Decode quoted printable correct

Question

I have the following string:

=?utf-8?Q?=5Bproconact_=2D_Verbesserung_=23=32=37=39=5D_=28Neu=29_Stellvertretungen_Benutzerrecht_=2D_andere_k=C3=B6nnen_f=C3=BCr_andere_Stellvertretungen_erstellen_=C3=A4ndern_usw=2E_dadurch_ist_der_Schutz_der_Aktivi=C3=A4ten_Mails_nicht_gew=C3=A4hrt=...

which is an encoding of

[proconact-Verbesserung #279] (Neu) Stellvertretungen Benutzerrecht - andere können für andere Stellvertretungen erstellen ändern usw. dadurch ist der Schutz der Aktiviäten Mails nicht gewährt.

I am searching for a way do decode the quoted string.

I have tried:

private static string DecodeQuotedPrintables(string input, string charSet) {
    Encoding enc = new ASCIIEncoding();
    try {
        enc = Encoding.GetEncoding(charSet);
    } catch {
        enc = new UTF8Encoding();
    }

    var occurences = new Regex(@"(=[0-9A-Z]{2}){1,}", RegexOptions.Multiline);
    var matches = occurences.Matches(input);

    foreach (Match match in matches) {
        try {
            byte[] b = new byte[match.Groups[0].Value.Length / 3];
            for (int i = 0; i < match.Groups[0].Value.Length / 3; i++) {
                b[i] = byte.Parse(match.Groups[0].Value.Substring(i * 3 + 1, 2), System.Globalization.NumberStyles.AllowHexSpecifier);
            }
            char[] hexChar = enc.GetChars(b);
            input = input.Replace(match.Groups[0].Value, hexChar[0].ToString());
        } catch { ;}
    }
    input = input.Replace("?=", "").Replace("=\r\n", "");

    return input;
}

when I call (where s is my string)

var x = DecodeQuotedPrintables(s, "utf-8");

this will return

=?utf-8?Q?[proconact_-_Verbesserung_#_(Neu)_Stellvertretungen_Benutzerrecht_-_andere_können_für_andere_Stellvertretungen_erstellen_ändern_usw._dadurch_ist_der_Schutz_der_Aktiviäten_Mails_nicht_gewährt=...

What can I do, that there will also the _ and the starting =?utf-8?Q? and the trailing =.. be removed?

Answer 1

The text you’re trying to decode is typically found in MIME headers, and is encoded according to the specification defined in the following Internet standard: RFC 2047: MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text.

There is a sample implementation for such a decoder on GitHub; maybe you can draw some ideas from it: RFC2047 decoder in C#.

You can also use this online tool for comparing your results: Online MIME Headers Decoder.

Note that your sample text is incorrect. The specification declares:

encoded-word = "=?" charset "?" encoding "?" encoded-text "?="

Per the specification, any encoded word must end in ?=. Thus, your sample must be corrected from:

=?utf-8?Q?=5Bproconact_=2D_Verbesserung_=23=32=37=39=5D_=28Neu=29_Stellvertretungen_Benutzerrecht_=2D_andere_k=C3=B6nnen_f=C3=BCr_andere_Stellvertretungen_erstellen_=C3=A4ndern_usw=2E_dadurch_ist_der_Schutz_der_Aktivi=C3=A4ten_Mails_nicht_gew=C3=A4hrt=

…to (scroll to the far right):

=?utf-8?Q?=5Bproconact_=2D_Verbesserung_=23=32=37=39=5D_=28Neu=29_Stellvertretungen_Benutzerrecht_=2D_andere_k=C3=B6nnen_f=C3=BCr_andere_Stellvertretungen_erstellen_=C3=A4ndern_usw=2E_dadurch_ist_der_Schutz_der_Aktivi=C3=A4ten_Mails_nicht_gew=C3=A4hrt?=

Strictly speaking, your sample is also invalid because it exceeds the 75-character limit imposed on any encoded word; however, most decoders tend to be tolerant of this non-conformity.

Answer 2

I've tested 5+ of code snippets and this is the working one: I've modified the regex part:

Test line:

    im sistemlerimizde bak=FDm =E7al=FD=FEmas=FD yap=FDlaca=F0=FDndan; www.gib.=

Sample call:

    string encoding = "windows-1254";
    string input = "im sistemlerimizde bak=FDm =E7al=FD=FEmas=FD yap=FDlaca=F0=FDndan; www.gib.=";
    DecodeQuotedPrintables(input, encoding);

Code snippet:

    private static string DecodeQuotedPrintables(string input, string charSet)
    {


        System.Text.Encoding enc = System.Text.Encoding.UTF7;

        try
        {
            enc = Encoding.GetEncoding(charSet);
        }
        catch
        {
            enc = new UTF8Encoding();
        }



        ////parse looking for =XX where XX is hexadecimal
        //var occurences = new Regex(@"(=[0-9A-Z]{2}){1,}", RegexOptions.Multiline);
        var occurences = new Regex("(\\=([0-9A-F][0-9A-F]))", RegexOptions.Multiline);
        var matches = occurences.Matches(input);

        foreach (Match match in matches)
        {
            try
            {
                byte[] b = new byte[match.Groups[0].Value.Length / 3];
                for (int i = 0; i < match.Groups[0].Value.Length / 3; i++)
                {
                    b[i] = byte.Parse(match.Groups[0].Value.Substring(i * 3 + 1, 2), System.Globalization.NumberStyles.AllowHexSpecifier);
                }
                char[] hexChar = enc.GetChars(b);
                input = input.Replace(match.Groups[0].Value, hexChar[0].ToString());
            }
            catch
            { ;}
        }
        input = input.Replace("?=", "").Replace("=\r\n", "");

        return input;
    }

Answer 3

As mentioned at standard class .NET is exist for this purpose.

string unicodeString =
            "=?UTF-8?Q?YourText?=";
        System.Net.Mail.Attachment attachment = System.Net.Mail.Attachment.CreateAttachmentFromString("", unicodeString);
        Console.WriteLine(attachment.Name);

Answer 4

Following my comment I'd suggest

private static string MessedUpUrlDecode(string input, string encoding)
{
    Encoding enc = new ASCIIEncoding();

    try
    {
        enc = Encoding.GetEncoding(charSet);
    }
    catch
    {
        enc = new UTF8Encoding();
    }

    string messedup = input.Split('?')[3];
    string cleaned = input.Replace("_", " ").Replace("=...", ".").Replace("=", "%");

    return System.Web.HttpUtility.UrlDecode(cleaned, enc);
}

assuming that the mutilating of the source strings is consistent.

Answer 5

I am not too sure on how to remove the

=?utf-8?Q?

Unless it appears all the time, if it does, you can do this:

input = input.Split('?')[3];

To get rid of the trailing '=' you can remove it by:

input = input.Remove(input.Length - 1);

You can get rid of the '_' by replacing it with a space:

input = input.Replace("_", " ");

You can use those pieces of code in your DecodeQuotedPrintables function.

Hope this Helps!