C# Support

Facility supports tools and libraries for using C# (.NET) with Facility Service Definitions.

Tools

Generate C# for your Facility Service Definition by doing one of the following:

• Use the Facility Editor. Enter an API definition in the left pane, choose the "C#" generator, review the generated files, and click Download.
• Run the fsdgencsharp tool on the command line or in a build script.
• Use the Facility.CodeGen.CSharp .NET library (NuGet Package) in your own build tool.

fsdgencsharp

fsdgencsharp is a command-line tool that generates C# for a Facility Service Definition.

Install fsdgencsharp as documented from its NuGet package.

fsdgencsharp generates multiple C# files and supports the standard command-line options as well as the following additional command-line options:

• --namespace <name>: Sets the namespace used by the generated C#.
• --csproj: Updates any .csproj files in the output directory. Specifically, it adds any missing .g.cs files and removes any .g.cs files no longer needed.

Events

Events in Facility enable streaming responses using server-sent events (SSE). The C# code generator produces special method signatures for events that return streams of responses.

For an event defined as:

event streamChat
{
  prompt: string;
}:
{
  textDelta: string;
}

The generated C# interface includes:

Task<ServiceResult<IAsyncEnumerable<ServiceResult<StreamChatResponseDto>>>> StreamChatAsync(
  StreamChatRequestDto request, 
  CancellationToken cancellationToken = default);

Using Events in C#

Clients can consume event streams using await foreach:

var request = new StreamChatRequestDto { Prompt = "Hello" };
var result = await client.StreamChatAsync(request);

if (result.IsFailure)
{
  // Handle error
  Console.WriteLine($"Error: {result.Error.Message}");
  return;
}

await foreach (var chunkResult in result.Value)
{
  if (chunkResult.IsFailure)
  {
    // Handle error in stream
    Console.WriteLine($"Stream error: {chunkResult.Error.Message}");
    break;
  }
  
  var chunk = chunkResult.Value;
  Console.Write(chunk.TextDelta);
}

The HTTP client implementation uses server-sent events to receive response chunks from the server, automatically deserializing each SSE event into a response DTO.