Docker to Docker Networking Between TCP Client and Server
A TCP-based client and server are a frequently needed setup in IoT-based applications.
Presented in this article are:
- A method to create a Java-based client and server to send and receive binary data
- The client and server, each run inside a Docker container and communicating through Docker networking.
You may also enjoy: Understanding Docker Networking
Create a TCPClient.java as per the code provided below
Java
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import java.net.*;
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import java.io.*;
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import java.security.SecureRandom;
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import java.nio.charset.Charset;
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public class TCPClient
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{
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// initialize socket and input output streams
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private Socket socket = null;
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private DataInputStream input = null;
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private DataOutputStream out = null;
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private static final String CHAR_LOWER = "abcdefghijklmnopqrstuvwxyz";
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private static final String CHAR_UPPER = CHAR_LOWER.toUpperCase();
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private static final String NUMBER = "0123456789";
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private static final String DATA_FOR_RANDOM_STRING = CHAR_LOWER + CHAR_UPPER + NUMBER;
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private static SecureRandom random = new SecureRandom();
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// constructor to put ip address and port
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public TCPClient(String address, int port)
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{
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// establish a connection
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try
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{
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socket = new Socket(address, port);
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System.out.println("Connected");
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}
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catch(UnknownHostException u)
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{
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System.out.println(u);
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}
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catch(IOException i)
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{
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System.out.println(i);
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}
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// string to read message from input
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String line = "";
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int linecount = 0;
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// keep reading until "Over" is input
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while (linecount++ != 300)
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{
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try{
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String name = generateRandomString(8);
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InputStream is = new ByteArrayInputStream(name.getBytes(Charset.forName("UTF-8")));
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// takes input from terminal
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input = new DataInputStream(is);
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// sends output to the socket
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out = new DataOutputStream(socket.getOutputStream());
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}
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catch(UnknownHostException u)
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{
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System.out.println(u);
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}
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catch(IOException i)
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{
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System.out.println(i);
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}
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try
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{
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line = input.readLine();
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out.writeUTF(line);
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}
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catch(IOException i)
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{
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System.out.println(i);
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}
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}
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// close the connection
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try
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{
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input.close();
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out.close();
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socket.close();
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}
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catch(IOException i)
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{
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System.out.println(i);
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}
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}
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public static String generateRandomString(int length) {
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if (length < 1) throw new IllegalArgumentException();
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StringBuilder sb = new StringBuilder(length);
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for (int i = 0; i < length; i++) {
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// 0-62 (exclusive), random returns 0-61
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int rndCharAt = random.nextInt(DATA_FOR_RANDOM_STRING.length());
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char rndChar = DATA_FOR_RANDOM_STRING.charAt(rndCharAt);
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// debug
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System.out.format("%d\t:\t%c%n", rndCharAt, rndChar);
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sb.append(rndChar);
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}
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return sb.toString();
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}
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public static void main(String args[])
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{
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TCPClient client = new TCPClient("server", 5678);
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}
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}
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Create a manifest file for the TCPClient as is shown below:
Java
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Manifest-Version: 1.0
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Created-By: Me
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Main-Class: TCPClient
Create a Dockerfile for TCPClient as below:
Dockerfile
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FROM java:8
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WORKDIR /
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ADD TCPClient.jar TCPClient.jar
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EXPOSE 5678
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CMD java -jar TCPClient.jar
Create a TCPServer.java as per the code provided below:
Java
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import java.net.*;
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import java.io.*;
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public class TCPServer
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{
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//initialize socket and input stream
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private Socket socket = null;
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private ServerSocket server = null;
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private DataInputStream in = null;
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private File file;
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private FileWriter fileWriter;
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// constructor with port
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public TCPServer(int port)
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{
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// starts server and waits for a connection
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try
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{
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server = new ServerSocket(port);
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System.out.println("Server started");
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System.out.println("Waiting for a client ...");
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socket = server.accept();
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System.out.println("Client accepted");
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// takes input from the client socket
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in = new DataInputStream(
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new BufferedInputStream(socket.getInputStream()));
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String line = "";
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int linecount = 0;
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file = new File("outfile.txt");
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fileWriter = new FileWriter(file);
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// reads message from client until "Over" is sent
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while (linecount++ != 300)
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{
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try
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{
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line = in.readUTF();
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System.out.println(line);
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fileWriter.write(line);
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}
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catch(IOException i)
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{
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System.out.println(i);
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}
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}
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System.out.println("Closing connection");
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fileWriter.flush();
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fileWriter.close();
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// close connection
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socket.close();
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in.close();
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}
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catch(IOException i)
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{
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System.out.println(i);
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}
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}
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public static void main(String args[])
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{
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TCPServer server = new TCPServer(5678);
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}
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}
Create a manifest file for TCPServer as below:
Shell
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Manifest-Version: 1.0
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Created-By: Me
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Main-Class: TCPServer
Create a Dockerfile for TCPServer as below
Shell
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FROM java:8
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WORKDIR /
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ADD TCPServer.jar TCPServer.jar
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EXPOSE 5678
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CMD java -jar TCPServer.jar
The directory structure should be as displayed as shown below:
Run the following commands at the unix prompt:
Shell
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javac TCPServer.java
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javac TCPClient.java
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jar cfm TCPServer.jar manifest.txt TCPServer.class
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jar cfm TCPClient.jar manifest.txt TCPClient.class
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docker build -t tcpserver .
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docker build -t tcpclient .
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docker images (to list the docker images)
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docker tag 00c5f2d27133 docker.io/<your account name>/<repo name>:tcpserver
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docker push docker.io/<your account name>/<repo name>:tcpserver
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docker images (to list the docker images)
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docker tag 00c5f2d27133 docker.io/<your account name>/<repo name>:tcpclient
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docker push docker.io/<your account name>/<repo name>:tcpclient
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docker pull docker.io/<your account name>/<repo name>:tcpserver
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docker pull docker.io/<your account name>/<repo name>:tcpclient
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docker run <your account name>/<repo name>:tcpserver
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docker run <your account name>/<repo name>:tcpclient
Create the network:
Shell
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sudo docker network create client_server_network
Run the server:
Shell
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docker run --network-alias server --network client_server_network -it <your account name>/<repo name>:tcpserver
Run the client:
Shell
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docker run --network client_server_network -it <your account name>/<repo name>:tcpclient
You should see the client output as shown below:
And the server output should be as shown below:
