Networking : Your First TCP/IP Server and Client in Go

? What We'll Learn

In this tutorial, we'll demystify network programming by building a simple yet robust TCP/IP server and client. If you've ever wondered how applications communicate over a network, this guide is for you!

? Prerequisites

• Basic Go programming knowledge
• Curiosity about networking
• A text editor
• Go installed on your computer
• Go module added (use go mod init tcpIp)

? Understanding Network Communication

Before we dive into code, let's break down what's happening when two computers talk:

1. TCP/IP: Think of it like a phone call

   • TCP (Transmission Control Protocol): Ensures messages are delivered completely and in order
   • IP (Internet Protocol): Helps route messages to the right device

2. Server and Client Roles:

   • Server: Waits and listens for incoming connections
   • Client: Initiates contact and sends requests

?️ Project Structure

tcp-chat-app/
├── server/
│   └── server.go   # Server-side logic
├── client/
│   └── client.go   # Client-side logic
└── main.go         # Starts both server and client

? Step 1: Creating the Server

Understanding the Server Code

package server

import (
    "log"
    "net"
)

// StartServer: Our digital receptionist 
func StartServer() {
    // Choose a "phone number" (address)
    address := "localhost:8080"

    // Set up a "phone line" to listen for calls
    listener, err := net.Listen("tcp", address)
    if err != nil {
        log.Fatalf("Couldn't set up the phone line: %v", err)
    }
    defer listener.Close()

    log.Printf("Server is ready, waiting for connections on %s", address)

    // Forever wait for incoming "calls"
    for {
        // Accept a new connection
        conn, err := listener.Accept()
        if err != nil {
            log.Printf("Missed a call: %v", err)
            continue
        }

        // Handle each "caller" in a separate conversation
        go handleClient(conn)
    }
}

Key Concepts Explained

• net.Listen(): Creates a network "socket" to receive connections
• listener.Accept(): Waits for and accepts incoming connections
• go handleClient(conn): Handles each client in a separate thread (goroutine)

? Handling Client Connections

func handleClient(conn net.Conn) {
    // Always clean up after the conversation
    defer conn.Close()

    log.Printf("New client connected: %s", conn.RemoteAddr())

    // Prepare a message buffer
    buffer := make([]byte, 1024)

    // Keep the conversation going
    for {
        // Read message from client
        n, err := conn.Read(buffer)
        if err != nil {
            log.Printf("Connection error: %v", err)
            return
        }

        // Echo the message back
        message := string(buffer[:n])
        log.Printf("Received: %s", message)
        conn.Write([]byte("Server says: " + message))
    }
}

What's Happening Here?

• buffer: A temporary storage for incoming messages
• conn.Read(): Receives messages from the client
• conn.Write(): Sends messages back to the client

?️ Step 2: Creating the Client

package client

import (
    "bufio"
    "fmt"
    "log"
    "net"
    "os"
)

func StartClient() {
    // Dial the server (like making a phone call)
    conn, err := net.Dial("tcp", "localhost:8080")
    if err != nil {
        log.Printf("Could not connect to server: %v", err)
        return
    }
    defer conn.Close()

    fmt.Println("Connected to server. Start chatting!")

    // Read user input and send to server
    scanner := bufio.NewScanner(os.Stdin)
    for {
        fmt.Print("> ")
        if !scanner.Scan() {
            break
        }

        message := scanner.Text()
        if message == "exit" {
            break
        }

        // Send message to server
        conn.Write([]byte(message + "\n"))

        // Wait for server's response
        response := make([]byte, 1024)
        n, err := conn.Read(response)
        if err != nil {
            log.Printf("Error receiving response: %v", err)
            break
        }

        fmt.Println(string(response[:n]))
    }
}

Client Mechanics

• net.Dial(): Connect to the server
• scanner.Scan(): Read user's keyboard input
• conn.Write(): Send message to server
• conn.Read(): Receive server's response

? Bringing It All Together: main.go

package main

import (
    "time"
    "tcpIp/server"
    "tcpIp/client"
)

func main() {
    // Start server in background
    go func() {
        server.StartServer()
    }()

    // Give server a moment to start
    time.Sleep(time.Second)

    // Launch client
    client.StartClient()
}

?‍♂️ Running Your Network App

go run main.go

? What You've Learned

1. Basic network communication concepts
2. Creating a TCP server in Go
3. Connecting a client to the server
4. Handling network connections safely
5. Basic error management in network programming

? Potential Improvements

• Authentication
• Multiple client support
• Robust error handling
• Encryption

? Resources

• Go's net package documentation
• TCP/IP protocol basics
• Concurrent programming in Go

References

Administración.(2023, August 9). Learn TCP/IP with the Free Switching and Routing Guide for Everyone. Cursin. https://cursin.net/en/learn-tcp-ip-with-the-free-switching-and-routing-guide-for-everyone/

Woodbeck, A. (2021). Network Programming with Go. No Starch Press, Inc.

Happy Networking! ??

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