Allow JsonSerializerOptions parameters for user-defined and inputs and hardcode everything else to the source generator. (#182)

* Allow user-defined JsonSerializerOptions for user-defined and inputs and hardcode everything else to the source generator.

* Add validation for user-defined JsonSerializerOptions.

* Remove out of date comment.

* Address feedback and add tests

src/ModelContextProtocol/Protocol/Messages/JsonRpcNotification.cs

@@ -1,4 +1,5 @@
-using System.Text.Json.Serialization;
+using System.Text.Json.Nodes;
+using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol.Messages;
 
@@ -23,5 +24,5 @@ public record JsonRpcNotification : IJsonRpcMessage
     /// Optional parameters for the notification.
     /// </summary>
     [JsonPropertyName("params")]
-    public object? Params { get; init; }
+    public JsonNode? Params { get; init; }
 }

src/ModelContextProtocol/Protocol/Messages/JsonRpcRequest.cs

@@ -1,4 +1,5 @@
-using System.Text.Json.Serialization;
+using System.Text.Json.Nodes;
+using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol.Messages;
 
@@ -29,5 +30,5 @@ public record JsonRpcRequest : IJsonRpcMessageWithId
     /// Optional parameters for the method.
     /// </summary>
     [JsonPropertyName("params")]
-    public object? Params { get; init; }
+    public JsonNode? Params { get; init; }
 }

src/ModelContextProtocol/Protocol/Messages/JsonRpcResponse.cs

@@ -1,4 +1,4 @@
-
+using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol.Messages;
@@ -23,5 +23,5 @@ public record JsonRpcResponse : IJsonRpcMessageWithId
     /// The result of the method invocation.
     /// </summary>
     [JsonPropertyName("result")]
-    public required object? Result { get; init; }
+    public required JsonNode? Result { get; init; }
 }

src/ModelContextProtocol/Protocol/Transport/SseClientSessionTransport.cs

@@ -24,7 +24,6 @@ internal sealed class SseClientSessionTransport : TransportBase
     private Task? _receiveTask;
     private readonly ILogger _logger;
     private readonly McpServerConfig _serverConfig;
-    private readonly JsonSerializerOptions _jsonOptions;
     private readonly TaskCompletionSource<bool> _connectionEstablished;
 
     private string EndpointName => $"Client (SSE) for ({_serverConfig.Id}: {_serverConfig.Name})";
@@ -50,7 +49,6 @@ internal sealed class SseClientSessionTransport : TransportBase
         _httpClient = httpClient;
         _connectionCts = new CancellationTokenSource();
         _logger = (ILogger?)loggerFactory?.CreateLogger<SseClientTransport>() ?? NullLogger.Instance;
-        _jsonOptions = McpJsonUtilities.DefaultOptions;
         _connectionEstablished = new TaskCompletionSource<bool>();
     }
 
@@ -94,7 +92,7 @@ internal sealed class SseClientSessionTransport : TransportBase
             throw new InvalidOperationException("Transport not connected");
 
         using var content = new StringContent(
-            JsonSerializer.Serialize(message, _jsonOptions.GetTypeInfo<IJsonRpcMessage>()),
+            JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.IJsonRpcMessage),
             Encoding.UTF8,
             "application/json"
         );
@@ -127,7 +125,7 @@ internal sealed class SseClientSessionTransport : TransportBase
             }
             else
             {
-                JsonRpcResponse initializeResponse = JsonSerializer.Deserialize(responseContent, _jsonOptions.GetTypeInfo<JsonRpcResponse>()) ??
+                JsonRpcResponse initializeResponse = JsonSerializer.Deserialize(responseContent, McpJsonUtilities.JsonContext.Default.JsonRpcResponse) ??
                     throw new McpTransportException("Failed to initialize client");
 
                 _logger.TransportReceivedMessageParsed(EndpointName, messageId);
@@ -259,7 +257,7 @@ internal sealed class SseClientSessionTransport : TransportBase
 
         try
         {
-            var message = JsonSerializer.Deserialize(data, _jsonOptions.GetTypeInfo<IJsonRpcMessage>());
+            var message = JsonSerializer.Deserialize(data, McpJsonUtilities.JsonContext.Default.IJsonRpcMessage);
             if (message == null)
             {
                 _logger.TransportMessageParseUnexpectedType(EndpointName, data);

src/ModelContextProtocol/Protocol/Types/CallToolRequestParams.cs

@@ -1,4 +1,6 @@
-namespace ModelContextProtocol.Protocol.Types;
+using System.Text.Json;
+
+namespace ModelContextProtocol.Protocol.Types;
 
 /// <summary>
 /// Used by the client to invoke a tool provided by the server.
@@ -16,5 +18,5 @@ public class CallToolRequestParams : RequestParams
     /// Optional arguments to pass to the tool.
     /// </summary>
     [System.Text.Json.Serialization.JsonPropertyName("arguments")]
-    public Dictionary<string,object>? Arguments { get; init; }
+    public Dictionary<string, JsonElement>? Arguments { get; init; }
 }

src/ModelContextProtocol/Protocol/Types/LoggingMessageNotificationParams.cs

@@ -24,7 +24,7 @@ public class LoggingMessageNotificationParams
     public string? Logger { get; init; }
 
     /// <summary>
-    /// The data to be logged, such as a string message or an object. Any JSON serializable type is allowed here.
+    /// The data to be logged, such as a string message or an object.
     /// </summary>
     [JsonPropertyName("data")]
     public JsonElement? Data { get; init; }

src/ModelContextProtocol/Protocol/Types/ResourceContents.cs

@@ -61,6 +61,8 @@ public abstract class ResourceContents
                 }
 
                 string? propertyName = reader.GetString();
+                bool success = reader.Read();
+                Debug.Assert(success, "STJ must have buffered the entire object for us.");
 
                 switch (propertyName)
                 {