pricing: enrich pricelist items with stock and tighten CORS

internal/middleware/cors.go

@@ -1,22 +1,55 @@
 package middleware
 
 import (
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+
 	"github.com/gin-gonic/gin"
 )
 
 func CORS() gin.HandlerFunc {
 	return func(c *gin.Context) {
-		c.Header("Access-Control-Allow-Origin", "*")
-		c.Header("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS")
-		c.Header("Access-Control-Allow-Headers", "Origin, Content-Type, Accept, Authorization")
-		c.Header("Access-Control-Expose-Headers", "Content-Length, Content-Disposition")
-		c.Header("Access-Control-Max-Age", "86400")
+		origin := strings.TrimSpace(c.GetHeader("Origin"))
+		if origin != "" {
+			if isLoopbackOrigin(origin) {
+				c.Header("Access-Control-Allow-Origin", origin)
+				c.Header("Vary", "Origin")
+				c.Header("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS")
+				c.Header("Access-Control-Allow-Headers", "Origin, Content-Type, Accept, Authorization")
+				c.Header("Access-Control-Expose-Headers", "Content-Length, Content-Disposition")
+				c.Header("Access-Control-Max-Age", "86400")
+			} else if c.Request.Method == http.MethodOptions {
+				c.AbortWithStatus(http.StatusForbidden)
+				return
+			}
+		}
 
-		if c.Request.Method == "OPTIONS" {
-			c.AbortWithStatus(204)
+		if c.Request.Method == http.MethodOptions {
+			c.AbortWithStatus(http.StatusNoContent)
 			return
 		}
 
 		c.Next()
 	}
 }
+
+func isLoopbackOrigin(origin string) bool {
+	u, err := url.Parse(origin)
+	if err != nil {
+		return false
+	}
+	if u.Scheme != "http" && u.Scheme != "https" {
+		return false
+	}
+	host := strings.TrimSpace(u.Hostname())
+	if host == "" {
+		return false
+	}
+	if strings.EqualFold(host, "localhost") {
+		return true
+	}
+	ip := net.ParseIP(host)
+	return ip != nil && ip.IsLoopback()
+}