Revert change making it possible to change FormatOptions.Default prop…

…erty values

This reverts the following commits:
* 4b77a9f: Allow changing the FormatOptions.Default values
* e3bab7b: Improve Header.GetRawValue() logic
* 22881de: Cache more of the FormatOptions in each Header
* 9570ebd: Added FormatOptions.ReformatHeaders and fixed unit tests

...And reopens issue #993.

I will be revisiting this set of changes for v5.0 when I'll have more flexibility with
behavioral changes. The problem with this set was not that it "didn't work", but rather
that it changed expected behavior. I also wasn't sure if I really liked the new
FormatOptions.ReformatHeaders property naming.

MimeKit/Cryptography/ArcVerifier.cs

@@ -396,6 +396,9 @@ async Task<bool> VerifyArcMessageSignatureAsync (FormatOptions options, MimeMess
 			if (!IsEnabled (signatureAlgorithm))
 				return false;
 
+			options = options.Clone ();
+			options.NewLineFormat = NewLineFormat.Dos;
+
 			// first check the body hash (if that's invalid, then the entire signature is invalid)
 			if (!VerifyBodyHash (options, message, signatureAlgorithm, bodyAlgorithm, maxLength, bh))
 				return false;
@@ -430,6 +433,9 @@ async Task<bool> VerifyArcSealAsync (FormatOptions options, ArcHeaderSet[] sets,
 			if ((key is RsaKeyParameters rsa) && rsa.Modulus.BitLength < MinimumRsaKeyLength)
 				return false;
 
+			options = options.Clone ();
+			options.NewLineFormat = NewLineFormat.Dos;
+
 			using (var stream = new DkimSignatureStream (CreateVerifyContext (algorithm, key))) {
 				using (var filtered = new FilteredStream (stream)) {
 					filtered.Add (options.CreateNewLineFilter ());
@@ -667,7 +673,6 @@ async Task<ArcValidationResult> VerifyAsync (FormatOptions options, MimeMessage
 			int newest = count - 1;
 
 			result.Seals = new ArcHeaderValidationResult[count];
-			options = GetVerifyOptions (options);
 
 			// validate the most recent Arc-Message-Signature
 			try {
@@ -783,7 +788,7 @@ public Task<ArcValidationResult> VerifyAsync (FormatOptions options, MimeMessage
 		/// </exception>
 		public ArcValidationResult Verify (MimeMessage message, CancellationToken cancellationToken = default)
 		{
-			return Verify (FormatOptions.VerifySignature, message, cancellationToken);
+			return Verify (FormatOptions.Default, message, cancellationToken);
 		}
 
 		/// <summary>
@@ -806,7 +811,7 @@ public ArcValidationResult Verify (MimeMessage message, CancellationToken cancel
 		/// </exception>
 		public Task<ArcValidationResult> VerifyAsync (MimeMessage message, CancellationToken cancellationToken = default)
 		{
-			return VerifyAsync (FormatOptions.VerifySignature, message, cancellationToken);
+			return VerifyAsync (FormatOptions.Default, message, cancellationToken);
 		}
 	}
 }

MimeKit/Cryptography/DkimVerifier.cs

@@ -125,7 +125,8 @@ async Task<bool> VerifyAsync (FormatOptions options, MimeMessage message, Header
 			if (!IsEnabled (signatureAlgorithm))
 				return false;
 
-			options = GetVerifyOptions (options);
+			options = options.Clone ();
+			options.NewLineFormat = NewLineFormat.Dos;
 
 			// first check the body hash (if that's invalid, then the entire signature is invalid)
 			if (!VerifyBodyHash (options, message, signatureAlgorithm, bodyAlgorithm, maxLength, bh))
@@ -241,7 +242,7 @@ public Task<bool> VerifyAsync (FormatOptions options, MimeMessage message, Heade
 		/// </exception>
 		public bool Verify (MimeMessage message, Header dkimSignature, CancellationToken cancellationToken = default)
 		{
-			return Verify (FormatOptions.VerifySignature, message, dkimSignature, cancellationToken);
+			return Verify (FormatOptions.Default, message, dkimSignature, cancellationToken);
 		}
 
 		/// <summary>
@@ -273,7 +274,7 @@ public bool Verify (MimeMessage message, Header dkimSignature, CancellationToken
 		/// </exception>
 		public Task<bool> VerifyAsync (MimeMessage message, Header dkimSignature, CancellationToken cancellationToken = default)
 		{
-			return VerifyAsync (FormatOptions.VerifySignature, message, dkimSignature, cancellationToken);
+			return VerifyAsync (FormatOptions.Default, message, dkimSignature, cancellationToken);
 		}
 	}
 }

MimeKit/Cryptography/DkimVerifierBase.cs

@@ -150,22 +150,6 @@ public bool IsEnabled (DkimSignatureAlgorithm algorithm)
 			return (enabledSignatureAlgorithms & (1 << (int) algorithm)) != 0;
 		}
 
-		/// <summary>
-		/// Get the formatting options for use with verifying DKIM signatures.
-		/// </summary>
-		/// <param name="format">The user-requested formatting options.</param>
-		/// <returns>The formatting options.</returns>
-		internal static FormatOptions GetVerifyOptions (FormatOptions format)
-		{
-			var options = format.Clone ();
-			options.NewLineFormat = NewLineFormat.Dos;
-			options.VerifyingSignature = true;
-			options.ReformatHeaders = false;
-			options.HiddenHeaders.Clear ();
-			options.EnsureNewLine = false;
-			return options;
-		}
-
 		static bool IsWhiteSpace (char c)
 		{
 			return c == ' ' || c == '\t';

MimeKit/Cryptography/MultipartSigned.cs

@@ -767,7 +767,6 @@ public DigitalSignatureCollection Verify (CryptographyContext ctx, CancellationT
 					var options = FormatOptions.Default.Clone ();
 					options.NewLineFormat = NewLineFormat.Dos;
 					options.VerifyingSignature = true;
-					options.ReformatHeaders = false;
 
 					this[0].WriteTo (options, cleartext, cancellationToken);
 					cleartext.Position = 0;
@@ -838,7 +837,6 @@ public async Task<DigitalSignatureCollection> VerifyAsync (CryptographyContext c
 					var options = FormatOptions.Default.Clone ();
 					options.NewLineFormat = NewLineFormat.Dos;
 					options.VerifyingSignature = true;
-					options.ReformatHeaders = false;
 
 					await this[0].WriteToAsync (options, cleartext, cancellationToken);
 					cleartext.Position = 0;