Institute of Information Science - University of Miskolc

The client sends requests to the server over a TCP socket connection, and the server responds to these requests. Here are the basic steps involved in integrating software systems or components using TCP socket communication:

1. Select a protocol: TCP/IP is a common protocol for socket communication, but other protocols like UDP can also be used depending on the requirements.
2. Determine the message format: Decide on the format of the messages that will be exchanged between the client and server. This could be a simple text-based format or a more complex binary format.
3. Define the communication interface: Define the functions or APIs that will be used for communication between the client and server.
4. Create the server: Write the code for the server that listens for incoming client connections and handles incoming requests.
5. Create the client: Write the code for the client that connects to the server and sends requests.
6. Handle errors: Implement error handling mechanisms to ensure that communication errors are handled gracefully and do not cause the system to crash or become unstable.
7. Test and iterate: Test the system thoroughly and make any necessary changes or improvements to ensure that it is functioning correctly.

Features:

• Socket ::= IP address + (TCP/UPD) port number. A Socket is a combination of ip address and port number.
• TCP Sockets provides 'real-time' data transfer
  • binary data transfer but can be normal text or JSON, XML as well
  • no direct method sharing (can be implemented by hand)
  • TCP and UDP connections are possible. UDP is min 3 times quicker but one-way communication
• Persistent or On-Demand communication channel
  • because of connection time-loss usually persistent channels are better, but periodically 'ping' messages should be sent. (in order to avoid connection closing). In case of any problems reconnection is possible
  • in case of UDP channels an extra TCP channel is available for synchronizing - in online games
• Results in the fastest possible transmission:
  • Where the number of transactions per second up to ~ 50 transactions, there should have been applied. (20ms / sec transfer)

Reading:

• http://tutorials.jenkov.com/java-nio/nio-vs-io.html
• http://www.javaworld.com/article/2073344/core-java/use-select-for-high-speed-networking.html

   ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
 
   serverSocketChannel.socket().bind(new InetSocketAddress(9999));
   serverSocketChannel.configureBlocking(false);  // ez a sor jelzi a blokkolásmentes működést
 
   while(true){
    SocketChannel socketChannel = serverSocketChannel.accept();
 
    if(socketChannel != null){
        // the connection is accepted
    }
   }

Java example for Blocking and Non-Blocking Socket

Exercise 1.

Create a simplified FTP (file transport) client and blocking server where the client can send or download text files from the server:

1. ) Client connects to the server and sends a 'file listing' message
2. ) Server sends back the list of the downloadable files
3. ) Client lists the files and asks the user what action they want to take? Upload or download? ('u' or 'd')
4. ) In both cases users must give the full file name with extension
5. ) The client sends the selected file to the server (upload) or downloads the selected file from the server to a specific directory.

1. ) After connecting, it reads the files from the /store subdirectory and sends the file names to the client after receiving the listing message.
2. ) We are waiting for the client's 'u' or 'd' operation
3. ) We get a filename from the client and if the action is 'd' (download), we read the file content and return its contents
4. ) If the operation is 'u' (upload), we open a new file with the specified name and wait for the data to be written to the file.

1. ) The client connects and waits for the list of files coming back and writes it to the console
2. ) We ask for the “u” or “d” key
3. ) Then we'll ask for the file-name as well.
4. ) The client reads the files from the /files folder, or creates the downloaded file here
5. ) If you press “d”, it creates /files/ and writes data from the server
6. ) If you press “u”, /files/ is sent to the server

Exercise 2. Modify the non-blocking code so that you can transfer a burned-in name and existing text or image file larger than 2 kbytes and verify that it was successfully sent.