Network, HTTP Protocol and Client/Server

Week 1 - Tuesday: Client-Server Interactions/Protocols

  • Topics: Network protocols, TCP/IP, HTTP, HTTPS, DNS, DHCP, IP address, MAC address, Ports, Socket, Client, Server, Request, Response, HTTP methods, HTTP status codes, HTTP headers, HTTP cookies
  • Introduction to Networking in Java
    • Basics: What is a network? IP addresses, ports, protocols (focus on TCP and HTTP).
    • Java networking classes: Socket, ServerSocket - Code Together.
    • Demonstrate a simple client-server interaction (e.g., a server sending “Hello” to the client).
  • Protocals and HTTP Basics
    • Explain how protocols like HTTP work at a high level.
    • URL structure: http://host:port/path?query.
    • Role of DNS and localhost (127.0.0.1).
  • Assignment Introduction
    • Explain the goal: Build a chat server by the end of Week 2.
    • Break it down: This week focuses on networking and server basics.

Preparation before class

Exercises to do in class

Part 1

  • Kahoot Quiz: Networking Basics

Part 2

  • In IntelliJ build a tcp server that can handle a single client and send a single message to the client.
  • Connect to the server with telnet and see the message.
  • Build a simple client that can connect to the server and receive the message.

Part 3

  • Look at HTTP basics: curl -v http://www.example.com
  • And in the browsers network tab
  • Explore Real-World Servers
    • Example: Use telnet to interact with a web server or check HTTP headers.
    • Learning Objectives:
      • Understand the basics of TCP/IP communication.
      • Learn how HTTP requests and responses work.
      • Use telnet to manually interact with web servers.
    • Preparation:
    • Choose Accessible Servers:
      • Select common servers that students can test safely:
        • www.example.com
        • www.google.com
        • httpbin.org (great for exploring HTTP)
    • Explain the Basics of Telnet
      • Telnet is a tool that allows you to open a raw TCP connection to a server.
      • It works at the application layer and lets you send custom requests manually.
    • Connect to a Web Server
      • Demonstrate how to use telnet to connect to a server on port 80 (HTTP).
      • Example:
        • telnet www.example.com 80 (type quit to exit telnet prompt)
    • Explain:
      • www.example.com: The hostname of the web server.
      • 80: The port number for HTTP communication.
    • Manually Send an HTTP Request
      • Once connected, type an HTTP GET request manually:
      •   GET / HTTP/1.1
  Host: www.example.com
      • Follow this with an empty line (press Enter twice) to signal the end of the request.
      • Explain the components of the request:
        • GET: HTTP method to request data.
        • /: The path (root in this case).
        • HTTP/1.1: HTTP version.
        • Host: Specifies the server’s domain.
      • Use curl -v http://www.example.com to show the same request in a more user-friendly way.
    • Analyze the Response
      • After sending the request, the server will respond with:
      • HTTP headers (e.g., HTTP/1.1 200 OK, Content-Type, Date, etc.).
      • The content of the page (if any).
      • Example Response:
      HTTP/1.1 200 OK
  Date: Sun, 26 Jan 2025 10:00:00 GMT
  Server: ECS (dcb/7F3B)
  Content-Type: text/html; charset=UTF-8
  Content-Length: 1256
  Connection: keep-alive

  <!doctype html>
  <html>
    <head>
      <title>Example Domain</title>
    </head>
    <body>
      <h1>Example Domain</h1>
      ...
      </body>
  </html>
    • Experiment with Other Paths and Methods - Request a different path: GET /robots.txt HTTP/1.1 Host: www.example.com - Send a bad request and observe the response: GET /nonexistent HTTP/1.1 Host: www.example.com - Try other methods like HEAD or POST (explain they might behave differently).
    • Explore HTTP in the browsers network tab - Open the browser’s developer tools (F12) and go to the Network tab. - Visit a website and observe the requests and responses. -

Week 1 - Wednesday - Codelab

Week 1 - Thursday: Threads

  • Introduction to Multithreading in Java
    • Threads: What are they? Why use them?
    • Java thread basics: Thread class and Runnable interface.
    • Race conditions, Locks and synchronization.
    • Volatile keyword.
    • Threads vs. Processes
    • Atomic operations
    • Deadlocks
    • How multithreading solves the “one client at a time” problem in networking.
  • Building a Threaded Server
    • Show how to handle multiple clients using threads.
    • Example: A server where each client connection is handled in its own thread.
  • Challenges with Threads
    • Discuss thread safety and common issues: race conditions, synchronization, deadlocks.
    • Introduce the concept of shared resources (e.g., a shared List of clients).

Preparation before class

In-class Exercises

  • Threaded Server (How to handle multiple clients using threads)
  • Working with text-based protocols (How to parse requests and send responses in java code)

Exercise

  • Create a multithreaded “http validation” server, that can handle multiple clients at the same time and handle HTTP with headers like:
    • Request: User-Agent (User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/112.0.0.0 Safari/537.36)
    • Response: Status-Line (HTTP/1.1 200 OK),
    • Response: Date (Date: Sun, 26 Jan 2025 10:00:00 GMT),
    • Response: Server (Server: AkamaiGHost),
    • Response: Content-Type (Content-Type: text/html; charset=UTF-8),
    • Response: Content-Length (Content-Length: 12345)
  • The server must evaluate the request and send back a response with the correct headers, status code and content (saying whether the request is valid http or not).

Week 1 - Friday

  • Weekly Exercise

Assignment Goal:

  • Implement a multithreaded HTTP server:
    • The server should accept multiple clients.
    • Use Threads to manage client connections.
    • Parse HTTP requests and send appropriate responses using the HTTP protocol with headers like User-Agent, Date, Server, Content-Type, Content-Length.
    • Provide 3 different GET resources (/hello, /time, /echo ).
    • Provide a POST resource that stores the message and returns it on a subsequent GET request (eg: /echo).

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2. semester forår 2025