add cors example

cors-middleware/README.md

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+# CORS Middleware Example
+
+This example demonstrates how to enable **Cross-Origin Resource Sharing (CORS)** in a Gin web server.  
+It also provides basic RESTful endpoints (`GET`, `POST`, `PUT`, `DELETE`) to verify that cross-origin requests are properly handled.
+
+---
+
+## Features
+- Custom CORS middleware allowing all origins (`*`)
+- RESTful routes for `/ping` and `/data/:id`
+- JSON responses with timestamps
+- Handles `OPTIONS` preflight requests
+- Includes logging for incoming requests
+
+---
+
+## Run
+
+```bash
+go run main.go

cors-middleware/main.go

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+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+func CORSMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		c.Writer.Header().Set("Access-Control-Allow-Origin", "*")
+		c.Writer.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE, UPDATE")
+		c.Writer.Header().Set("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept, Authorization")
+		c.Writer.Header().Set("Access-Control-Allow-Credentials", "true")
+		if c.Request.Method == "OPTIONS" {
+			c.Writer.Header().Set("Access-Control-Max-Age", "86400")
+			c.AbortWithStatus(http.StatusNoContent)
+			return
+		}
+		c.Next()
+	}
+}
+
+func main() {
+	r := gin.Default()
+	r.Use(CORSMiddleware())
+	r.GET("/ping", func(c *gin.Context) {
+		log.Println("Received a GET /ping request.")
+		c.JSON(http.StatusOK, gin.H{
+			"message": "pong",
+			"time":    time.Now().Format(time.RFC3339),
+		})
+	})
+	r.POST("/data", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{
+			"status":  "success",
+			"action":  "Created",
+			"message": "Data processed successfully via POST.",
+		})
+	})
+	r.PUT("/data/:id", func(c *gin.Context) {
+		id := c.Param("id")
+		c.JSON(http.StatusOK, gin.H{
+			"status":  "success",
+			"action":  "Updated",
+			"message": fmt.Sprintf("Successfully processed PUT for resource ID: %s", id),
+		})
+	})
+	r.DELETE("/data/:id", func(c *gin.Context) {
+		id := c.Param("id")
+		c.JSON(http.StatusOK, gin.H{
+			"status":  "success",
+			"action":  "Deleted",
+			"message": fmt.Sprintf("Successfully processed DELETE for resource ID: %s", id),
+		})
+	})
+	log.Fatal(r.Run(":8080"))
+}