This content originally appeared on DEV Community and was authored by Eduardo Julião
For this post, we're going to explore a way to stream data to the client using a Web Api and C#.
Picture this requirement, you need to process an array of data, lets say of a 100 items, once each item is processed, the api should return to the client, without TCP/IP and SignalR, just pure HttpRequest.
To do this, in this example, we will have an worker that will return a IAsyncEnumerable and between each iteration, the method will wait between 5 to 10 seconds.
//Service.cs
private static readonly Random _random = new Random();
public async IAsyncEnumerable<int> GetData(int amount)
{
foreach(var item in Enumerable.Range(0, amount))
{
// Wait a random amount of time to simulate some work.
var secondsToWait = _random.Next(5,10);
await Task.Delay(Timespan.FromSeconds(secondsToWait));
yield return item;
}
}
With the simulated service in place, we can move on to the Controller. For the endpoint, we're going to have an async Task Get method that will write the result to the Response and send it for every item it was processed.
// StreamController.cs
private readonly IService _service;
public StreamController(IService service)
{
_service = service;
}
[HttpGet("{amount:int:min(1)}")]
public async Task GetStreamData(int amount)
{
// Set Content-Type to text/event-stream
Response.Headers.Add("Content-Type", "text/event-stream");
await foreach(var data in _service.GetData(amount))
{
// this can be anything, even just a json object
string dataItem = $"data: {data}\n\n";
// Convert the text to a byte array
var utf8DataitemBytes = Encoding.UTF8.GetBytes(dataItem);
// Write the byte array to the HttpResponse
await Response.Body.WriteAsync(utf8DataitemBytes, 0, utf8DataitemBytes.Length);
// Push
await Response.Body.FlushAsync();
}
}
When the endpoint is called, it'll send a new "line" of data instead of waiting for all items to be processed to be sent at once.
This content originally appeared on DEV Community and was authored by Eduardo Julião
Eduardo Julião | Sciencx (2021-07-22T20:38:23+00:00) Event Stream – Server Side. Retrieved from https://www.scien.cx/2021/07/22/event-stream-server-side/
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