Avoid array -> span -> array in COSE ToBeSignedBuilder.

The ToBeSignedBuilder for hash and pure modes had an Append that accepts a ReadOnlySpan. For .NET Framework and .NET Standard, IncrementalHash and MemoryStream cannot operate on a ReadOnlySpan, so they were getting converted to an array again. There were a number of places where we already had an array though.

This change avoids to array to span to array conversation by introducing
a new AppendToBeSigned overload that accepts an array with an offset and
length, which avoids a ToArray().

Co-authored-by: Jeremy Barton <[email protected]>

Author: vcsjones

src/libraries/System.Security.Cryptography.Cose/src/System/Security/Cryptography/Cose/CoseMessage.cs

@@ -439,7 +439,7 @@ internal static void AppendToBeSigned(
                 {
                     while ((bytesRead = contentStream.Read(contentBuffer, 0, contentBuffer.Length)) > 0)
                     {
-                        toBeSignedBuilder.AppendToBeSigned(contentBuffer.AsSpan(0, bytesRead));
+                        toBeSignedBuilder.AppendToBeSigned(contentBuffer, 0, bytesRead);
                     }
                 }
                 finally
@@ -462,7 +462,7 @@ internal static async Task AppendToBeSignedAsync(
             int bytesWritten = CreateToBeSigned(buffer, context, bodyProtected.Span, signProtected.Span, associatedData.Span, ReadOnlySpan<byte>.Empty);
             bytesWritten -= 1; // Trim the empty bstr content, it is just a placeholder.
 
-            toBeSignedBuilder.AppendToBeSigned(buffer.AsSpan(0, bytesWritten));
+            toBeSignedBuilder.AppendToBeSigned(buffer, 0, bytesWritten);
 
             //content length
             CoseHelpers.WriteByteStringLength(toBeSignedBuilder, (ulong)(content.Length - content.Position));
@@ -476,7 +476,7 @@ internal static async Task AppendToBeSignedAsync(
             while ((bytesRead = await content.ReadAsync(contentBuffer, cancellationToken).ConfigureAwait(false)) > 0)
 #endif
             {
-                toBeSignedBuilder.AppendToBeSigned(contentBuffer.AsSpan(0, bytesRead));
+                toBeSignedBuilder.AppendToBeSigned(contentBuffer, 0, bytesRead);
             }
 
             ArrayPool<byte>.Shared.Return(contentBuffer, clearArray: true);

src/libraries/System.Security.Cryptography.Cose/src/System/Security/Cryptography/Cose/HashToBeSignedBuilder.cs

@@ -23,6 +23,11 @@ internal override void AppendToBeSigned(ReadOnlySpan<byte> data)
             _incrementalHash.AppendData(data);
         }
 
+        internal override void AppendToBeSigned(byte[] data, int offset, int length)
+        {
+            _incrementalHash.AppendData(data, offset, length);
+        }
+
         internal override void WithDataAndResetAfterOperation(Span<byte> arg, ToBeSignedOperation operation)
         {
 #if NETSTANDARD2_0 || NETFRAMEWORK

src/libraries/System.Security.Cryptography.Cose/src/System/Security/Cryptography/Cose/PureDataToBeSignedBuilder.cs

@@ -27,6 +27,11 @@ internal override void AppendToBeSigned(ReadOnlySpan<byte> data)
 #endif
         }
 
+        internal override void AppendToBeSigned(byte[] data, int offset, int length)
+        {
+            _stream.Write(data, offset, length);
+        }
+
         internal override void WithDataAndResetAfterOperation(Span<byte> arg, ToBeSignedOperation operation)
         {
 #if NETSTANDARD2_0 || NETFRAMEWORK

src/libraries/System.Security.Cryptography.Cose/src/System/Security/Cryptography/Cose/ToBeSignedBuilder.cs

@@ -25,6 +25,7 @@ public void Dispose()
         }
 
         internal abstract void AppendToBeSigned(ReadOnlySpan<byte> data);
+        internal abstract void AppendToBeSigned(byte[] data, int offset, int length);
 
         // arg is passthrough - we don't do anything with it but all usages need to pass in extra Span and it's not allowed to do through closure.
         internal abstract void WithDataAndResetAfterOperation(Span<byte> arg, ToBeSignedOperation operation);