Mega Code Archive
Decodes all or part of the input base64 encoded StringBuffer
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//
// Novell.Directory.Ldap.Utilclass.Base64.cs
//
// Author:
// Sunil Kumar (Sunilk@novell.com)
//
// (C) 2003 Novell, Inc (http://www.novell.com)
//
using System;
namespace Novell.Directory.Ldap.Utilclass
{
/// <summary> The Base64 utility class performs base64 encoding and decoding.
///
/// The Base64 Content-Transfer-Encoding is designed to represent
/// arbitrary sequences of octets in a form that need not be humanly
/// readable. The encoding and decoding algorithms are simple, but the
/// encoded data are consistently only about 33 percent larger than the
/// unencoded data. The base64 encoding algorithm is defined by
/// RFC 2045.
/// </summary>
public class Base64
{
/// <summary> Decodes a base64 encoded StringBuffer.
/// Decodes all or part of the input base64 encoded StringBuffer, each
/// Character value representing a base64 character. The resulting
/// binary data is returned as an array of bytes.
///
/// </summary>
/// <param name="encodedSBuf">The StringBuffer object that contains base64
/// encoded data.
/// </param>
/// <param name="start"> The start index of the base64 encoded data.
/// </param>
/// <param name="end"> The end index + 1 of the base64 encoded data.
///
/// </param>
/// <returns> The decoded byte array
/// </returns>
public static sbyte[] decode(System.Text.StringBuilder encodedSBuf, int start, int end)
{
/// <summary>conversion table for decoding from base64.
///
/// dmap is a base64 (8-bit) to six-bit value converstion table.
/// For example the ASCII character 'P' has a value of 80.
/// The value in the 80th position of the table is 0x0f or 15.
/// 15 is the original 6-bit value that the letter 'P' represents.
/// </summary>
/*
* 6-bit decoded value base64 base64
* encoded character
* value
*
* Note: about half of the values in the table are only place holders
*/
sbyte[] dmap = new sbyte[]{(sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x3e), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x3f), (sbyte) (0x34), (sbyte) (0x35), (sbyte) (0x36), (sbyte) (0x37), (sbyte) (0x38), (sbyte) (0x39), (sbyte) (0x3a), (sbyte) (0x3b), (sbyte) (0x3c), (sbyte) (0x3d), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x01), (sbyte) (0x02), (sbyte) (0x03), (sbyte) (0x04), (sbyte) (0x05), (sbyte) (0x06), (sbyte) (0x07), (sbyte) (0x08), (sbyte) (0x09), (sbyte) (0x0a), (sbyte) (0x0b), (sbyte) (0x0c), (sbyte) (0x0d), (sbyte) (0x0e), (sbyte) (0x0f), (sbyte) (0x10), (sbyte) (0x11), (sbyte) (0x12), (sbyte) (0x13), (sbyte) (0x14), (sbyte) (0x15), (sbyte) (0x16), (sbyte) (0x17), (sbyte) (0x18), (sbyte) (0x19), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x1a), (sbyte) (0x1b), (sbyte) (0x1c), (sbyte) (0x1d), (sbyte) (0x1e), (sbyte) (0x1f), (sbyte) (0x20), (sbyte) (0x21), (sbyte) (0x22), (sbyte) (0x23), (sbyte) (0x24), (sbyte) (0x25), (sbyte) (0x26), (sbyte) (0x27), (sbyte) (0x28), (sbyte) (0x29), (sbyte) (0x2a), (sbyte) (0x2b), (sbyte) (0x2c), (sbyte) (0x2d), (sbyte) (0x2e), (sbyte) (0x2f), (sbyte) (0x30), (sbyte) (0x31), (sbyte) (0x32), (sbyte) (0x33), (sbyte) (0x00), (
sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00), (sbyte) (0x00)}; // 120-127 'xyz '
int i, j, k;
int esbLen = end - start; // length of the encoded part
int gn = esbLen / 4; // number of four-bytes group in ebs
int dByteLen; // length of dbs, default is '0'
bool onePad = false, twoPads = false;
sbyte[] decodedBytes; // decoded bytes
if (encodedSBuf.Length == 0)
{
return new sbyte[0];
}
// the number of encoded bytes should be multiple of number 4
if ((esbLen % 4) != 0)
{
throw new System.SystemException("Novell.Directory.Ldap.ldif_dsml." + "Base64Decoder: decode error: mal-formatted encode value");
}
// every four-bytes in ebs, except the last one if it in the form of
// three bytes.
if ((encodedSBuf[end - 1] == (int)'=') && (encodedSBuf[end - 2] == (int)'='))
{
// the last four bytes of ebs is in the form of '**=='
twoPads = true;
// the first two bytes of the last four-bytes of ebs will be
// decoded into one byte.
dByteLen = gn * 3 - 2;
decodedBytes = new sbyte[dByteLen];
}
else if (encodedSBuf[end - 1] == (int)'=')
{
// the last four bytes of ebs is in the form of '***='
onePad = true;
// the first two bytes of the last four-bytes of ebs will be
// decoded into two bytes.
dByteLen = gn * 3 - 1;
decodedBytes = new sbyte[dByteLen];
}
else
{
// the last four bytes of ebs is in the form of '****', eg. no pad.
dByteLen = gn * 3;
decodedBytes = new sbyte[dByteLen];
}
// map of encoded and decoded bits
// no padding:
// bits in 4 encoded bytes: 76543210 76543210 76543210 76543210
// bits in 3 decoded bytes: 765432 107654 321076 543210
// base64 string "QUFB":00010000 00010100 000001010 0000001
// plain string "AAA": 010000 010100 000101 000001
// one padding:
// bits in 4 encoded bytes: 76543210 76543210 76543210 76543210
// bits in 2 decoded bytes: 765432 107654 3210
// base64 string "QUE=": 00010000 000101000 0000100 00111101
// plain string "AA": 010000 010100 0001
// two paddings:
// bits in 4 encoded bytes: 76543210 76543210 76543210 76543210
// bits in 1 decoded bytes: 765432 10
// base64 string "QQ==": 00010000 00010000 00111101 00111101
// plain string "A": 010000 01
for (i = 0, j = 0, k = 1; i < esbLen; i += 4, j += 3, k++)
{
// build decodedBytes[j].
decodedBytes[j] = (sbyte)(dmap[encodedSBuf[start + i]] << 2 | (dmap[encodedSBuf[start + i + 1]] & 0x30) >> 4);
// build decodedBytes[j+1]
if ((k == gn) && twoPads)
{
break;
}
else
{
decodedBytes[j + 1] = (sbyte)((dmap[encodedSBuf[start + i + 1]] & 0x0f) << 4 | (dmap[encodedSBuf[start + i + 2]] & 0x3c) >> 2);
}
// build decodedBytes[j+2]
if ((k == gn) && onePad)
{
break;
}
else
{
decodedBytes[j + 2] = (sbyte)((dmap[encodedSBuf[start + i + 2]] & 0x03) << 6 | dmap[encodedSBuf[start + i + 3]] & 0x3f);
}
}
return decodedBytes;
}
}
}
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