Java decoder implementation based on the php version

README.md

@@ -2,6 +2,7 @@
 
  * `site_decr_code.js` — код расшифровки с `vk.com`
  * `decr_code.php` — аналогичный код на PHP
+ * `VkAudioUrlDecoder.java` — аналогичный код на Java
  * `enc_code.html` — код шифровки на JavaScript
  * `token_usage.php` — пример использования токена
 

VkAudioUrlDecoder.java

@@ -0,0 +1,117 @@
+public class VkAudioUrlDecoder {
+
+    private static final String ALL_SYMBOLS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN0PQRSTUVWXYZO123456789+/=";
+    private static final String ALL_SYMBOLS_2X = ALL_SYMBOLS + ALL_SYMBOLS;
+
+
+    public static String decode(String originalUrl, String userId) {
+        String[] vals = originalUrl.split("/?extra=")[1].split("#");
+        String tstr = vk_o(vals[0]);
+        String ops = vk_o(vals[1]);
+        String[] ops_arr = ops.split("\u0009");
+        for (int i = ops_arr.length - 1; i >= 0; i--) {
+            String[] args_arr = ops_arr[i].split("\u000B");
+            String op_ind = array_shift(args_arr);
+            switch (op_ind) {
+                case "v":
+                    tstr = vk_v(tstr);
+                    break;
+                case "r":
+                    tstr = vk_r(tstr, Integer.parseInt(args_arr[0]));
+                    break;
+                case "x":
+                    tstr = vk_x(tstr, args_arr[0]);
+                    break;
+                case "s":
+                    tstr = vk_s(tstr, Integer.parseInt(args_arr[0]));
+                    break;
+                case "i":
+                    tstr = vk_i(tstr, Integer.parseInt(args_arr[0]), Integer.parseInt(userId));
+                    break;
+            }
+        }
+        return tstr;
+    }
+
+    private static String vk_o(String str) {
+        StringBuilder result = new StringBuilder();
+        int i = 0;
+        for (int s = 0, index2 = 0; s < str.length(); s++) {
+            int sym_index = ALL_SYMBOLS.indexOf(str.charAt(s));
+            if (sym_index >= 0) {
+                if ((index2 % 4) != 0)
+                    i = (i << 6) + sym_index;
+                else
+                    i = sym_index;
+
+                if ((index2 % 4) != 0) {
+                    index2++;
+                    int shift = -2 * index2 & 6;
+                    result.append(((char) (0xFF & (i >> shift))));
+                } else {
+                    index2++;
+                }
+            }
+        }
+        return result.toString();
+    }
+
+    private static String vk_s(String str, int start) {
+        int len = str.length();
+        if (len <= 0)
+            return str;
+
+        int cur = Math.abs(start);
+        int[] shuffle_pos = new int[len];
+        for (int i = len - 1; i >= 0; i--)
+            shuffle_pos[i] = cur = ((len * (i + 1)) ^ cur + i) % len;
+        for (int i = 1; i < len; i++)
+            str = swap(str, i, shuffle_pos[len - i - 1]);
+
+        return str;
+    }
+
+    private static String vk_i(String str, int i, int userId) {
+        return vk_s(str, i ^ userId);
+    }
+
+    private static String vk_v(String str) {
+        return new StringBuilder(str).reverse().toString();
+    }
+
+    private static String vk_r(String str, int i) {
+        StringBuilder result = new StringBuilder();
+        for (int s = 0; s < str.length(); s++) {
+            int index = ALL_SYMBOLS_2X.indexOf(str.charAt(s));
+            if (index >= 0) {
+                int offset = index - i;
+                if (offset < 0)
+                    offset += ALL_SYMBOLS_2X.length();
+                result.append(ALL_SYMBOLS_2X.charAt(offset));
+            } else
+                result.append(str.charAt(s));
+        }
+        return result.toString();
+    }
+
+    private static String vk_x(String str, String arg) {
+        char xor_val = arg.charAt(0);
+        StringBuilder result = new StringBuilder();
+        for (int i = 0; i < str.length(); i++)
+            result.append((char) (str.charAt(i) ^ xor_val));
+        return result.toString();
+    }
+
+    private static String swap(String str, int i, int j) {
+        StringBuilder builder = new StringBuilder(str);
+        builder.setCharAt(i, str.charAt(j));
+        builder.setCharAt(j, str.charAt(i));
+        return builder.toString();
+    }
+
+    private static String array_shift(String[] args) {
+        String firstArg = args[0];
+        System.arraycopy(args, 1, args, 0, args.length - 1);
+        return firstArg;
+    }
+}