Add DocumentJsonConverter for System.Text.Json serialization support

generator/.DevConfigs/180bd698-bd6a-4799-a23e-db90f89660d6.json

@@ -0,0 +1,9 @@
+{
+  "core": {
+    "changeLogMessages": [
+      "Add DocumentJsonConverter to fix System.Text.Json serialization of Document types. Document's IEnumerable interfaces caused STJ to treat it as a collection, throwing InvalidDocumentTypeConversionException."
+    ],
+    "type": "patch",
+    "updateMinimum": false
+  }
+}

sdk/src/Core/Amazon.Runtime/Documents/Document.cs

@@ -20,8 +20,10 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq;
-using ThirdParty.RuntimeBackports;
 using System.Text.Json;
+using System.Text.Json.Serialization;
+
+using ThirdParty.RuntimeBackports;
 namespace Amazon.Runtime.Documents
 {
     /// <summary>
@@ -51,6 +53,7 @@ namespace Amazon.Runtime.Documents
     /// Document Types specification specifies support for arbitrary precision integers.  However, the dotnet implementation
     /// is limited to representing numbers as either <see cref="double"/>, <see cref="int"/> or <see cref="long"/>.
     /// </remarks>
+    [JsonConverter(typeof(DocumentJsonConverter))]
     public partial struct Document : IEquatable<Document>, IEnumerable<Document>, IEnumerable<KeyValuePair<string, Document>>
     {
         private readonly bool _dataBool;
@@ -438,6 +441,8 @@ private static Document FromObject(JsonElement jsonElement)
                 case JsonValueKind.True:
                     return new Document(jsonElement.GetBoolean());
                 case JsonValueKind.Number:
+                    if (jsonElement.TryGetInt32(out int intValue))
+                        return new Document(intValue);
                     if (jsonElement.TryGetInt64(out long longValue))
                         return new Document(longValue);
                     if (jsonElement.TryGetDouble(out double doubleValue))

sdk/src/Core/Amazon.Runtime/Documents/DocumentJsonConverter.cs

@@ -0,0 +1,93 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+using System;
+using System.Collections.Generic;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Amazon.Runtime.Documents.Internal.Transform;
+
+namespace Amazon.Runtime.Documents
+{
+    /// <summary>
+    /// Custom <see cref="JsonConverter{T}"/> for <see cref="Document"/> that prevents
+    /// System.Text.Json from treating Document as a collection (due to its IEnumerable implementations)
+    /// and instead serializes/deserializes it according to its actual document type.
+    /// </summary>
+    internal sealed class DocumentJsonConverter : JsonConverter<Document>
+    {
+        /// <inheritdoc/>
+        public override Document Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            return ReadDocument(ref reader);
+        }
+
+        /// <inheritdoc/>
+        public override void Write(Utf8JsonWriter writer, Document value, JsonSerializerOptions options)
+        {
+            DocumentMarshaller.Instance.Write(writer, value);
+        }
+
+        private static Document ReadDocument(ref Utf8JsonReader reader)
+        {
+            switch (reader.TokenType)
+            {
+                case JsonTokenType.Null:
+                    return new Document();
+
+                case JsonTokenType.True:
+                case JsonTokenType.False:
+                    return new Document(reader.GetBoolean());
+
+                case JsonTokenType.Number:
+                    if (reader.TryGetInt32(out int intValue))
+                        return new Document(intValue);
+                    if (reader.TryGetInt64(out long longValue))
+                        return new Document(longValue);
+                    if (reader.TryGetDouble(out double doubleValue))
+                        return new Document(doubleValue);
+                    throw new JsonException("Unsupported number type.");
+
+                case JsonTokenType.String:
+                    return new Document(reader.GetString());
+
+                case JsonTokenType.StartArray:
+                    var list = new List<Document>();
+                    while (reader.Read())
+                    {
+                        if (reader.TokenType == JsonTokenType.EndArray)
+                            break;
+                        list.Add(ReadDocument(ref reader));
+                    }
+                    return new Document(list);
+
+                case JsonTokenType.StartObject:
+                    var dict = new Dictionary<string, Document>();
+                    while (reader.Read())
+                    {
+                        if (reader.TokenType == JsonTokenType.EndObject)
+                            break;
+                        var key = reader.GetString();
+                        reader.Read();
+                        dict.Add(key, ReadDocument(ref reader));
+                    }
+                    return new Document(dict);
+
+                default:
+                    throw new JsonException($"Unexpected JSON token type: {reader.TokenType}");
+            }
+        }
+    }
+}