214_Streaming_and_Server-Sent_Events_SSE

Streaming and Server-Sent Events (SSE)

Wolverine.HTTP endpoints can return ASP.NET Core’s IResult type, which means you can take full advantage of the built-in Results.Stream() method for streaming responses and Server-Sent Events (SSE). No special Wolverine infrastructure is needed — this is standard ASP.NET Core functionality that works seamlessly with Wolverine’s endpoint model.

Server-Sent Events (SSE)

Server-Sent Events allow a server to push real-time updates to the client over a single HTTP connection. To create an SSE endpoint, return Results.Stream() with the text/event-stream content type:

[WolverineGet("/api/sse/events")]
public static IResult GetSseEvents()
{
    return Results.Stream(async stream =>
    {
        await using var writer = new StreamWriter(stream);
        for (var i = 0; i < 3; i++)
        {
            await writer.WriteAsync($"data: Event {i}\n\n");
            await writer.FlushAsync();
        }
    }, contentType: "text/event-stream");
}

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SSE messages follow the EventSource format, where each event is prefixed with data: and terminated by two newline characters (\n\n).

Plain Streaming Responses

For streaming plain text or other content types without the SSE protocol, you can use the same Results.Stream() approach with a different content type:

[WolverineGet("/api/stream/data")]
public static IResult GetStreamData()
{
    return Results.Stream(async stream =>
    {
        await using var writer = new StreamWriter(stream);
        for (var i = 0; i < 5; i++)
        {
            await writer.WriteLineAsync($"line {i}");
            await writer.FlushAsync();
        }
    }, contentType: "text/plain");
}

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Integration with Wolverine Services

Since Wolverine HTTP endpoints support dependency injection, you can combine streaming with other Wolverine capabilities. For example, you could stream events from a Wolverine message handler or publish messages during a streaming session:

[WolverineGet("/api/sse/orders")]
public static IResult StreamOrderUpdates(IMessageBus bus)
{
    return Results.Stream(async stream =>
    {
        var writer = new StreamWriter(stream);
 
        // Your streaming logic here, potentially using
        // Wolverine's IMessageBus for publishing side effects
        await writer.WriteAsync("data: connected\n\n");
        await writer.FlushAsync();
    }, contentType: "text/event-stream");
}

Key Points

• Wolverine endpoints that return IResult work with Results.Stream() out of the box
• No special Wolverine middleware or configuration is required for streaming
• SSE endpoints should use the text/event-stream content type
• Each SSE event must be formatted as data: <payload>\n\n
• Always call FlushAsync() after writing each event to ensure timely delivery to the client
• The Results.Stream() API is part of ASP.NET Core and is available in .NET 8+

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