[Client encryption]: Adds new tests for StreamProcessor (#5370)

# Pull Request Template

#4678 

## Description

Introduces tests for Decrypt and Encrypt paths of the StreamProcessor.

---------

Co-authored-by: Kiran Kumar Kolli <kirankk@microsoft.com>

Author: adamnova

Microsoft.Azure.Cosmos.Encryption.Custom/src/Transformation/StreamProcessor.Decryptor.cs

@@ -140,7 +140,7 @@ long TransformDecryptBuffer(ReadOnlySpan<byte> buffer)
                             decryptPropertyName = null;
                             writer.WriteRawValue(reader.ValueSpan);
                             break;
-                        case JsonTokenType.None:
+                        case JsonTokenType.None: // Unreachable: pre-first-Read state
                             decryptPropertyName = null;
                             break;
                         case JsonTokenType.StartObject:
@@ -177,7 +177,7 @@ long TransformDecryptBuffer(ReadOnlySpan<byte> buffer)
 
                             writer.WritePropertyName(reader.ValueSpan);
                             break;
-                        case JsonTokenType.Comment:
+                        case JsonTokenType.Comment: // Skipped via reader options
                             break;
                         case JsonTokenType.True:
                             decryptPropertyName = null;
@@ -213,7 +213,7 @@ void TransformDecryptProperty(ref Utf8JsonReader reader)
 
                 (byte[] bytes, int processedBytes) = this.Encryptor.Decrypt(encryptionKey, cipherTextWithTypeMarker, cipherTextLength, arrayPoolManager);
 
-                if (containsCompressed && properties.CompressedEncryptedPaths?.TryGetValue(decryptPropertyName, out int decompressedSize) == true)
+                if (containsCompressed && properties.CompressedEncryptedPaths.TryGetValue(decryptPropertyName, out int decompressedSize))
                 {
                     BrotliCompressor decompressor = new ();
                     byte[] buffer = arrayPoolManager.Rent(decompressedSize);
@@ -237,7 +237,7 @@ void TransformDecryptProperty(ref Utf8JsonReader reader)
                     case TypeMarker.Boolean:
                         writer.WriteBooleanValue(SqlBoolSerializer.Deserialize(bytesToWrite));
                         break;
-                    case TypeMarker.Null:
+                    case TypeMarker.Null: // Produced only if ciphertext was forged or future versions choose to encrypt nulls; current encryptor skips nulls.
                         writer.WriteNullValue();
                         break;
                     default:

Microsoft.Azure.Cosmos.Encryption.Custom/src/Transformation/StreamProcessor.Encryptor.cs

@@ -107,7 +107,7 @@ long TransformEncryptBuffer(ReadOnlySpan<byte> buffer)
 
                     switch (tokenType)
                     {
-                        case JsonTokenType.None:
+                        case JsonTokenType.None: // Unreachable after first Read()
                             break;
                         case JsonTokenType.StartObject:
                             if (encryptPropertyName != null && encryptionPayloadWriter == null)
@@ -187,7 +187,7 @@ long TransformEncryptBuffer(ReadOnlySpan<byte> buffer)
 
                             currentWriter.WritePropertyName(reader.ValueSpan);
                             break;
-                        case JsonTokenType.Comment:
+                        case JsonTokenType.Comment: // Skipped via reader options
                             currentWriter.WriteCommentValue(reader.ValueSpan);
                             break;
                         case JsonTokenType.String:
@@ -249,6 +249,7 @@ long TransformEncryptBuffer(ReadOnlySpan<byte> buffer)
                             break;
                         case JsonTokenType.Null:
                             currentWriter.WriteNullValue();
+                            encryptPropertyName = null;
                             break;
                     }
                 }
@@ -287,18 +288,21 @@ private static (byte[] buffer, int length) Serialize(bool value, ArrayPoolManage
 
         private static (TypeMarker typeMarker, byte[] buffer, int length) SerializeNumber(ReadOnlySpan<byte> utf8bytes, ArrayPoolManager arrayPoolManager)
         {
-            if (long.TryParse(utf8bytes, out long longValue))
+            if (System.Buffers.Text.Utf8Parser.TryParse(utf8bytes, out long longValue, out int consumedLong) && consumedLong == utf8bytes.Length)
             {
                 return Serialize(longValue, arrayPoolManager);
             }
-            else if (double.TryParse(utf8bytes, out double doubleValue))
-            {
-                return Serialize(doubleValue, arrayPoolManager);
-            }
-            else
+
+            if (System.Buffers.Text.Utf8Parser.TryParse(utf8bytes, out double doubleValue, out int consumedDouble) && consumedDouble == utf8bytes.Length)
             {
-                throw new InvalidOperationException("Unsupported Number type");
+                // Reject non-finite numbers to keep JSON contract compatibility
+                if (double.IsFinite(doubleValue))
+                {
+                    return Serialize(doubleValue, arrayPoolManager);
+                }
             }
+
+            throw new InvalidOperationException("Unsupported Number type");
         }
 
         private static (TypeMarker typeMarker, byte[] buffer, int length) Serialize(long value, ArrayPoolManager arrayPoolManager)

Microsoft.Azure.Cosmos.Encryption.Custom/tests/Microsoft.Azure.Cosmos.Encryption.Custom.Tests/Microsoft.Azure.Cosmos.Encryption.Custom.Tests.csproj

@@ -22,6 +22,8 @@
     <PackageReference Include="MSTest.TestAdapter" Version="1.2.0" />
     <PackageReference Include="MSTest.TestFramework" Version="1.2.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
+    <PackageReference Include="coverlet.collector" Version="6.0.0" />
+    <PackageReference Include="coverlet.msbuild" Version="6.0.0" />
   </ItemGroup>
 
   <ItemGroup>