git.gag.com Git - debian/openrocket/blob - android/src/net/sf/openrocket/android/thrustcurve/Base64Decoder.java

   1 package net.sf.openrocket.android.thrustcurve;\r
   2 \r
   3 import java.io.IOException;\r
   4 import java.io.Reader;\r
   5 import java.io.StringReader;\r
   6 import java.io.StringWriter;\r
   7 \r
   8 public abstract class Base64Decoder {\r
   9 \r
  10         private static final String BASE64_CHARS =\r
  11                 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";\r
  12         private static final char PAD_CHAR = '=';\r
  13 \r
  14         private final static short[]  _charToBits = new short[128];\r
  15 \r
  16         static {\r
  17 \r
  18                 for (int i = 0; i < _charToBits.length; i++)\r
  19                         _charToBits[i] = -1;\r
  20 \r
  21                 for (int i = 0; i < BASE64_CHARS.length(); i++)\r
  22                         _charToBits[BASE64_CHARS.charAt(i)] = (byte) i;\r
  23                 _charToBits[PAD_CHAR] = 0;\r
  24 \r
  25         }\r
  26         \r
  27         /**\r
  28          * Decode the specified Base64 string and write binary data\r
  29          * to the given stream.\r
  30          * @param str Base64 encoded string\r
  31          * @param w output stream\r
  32          */\r
  33         public static String decodeData(String str) throws IOException\r
  34         {\r
  35                 StringReader  r;\r
  36                 int           c1;\r
  37 \r
  38                 if (str == null || str.length() < 1)\r
  39                         return null;\r
  40 \r
  41                 r = new StringReader(str);\r
  42                 \r
  43                 StringWriter w = new StringWriter();\r
  44 \r
  45                 // spin through the input string\r
  46                 c1 = readToNonSpace(r);\r
  47                 while (c1 > 0)\r
  48                 {\r
  49                         int  c2, c3, c4;\r
  50                         int  p1, p2, p3, p4;\r
  51                         int  pad, n;\r
  52 \r
  53                         pad = 0;\r
  54 \r
  55                         c2 = readToNonSpace(r);\r
  56                         c3 = readToNonSpace(r);\r
  57                         c4 = readToNonSpace(r);\r
  58                         if (c4 < 0)\r
  59                                 throw new IllegalArgumentException("Encoded string ends prematurely.");\r
  60 \r
  61                         p1 = charToBits(c1);\r
  62                         p2 = charToBits(c2);\r
  63 \r
  64                         if (c3 == PAD_CHAR)\r
  65                         {\r
  66                                 p3 = 0;\r
  67                                 pad++;\r
  68                         }\r
  69                         else\r
  70                                 p3 = charToBits(c3);\r
  71 \r
  72                         if (c4 == PAD_CHAR)\r
  73                         {\r
  74                                 p4 = 0;\r
  75                                 pad++;\r
  76                         }\r
  77                         else\r
  78                                 p4 = charToBits(c4);\r
  79 \r
  80                         if (p1 < 0 || p2 < 0 || p3 < 0 || p4 < 0)\r
  81                                 throw new IllegalArgumentException("Encoded string contains invalid characters.");\r
  82 \r
  83                         n = (p1 << 18) | (p2 << 12) | (p3 << 6) | p4;\r
  84 \r
  85                         w.write((byte) ((n & 0xFF0000) >> 16));\r
  86                         if (pad < 2)\r
  87                                 w.write((byte) ((n & 0x00FF00) >> 8));\r
  88                         if (pad < 1)\r
  89                                 w.write((byte) (n & 0x0000FF));\r
  90 \r
  91                         c1 = readToNonSpace(r);\r
  92                         if (c1 > 0 && pad > 0)\r
  93                                 throw new IllegalArgumentException("Extra characters found after padding.");\r
  94                 }\r
  95                 \r
  96                 return w.toString();\r
  97         }\r
  98 \r
  99 \r
 100         private static int readToNonSpace(Reader r)\r
 101         throws IOException\r
 102         {\r
 103                 int  c;\r
 104 \r
 105                 c = r.read();\r
 106                 while (c >= 0 && Character.isWhitespace(c))\r
 107                         c = r.read();\r
 108 \r
 109                 return c;\r
 110         }\r
 111 \r
 112         private static int charToBits(int c)\r
 113         {\r
 114                 // use it to look up the value\r
 115                 if (c < 0 || c >= _charToBits.length)\r
 116                         return -1;\r
 117                 else\r
 118                         return _charToBits[c];\r
 119         }\r
 120 \r
 121 \r
 122 }\r