Fix serialization of FunctionArguments

Author: joseharriaga

src/Custom/Responses/Items/FunctionTool/FunctionCallResponseItem.Serialization.cs

@@ -0,0 +1,29 @@
+using System;
+using System.ClientModel.Primitives;
+using System.Runtime.CompilerServices;
+using System.Text.Json;
+
+namespace OpenAI.Responses;
+
+[CodeGenSerialization(nameof(FunctionArguments), SerializationValueHook = nameof(SerializeFunctionArgumentsValue), DeserializationValueHook = nameof(DeserializeFunctionArgumentsValue))]
+public partial class FunctionCallResponseItem : IJsonModel<FunctionCallResponseItem>
+{
+    // CUSTOM: The REST API serializes this as a string.
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private void SerializeFunctionArgumentsValue(Utf8JsonWriter writer, ModelReaderWriterOptions options)
+    {
+        string value = FunctionArguments.ToMemory().IsEmpty
+            ? string.Empty
+            : FunctionArguments.ToString();
+        writer.WriteStringValue(value);
+    }
+
+    // CUSTOM: Replaced the call to GetRawText() for a call to GetString() because otherwise the starting and ending
+    // quotes of the string are included in the BinaryData. While this is actually a string in the REST API, we want to
+    // handle it as JSON binary data instead.
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static void DeserializeFunctionArgumentsValue(JsonProperty property, ref BinaryData functionArguments, ModelReaderWriterOptions options = null)
+    {
+        functionArguments = BinaryData.FromString(property.Value.GetString());
+    }
+}

src/Generated/Models/Responses/FunctionCallResponseItem.Serialization.cs

@@ -44,14 +44,7 @@ protected override void JsonModelWriteCore(Utf8JsonWriter writer, ModelReaderWri
             if (_additionalBinaryDataProperties?.ContainsKey("arguments") != true)
             {
                 writer.WritePropertyName("arguments"u8);
-#if NET6_0_OR_GREATER
-                writer.WriteRawValue(FunctionArguments);
-#else
-                using (JsonDocument document = JsonDocument.Parse(FunctionArguments))
-                {
-                    JsonSerializer.Serialize(writer, document.RootElement);
-                }
-#endif
+                SerializeFunctionArgumentsValue(writer, options);
             }
             // Plugin customization: remove options.Format != "W" check
             // Plugin customization: apply Optional.Is*Defined() check based on type name dictionary lookup
@@ -112,7 +105,7 @@ internal static FunctionCallResponseItem DeserializeFunctionCallResponseItem(Jso
                 }
                 if (prop.NameEquals("arguments"u8))
                 {
-                    functionArguments = BinaryData.FromString(prop.Value.GetRawText());
+                    DeserializeFunctionArgumentsValue(prop, ref functionArguments);
                     continue;
                 }
                 if (prop.NameEquals("status"u8))