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.

.NET

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);
    }
}

TypeScript

export class SaveRequestHandler implements Middleware {
    next: Middleware | undefined;
    public execute(url: string, requestInit: RequestInit, requestOptions?: Record<string, RequestOption>): Promise<Response> {
        console.log(`Request: ${requestInit.body}`);
        return await this.next?.execute(url, requestInit as RequestInit, requestOptions);
    }
}

Register middleware

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

.NET

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

TypeScript

const handlers = MiddlewareFactory.getDefaultMiddlewares();
handlers.unshift(new SaveRequestHandler());

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

.NET

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

TypeScript

// this step is not required for TypeScript

Finally, create a request adapter using an HTTP client. 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.

.NET

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

TypeScript

const httpClient = KiotaClientFactory.create(undefined, handlers);
const adapter = new FetchRequestAdapter(authProvider, undefined, undefined, httpClient);
const client = createApiClient(adapter);

Middleware handlers

The following table describes which middleware handlers are implemented by the HTTP package, and which ones are included by default with any new request adapter.

Name	Description	C# Support	Go Support	Java Support	TypeScript Support	PHP Support	Python Support
Authorization	Adds an access token to the request when using a native HTTP client.	Yes	No	Yes	No	No	No
Body Inspection	Allows the client application to inspect the request and response body through the associated options.	No	No	No	No	No	No
Chaos	For testing purposes only. Randomly fails requests to allow testing clients' resilience.	Yes	Yes	Yes	Yes	Yes	No
Headers Inspection	Allows the client application to inspect the request and response headers through the associated options.	Default	Default	Default	Default	Default	Default
Parameters Name Decoding	Decodes query parameter names that were encoded when building the URL because they contained characters not allowed by RFC 6570.	Default	Default	Default	Default	Default	Default
Redirect	Automatically follows Location response headers when a 301 or 302 response status code is received.	Default	Default	Default	Default	Default	Default
Request Compression	Compresses request bodies and retries requests without compression when a 415 response status code is received.	No	Default	No	Default	No	No
Response Decompression	Adds an Accept-Encoding request header and decompresses any response body with a Content-Encoding response header.	N/A	N/A	N/A	N/A	N/A	N/A
Retry	Automatically retries requests when a 429 or a 503 response status code is received.	Default	Default	Default	Default	Default	Default
Sunset	Logs a warning message with Open Telemetry upon receiving a Sunset response header.	No	No	No	No	No	No
Telemetry	Adds an extension point to augment the request with telemetry headers.	Yes	No	No	Yes	Yes	No
Uri Replacement	Enables replacement of segments of the request URI before it's sent out.	Default	Yes	Default	Yes	Yes	Default
User Agent	Adds the kiota http library version to the user agent request header.	Default	Default	Default	Default	Default	Default

Note

Languages with N/A in the response decompression column leverage the native response decompression offered by the HTTP client instead.

Note

Languages with Default for the handler support value include the handler by default when creating the request adapter with no additional configuration.

Note

Request body decompression is not enabled by default in ASP.NET Core APIs and needs to be enabled. Find out how to enable it with Request Decompression in ASP.NET core.