+import java.time.Instant;
+
+public class PingCommand extends AbstractCommand {
+    private final long time;
+
+    public PingCommand() {
+        this.time = Instant.now().toEpochMilli();
+    }
+
+    public long getTime() {
+        return time;
+    }
+
+    @Override
+    public String toString() {
+        return "PingCommand{" +
+                "time=" + time +
+                '}';
+    }
+}

src/main/java/me/bvn13/sewy/command/PongCommand.java

@@ -0,0 +1,38 @@
+package me.bvn13.sewy.command;
+
+import java.time.Instant;
+
+public class PongCommand extends AbstractCommand {
+    private final long time;
+    private long pingTime;
+
+    public PongCommand(PingCommand ping) {
+        this.pingTime = ping.getTime();
+        this.time = Instant.now().toEpochMilli();
+    }
+
+    public long getTime() {
+        return time;
+    }
+
+    public long getPingTime() {
+        return pingTime;
+    }
+
+    public void setPingTime(long pingTime) {
+        this.pingTime = pingTime;
+    }
+
+    public long getLatency() {
+        return time - pingTime;
+    }
+
+    @Override
+    public String toString() {
+        return "PongCommand{" +
+                "time=" + time +
+                ", pingTime=" + pingTime +
+                ", latency=" + getLatency() +
+                '}';
+    }
+}

src/test/java/me/bvn13/sewy/EchoClientListener.java

@@ -1,16 +1,40 @@
+/*
+   Copyright 2022 Vyacheslav Boyko
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+ */
 package me.bvn13.sewy;
 
 import java.net.Socket;
 
+/**
+ * Simple ECHOed client listener
+ * Writes into socket all the data received before
+ */
 public class EchoClientListener extends AbstractClientListener {
     public EchoClientListener(Socket socket) {
         super(socket);
     }
 
+    /**
+     * Thread runner
+     */
     @Override
     public void run() {
         while (socket.isConnected()) {
-            writeLine(readLine());
+            Thread.yield();
+            final String data = readLine();
+            writeLine(data);
         }
     }
 }

src/test/java/me/bvn13/sewy/ServerTest.java

@@ -1,9 +1,29 @@
+/*
+   Copyright 2022 Vyacheslav Boyko
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+ */
 package me.bvn13.sewy;
 
+import me.bvn13.sewy.command.AbstractCommand;
+import me.bvn13.sewy.command.PingCommand;
+import me.bvn13.sewy.command.PongCommand;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 
+import java.util.concurrent.atomic.AtomicLong;
+
 public class ServerTest {
 
     private static final int START_PORT = 12345;
@@ -21,7 +41,7 @@ public class ServerTest {
     @ValueSource(ints = START_PORT + 2)
     void givenServerRunning_whenClientConnects_thenServerCanStopClientListener(int port) throws InterruptedException {
         Server server = new Server("localhost", port);
-        Client client = new Client("localhost", port);
+        Client<SimpleClientListener> client = new Client<>("localhost", port, SimpleClientListener.class);
         Thread.sleep(1000);
         Assertions.assertTrue(server.isListening());
         Assertions.assertTrue(client.isConnected());
@@ -39,13 +59,8 @@ public class ServerTest {
 
     @ParameterizedTest
     @ValueSource(ints = START_PORT + 4)
-    void serverStartedWithLambdaProvidedClientListener(int port) throws InterruptedException {
-        Server server = new Server("localhost", port, (socket) -> new AbstractClientListener(socket) {
-            @Override
-            public void run() {
-
-            }
-        });
+    void serverIsAbleToStartWithLambdaProvidedClientListener(int port) throws InterruptedException {
+        Server server = new Server("localhost", port, SimpleClientListener.class);
         Thread.sleep(1000);
         Assertions.assertTrue(server.isListening());
         server.stop();
@@ -54,8 +69,8 @@ public class ServerTest {
     @ParameterizedTest
     @ValueSource(ints = START_PORT + 5)
     void simpleEchoClientServer(int port) {
-        new Server("localhost", port, EchoClientListener.class);
-        Client client = new Client("localhost", port);
+        new Server("192.168.0.153", port, EchoClientListener.class);
+        Client<SimpleClientListener> client = new Client<>("192.168.0.153", port, SimpleClientListener.class);
         client.writeLine("hello");
         String response1 = client.readLine();
         Assertions.assertEquals("hello", response1);
@@ -64,4 +79,37 @@ public class ServerTest {
         Assertions.assertEquals("olleh", response2);
     }
 
+    @ParameterizedTest
+    @ValueSource(ints = START_PORT + 6)
+    void serverIsAbleToPingPong(int port) throws InterruptedException {
+        Sewy.register(PingCommand.class);
+        Sewy.register(PongCommand.class);
+
+        Server server = new Server("localhost", port, (socket) -> new CommandClientListener(socket) {
+            @Override
+            public AbstractCommand onCommand(AbstractCommand command) {
+                if (command instanceof PingCommand) {
+                    return new PongCommand((PingCommand) command);
+                }
+                throw new IllegalArgumentException(command.toString());
+            }
+        });
+
+        AtomicLong latency = new AtomicLong(0);
+        CommandClient client = new CommandClient("localhost", port, (socket) -> new CommandClientListener(socket) {
+            @Override
+            public AbstractCommand onCommand(AbstractCommand command) {
+                if (command instanceof PongCommand) {
+                    latency.set(((PongCommand)command).getLatency());
+                    return null;
+                } else {
+                    throw new IllegalArgumentException(command.toString());
+                }
+            }
+        });
+        client.send(new PingCommand());
+        Thread.sleep(1000);
+        Assertions.assertTrue(latency.get() > 0);
+    }
+
 }

src/test/resources/logback.xml

@@ -0,0 +1,11 @@
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} \(%class{0}.java:%line\) - %msg%n</pattern>
+        </encoder>
+    </appender>
+
+    <root level="trace">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>