ASP.NET下載檔案包含中文檔名Header處理

HeaderUtil.cs

// 下載檔案包含中文檔名Header處理
// Wang, Jian-Zhong
 
using System.Text;
 
namespace JZLib
{
    public static class HeaderUtil
    {
        private const string HexDigits = "0123456789ABCDEF";
 
        private static void AddByteToStringBuilder(byte b, StringBuilder builder)
        {
            builder.Append('%');
 
            int i = b;
            AddHexDigitToStringBuilder(i >> 4, builder);
            AddHexDigitToStringBuilder(i % 16, builder);
        }
 
        private static void AddHexDigitToStringBuilder(int digit, StringBuilder builder)
        {
            builder.Append(HexDigits[digit]);
        }
 
        private static string CreateRfc2231FileName(string filename)
        {
            StringBuilder builder = new StringBuilder("");
 
            byte[] filenameBytes = Encoding.UTF8.GetBytes(filename);
            foreach (byte b in filenameBytes)
            {
                if (IsByteValidHeaderValueCharacter(b))
                {
                    builder.Append((char)b);
                }
                else
                {
                    AddByteToStringBuilder(b, builder);
                }
            }
 
            return builder.ToString();
        }
 
        /// <summary>
        /// 取得下載檔案名稱含Unicode字元如中文的Content-Disposition Header值
        /// </summary>
        /// <param name="filename">含Unicdoe字元的檔案名稱</param>
        /// <param name="inline">true表示以inline的形式呈現於頁面中以瀏覽器預覽，false表示在Header中指定attachment強制瀏覽器下載</param>
        /// <returns>下載檔案名稱含Unicode字元如中文的Content-Disposition Header值</returns>
        /// <example>
        /// Response.AppendHeader("Content-Disposition", JZLib.HeaderUtil.GetUnicodeContentDisposition("測試中文.txt", false));
        /// </example>
        public static string GetUnicodeContentDisposition(string filename, bool inline = true)
        {
            return $"{(inline ? "inline" : "attachment")}; filename*=UTF-8''{CreateRfc2231FileName(filename)}";
        }
 
        // Application of RFC 2231 Encoding to Hypertext Transfer Protocol (HTTP) Header Fields, sec. 3.2
        // http://greenbytes.de/tech/webdav/draft-reschke-rfc2231-in-http-latest.html
        private static bool IsByteValidHeaderValueCharacter(byte b)
        {
            if ((byte)'0' <= b && b <= (byte)'9')
            {
                return true; // is digit
            }
            if ((byte)'a' <= b && b <= (byte)'z')
            {
                return true; // lowercase letter
            }
            if ((byte)'A' <= b && b <= (byte)'Z')
            {
                return true; // uppercase letter
            }
 
            switch (b)
            {
                case (byte)'-':
                case (byte)'.':
                case (byte)'_':
                case (byte)'~':
                case (byte)':':
                case (byte)'!':
                case (byte)'$':
                case (byte)'&':
                case (byte)'+':
                    return true;
            }
 
            return false;
        }
    }
}