校验文件类型是否在白名单内。

class Program
    {
        static void Main(string[] args)
        {
            using (var Stream = new FileStream(@"C:\Users\qa_weiwa\Downloads\core 6.0.exe", FileMode.Open))
            {
                var inspector = new FileFormatInspector();
                var rt = FileExtensionValid.IsValid(inspector, Stream);
                if (rt.Item1)
                {
                    Console.WriteLine("附件类型符合要求");
                }
                else {
                    Console.WriteLine(rt.Item2);
                }
                Console.ReadKey();
            }
        }

        public static class FileExtensionValid
        {
            /// <summary>
            /// 校验文件类型是否在白名单内。
            /// 白名单：jpg、png、tif、gif、zip、pdf、doc、docx、xls、xlsx、msg
            /// </summary>
            /// <param name="fileFormatInspector"></param>
            /// <param name="stream"></param>
            /// <returns></returns>
            public static Tuple<bool, string> IsValid(FileFormatInspector fileFormatInspector,Stream stream)
            {
                var format = fileFormatInspector.DetermineFileFormat(stream);
                return FileExtensionIsInWhiteList(format);
            }
            private static Tuple<bool, string> FileExtensionIsInWhiteList(FileFormat fileFormat)
            {
                // Jpeg 
                if (fileFormat is null || fileFormat is Jpeg || fileFormat is Png || fileFormat is Tiff || fileFormat is Gif
                    || fileFormat is Gif || fileFormat is Zip || fileFormat is Pdf
                    || fileFormat is Word || fileFormat is Excel || fileFormat is OutlookMessage
                    )
                {
                    return new Tuple<bool, string>(true, "");
                }
                else { 
                    return new Tuple<bool, string>(false, "上传的文件类型不正确，请上传jpg、png、tif、gif、zip、pdf、doc、docx、xls、xlsx、msg类型的附件");
                }
            }
        }

}