How to register HttpClient Handler in Blazor Client?

Question

I want to preprocess and postprocess all outgoing requests that are going from my Blazor client to Server API. The best solution is to add custom HttpMessageHandler.

Handler code:

public class NameOfMyHandler : DelegatingHandler
{
    public NameOfMyHandler()
    {
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        Debug.WriteLine("Process request");
        var response = await base.SendAsync(request, cancellationToken);
        Debug.WriteLine("Process response");
        return response;
    }
}

Code in Client->Program.cs->Main:

builder.Services.AddScoped<NameOfMyHandler>();
            builder.Services.AddHttpClient("ThisIsClientCustomName", client => client.BaseAddress = new Uri(builder.HostEnvironment.BaseAddress))
                .AddHttpMessageHandler<NameOfMyHandler>();

But when I try to do so I get an error:

An invalid request URI was provided. The request URI must either be an absolute URI or BaseAddress must be set.

but as you can see in the code I do specify the BaseAddress and I am sure it is correct.

Where is the problem ? What am I doing wrong ?

Answer 1

After some time I found out it requires more than adding that handler. And also it is possible to do it with AddHttpClient or pure HttpClient.

AddHttpClient example:

builder.Services.AddScoped<NameOfMyHandler>();
builder.Services.AddHttpClient("ThisIsClientCustomName", 
    client => client.BaseAddress = new Uri(builder.HostEnvironment.BaseAddress))
    .AddHttpMessageHandler<NameOfMyHandler>();
// Supply HttpClient instances that include access tokens when making requests to the server project
builder.Services.AddTransient(sp => sp.GetRequiredService<IHttpClientFactory>()
    .CreateClient("ThisIsClientCustomName"));

or

Pure HttpClient:

HttpMessageHandler httpMessageHandler = new NameOfMyHandler()
{
    InnerHandler = new HttpClientHandler()
};
builder.Services.AddScoped<NameOfMyHandler>(sc => httpMessageHandler);
var httpClient = new HttpClient(httpMessageHandler)
{
    BaseAddress = new Uri(builder.HostEnvironment.BaseAddress)
};
builder.Services.AddScoped(sp => httpClient);