Ben Nadel
On User Experience (UX) Design, JavaScript, ColdFusion, Node.js, Life, and Love.

Embedding Foreign Characters In Your Content-Disposition Filename Header

By Ben Nadel on
Tags: ColdFusion

Since English is my primary language, I sometimes don't realize that aspects of my web applications don't play nicely with non-US ASCII characters. Such is the case with the "Content-Disposition" header. I've been using it for years; but, only found out last week that the "filename" portion of the Content-Disposition header doesn't naturally handle non-US ASCII characters. Luckily, modern browsers support an extension to the Content-Disposition header that allows for UTF-8 encoded characters.

With some Googling, I came across this page, which has a ton of test cases for the Content-Disposition header. Among the tests, it suggests that you can use a special notation that allows for the standard filename plus a UTF-8 filename with URL-encoded characters.

  • <!---
  • Query for the files in the directory.
  • --
  • NOTE: I am doing this so I don't have to embed high-ascii characters
  • in the code - I don't think my blog has the proper support for UTF-8
  • encoding? Not sure.
  • --->
  • <cfset files = directoryList( expandPath( "./" ), false, "name", "Data*" ) />
  • <!--- Isolate the file with foreign characters. --->
  • <cfset fileName = files[ 1 ] />
  • <cfset filePath = expandPath( fileName ) />
  • <!---
  • By default, the filename portion of the Content-Disposition header
  • only allows for US-ASCII values. In order to account for foreign /
  • exnteded ASCII values, we have to jump through some funky notation.
  • In this case, we are attempting to provide fallbacks. The first
  • instance of "filename" is for browsers that do not support the RFC
  • 5987 encoding (they ignore the filename*= after the filename).
  • Then, for browsers that DO support the encoding, they will pick
  • up the UTF-8 encoding.
  • Notice that the UTF-encoded value doesn't need to be quoted since
  • the embeded spaces are url-encoded.
  • --->
  • <cfheader
  • name="content-disposition"
  • value="attachment; filename=""#fileName#""; filename*=UTF-8''#urlEncodedFormat( fileName )#"
  • />
  • <cfcontent
  • type="text/plain; charset=utf-8"
  • file="#filePath#"
  • />

In this case, the "filename*=UTF-8''" notation will be honored by modern browsers and ignored by older browsers, which will use the "filename" value as the fallback.

When I run the above code, I am prompted for a file download:


 High-ascii values in the Content-Disposition header. 

Notice that the foreign characters (French) are present. This seems to work on all my modern browsers, including the latest releases of IE.

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