Feat: Add Base45 Decoder

eu-digital-green-certificates · Jan 17, 2022 · e66da9c · e66da9c
2 parents c59d810 + f28b2ab
commit e66da9c
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Showing 2 changed files with 54 additions and 1 deletion.
diff --git a/src/main/java/eu/europa/ec/dgc/generation/Base45Encoder.java b/src/main/java/eu/europa/ec/dgc/generation/Base45Encoder.java
@@ -34,4 +34,42 @@ public static String encodeToString(byte[] bytes) {
         }
         return result.toString();
     }
+
+    /**
+     * Decode base45 string to byte array.
+     *
+     * @param encodedString string
+     * @return bytes
+     */
+    public static byte[] decodeFromString(String encodedString) {
+        int remainderSize = encodedString.length() % 3;
+        if (remainderSize == 1) {
+            throw new IllegalArgumentException("wrong remainder length: " + remainderSize);
+        }
+        int wholeChunkCount = encodedString.length() / 3;
+        byte[] result = new byte[wholeChunkCount * 2 + (remainderSize == 2 ? 1 : 0)];
+        int resultIndex = 0;
+        int wholeChunkLength = wholeChunkCount * 3;
+        for (int i = 0; i < wholeChunkLength; ) {
+            int c0 = ALPHABET.indexOf(encodedString.charAt(i++));
+            int c1 = ALPHABET.indexOf(encodedString.charAt(i++));
+            int c2 = ALPHABET.indexOf(encodedString.charAt(i++));
+            if (c0 < 0 || c1 < 0 || c2 < 0) {
+                throw new IllegalArgumentException("unsupported input character near pos: " + i);
+            }
+            int val = c0 + 45 * c1 + 45 * 45 * c2;
+            if (val > 0xFFFF) {
+                throw new IllegalArgumentException();
+            }
+            result[resultIndex++] = (byte) (val / 256);
+            result[resultIndex++] = (byte) (val % 256);
+        }
+
+        if (remainderSize != 0) {
+            int c0 = ALPHABET.indexOf(encodedString.charAt(encodedString.length() - 2));
+            int c1 = ALPHABET.indexOf(encodedString.charAt(encodedString.length() - 1));
+            result[resultIndex] = (byte) (c0 + 45 * c1);
+        }
+        return result;
+    }
 }
diff --git a/src/test/java/eu/europa/ec/dgc/generation/Base45EncoderTest.java b/src/test/java/eu/europa/ec/dgc/generation/Base45EncoderTest.java
@@ -1,6 +1,8 @@
 package eu.europa.ec.dgc.generation;
 
 import java.nio.charset.StandardCharsets;
+import java.util.Random;
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import org.junit.jupiter.api.Test;
 
@@ -13,4 +15,17 @@ void encodeTest() {
         byte[] bytes = new byte[] { 0, 2, -2, 30, -12, 23, -23, -40};
         assertEquals("200T5WR%UEPT",Base45Encoder.encodeToString(bytes));
     }
-}
+
+    @Test
+    void encodingDecoding() {
+        for (int i = 16; i<20; i++) {
+            byte[] in = new byte[i];
+            Random rnd = new Random();
+            rnd.nextBytes(in);
+
+            String encoded = Base45Encoder.encodeToString(in);
+            byte[] out = Base45Encoder.decodeFromString(encoded);
+            assertArrayEquals(in, out);
+        }
+    }
+}