How do I encode a file name for download?

Question

When the file name is "Algunas MARCAS que nos acompañan" ASP.NET MVC raise an System.FormatException when I try to download that file. But if the file name is "Asistente de Gerencia Comercial" it doesn't.

I guess this is because something related to UTF-8 encoding, but I don't know how to encode that string.

If I'm right, how can I encode the string in UTF-8 encoding? If I'm not right, what is my problem?

Solution 1

I encode file name like this for downloading,

HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment;filename= " + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));

Solution 2

Based on ZZ Coder answer, and because I'm using FileResult, I decided to encode the file name as:

HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8)

Solution 3

We had an issue where Chrome was changing filenames that contained underscores to the name of the page the file was being downloaded from.

Using HttpUtility.UrlPathEncode(filename) as suggested by Furkan Ekinci in the comments fixed it for us.

Solution 4

The only trick that works (in all browsers) for me is:

Dim headerFileName As String = IIf(Request.Browser.Browser = "InternetExplorer" Or Request.UserAgent.Contains("Edge"), Uri.EscapeDataString(file.Name), file.Name)
Response.AddHeader("Content-Disposition", "attachment; filename=""" + headerFileName + """")

Solution 5

This issue has been known for years. As far as I can tell, there currently is no interoperable way to do this, so the answer is to only support one set of browsers, or to do User Agent sniffing.

Test cases and links at: http://greenbytes.de/tech/tc2231/

View more solutions

Comments

[Sixten Otto]

How are you sending the file back to the user now? Using System.Web.Mvc.FileResult? Can you post your code?

[Sixten Otto]

The weird thing is that System.Web.Mvc.FileResult internally uses System.Net.Mime.ContentDisposition to generate the header that it adds to the response. I would have expected that class to be able to handle whatever string encoding is necessary to make this work.

[Cosmin]

This replaces spaces with +, which may not be what you want.

[Oskar Berggren]

NOTE: For the correct solution in modern times, see RFC6266: tools.ietf.org/html/rfc6266

[Furkan Ekinci]

HttpUtility.UrlEncode causes replacing spaces with plus signs, HttpUtility.UrlPathEncode is solution for plus sign problem.