Understanding the Basics of a Go HTTP Server (Quick introduction)

1️⃣ What is an HTTP server ?

An HTTP server is a program that :

• 1- Listens on a port (e.g., 8080)
• 2- Waits for requests (GET, POST, etc.)
• 3- Responds with content (HTML, JSON, text...)

👉 Real-world example : When you visit http://example.com, your browser sends a request to the server, which responds with the webpage.

2️⃣ How does a server work in Go ?

In Go, we use thenet/httppackage to create a server. Here are the basic components :

a- Starting a server :

A Go server starts with http.ListenAndServe(port, handler), where :

• port = the number it listens on (e.g., :8080)
• handler = a function that processes requests (e.g., a route / that displays "Hello, World!")

b- Creating a route :

We use http.HandleFunc("/route", myFunction) to define routes.

👉 Minimal example :

                    package main

                    import (
                        "fmt"
                        "net/http"
                    )
                    
                    func handler(w http.ResponseWriter, r *http.Request) {
                        fmt.Fprintf(w, "Welcome to my Go server!")
                    }
                    
                    func main() {
                        http.HandleFunc("/", handler)
                        http.ListenAndServe(":8080", nil)
                    }
                    

            

📌 Explanation :

• 1- We define a functionhandler()that writes a response message.
• 2- We link this function to / usinghttp.HandleFunc("/") .
• 3- We start the server on port 8080 (http://localhost:8080).
• 4-You can try this code and run it , open your browser(http://localhost:8080) you will see the message : "Welcome to my Go server!"

3️⃣ Going further: Multiple routes

We can add multiple routes like this :

package main

import (
	"fmt"
	"net/http"
)

func homeHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Welcome to the homepage!")
}

func aboutHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "About this server.")
}

func main() {
	http.HandleFunc("/", homeHandler)
	http.HandleFunc("/about", aboutHandler)
	http.ListenAndServe(":8080", nil)
}

            

📌 Explanation :

• 1- http.HandleFunc("/")→ Main route (/).
• 2- http.HandleFunc("/about")→ Route /about.
• 3- each handler responds with a different message.

Run the Go Server and Test the Endpoints

4️⃣ Serving static files (CSS, images...)

f you want to serve files like index.html, style.css, etc., you can use :

fs := http.FileServer(http.Dir("./static"))
http.Handle("/static/", http.StripPrefix("/static/", fs))

            

📌 Explanation :

• http.FileServer(http.Dir("./static")) → Tells Go that the files are inside the static/ folder.
• http.StripPrefix("/static/", fs) → Removes /static/ from the path to find files correctly.

5️⃣ Sending a JSON response

If you want to send JSON data (used in APIs), here's how :

package main

import (
	"encoding/json"
	"net/http"
)

type Message struct {
	Text string `json:"text"`
}

func jsonHandler(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json") // Set response type to JSON
	message := Message{Text: "Hello, JSON!"}
	json.NewEncoder(w).Encode(message)
}

func main() {
	http.HandleFunc("/api", jsonHandler)
	http.ListenAndServe(":8080", nil)
}

            

📌 Explanation :

• Messageis a Go struct converted into JSON.
• w.Header().Set("Content-Type", "application/json") → Tells the client we're sending JSON.
• json.NewEncoder(w).Encode(message) → Encodes and sends the response.