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Concerns

Concerns

Concerns allow to add behavior to a section of your web application by intercepting requests and responses. The framework allows any handler to be extended by using concerns. The following example will add a custom HTTP header to every response generated by the server:

using GenHTTP.Api.Content;
using GenHTTP.Api.Protocol;

using GenHTTP.Engine.Internal;

using GenHTTP.Modules.IO;
using GenHTTP.Modules.Layouting;

public class CustomConcern : IConcern
{

    public IHandler Content { get; }

    public CustomConcern(IHandler content)
    {
        Content = content;
    }

    public ValueTask PrepareAsync() => Content.PrepareAsync();

    public async ValueTask<IResponse?> HandleAsync(IRequest request)
    {
        var response = await Content.HandleAsync(request);
        
        if (response != null) 
        {
            response.Headers.Add("X-Custom-Header", "Custom Concern");
        }

        return response;
    }

}

public class CustomConcernBuilder : IConcernBuilder
{

    public IConcern Build(IHandler content)
    {
        return new CustomConcern(content);
    }

}

var handler = Layout.Create()
                    .Index(Content.From(Resource.FromString("Hello World")))
                    .Add(new CustomConcernBuilder());

await Host.Create()
          .Handler(handler)
          .RunAsync();

The GenHTTP SDK uses the same mechanism to achieve functionality such as compression or support for CORS.

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