IAsyncEnumerable & Streaming APIs

Mind Map Summary

• Topic: IAsyncEnumerable & Streaming APIs
• Core Concepts:
  • IAsyncEnumerable<T>: An interface that represents an asynchronous sequence of values. It allows you to iterate over a sequence of values that are generated asynchronously.
  • yield return: A C# feature that allows you to create an iterator that returns one value at a time.
  • Streaming: The process of sending and receiving data in a continuous flow, rather than all at once.
• IAsyncEnumerable<T> vs. Task<IEnumerable<T>>:
  • Task<IEnumerable<T>>: Returns a single task that completes when all the data is available. The entire collection is buffered in memory before it is returned.
  • IAsyncEnumerable<T>: Returns an asynchronous stream of data. The data is processed as it becomes available, without having to buffer the entire collection in memory.
• Benefits of IAsyncEnumerable<T>:
  • Reduced Memory Usage: Avoids buffering large amounts of data in memory.
  • Improved Responsiveness: The client can start processing the data as soon as the first chunk is available.
  • More Scalable: Can handle large datasets that would not fit in memory.

Practice Exercise

Create an ASP.NET Core API endpoint that returns an IAsyncEnumerable<string>. The method should simulate fetching data in chunks (e.g., with Task.Delay) and yield return each chunk. Show how a client can consume this streaming response.

Answer

1. API Controller:

using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;
using System.Threading.Tasks;

[ApiController]
[Route("[controller]")]
public class DataController : ControllerBase
{
    [HttpGet]
    public async IAsyncEnumerable<string> Get()
    {
        for (int i = 0; i < 10; i++)
        {
            await Task.Delay(1000); // Simulate fetching data in chunks
            yield return $"Data chunk {i}";
        }
    }
}

2. Client Console Application:

using System.Net.Http;
using System.Net.Http.Json;
using System.Threading.Tasks;

class Program
{
    static async Task Main(string[] args)
    {
        var client = new HttpClient();
        var response = await client.GetAsync("http://localhost:5000/data", HttpCompletionOption.ResponseHeadersRead);

        await foreach (var chunk in response.Content.ReadFromJsonAsAsyncEnumerable<string>())
        {
            System.Console.WriteLine(chunk);
        }
    }
}

Explanation:

• The API controller returns an IAsyncEnumerable<string> and uses yield return to stream the data to the client.
• The client uses HttpCompletionOption.ResponseHeadersRead to start processing the response as soon as the headers are available.
• The client then uses ReadFromJsonAsAsyncEnumerable to consume the streaming response.