/// <summary>

    /// Validation attribute to validate size of the file.

    /// </summary>

    public class MaxFileSizeAttribute : ValidationAttribute

    {

        private readonly int _maxFileSize;

        public MaxFileSizeAttribute(int maxFileSize)

        {

            _maxFileSize = maxFileSize;

        }

​

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)

        {

            var file = value as IFormFile;

​

            if (file != null)

            {

                if (file.Length > _maxFileSize)

                {

                    return new ValidationResult(GetErrorMessage());

                }

            }

​

            return ValidationResult.Success;

        }

​

        public string GetErrorMessage()

        {

            return $"Maximum allowed file size is { _maxFileSize} bytes.";

        }

    }