Implementing middleware

By registering custom middleware handlers, you can perform operations before a request is made. For example, auditing and filtering the request before the client sends it.

Middleware

Create your middleware class and add your business requirements. For example, you might wish to add custom headers to the request or filter headers and content.

public class SaveRequestHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var jsonContent = await request.Content.ReadAsStringAsync(cancellationToken);
        Console.WriteLine($"Request: {jsonContent}");

        return await base.SendAsync(request, cancellationToken);
    }
}

Register middleware

Create a middleware handlers array and use the existing middleware already implemented within Microsoft.Kiota.HttpClientLibrary that includes existing handlers like retry, redirect, and more.

var handlers = KiotaClientFactory.CreateDefaultHandlers();
handlers.Add(new SaveRequestHandler());

Next you need to create a delegate chain so the middleware handlers are registered in the right order.

var httpMessageHandler =
    KiotaClientFactory.ChainHandlersCollectionAndGetFirstLink(
        KiotaClientFactory.GetDefaultHttpMessageHandler(),
        handlers.ToArray());

Finally, create a request adapter using an HttpClient with the message handler. This adapter can then be used when submitting requests from the generated client. This design means different adapters/middleware can be used when calling APIs and therefore gives flexibility to how and when a middleware handler is used.

var httpClient = new HttpClient(httpMessageHandler!);
var adapter = new HttpClientRequestAdapter(authProvider, httpClient:httpClient);
var client = new PostsClient(adapter); // the name of the client will vary based on your generation parameters