extending-policy-options-validation.md

Extending the policy options validation

• Summary
• Extend validation inline
• Extend validation with the IValidateOptions interface

Summary

All of the options from the following extension methods have a default validation that can be extended:

• Add a timeout policy to an HttpClient
• Add a retry policy to an HttpClient
• Add a circuit breaker policy to an HttpClient

Let's see how we can extend the validation of the TimeoutOptions from the AddTimeoutPolicy extension method. The same can be applied to the options of any of the other extension methods.

Note

the variable services in the examples below is of type IServiceCollection. On the default template for a Web API you can access it via builder.services. Example:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();

Extend validation inline

The TimeoutOptions has a default validation but you can extend it as follows:

services
    .AddHttpClientTimeoutOptions("my-timeout-options")
    .Bind(Configuration.GetSection("MyHttpClient"))
    .Validate(options => options.TimeoutInSecs is >= 2 and <= 4); // extend the default validation

services
    .AddHttpClient("my-http-client")
    .AddTimeoutPolicy("my-timeout-options");

With the above even though the default validation only required the TimeoutInSecs to be a positive number, it's now further restricted to a number between 2 and 4.

Extend validation with the IValidateOptions interface

You can extend the validation in any way provided by dotnet. For instance, you could also extend the validation using the IValidateOptions interface instead.

You would start by implementing the IValidateOptions interface for the TimeoutOptions type:

internal class MyTimeoutOptionsValidation : IValidateOptions<TimeoutOptions>
{
    public ValidateOptionsResult Validate(string name, TimeoutOptions options)
    {
        if (options.TimeoutInSecs is >= 2 or <= 4)
        {
            return ValidateOptionsResult.Success;
        }
        return ValidateOptionsResult.Fail($"{nameof(options.TimeoutInSecs)} must be a value between 2 and 4");
    }
}

Then you add the validation to the IServiceCollection:

// with this when an instance of TimeoutOptions is requested the MyTimeoutOptionsValidation.Validate method will execute
services.AddSingleton<IValidateOptions<TimeoutOptions>, MyTimeoutOptionsValidation>();

And finally you add the timeout policy:

services
    .AddHttpClientTimeoutOptions("my-timeout-options")
    .Bind(Configuration.GetSection("MyHttpClient"));

services
    .AddHttpClient("my-http-client")
    .AddTimeoutPolicy("my-timeout-options");