Add Email Header Unfolding logic

Author: tinohager

src/Nager.EmailAuthentication.UnitTest/DkimSignatureTests/FragmentParser/BasicTest.cs

@@ -20,7 +20,7 @@ public void TryParse_ValidDkimSignature1_ReturnsTrueAndPopulatesDataFragment()
         [TestMethod]
         public void TryParse_ValidDkimSignatureWithTabs_ReturnsTrueAndPopulatesDataFragment()
         {
-            var dkimSignature = "v=1; a=rsa-sha256; c=relaxed/relaxed; d=domain.com;\r\n s=testselector;\r\n h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck;\r\n bh=qxq6it6URJf9QDr82aTOS1esfmgKTsALYByECu5Ypjo=;\r\n b=Ps4k/pVqXOLkxP1x8YJL+ofgVAfNYNPGT0ln4pSQ5M7T+KTND8ijzYrPIocjiE40qLmQAnccrxMRS56weM2Jgb4F0cXkWJop1wJnUmKsFpMOYzaIXKUy4XnTaakR592E5t9ejoAgZIfE/jl3fcjKUIhNZuDGCSUYDAd64a1UndacEG+efXBG57bclUNmzuwx2tHXTBdKLecm0fZ0ST2OfAosrE8lwFyprzxSEoOFb8/PiA20MI1b2tMg7tH0pOcbLkdTHiSvkGuQFTvX87zCJk6WxW92bEP35kekPlqiFDKjpC5cVoIuC5UN9cHTsWvJLanaJJI+Ol9GB18dmqmCKw==";
+            var dkimSignature = "v=1; a=rsa-sha256; c=relaxed/relaxed; d=domain.com;\r\n s=testselector;\r\n h=From:Date:Subject:Message-ID:Content-Type:MIME-Version\r\n :X-MS-Exchange-SenderADCheck;\r\n bh=qxq6it6URJf9QDr82aTOS1esfmgKTsALYByECu5Ypjo=;\r\n b=Ps4k/pVqXOLkxP1x8YJL+ofgVAfNYNPGT0ln4pSQ5M7T+KTND8ijzYrPIocjiE40qLmQAnccrxMRS56weM2Jgb4F0cXkWJop1wJnUmKsFpMOYzaIXKUy4XnTaakR592E5t9ejoAgZIfE/jl3fcjKUIhNZuDGCSUYDAd64a1UndacEG+efXBG57bclUNmzuwx2tHXTBdKLecm0fZ0ST2OfAosrE8lwFyprzxSEoOFb8/PiA20MI1b2tMg7tH0pOcbLkdTHiSvkGuQFTvX87zCJk6WxW92bEP35kekPlqiFDKjpC5cVoIuC5UN9cHTsWvJLanaJJI+Ol9GB18dmqmCKw==";
             //TODO: Add logic for removing tabs and line breaks
 
             var isSuccessful = DkimSignatureDataFragmentParserV1.TryParse(dkimSignature, out var dkimSignatureDataFragment, out var parsingResults);

src/Nager.EmailAuthentication/FragmentParsers/DkimSignatureDataFragmentParserV1.cs

@@ -1,4 +1,5 @@
 using Nager.EmailAuthentication.Handlers;
+using Nager.EmailAuthentication.Helpers;
 using Nager.EmailAuthentication.Models;
 using Nager.EmailAuthentication.Models.Dkim;
 using Nager.EmailAuthentication.RegexProviders;
@@ -136,8 +137,10 @@ public static bool TryParse(
                 }
             };
 
+            var unfoldDkimSignatureHeader = MailHeaderHelper.UnfoldingHeader(dkimSignature);
+
             var parserBase = new KeyValueParserBase<DkimSignatureDataFragmentV1>(handlers);
-            return parserBase.TryParse(dkimSignature, out dkimSignatureDataFragment, out parsingResults);
+            return parserBase.TryParse(unfoldDkimSignatureHeader, out dkimSignatureDataFragment, out parsingResults);
         }
 
         private static ParsingResult[] ValidatePositiveNumber(

src/Nager.EmailAuthentication/Helpers/MailHeaderHelper.cs

@@ -0,0 +1,55 @@
+namespace Nager.EmailAuthentication.Helpers
+{
+    /// <summary>
+    /// Mail Header Helper
+    /// </summary>
+    public static class MailHeaderHelper
+    {
+        /// <summary>
+        /// Unfolding Mail Header
+        /// </summary>
+        /// <param name="header"></param>
+        /// <returns></returns>
+        public static string UnfoldingHeader(string header)
+        {
+            Span<char> buffer = stackalloc char[header.Length];
+            int bufferIndex = 0;
+            bool newLine = false;
+
+            for (var i = 0; i < header.Length;)
+            {
+                if (i < header.Length)
+                {
+                    if (header[i] == '\r' && header[i + 1] == '\n')
+                    {
+                        i += 2;
+                        newLine = true;
+                        continue;
+                    }
+                }
+
+                if (newLine)
+                {
+                    newLine = false;
+
+                    if (header[i] == '\t')
+                    {
+                        i++;
+                        continue;
+                    }
+
+                    if (header[i] == ' ')
+                    {
+                        i++;
+                        continue;
+                    }
+                }
+
+                buffer[bufferIndex++] = header[i];
+                i++;
+            }
+
+            return new string(buffer[..bufferIndex]);
+        }
+    }
+}