All geek questions in one place

Encoding IMAP folder path (IMAP UTF-7) for .NET?

The IMAP specification ( RFC 2060 , 5.1.3. International Convention on Mailbox Names) describes how to process non-ASCII characters in folder names. It defines the encoding of the modified UTF-7:

By convention, international mailbox names are specified using a modified version of the UTF-7 encoding described in [UTF-7]. The purpose of these changes is to fix the following problems with UTF-7:

  • UTF-7 uses the "+" symbol to switch; this contradicts the general use of "+" in mailbox names, in particular USENET newsgroup names.

  • UTF-7 encoding is a BASE64 that uses the "/" character; this conflicts using "/" as a popular hierarchy delimiter.

  • UTF-7 prohibits the use of "\"; this contradicts the use of "\" as a popular hierarchy delimiter.

  • UTF-7 prohibits the use of "~" without restriction; this contradicts the use of "~" on some servers as an indicator of the home directory.

  • UTF-7 allows multiple alternative forms to represent the same string; in particular, printed US-ASCII characters may be encoded.

UTF-7, US-ASCII-, "&" ; 0x20-0x25 0x27-0x7e. "&" (0x26) "& -".

( 0x00-0x1f, 0x7f-0xff 16- Unicode) BASE64, [UTF-7], "," "/" .
BASE64 US-ASCII .

"&" BASE64 "-", US-ASCII. US-ASCII, US-ASCII ( , , 16- Unicode "-" ).

, : .NET code/library ( ), ? .NET( /).

!

+3
3

, . , - Codeplex, "", , , us-ascii, IMAP.

, 30 . , 0x20 0x7e ( "-" "&" ), -us-ascii , UTF7 ( UTF8 + base64, ), "/" ",". , " ", . non-us-ascii us-ascii "&" "-" .

+2

, MIT- , :

    /// <summary>
    /// Takes a UTF-16 encoded string and encodes it as modified UTF-7.
    /// </summary>
    /// <param name="s">The string to encode.</param>
    /// <returns>A UTF-7 encoded string</returns>
    /// <remarks>IMAP uses a modified version of UTF-7 for encoding international mailbox names. For
    /// details, refer to RFC 3501 section 5.1.3 (Mailbox International Naming Convention).</remarks>
    internal static string UTF7Encode(string s) {
        StringReader reader = new StringReader(s);
        StringBuilder builder = new StringBuilder();
        while (reader.Peek() != -1) {
            char c = (char)reader.Read();
            int codepoint = Convert.ToInt32(c);
            // It a printable ASCII character.
            if (codepoint > 0x1F && codepoint < 0x7F) {
                builder.Append(c == '&' ? "&-" : c.ToString());
            } else {
                // The character sequence needs to be encoded.
                StringBuilder sequence = new StringBuilder(c.ToString());
                while (reader.Peek() != -1) {
                    codepoint = Convert.ToInt32((char)reader.Peek());
                    if (codepoint > 0x1F && codepoint < 0x7F)
                        break;
                    sequence.Append((char)reader.Read());
                }
                byte[] buffer = Encoding.BigEndianUnicode.GetBytes(
                    sequence.ToString());
                string encoded = Convert.ToBase64String(buffer).Replace('/', ',').
                    TrimEnd('=');
                builder.Append("&" + encoded + "-");
            }
        }
        return builder.ToString();
    }

    /// <summary>
    /// Takes a modified UTF-7 encoded string and decodes it.
    /// </summary>
    /// <param name="s">The UTF-7 encoded string to decode.</param>
    /// <returns>A UTF-16 encoded "standard" C# string</returns>
    /// <exception cref="FormatException">The input string is not a properly UTF-7 encoded
    /// string.</exception>
    /// <remarks>IMAP uses a modified version of UTF-7 for encoding international mailbox names. For
    /// details, refer to RFC 3501 section 5.1.3 (Mailbox International Naming Convention).</remarks>
    internal static string UTF7Decode(string s) {
        StringReader reader = new StringReader(s);
        StringBuilder builder = new StringBuilder();
        while (reader.Peek() != -1) {
            char c = (char)reader.Read();
            if (c == '&' && reader.Peek() != '-') {
                // The character sequence needs to be decoded.
                StringBuilder sequence = new StringBuilder();
                while (reader.Peek() != -1) {
                    if ((c = (char)reader.Read()) == '-')
                        break;
                    sequence.Append(c);
                }
                string encoded = sequence.ToString().Replace(',', '/');
                int pad = encoded.Length % 4;
                if (pad > 0)
                    encoded = encoded.PadRight(encoded.Length + (4 - pad), '=');
                try {
                    byte[] buffer = Convert.FromBase64String(encoded);
                    builder.Append(Encoding.BigEndianUnicode.GetString(buffer));
                } catch (Exception e) {
                    throw new FormatException(
                        "The input string is not in the correct Format.", e);
                }
            } else {
                if (c == '&' && reader.Peek() == '-')
                    reader.Read();
                builder.Append(c);
            }
        }
        return builder.ToString();
    }

, [...] UTF7.GetBytes([...]) [...].Replace('+', '&') - .NET UTF-7 ( ) + & . , " " + & ( ), + base64 ( &).

0
//
// ImapEncoding.cs
//
// Author: Jeffrey Stedfast <jestedfa@microsoft.com>
//
// Copyright (c) 2013-2019 Microsoft Corp. (www.microsoft.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.Text;

namespace MailKit.Net.Imap {
    static class ImapEncoding
    {
        const string utf7_alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";

        static readonly byte[] utf7_rank = {
            255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
            255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
            255,255,255,255,255,255,255,255,255,255,255, 62, 63,255,255,255,
             52, 53, 54, 55, 56, 57, 58, 59, 60, 61,255,255,255,255,255,255,
            255,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
             15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,255,255,255,255,255,
            255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
             41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,255,255,255,255,255,
        };

        public static string Decode (string text)
        {
            var decoded = new StringBuilder ();
            bool shifted = false;
            int bits = 0, v = 0;
            int index = 0;
            char c;

            while (index < text.Length) {
                c = text[index++];

                if (shifted) {
                    if (c == '-') {
                        // shifted back out of modified UTF-7
                        shifted = false;
                        bits = v = 0;
                    } else if (c > 127) {
                        // invalid UTF-7
                        return text;
                    } else {
                        byte rank = utf7_rank[(byte) c];

                        if (rank == 0xff) {
                            // invalid UTF-7
                            return text;
                        }

                        v = (v << 6) | rank;
                        bits += 6;

                        if (bits >= 16) {
                            char u = (char) ((v >> (bits - 16)) & 0xffff);
                            decoded.Append (u);
                            bits -= 16;
                        }
                    }
                } else if (c == '&' && index < text.Length) {
                    if (text[index] == '-') {
                        decoded.Append ('&');
                        index++;
                    } else {
                        // shifted into modified UTF-7
                        shifted = true;
                    }
                } else {
                    decoded.Append (c);
                }
            }

            return decoded.ToString ();
        }

        static void Utf7ShiftOut (StringBuilder output, int u, int bits)
        {
            if (bits > 0) {
                int x = (u << (6 - bits)) & 0x3f;
                output.Append (utf7_alphabet[x]);
            }

            output.Append ('-');
        }

        public static string Encode (string text)
        {
            var encoded = new StringBuilder ();
            bool shifted = false;
            int bits = 0, u = 0;

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

                if (c >= 0x20 && c < 0x7f) {
                    // characters with octet values 0x20-0x25 and 0x27-0x7e
                    // represent themselves while 0x26 ("&") is represented
                    // by the two-octet sequence "&-"

                    if (shifted) {
                        Utf7ShiftOut (encoded, u, bits);
                        shifted = false;
                        bits = 0;
                    }

                    if (c == 0x26)
                        encoded.Append ("&-");
                    else
                        encoded.Append (c);
                } else {
                    // base64 encode
                    if (!shifted) {
                        encoded.Append ('&');
                        shifted = true;
                    }

                    u = (u << 16) | (c & 0xffff);
                    bits += 16;

                    while (bits >= 6) {
                        int x = (u >> (bits - 6)) & 0x3f;
                        encoded.Append (utf7_alphabet[x]);
                        bits -= 6;
                    }
                }
            }

            if (shifted)
                Utf7ShiftOut (encoded, u, bits);

            return encoded.ToString ();
        }
    }
}
0

Source: https://habr.com/ru/post/1703568/

More articles:


All Articles