Json serialization exception for standard AspNetCore log message, which results in broken log messages

[saithis]

We wanted to switch to ZLogger, but now immediatelly encountered this issue after trying it out:

ZLogger error: System.NotSupportedException: Serialization and deserialization of 'System.Reflection.RuntimeMethodInfo' instances is not supported. The unsupported member type is located on type 'System.Object'. Path: $.Metadata.
 ---> System.NotSupportedException: Serialization and deserialization of 'System.Reflection.RuntimeMethodInfo' instances is not supported.
   at System.Text.Json.Serialization.Converters.UnsupportedTypeConverter`1.Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
   at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.JsonConverter`1.TryWriteAsObject(Utf8JsonWriter writer, Object value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.Converters.IEnumerableDefaultConverter`2.OnWriteResume(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.JsonCollectionConverter`2.OnTryWrite(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.GetMemberAndWriteJson(Object obj, WriteStack& state, Utf8JsonWriter writer)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryWrite(Utf8JsonWriter writer, T value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.JsonConverter`1.WriteCore(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
   --- End of inner exception stack trace ---
   at System.Text.Json.ThrowHelper.ThrowNotSupportedException(WriteStack& state, Exception innerException)
   at System.Text.Json.Serialization.JsonConverter`1.WriteCore(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.Serialize(Utf8JsonWriter writer, T& rootValue, Object rootValueBoxed)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.SerializeAsObject(Utf8JsonWriter writer, Object rootValue)
   at System.Text.Json.JsonSerializer.Serialize(Utf8JsonWriter writer, Object value, Type inputType, JsonSerializerOptions options)
   at ZLogger.LogStates.StringFormatterLogState`1.WriteJsonParameterKeyValues(Utf8JsonWriter jsonWriter, JsonSerializerOptions jsonSerializerOptions, IKeyNameMutator keyNameMutator)
   at ZLogger.ZLoggerEntry`1.WriteJsonParameterKeyValues(Utf8JsonWriter jsonWriter, JsonSerializerOptions jsonSerializerOptions, IKeyNameMutator keyNameMutator)
   at ZLogger.Formatters.SystemTextJsonZLoggerFormatter.FormatLogEntry(IBufferWriter`1 writer, IZLoggerEntry entry)
   at ZLogger.ZLoggerEntry`1.FormatUtf8(IBufferWriter`1 writer, IZLoggerFormatter formatter)
   at ZLogger.AsyncStreamLineMessageWriter.WriteLoop()
{
  "Timestamp": "2025-08-06T09:50:41.6766875+02:00",
  "LogLevel": "Information",
  "Category": "Microsoft.AspNetCore.Routing.EndpointMiddleware",
  "Message": "Executed endpoint 'HTTP: POST /validation/body => Handle'",
  "SpanId": "926ae9e59ec8abfc",
  "TraceId": "ececed91e60b6005911ce384052b4b56",
  "ParentId": "0000000000000000",
  "ConnectionId": "0HNEKNNOFC647",
  "RequestId": "0HNEKNNOFC647:00000001",
  "RequestPath": "/validation/body",
  "User": "anonymous"{ // <---- here ------------------------------
  "Timestamp": "2025-08-06T09:50:41.6820922+02:00",
  "LogLevel": "Information",
  "Category": "Microsoft.AspNetCore.Hosting.Diagnostics",
  "Message": "Request finished HTTP/1.1 POST http://localhost:5097/validation/body - 400 - application/problem+json 318.6568ms",
  "SpanId": "926ae9e59ec8abfc",
  "TraceId": "ececed91e60b6005911ce384052b4b56",
  "ParentId": "0000000000000000",
  "ConnectionId": "0HNEKNNOFC647",
  "RequestId": "0HNEKNNOFC647:00000001",
  "RequestPath": "/validation/body",
  "ElapsedMilliseconds": 318.6568,
  "StatusCode": 400,
  "ContentType": "application/problem+json",
  "ContentLength": null,
  "Protocol": "HTTP/1.1",
  "Method": "POST",
  "Scheme": "http",
  "Host": "localhost:5097",
  "PathBase": "",
  "Path": "/validation/body",
  "QueryString": ""
}

It just starts with the next log message without finishing the first one.
But this is just a standard asp net core log message, so I expected ZLogger to be able to handle that.

Our ZLogger config is like this:

        hostBuilder.ConfigureLogging(builder => builder
            .ClearProviders()
            .AddZLoggerConsole(o =>
            {
                o.IncludeScopes = true;
                o.InternalErrorLogger = ex => Console.Error.WriteLine($"ZLogger error: {ex}");
                o.UseJsonFormatter(formatter =>
                {
                    formatter.JsonSerializerOptions.WriteIndented = true;
                });
            }));

And since it is exactly after the User property each time, maybe this is also important:

app.Use(async (ctx, next) => 
{
    var logger = ctx.RequestServices.GetRequiredService<ILogger<Program>>();
    using var loggerScope = logger.BeginScope(new Dictionary<string, object>
    {
        {"User", ctx.User.FindFirst("sub")?.Value ?? "anonymous" },
    });
    await next();
});

[saithis]

I figured out now, that the System.Reflection.RuntimeMethodInfo is the minimal api Microsoft.AspNetCore.Routing.RouteEndpoint that is passed to JsonSerializer.Serialize(jsonWriter, x.Value, valueType, jsonSerializerOptions); here and then throws.

Would it make sense to fall back to a simple .ToString(), if the JsonSerializer fails?

Edit: Nope, ToString results in the whole endpoint object being inserted as json.

[saithis]

hmm, while experimenting I also encountered this quite frequently:

ZLogger error: System.ObjectDisposedException: IFeatureCollection has been disposed.
Object name: 'Collection'.
   at Microsoft.AspNetCore.Http.Features.FeatureReferences`1.ThrowContextDisposed()
   at Microsoft.AspNetCore.Http.Features.FeatureReferences`1.ContextDisposed()
   at Microsoft.AspNetCore.Http.Features.FeatureReferences`1.Fetch[TFeature](TFeature& cached, Func`2 factory)
   at Microsoft.AspNetCore.Http.DefaultHttpResponse.get_StatusCode()
   at Microsoft.AspNetCore.Hosting.HostingRequestFinishedLog.get_Item(Int32 index)
   at ZLogger.LogStates.StringFormatterLogState`1.WriteJsonParameterKeyValues(Utf8JsonWriter jsonWriter, JsonSerializerOptions jsonSerializerOptions, IKeyNameMutator keyNameMutator) in C:\workspace\ZLogger\src\ZLogger\LogStates\StringFormatterLogState.cs:line 94
   at ZLogger.ZLoggerEntry`1.WriteJsonParameterKeyValues(Utf8JsonWriter jsonWriter, JsonSerializerOptions jsonSerializerOptions, IKeyNameMutator keyNameMutator) in C:\workspace\ZLogger\src\ZLogger\ZLoggerEntry.cs:line 70
   at ZLogger.Formatters.SystemTextJsonZLoggerFormatter.FormatLogEntry(IBufferWriter`1 writer, IZLoggerEntry entry) in C:\workspace\ZLogger\src\ZLogger\Formatters\SystemTextJsonZLoggerFormatter.cs:line 192
   at ZLogger.ZLoggerEntry`1.FormatUtf8(IBufferWriter`1 writer, IZLoggerFormatter formatter) in C:\workspace\ZLogger\src\ZLogger\ZLoggerEntry.cs:line 76
   at ZLogger.AsyncStreamLineMessageWriter.WriteLoop() in C:\workspace\ZLogger\src\ZLogger\AsyncStreamLineMessageWriter.cs:line 125

[djeikyb]

I run into this same issue when trying to use the json formatter. Been meaning to compare the approach here with Serilog's. Maybe need something like in JsonValueFormatter

[saithis]

I figured out that if you disable serialization of the logs State property (information, that was merged into the message), then it doesn't corrupt the logs.

    .AddZLoggerConsole(o =>
    {
        o.IncludeScopes = true;
        o.InternalErrorLogger = ex => Console.Error.WriteLine($"ZLogger error: {ex}");
        o.UseJsonFormatter(f =>
        {
            f.IncludeProperties &= ~IncludeProperties.ParameterKeyValues; // This prevents the broken log messages
        });
    });

[saithis]

I made it reproducible with a little sample app here: saithis@3cb6d47
Unfortunatelly I'm on vacation for 3 weeks starting in a few hours, so I won't be able to continue to investigate further any time soon.

[bluetianx]

I made it reproducible with a little sample app here: saithis@3cb6d47 Unfortunatelly I'm on vacation for 3 weeks starting in a few hours, so I won't be able to continue to investigate further any time soon.

let me try to fix this issue

[bluetianx]

We wanted to switch to ZLogger, but now immediatelly encountered this issue after trying it out:

ZLogger error: System.NotSupportedException: Serialization and deserialization of 'System.Reflection.RuntimeMethodInfo' instances is not supported. The unsupported member type is located on type 'System.Object'. Path: $.Metadata.
 ---> System.NotSupportedException: Serialization and deserialization of 'System.Reflection.RuntimeMethodInfo' instances is not supported.

It just starts with the next log message without finishing the first one. But this is just a standard asp net core log message, so I expected ZLogger to be able to handle that.

Our ZLogger config is like this:

    hostBuilder.ConfigureLogging(builder => builder
        .ClearProviders()
        .AddZLoggerConsole(o =>
        {
            o.IncludeScopes = true;
            o.InternalErrorLogger = ex => Console.Error.WriteLine($"ZLogger error: {ex}");
            o.UseJsonFormatter(formatter =>
            {
                formatter.JsonSerializerOptions.WriteIndented = true;
            });
        }));

And since it is exactly after the User property each time, maybe this is also important:

app.Use(async (ctx, next) =>
{
var logger = ctx.RequestServices.GetRequiredService<ILogger>();
using var loggerScope = logger.BeginScope(new Dictionary<string, object>
{
{"User", ctx.User.FindFirst("sub")?.Value ?? "anonymous" },
});
await next();
});

@saithis, you need to add a JSON converter for Microsoft.AspNetCore.Routing.RouteEndpoint
Resolving Codes as follows

builder.Logging
    .ClearProviders()
    .AddZLoggerConsole(o =>
    {
        o.IncludeScopes = true;
        o.InternalErrorLogger = ex => Console.Error.WriteLine($"ZLogger error: {ex}");
        o.UseJsonFormatter(f =>
        {
            f.JsonSerializerOptions.WriteIndented = true;
            //f.IncludeProperties &= ~IncludeProperties.ParameterKeyValues; // This prevents the broken log messages
            f.JsonSerializerOptions.Converters.Add(new RouteEndpointConverter());
        });
    });


public class RouteEndpointConverter : JsonConverter<Microsoft.AspNetCore.Routing.RouteEndpoint>
{
    public override Microsoft.AspNetCore.Routing.RouteEndpoint? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        throw new NotSupportedException();
    }

    public override void Write(Utf8JsonWriter writer, Microsoft.AspNetCore.Routing.RouteEndpoint value, JsonSerializerOptions options)
    {
        writer.WriteStringValue(value.ToString());
    }
}

[bluetianx]

hmm, while experimenting I also encountered this quite frequently:

ZLogger error: System.ObjectDisposedException: IFeatureCollection has been disposed.
Object name: 'Collection'.
   at Microsoft.AspNetCore.Http.Features.FeatureReferences`1.ThrowContextDisposed()
   at Microsoft.AspNetCore.Http.Features.FeatureReferences`1.ContextDisposed()
   at Microsoft.AspNetCore.Http.Features.FeatureReferences`1.Fetch[TFeature](TFeature& cached, Func`2 factory)
   at Microsoft.AspNetCore.Http.DefaultHttpResponse.get_StatusCode()
   at Microsoft.AspNetCore.Hosting.HostingRequestFinishedLog.get_Item(Int32 index)
   at ZLogger.LogStates.StringFormatterLogState`1.WriteJsonParameterKeyValues(Utf8JsonWriter jsonWriter, JsonSerializerOptions jsonSerializerOptions, IKeyNameMutator keyNameMutator) in C:\workspace\ZLogger\src\ZLogger\LogStates\StringFormatterLogState.cs:line 94
   at ZLogger.ZLoggerEntry`1.WriteJsonParameterKeyValues(Utf8JsonWriter jsonWriter, JsonSerializerOptions jsonSerializerOptions, IKeyNameMutator keyNameMutator) in C:\workspace\ZLogger\src\ZLogger\ZLoggerEntry.cs:line 70
   at ZLogger.Formatters.SystemTextJsonZLoggerFormatter.FormatLogEntry(IBufferWriter`1 writer, IZLoggerEntry entry) in C:\workspace\ZLogger\src\ZLogger\Formatters\SystemTextJsonZLoggerFormatter.cs:line 192
   at ZLogger.ZLoggerEntry`1.FormatUtf8(IBufferWriter`1 writer, IZLoggerFormatter formatter) in C:\workspace\ZLogger\src\ZLogger\ZLoggerEntry.cs:line 76
   at ZLogger.AsyncStreamLineMessageWriter.WriteLoop() in C:\workspace\ZLogger\src\ZLogger\AsyncStreamLineMessageWriter.cs:line 125

@saithis I have resolved this bug at PR

[djeikyb]

tl;dr I'm not confident zlogger should change, you can choose your own json behaviour

I came to this wanting to send logs to seq, so I copied the sample clef formatter, which is a nice example of how to implement an IZLoggerFormatter. It has this line, which ends up invoking StringFormatterLogState:

entry.WriteJsonParameterKeyValues(jsonWriter, JsonSerializerOptions);

It loops over the message template parameters like you'd expect. But then there's a decision to make! How do you serialize each message template parameter value? The choice made by StringFormatterLogState and SystemTextJsonZLoggerFormatter is to serialize the template value as json:

var valueType = GetParameterType(i);
JsonSerializer.Serialize(jsonWriter, x.Value, valueType, jsonSerializerOptions);

This is not usually what I want. I take care to only use simple types in template parameters, but the libraries I use don't. Sometimes the objects being used can't be serialized as json without writing custom converters. When I bungle the binding of a string to a TextBlock in Avalonia, it logs a warning, and the StyledProperty is passed as a template parameter. That type has properties that aren't serializable by default. And so I get:

System.NotSupportedException: Serialization and deserialization of 'System.Type' instances is not supported. Path: $.PropertyType.
 ---> System.NotSupportedException: Serialization and deserialization of 'System.Type' instances is not supported.
   at System.Text.Json.Serialization.Converters.UnsupportedTypeConverter`1.Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
   at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
<snip>
   at ZLogger.LogStates.StringFormatterLogState`1.WriteJsonParameterKeyValues(Utf8JsonWriter jsonWriter, JsonSerializerOptions jsonSerializerOptions, IKeyNameMutator keyNameMutator)
<snip>

What I want — possibly always — is for simple stringification of template parameters. When I have a more complex object I want to shove in a log event, I use scope state properties. So I changed the sample clef formatter. This needs to be improved quite a bit to avoid boxing ints and the like. But it's roughly how I want template parameters to be logged. You could copy/paste/adapt the SystemTextJsonZLoggerFormatter in the exact same way.

         // Parameters
-        entry.WriteJsonParameterKeyValues(jsonWriter, JsonSerializerOptions);
+        for (int i = 0; i < entry.ParameterCount; i++)
+        {
+            var k = entry.GetParameterKeyAsString(i);
+            var v = entry.GetParameterValue(i);
+
+            switch (v)
+            {
+                case null:
+                    jsonWriter.WriteNull(k);
+                    break;
+                case string:
+                    jsonWriter.WriteString(k, (string)v);
+                    break;
+                default:
+                    jsonWriter.WriteString(k, v.ToString());
+                    break;
+            }
+        }

This is the approach Serilog takes, except Serilog writes json with a TextWriter instead of a Utf8JsonWriter. And Serilog has special syntax for when to json a template parameter instead of stringing it.

[bluetianx]

@djeikyb yep, your solution can resolve the first problem of this issue， another problem about the ** System.ObjectDisposedException ** can not be resolved