ASP.NET Web API Request Batching

Most applications I’m building today are using a kind of Web API. This works great, but leads to chatty interfaces, requiring a  large number of requests to get all the required data. In situations where the API is only for internal usage and you don’t want to share it with other applications, your application can benefit from a technique called ‘Request Batching’.

Remark: Be aware that Batch requests are not REST-compliant. So if you are creating a public API stop reading…

What is it?

Request batching combines multiple API requests into a single POST request. HTTP provides this out-of-the-box using a special content type called Multipart. On server-side, requests are unpacked and dispatched to the appropriate API methods. All responses are packed together and sent back to the client as a single HTTP response. The nice thing is that it is already supported by ASP.NET web API and you don’t need a lot of extra code to get it working.

Enable Request Batching in ASP.NET Web API

The only thing you need to do to get it working inside ASP.NET Web API is defining an extra route:

	config.Routes.MapHttpBatchRoute(
	routeName: "batch",
	routeTemplate: "api/batch",
	batchHandler: new CustomHttpBatchHandler(GlobalConfiguration.DefaultServer)
	);

view raw batchroute.cs hosted with ❤ by GitHub

Inside the route you can use the  DefaultHttpBatchHandler or create your own custom implementation:

	public class CustomHttpBatchHandler: DefaultHttpBatchHandler
	{
	public CustomHttpBatchHandler(HttpServer httpServer):base(httpServer)
	{
	this.ExecutionOrder = BatchExecutionOrder.NonSequential;
	}
	}

view raw CustomHttpBatchHandler.cs hosted with ❤ by GitHub

In the above sample I changed the ExecutionOrder property. By setting this to non-sequential, API requests are executed in parallel.

From the client, you can consume this Batch API like this:

	[TestFixture]
	public class BatchTests
	{
	[Test]
	public async Task Batch_Should_Send_Only_One_Request_To_Server()
	{
	//Arrange
	using (var browser = CreateBrowser())
	{
	HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, "http://localhost/api/simple");
	//Create the different parts of the multipart content
	HttpMessageContent queryContent1 = new HttpMessageContent(request);
	HttpMessageContent queryContent2 = new HttpMessageContent(request);
	HttpMessageContent queryContent3 = new HttpMessageContent(request);
	HttpMessageContent queryContent4 = new HttpMessageContent(request);
	//Create the multipart/mixed message content
	MultipartContent content = new MultipartContent("mixed", "batch_" + Guid.NewGuid().ToString());
	content.Add(queryContent1);
	content.Add(queryContent2);
	content.Add(queryContent3);
	content.Add(queryContent4);
	//Create the request to the batch service
	HttpRequestMessage batchRequest = new HttpRequestMessage(HttpMethod.Post, "http://localhost/api/batch");
	//Associate the content with the message
	batchRequest.Content = content;
	var response=await browser.SendAsync(batchRequest);
	//Assert
	Assert.IsTrue(response.IsSuccessStatusCode);
	}
	}
	private HttpClient CreateBrowser()
	{
	var httpServer = new HttpServer();
	//Enable batching support
	httpServer.Configuration.Routes.MapHttpBatchRoute(routeName: "batch", routeTemplate: "api/batch", batchHandler: new CustomHttpBatchHandler(httpServer));
	httpServer.Configuration.Routes.MapHttpRoute(name: "Default", routeTemplate: "api/{controller}/{id}", defaults: new { id = RouteParameter.Optional });
	return new HttpClient(httpServer);
	}
	}

view raw batchtests.cs hosted with ❤ by GitHub