docs/guide/csharp/troubleshooting.md

---
title: Troubleshooting
sidebar_position: 13
id: troubleshooting
license: |
  Licensed to the Apache Software Foundation (ASF) under one or more
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  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
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---

This page covers common C# issues and fixes.

## `TypeNotRegisteredException`

**Symptom**: `Type not registered: ...`

**Cause**: A user type was serialized/deserialized without registration.

**Fix**:

```csharp
Fory fory = Fory.Builder().Build();
fory.Register<MyType>(100);
```

Ensure the same type-ID/name mapping exists on both write and read sides.

## `InvalidDataException: xlang bitmap mismatch`

**Cause**: The payload is not an xlang Fory frame, or it came from a peer mode that does
not emit the xlang header C# requires.

**Fix**: Ensure the payload was produced by an xlang-compatible peer. C# always expects the
xlang header and does not expose a mode switch, so configure the writer instead:

```java
Fory fory = Fory.builder()
    .withXlang(true)
    .build();
```

```python
fory = pyfory.Fory(xlang=True)
```

## Schema Version Mismatch with Same-Schema Payloads

**Symptom**: `InvalidDataException` while deserializing generated struct types.

**Cause**: `Compatible(false)` with `CheckStructVersion(true)` checks schema hashes for intentional
same-schema payloads.

**Fix options**:

- Keep compatible mode enabled for schema evolution.
- Use `Compatible(false)` only when every reader and writer always uses the same schema.

## Circular Reference Failures

**Symptom**: Stack overflow-like recursion or graph reconstruction issues.

**Cause**: Cyclic graphs with `TrackRef(false)`.

**Fix**:

```csharp
Fory fory = Fory.Builder().TrackRef(true).Build();
```

## Concurrency Issues

**Cause**: Sharing a single `Fory` instance across threads.

**Fix**: Use `BuildThreadSafe()`.

## Generated gRPC Compile Errors

**Symptom**: Generated `*Grpc.cs` files cannot find `Grpc.Core` types.

**Cause**: gRPC packages are application dependencies. The `Apache.Fory`
package does not add gRPC as a hard dependency.

**Fix**: Add `Grpc.Core.Api` and your chosen gRPC server or client package, such
as `Grpc.AspNetCore` for server hosting or `Grpc.Net.Client` for clients. See
[gRPC Support](grpc-support.md).

## Protobuf Client Cannot Decode a Fory gRPC Service

**Cause**: Fory gRPC companions use gRPC transports with Fory-encoded message
bodies. They do not send protobuf message bytes.

**Fix**: Use a Fory-generated client and server for the Fory endpoint, or expose
a separate protobuf endpoint for generic protobuf clients.

## Validation Commands

Run C# tests from repo root:

```bash
cd csharp
dotnet test Fory.sln -c Release
```

## Related Topics

- [Configuration](configuration.md)
- [gRPC Support](grpc-support.md)
- [Schema Evolution](schema-evolution.md)
- [Thread Safety](thread-safety.md)