Path Model Binder for ASP.NET Core

PathModelBinderAttribute.cs

using System;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.ModelBinding;

namespace MyNameSpace
{
    public class PathModelBinderAttribute : ModelBinderAttribute
    {
        public PathModelBinderAttribute()
            : base(typeof(PathModelBinder))
        {
        }
    }

    public class PathModelBinder : IModelBinder
    {
        // Kestrel does not automatically decode %2F to / in parameters, so we need to do it ourselves
        // https://github.com/aspnet/KestrelHttpServer/issues/1425
        // https://github.com/aspnet/KestrelHttpServer/issues/2946

        private static readonly Regex EncodedPathCharRegex = new Regex("%2F", RegexOptions.IgnoreCase | RegexOptions.Compiled);

        public Task BindModelAsync(ModelBindingContext bindingContext)
        {
            if (bindingContext == null)
            {
                throw new ArgumentNullException(nameof(bindingContext));
            }

            if (bindingContext.ModelType != typeof(string))
            {
                return Task.CompletedTask;
            }

            var modelName = GetModelName(bindingContext);
            var valueProviderResult = bindingContext.ValueProvider.GetValue(modelName);
            if (valueProviderResult == ValueProviderResult.None)
            {
                return Task.CompletedTask;
            }

            bindingContext.ModelState.SetModelValue(modelName, valueProviderResult);

            var inputString = valueProviderResult.FirstValue;

            if (inputString == null || inputString.IndexOf("%2F", StringComparison.OrdinalIgnoreCase) == -1)
            {
                bindingContext.Result = ModelBindingResult.Success(inputString);
            }
            else
            {
                var outputString = EncodedPathCharRegex.Replace(inputString, "/");
                bindingContext.Result = ModelBindingResult.Success(outputString);
            }

            return Task.CompletedTask;
        }

        private string GetModelName(ModelBindingContext bindingContext)
        {
            return string.IsNullOrEmpty(bindingContext.BinderModelName)
                ? bindingContext.ModelName
                : bindingContext.BinderModelName;
        }
    }
}