AspNetCore.Docs.Samples/fundamentals/streaming/SynchronousWithNewtonsoftJson/Middleware/SongLyricsMiddleware.cs

namespace SynchronousWithNewtonsoftJson.Middleware;

using Microsoft.AspNetCore.Http;
using Newtonsoft.Json;
using SynchronousWithNewtonsoftJson.Model;

public class SongLyricsMiddleware
{
    RequestDelegate _next;
    ILyricsSource _lyricsSource;
    JsonSerializer _serializer;

    public SongLyricsMiddleware(RequestDelegate next, ILyricsSource lyricsSource, JsonSerializer serializer)
    {
        _next = next;
        _lyricsSource = lyricsSource;
        _serializer = serializer;
    }

    public Task InvokeAsync(HttpContext context)
    {
        if (!context.Request.Path.StartsWithSegments(new PathString("/middleware/sing")))
            return _next(context);
        else
            return InvokeAsyncImplementation(context);
    }

    static readonly byte[] JSONArrayStart = new byte[] { (byte)'[' };
    static readonly byte[] JSONArraySeparator = new byte[] { (byte)',' };

    public async Task InvokeAsyncImplementation(HttpContext context)
    {
        await context.Response.Body.WriteAsync(JSONArrayStart, context.RequestAborted);

        while (true)
        {
            foreach (string line in _lyricsSource.GetSongLyrics())
            {
                // Since we are performing our own writes outside of the JsonTextWriter, we need it to be logically
                // set up and torn down for each object we output. Simply calling Flush() might work in practice but
                // is assuming internal implementation details.
                using (var streamWriter = new StreamWriter(context.Response.Body))
                using (var jsonWriter = new JsonTextWriter(streamWriter))
                    _serializer.Serialize(jsonWriter, line);

                await context.Response.Body.WriteAsync(JSONArraySeparator, context.RequestAborted);

                await context.Response.Body.FlushAsync(context.RequestAborted);

                await Task.Delay(200);
            }
        }

        // No JSONArrayEnd needs to be written, because the above loop will never exit.
    }
}