Optimize dkim validation logic

Author: tinohager

src/Nager.EmailAuthentication.UnitTest/DkimSignatureParserTests/SelectorTest.cs

@@ -19,6 +19,10 @@ public void TryParse_ValidSelector_ReturnsTrueAndPopulatesDataFragment(string se
         }
 
         [DataRow("verylongandinvalidselectorverylongandinvalidselectorverylongandinvalidselector")]
+        [DataRow("-test")]
+        [DataRow("-test-")]
+        [DataRow("_test")]
+        [DataRow("test_")]
         [DataTestMethod]
         public void TryParse_InvalidSelector_ReturnsTrueAndPopulatesDataFragment(string selector)
         {

src/Nager.EmailAuthentication.UnitTest/DmarcRecordParserTests/ComplexTest.cs

@@ -22,6 +22,7 @@ public void TryParse_ValidDmarcString1_ReturnsTrueAndPopulatesDmarcRecord()
         public void TryParse_ValidDmarcString2_ReturnsTrueAndPopulatesDmarcRecord()
         {
             var isSuccessful = DmarcRecordDataFragmentParser.TryParse("v=DMARC1; p=reject; rua=mailto:[email protected], mailto:[email protected]; pct=100; adkim=s; aspf=s", out var dmarcDataFragment, out var parsingResults);
+            Assert.IsNotNull(dmarcDataFragment);
 
             var isSuccessful2 = DmarcRecordParser.TryParse(dmarcDataFragment, out var dmarcRecord);
             Assert.IsTrue(isSuccessful2);

src/Nager.EmailAuthentication/DkimSignatureDataFragmentParser.cs

@@ -1,5 +1,6 @@
 using Nager.EmailAuthentication.Handlers;
 using Nager.EmailAuthentication.Models;
+using Nager.EmailAuthentication.RegexProviders;
 using System.Diagnostics.CodeAnalysis;
 
 namespace Nager.EmailAuthentication
@@ -79,7 +80,8 @@ public static bool TryParse(
                 {
                     "d", new MappingHandler<DkimSignatureDataFragment>
                     {
-                        Map = (dataFragment, value) => dataFragment.SigningDomainIdentifier = value
+                        Map = (dataFragment, value) => dataFragment.SigningDomainIdentifier = value,
+                        Validate = ValidateDomain
                     }
                 },
                 {
@@ -228,6 +230,45 @@ private static ParsingResult[] ValidateSelector(ValidateRequest validateRequest)
                 });
             }
 
+            if (!DkimSelectorRegexProvider.GetRegex().IsMatch(validateRequest.Value))
+            {
+                errors.Add(new ParsingResult
+                {
+                    Status = ParsingStatus.Error,
+                    Field = validateRequest.Field,
+                    Message = "Selector syntax invalid"
+                });
+            }
+
+            return [.. errors];
+        }
+
+        private static ParsingResult[] ValidateDomain(ValidateRequest validateRequest)
+        {
+            var errors = new List<ParsingResult>();
+
+            if (string.IsNullOrEmpty(validateRequest.Value))
+            {
+                errors.Add(new ParsingResult
+                {
+                    Status = ParsingStatus.Error,
+                    Field = validateRequest.Field,
+                    Message = "Is empty"
+                });
+
+                return [.. errors];
+            }
+
+            if (!Uri.TryCreate($"https://{validateRequest.Value}", UriKind.Absolute, out _))
+            {
+                errors.Add(new ParsingResult
+                {
+                    Status = ParsingStatus.Critical,
+                    Field = validateRequest.Field,
+                    Message = "Invalid domain syntax"
+                });
+            }
+
             return [.. errors];
         }
 

src/Nager.EmailAuthentication/RegexProviders/DkimSelectorRegexProvider.cs

@@ -0,0 +1,10 @@
+using System.Text.RegularExpressions;
+
+namespace Nager.EmailAuthentication.RegexProviders
+{
+    internal static partial class DkimSelectorRegexProvider
+    {
+        [GeneratedRegex("^[a-z0-9]{1}[a-z0-9-]*[a-z0-9]{1}$", RegexOptions.IgnoreCase)]
+        internal static partial Regex GetRegex();
+    }
+}