Using DelegationHandler for HTTP Requests

sonal khatri 51

Hi, I have a requirement to use a DelegationHandler. I have a ServiceA class and an AuthHandler class that inherits from the DelegationHandler class. I created a RestClient class which has an HTTPClient injected, and in this class, I have the common logic to call HttpClient methods, set queryParameters, set headers, etc. My ServiceA class is injecting the RestClient class and, in turn, calls RestClient methods, which, in turn, make all the HTTP requests. I have implemented it like this as I want to keep a generic RestClient class so that all my services, like ServiceA, ServiceB, can call this class, and I do not need to repeat common code. But if I follow this approach, then I am not able to use the DelegationHandler, and it is not invoked. Can you suggest a way?

Brando Zhang-MSFT 3,446 Reputation points Microsoft Vendor

2024-01-31T02:59:03.7266667+00:00

Hi @sonal khatri, could you please share current cods you have used now? Which operation you need to set inside the DelegationHandler?

sonal khatri 51

I want to implement a scenario where I have a typed client named RestClient. I am injecting it and consuming it in two services, namely ServiceA and ServiceB. I have two different handlers for ServiceA and ServiceB, which will add Authorization headers to the ongoing request. However, I am unsure about how to register these services. I have a single typed service, 'RestClient,' as I want to have common logic for calling HTTP client methods that can be used by my ServiceA and ServiceB classes.

public class RestClient
{
    private readonly HttpClient _client;

    public RestClient1(HttpClient httpClient)
    {
        _client = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
        _client.BaseAddress = new Uri("");
    }

    public async Task<HttpResponseMessage> ProcessRequestAsync(HttpMethod httpMethod, string url,
        HttpContent content = null, Dictionary<string, string> headers = null, Dictionary<string, string> parameters = null)
    {
        using (HttpRequestMessage request = new HttpRequestMessage
        {
            Method = httpMethod,
            RequestUri = GetRequestUri(url),
            Content = content
        })

            return await _client.SendAsync(request);
    }
}

public class ServiceA : IServiceA
{
    private readonly RestClient _restClient;
    public ServiceA(RestClient restClient)
    {
        _restClient = restClient;
    }
}

public class ServiceB : IServiceB
{
    private readonly RestClient _restClient;
    public ServiceB(RestClient restClient)
    {
        _restClient = restClient;
    }
}

public class ServiceAAuthHandler : DelegatingHandler
{
    private string _accessToken = "";
    public ServiceAAuthHandler()
    {
    }

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        if (!request.Headers.Contains("Authorization"))
        {
            if (string.IsNullOrEmpty(_accessToken))
                _accessToken = $"Bearer xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

            request.Headers.Add("Authorization", _accessToken);
        }

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

public class ServiceBAuthHandler : DelegatingHandler
{
    private string _accessToken = "";
    public ServiceBAuthHandler()
    {
    }

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        if (!request.Headers.Contains("Authorization"))
        {
            if (string.IsNullOrEmpty(_accessToken))
                _accessToken = $"Bearer xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

            request.Headers.Add("Authorization", _accessToken);
        }

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

Brando Zhang-MSFT 3,446 Reputation points Microsoft Vendor

2024-02-01T02:57:01.2633333+00:00

Thanks for your response, according to your code, why you don't create two typed httpclients? And if you want to use them in difference service, you could inject them into that service instead of using the DelegatingHandler.
sonal khatri 51 Reputation points

2024-02-01T03:16:47.82+00:00

I don't want to have two typed clients. I am consolidating the common logic for calling HTTP client methods into the typed client. Other services can then inject the typed client.
Brando Zhang-MSFT 3,446 Reputation points Microsoft Vendor

2024-02-01T05:30:45.38+00:00
But you couldn't use DelegatingHandler as your codes, the DelegatingHandler is register like below codes. In my opinion, if you want to achieve your requirement , you should create different typed httpclient.

builder.Services.AddTransient<SampleHandler1>(); builder.Services.AddTransient<SampleHandler2>(); builder.Services.AddHttpClient("MultipleHttpMessageHandlers") .AddHttpMessageHandler<SampleHandler1>() .AddHttpMessageHandler<SampleHandler2>();

1 answer

Bruce (SqlWork.com) 61,731 Reputation points

2024-01-30T17:17:53.67+00:00

as the HttpClientFactory implements the delegate pipeline for httpclient, instead of injecting HttpClient, you should inject HttpClientFactory, or use named or typed HttpClients (which implicitly use the factory).

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-8.0#consumption-patterns
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Using DelegationHandler for HTTP Requests

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