src/main/java/net/pterodactylus/fcp/FreenetBase64.java

   1 package net.pterodactylus.fcp;
   2
   3 import java.io.ByteArrayOutputStream;
   4 import java.io.IOException;
   5
   6 /**
   7  * Freenet-specific Base64 implementation.
   8  *
   9  * @author <a href="mailto:bombe@freenetproject.org">David ‘Bombe’ Roden</a>
  10  */
  11 public class FreenetBase64 {
  12
  13         private static final char[] FREENET_BASE64_ALPHABET =
  14                 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789~-".toCharArray();
  15         private static final int[] REVERSE_FREENET_BASE64_ALPHABET = reverse(FREENET_BASE64_ALPHABET);
  16
  17         private static int[] reverse(char[] alphabet) {
  18                 String alphabetString = new String(alphabet);
  19                 int[] reversedAlphabet = new int[128];
  20                 for (int i = 0; i < 128; i++) {
  21                         if (alphabetString.indexOf(i) > -1) {
  22                                 reversedAlphabet[i] = alphabetString.indexOf(i);
  23                         } else {
  24                                 reversedAlphabet[i] = -1;
  25                         }
  26                 }
  27                 return reversedAlphabet;
  28         }
  29
  30         public String encode(byte[] data) {
  31                 StringBuilder result = new StringBuilder();
  32                 int currentValue = 0;
  33                 int index = 0;
  34                 while (index < data.length) {
  35                         currentValue = (currentValue << 8) | data[index];
  36                         if (index % 3 == 2) {
  37                                 result.append(FREENET_BASE64_ALPHABET[(currentValue >> 18) & 0b111111]);
  38                                 result.append(FREENET_BASE64_ALPHABET[(currentValue >> 12) & 0b111111]);
  39                                 result.append(FREENET_BASE64_ALPHABET[(currentValue >> 6) & 0b111111]);
  40                                 result.append(FREENET_BASE64_ALPHABET[currentValue & 0b111111]);
  41                         }
  42                         index++;
  43                 }
  44                 if (index % 3 == 1) {
  45                         result.append(FREENET_BASE64_ALPHABET[(currentValue >> 2) & 0b111111]);
  46                         result.append(FREENET_BASE64_ALPHABET[(currentValue << 4) & 0b111111]);
  47                         result.append("==");
  48                 } else if (index % 3 == 2) {
  49                         result.append(FREENET_BASE64_ALPHABET[(currentValue >> 10) & 0b111111]);
  50                         result.append(FREENET_BASE64_ALPHABET[(currentValue >> 4) & 0b111111]);
  51                         result.append(FREENET_BASE64_ALPHABET[(currentValue << 2) & 0b111111]);
  52                         result.append("=");
  53                 }
  54                 return result.toString();
  55         }
  56
  57         public byte[] decode(String data) {
  58                 try (ByteArrayOutputStream dataOutput = new ByteArrayOutputStream(data.length() * 3 / 4)) {
  59                         int currentValue = 0;
  60                         int index = 0;
  61                         for (char c : data.toCharArray()) {
  62                                 if (c == '=') {
  63                                         break;
  64                                 }
  65                                 currentValue = (currentValue << 6) | REVERSE_FREENET_BASE64_ALPHABET[c];
  66                                 if (index % 4 == 3) {
  67                                         dataOutput.write((currentValue >> 16) & 0b11111111);
  68                                         dataOutput.write((currentValue >> 8) & 0b11111111);
  69                                         dataOutput.write(currentValue & 0b11111111);
  70                                 }
  71                                 index++;
  72                         }
  73                         if (index % 4 == 2) {
  74                                 dataOutput.write((currentValue >> 4) & 0b11111111);
  75                         } else if (index % 4 == 3) {
  76                                 dataOutput.write((currentValue >> 10) & 0b11111111);
  77                                 dataOutput.write((currentValue >> 2) & 0b11111111);
  78                         }
  79                         return dataOutput.toByteArray();
  80                 } catch (IOException e) {
  81                         throw new RuntimeException(e);
  82                 }
  83         }
  84
  85 }