finalize refactoring & ready for the PR

MalwareMultiScan.Api/Attributes/IsHttpUrlAttribute.cs

@@ -0,0 +1,22 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+
+namespace MalwareMultiScan.Api.Attributes
+{
+    /// <summary>
+    /// Validate URI to be an absolute http(s) URL.
+    /// </summary>
+    internal class IsHttpUrlAttribute : ValidationAttribute
+    {
+        /// <inheritdoc />
+        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
+        {
+            if (!Uri.TryCreate((string)value, UriKind.Absolute, out var uri) 
+                || !uri.IsAbsoluteUri 
+                || uri.Scheme != "http" && uri.Scheme != "https")
+                return new ValidationResult("Only absolute http(s) URLs are supported");
+
+            return ValidationResult.Success;
+        }
+    }
+}