C# MailMessage Attachment 中文名附件发邮件-Firefox中文显示正常，网页打开邮件附件中文名乱码

一、故事

首先通过CDO.Message来获取邮件EML相关数据：邮件标题、邮件内容、邮件附件、发件人、收件人、ＣＣ主要就这么几个，其次通过MailMessage来组织邮件通过Python来发送邮件！

就这么简简单单的需求！！问题出现了，中文附件名！Web打开始终是乱码！使用邮件客户端FireFox是OK的，查看了FireFox源码发现是乱码，这点说明FireFox的强大，非常强大！

Content-Type: application/octet-stream; name=鎶ラ攢鍗昪s.xlsx
Content-Transfer-Encoding: base64
Content-Disposition: attachment

见图见图

……

二、折腾中

出了问题想办法，一定要抱着始终相信一定可以解决的尤其是搞IT的一定有方法！大事化小，小事化无。先找卧底！第一个想到的便是CDO.Message那就从他下手。最后发现他是平民！

先说说走的路，干货的路，其他摸索的方法想了下数数应该有4,5种了：

读取EML转换成流，再获取附件再解码，发现中文名OK

先看结果

再看看代码

public class AttachmentExtractor
    {
        private static int imageCount;

        public static void Method(string path)
        {
            StreamReader reader = null;
            try
            {
                reader = new StreamReader(path);
                string line;
                StringBuilder sb = new StringBuilder();
                while ((line = reader.ReadLine()) != null)
                {
                    sb.Append(line.ToLower());
                    if (line.ToLower().StartsWith("content-disposition:attachment;") || line.ToLower().StartsWith("content-disposition: attachment;")) // found attachment
                    {
                        string fileName = GetAttachment(reader, line);
                        fileName = System.Text.Encoding.UTF8.GetString(Convert.FromBase64String(fileName.Replace("=?utf-8?B?", "").Replace("?=", "")));
                    }
                    if (line.ToLower().StartsWith("content-type:image/")) // found embedded image
                    {
                        ExtractContent(reader, GetImage(reader, line));
                    }
                }
            }
            catch (IOException)
            {
                Console.WriteLine("找不到文件!");
            }
            finally
            {
                if (reader != null) reader.Close();
            }

        }

        private static string GetAttachment(TextReader reader, string line)
        {
            if (!line.Contains("filename"))
            {
                line = reader.ReadLine(); // Thunderbird: filename start at
                //second line
            }
            return GetFilenameNew(reader, line);
        }

        private static string GetImage(TextReader reader, string line)
        {
            if (!line.Contains("name"))
            {
                line = reader.ReadLine(); // Thunderbird: filename start at
                //second line
            }
            if (!line.Contains("name")) // embedded image does not have name
            {
                AdvanceToEmptyLine(reader);

                return "image" + imageCount++ + ".jpg"; // default to jpeg
            }

            return GetFilename(reader, line);
        }

        private static string GetFilename(TextReader reader, string line)
        {
            string filename;
            int filenameStart = line.IndexOf('"') + ;

            if (filenameStart > )
            {
                filename = line.Substring(filenameStart, line.Length -
                filenameStart - );
            }
            else // filename does not have quote
            {
                filenameStart = line.IndexOf('=') + ;
                filename = line.Substring(filenameStart, line.Length -
                filenameStart);
            }

            AdvanceToEmptyLine(reader);

            return filename;
        }

        private static string GetFilenameNew(TextReader reader, string line)
        {
            string filename;
            int filenameStart = line.IndexOf('"') + ;

            if (filenameStart > )
            {
                filename = line.Substring(filenameStart, line.Length -
                filenameStart - );
            }
            else // filename does not have quote
            {
                filenameStart = line.IndexOf('=') + ;
                filename = line.Substring(filenameStart, line.Length -
                filenameStart);
            } 

            return filename;
        }

        private static void AdvanceToEmptyLine(TextReader reader)
        {
            string line;

            while ((line = reader.ReadLine()) != null)
            {
                if (String.IsNullOrEmpty(line)) break;
            }
        }

        private static void ExtractContent(TextReader reader, string filename)
        {
            string line;
            var content = new StringBuilder();

            while ((line = reader.ReadLine()) != null)
            {
                if (String.IsNullOrEmpty(line)) break;

                content.Append(line);
            }

            if (content.Length > )
            {
                byte[] buffer = Convert.FromBase64String(content.ToString());
                #region 7.7
                if (!File.Exists(filename))
                {
                    return;
                }
                #endregion
                using (Stream writer = new FileStream(filename,
                FileMode.Create))
                {
                    writer.Write(buffer, , buffer.Length);
                }
            }
        }
    }

public RedEmail()
        {
            InitializeComponent();
            this.txtEmailPath.Text = "C:\\Users\\Administrator\\Desktop\\4a3266e6-23bd-11e5-9703-0050569a7cc2.eml";

            AttachmentExtractor.Method(txtEmailPath.Text);
        }

仔细看完代码会发现获取的附件名是编码过的，需要截取。这个要注意！发现经常不写写，不说说都不知道如何表达我那被困的感受！！！不过！有结果就是胜利！如下：

可喜的是，我找到了原因：CDO.Message不是卧底！是个良民！！！他只是一个善良的二道贩子！

三、看到曙光

好了，总共就两人，一个平民了，那么另一个一定是卧底咯-MailMessage

先看胜利的结果，这个喜悦之情那！！

一个是EML里面的附件-乱码，一个是通过改良后代码上传上去的-OK……（ps 写博客都不忘给我老婆店铺做广告，主要是因为我们博客园老牛B了，经常会被其他网站转载，又不写转载信息！）

搞IT的代码最直接看看代码，如下：

                //MemoryStream ms =
                //    new MemoryStream(File.ReadAllBytes(@"C:\\Users\\Administrator\\Desktop\\RDP_需求规格说明书.docx"));
                ////message.Attachments.Add(new System.Net.Mail.Attachment(ms, "RDP_需求规格说明书.docx"));

                //System.Net.Mime.ContentType ct = new System.Net.Mime.ContentType(System.Net.Mime.MediaTypeNames.Text.Plain);
                //System.Net.Mail.Attachment attach = new System.Net.Mail.Attachment(ms, ct);
                //attach.ContentDisposition.FileName = "产品经理2.docx";

                //attach.NameEncoding = Encoding.GetEncoding("utf-8");
                //      `message.Attachments.Add(attach);

                System.Net.Mail.Attachment attachment = AttachmentHelper.CreateAttachment(@"C:\\Users\\Administrator\\Desktop\\产品经理2.jpg", "产品经理2.jpg", TransferEncoding.Base64);

                message.Attachments.Add(attachment);
                //var attachment = new Attachment(new MemoryStream(File.ReadAllBytes(@"C:\\Users\\Administrator\\Desktop\\产品经理2.jpg")), new System.Net.Mime.ContentType("application/vnd.ms-excel"));
                ////bool flag = File.Exists(@"C:\\Users\\Administrator\\Desktop\\产品经理2.jpg");
                //FileStream fs = new FileStream(@"C:\\Users\\Administrator\\Desktop\\产品经理2.jpg", FileMode.Open, FileAccess.Read);
                //System.Net.Mime.ContentType ct = new System.Net.Mime.ContentType(System.Net.Mime.MediaTypeNames.Text.Plain);
                //System.Net.Mail.Attachment attach = new System.Net.Mail.Attachment(fs, ct);
                //attach.ContentDisposition.FileName =  "产品经理2.jpg";
                //fs.Close();
                //message.Attachments.Add(attach);   

看到了么！注释的就是实验的！我说我是折腾了半天解决的！

好了，揭开神秘的面纱AttachmentHelper　　

 public class AttachmentHelper
    {
        public static System.Net.Mail.Attachment CreateAttachment(string attachmentFile, string displayName, TransferEncoding transferEncoding)
        {
            System.Net.Mail.Attachment attachment = new System.Net.Mail.Attachment(attachmentFile);
            attachment.TransferEncoding = transferEncoding;

            string tranferEncodingMarker = String.Empty;
            string encodingMarker = String.Empty;
            int maxChunkLength = ;

            switch (transferEncoding)
            {
                case TransferEncoding.Base64:
                    tranferEncodingMarker = "B";
                    encodingMarker = "UTF-8";
                    maxChunkLength = ;
                    break;
                case TransferEncoding.QuotedPrintable:
                    tranferEncodingMarker = "Q";
                    encodingMarker = "ISO-8859-1";
                    maxChunkLength = ;
                    break;
                default:
                    throw (new ArgumentException(String.Format("The specified TransferEncoding is not supported: {0}", transferEncoding, "transferEncoding")));
            }

            attachment.NameEncoding = Encoding.GetEncoding(encodingMarker);

            string encodingtoken = String.Format("=?{0}?{1}?", encodingMarker, tranferEncodingMarker);
            string softbreak = "?=";
            string encodedAttachmentName = encodingtoken;

            if (attachment.TransferEncoding == TransferEncoding.QuotedPrintable)
                encodedAttachmentName = HttpUtility.UrlEncode(displayName, Encoding.Default).Replace("+", " ").Replace("%", "=");
            else
                encodedAttachmentName = System.Convert.ToBase64String(Encoding.UTF8.GetBytes(displayName));

            encodedAttachmentName = SplitEncodedAttachmentName(encodingtoken, softbreak, maxChunkLength, encodedAttachmentName);
            attachment.Name = encodedAttachmentName;

            return attachment;
        }

        private static string SplitEncodedAttachmentName(string encodingtoken, string softbreak, int maxChunkLength, string encoded)
        {
            int splitLength = maxChunkLength - encodingtoken.Length - (softbreak.Length * );
            var parts = SplitByLength(encoded, splitLength);

            string encodedAttachmentName = encodingtoken;

            foreach (var part in parts)
                encodedAttachmentName += part + softbreak + encodingtoken;

            encodedAttachmentName = encodedAttachmentName.Remove(encodedAttachmentName.Length - encodingtoken.Length, encodingtoken.Length);
            return encodedAttachmentName;
        }

        private static IEnumerable<string> SplitByLength(string stringToSplit, int length)
        {
            while (stringToSplit.Length > length)
            {
                yield return stringToSplit.Substring(, length);
                stringToSplit = stringToSplit.Substring(length);
            }

            if (stringToSplit.Length > ) yield return stringToSplit;
        }
    }

这个牛B的类不是我写的！声明下！我可没那么牛×，是哥千辛万苦+输入了英文才找到的！更坚定了我要学好英文的夙愿！！！！

四、后话

好了，可以安心改改代码，发布一个Demo了。

总结下：

1、要有不放弃不抛弃。

2、要敢自我调侃的娱乐精神。

3、关键时刻别忘了Google，国外的月亮有时候真的比国内圆！

一口气，好了，我去WC 憋死我了………………