一個文件下載接口引發的血案 Content-Disposition 之殤

今天在遷移一個老系統到新服務器的時候，在測試下載接口的時候發現：同一個接口，有些文件可以下載，有些文件不能下載。

調試了半天發現，好像是文件名的問題。

string fileName = "38374-fjf(1).13jk";
string contentDisposition = string.Format("attachment;filename={0}",fileName);
msg.Content.Headers.ContentDisposition = ContentDispositionHeaderValue.Parse(contentDisposition);

於是乎悲劇了。

然后我百度了一下，網上似乎都是什么書說文件名亂碼的，沒有一個說說是我這種清空情況。

無奈去查了一下標准文檔 http://www.ietf.org/rfc/rfc6266.txt

跳過前面的定義直接看例子

5.  Examples

   Direct the UA to show "save as" dialog, with a filename of
   "example.html":

     Content-Disposition: Attachment; filename=example.html

   Direct the UA to behave as if the Content-Disposition header field
   wasn't present, but to remember the filename "an example.html" for a
   subsequent save operation:

     Content-Disposition: INLINE; FILENAME= "an example.html"

   Note: This uses the quoted-string form so that the space character
   can be included.

   Direct the UA to show "save as" dialog, with a filename containing
   the Unicode character U+20AC (EURO SIGN):

     Content-Disposition: attachment;
                          filename*= UTF-8''%e2%82%ac%20rates

   Here, the encoding defined in [RFC5987] is also used to encode the
   non-ISO-8859-1 character.

   This example is the same as the one above, but adding the "filename"
   parameter for compatibility with user agents not implementing
   RFC 5987:

     Content-Disposition: attachment;
                          filename="EURO rates";
                          filename*=utf-8''%e2%82%ac%20rates

   Note: Those user agents that do not support the RFC 5987 encoding
   ignore "filename*" when it occurs after "filename".

　　Note: This uses the quoted-string form so that the space character
   can be included.

看到這句我似乎發現了什么。如果有空格就需要寫成字符串引用的格式。

string contentDisposition = string.Format("attachment;filename=\"{0}\"", fileName);

文件名有特殊符號是解決了，比如括號，空格什么的。但是如果文件名當中有中午，下載時候的默認文件名缺還是亂碼。

這個網上有一堆解決方案。

string fileName= HttpUtility.UrlEncode("啊fnam(4)e.ext",UTF8Encoding.UTF8);

其實只要對文件名做一次Encode轉碼就行了。

就這個簡單的問題，耗費了我一個小時。

今天就先到這里，晚安。