main.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
)

type MyContext struct {
	ID   int
	Name string
}

// ContextKey is a custom type to prevent key collisions in the context
type ContextKey string

const userContextKey ContextKey = "user"

// Middleware to inject User data into request context
func userMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Simulate fetching user data, e.g., from a session or token
		user := &MyContext{
			ID:   42,
			Name: "N S",
		}

		// Create a new context with user data
		ctx := context.WithValue(r.Context(), userContextKey, user)

		// Call the next handler with the updated context
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

// Handler to retrieve and use User data from the context
func helloHandler(w http.ResponseWriter, r *http.Request) {
	user, ok := Context(r)

	if !ok {
		http.Error(w, "User not found", http.StatusInternalServerError)
	}
	fmt.Fprintf(w, "Hello, %s (ID: %d)", user.Name, user.ID)
}

func main() {
	mux := http.NewServeMux()

	// Register handler with the middleware
	mux.Handle("/", userMiddleware(http.HandlerFunc(helloHandler)))

	log.Println("Server is running on :8080")
	http.ListenAndServe(":8080", mux)
}

func Context(r *http.Request) (*MyContext, bool) {
	user, ok := r.Context().Value(userContextKey).(*MyContext)
	return user, ok
}