ANTOOZA-BACKEND/SharedKernel/Attributes/AllowedExtensionsAttribute.cs

using Microsoft.AspNetCore.Http;
using System.Collections;
using System.ComponentModel.DataAnnotations;

namespace SharedKernel.Attributes;

/*
 * 파일 확장자 제한
 */
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public class AllowedExtensionsAttribute : ValidationAttribute
{
    private readonly string[] _extensions;

    public AllowedExtensionsAttribute(string extensions)
    {
        _extensions = extensions.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries).Select(x => x.Trim().TrimStart('.').ToLowerInvariant()).Where(x => x.Length > 0).ToArray();
    }

    public override bool IsValid(object? value)
    {
        if (value is IFormFile file)
        {
            return _checkExtension(file.FileName);
        }

        if (value is IEnumerable files)
        {
            foreach (var obj in files)
            {
                if (obj is IFormFile f && !_checkExtension(f.FileName))
                {
                    return false;
                }
            }
        }

        return true;
    }

    public override string FormatErrorMessage(string name)
    {
        var template = string.IsNullOrWhiteSpace(ErrorMessage) ? "{0}에 허용되지 않은 파일 형식이 있습니다.\n\n허용 확장자: [{1}]" : ErrorMessage;

        return string.Format(template, name, string.Join(", ", _extensions));
    }

    private bool _checkExtension(string fileName)
    {
        var ext = Path.GetExtension(fileName)?.TrimStart('.').ToLowerInvariant();

        return !string.IsNullOrEmpty(ext) && _extensions.Contains(ext);
    }
}