ContentDispositionUtils

ContentDispositionUtils.cs

/*
 * Copyright (c) 2011 Markus Olsson
 * var mail = string.Join(".", new string[] {"j", "markus", "olsson"}) + string.Concat('@', "gmail.com");
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this 
 * software and associated documentation files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify, merge, publish, 
 * distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING 
 * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, 
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */


using System;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Net.Mime;

namespace freakcode.Utilities
{
    public static class ContentDispositionUtils
    {
        // A bunch of characters most likely to be forbidden (or be troublesome to use) in a file system
        private static char[] invalids = "<>:\"/\\|?*~".ToCharArray();

        // We try to prevent theese characters from repeating in the resulting string.
        private static char[] spacingCharacters = { ' ', '_', '-' };

        /// <summary>
        /// Normalizes the given file name removing diacritics and special characters so as to maximize
        /// the compatibility with user agents regardless of system charsets. Note that this method does produce
        /// a strictly compliant header since it will not quote the string if neccessary. Use the GetHeaderValue 
        /// in order to produce a proper header value for use directly with an HttpResponse. The return value 
        /// of this method can be used directly with the File* actionresults in ASP.NET MVC.
        /// </summary>
        /// <example>
        /// Will convert "Übername / document.pdf" to "Ubername document.pdf" and "c:\foobar.pdf" to "c_foobar.pdf"
        /// </example>
        /// <exception cref="ArgumentNullException">fileName was null</exception>
        /// <exception cref="ArgumentException">fileName contained invalid Unicode characters.</exception>
        public static string NormalizeFileName(string fileName)
        {
            if (fileName == null)
                throw new ArgumentNullException("fileName");

            if (fileName.Length == 0)
                return string.Empty;

            // Normalize string in order to remove diacritics. This will convert
            // the string into a fully canonical form; ie Åäö will be converted to A°a¨o¨
            char[] normalized = fileName.Normalize(NormalizationForm.FormD).ToCharArray();

            // Set up a buffer for our return string that is at most (in case there's no diacritics and no forbidden characters)
            // the same length as our normalized string.
            char[] buf = new char[normalized.Length];
            int p = 0;

            for (int i = 0; i < normalized.Length; i++)
            {
                char c = normalized[i];

                // Remove all non spacing marks (ie modifiers to base characters, umlauts and such);
                if (CharUnicodeInfo.GetUnicodeCategory(c) == UnicodeCategory.NonSpacingMark)
                    continue;

                // Strip special characters and commonly forbidden file system characters
                if (c < 32 || c > 126 || invalids.Contains(c))
                    c = '_';

                // Prevent repeating spacing characters
                if (p != 0 && spacingCharacters.Contains(c) && spacingCharacters.Contains(buf[p - 1]))
                    continue;

                buf[p++] = c;
            }

            return new string(buf, 0, p);
        }

        /// <summary>
        /// Returns a content-disposition attachment header value with a filename parameter containing
        /// a normalized form of the provided filename (see NormalizeFileName for more information).
        /// </summary>
        /// <exception cref="ArgumentNullException">fileName was null</exception>
        /// <exception cref="ArgumentException">fileName contained invalid Unicode characters.</exception>
        public static string GetHeaderValue(string fileName)
        {
            if (fileName == null)
                throw new ArgumentNullException("fileName");

            var header = new ContentDisposition
            {
                FileName = NormalizeFileName(fileName)
            };

            return header.ToString();
        }
    }
}