Add Base64 char validation

src/main/java/com/pusher/client/util/Base64.java

@@ -1,39 +1,48 @@
 package com.pusher.client.util;
 
-// copied from: https://stackoverflow.com/a/4265472/501940
+import static java.util.Arrays.fill;
+
+// copied from: https://stackoverflow.com/a/4265472/501940 and improved (naming, char validation)
 public class Base64 {
 
-    private final static char[] ALPHABET =
+    private final static char[] CHAR_INDEX_TABLE =
             "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
 
-    private static int[] toInt = new int[128];
+    private static int[] charToIndexSparseMappingArray = new int[128];
 
     static {
-        for (int i = 0; i < ALPHABET.length; i++) {
-            toInt[ALPHABET[i]] = i;
+        fill(charToIndexSparseMappingArray, -1);
+        for (int i = 0; i < CHAR_INDEX_TABLE.length; i++) {
+            charToIndexSparseMappingArray[CHAR_INDEX_TABLE[i]] = i;
         }
     }
 
+    private static int toInt(char character) {
+        int retVal = charToIndexSparseMappingArray[character];
+        if (retVal == -1) throw new IllegalArgumentException("invalid char: " + character);
+        return retVal;
+    }
+
     public static byte[] decode(String base64String) {
-        int delta = base64String.endsWith("==") ? 2 : base64String.endsWith("=") ? 1 : 0;
-        byte[] buffer = new byte[base64String.length() * 3 / 4 - delta];
+        int paddingSize = base64String.endsWith("==") ? 2 : base64String.endsWith("=") ? 1 : 0;
+        byte[] retVal = new byte[base64String.length() * 3 / 4 - paddingSize];
         int mask = 0xFF;
         int index = 0;
         for (int i = 0; i < base64String.length(); i += 4) {
-            int c0 = toInt[base64String.charAt(i)];
-            int c1 = toInt[base64String.charAt(i + 1)];
-            buffer[index++] = (byte) (((c0 << 2) | (c1 >> 4)) & mask);
-            if (index >= buffer.length) {
-                return buffer;
+            int c0 = toInt(base64String.charAt(i));
+            int c1 = toInt(base64String.charAt(i + 1));
+            retVal[index++] = (byte) (((c0 << 2) | (c1 >> 4)) & mask);
+            if (index >= retVal.length) {
+                return retVal;
             }
-            int c2 = toInt[base64String.charAt(i + 2)];
-            buffer[index++] = (byte) (((c1 << 4) | (c2 >> 2)) & mask);
-            if (index >= buffer.length) {
-                return buffer;
+            int c2 = toInt(base64String.charAt(i + 2));
+            retVal[index++] = (byte) (((c1 << 4) | (c2 >> 2)) & mask);
+            if (index >= retVal.length) {
+                return retVal;
             }
-            int c3 = toInt[base64String.charAt(i + 3)];
-            buffer[index++] = (byte) (((c2 << 6) | c3) & mask);
+            int c3 = toInt(base64String.charAt(i + 3));
+            retVal[index++] = (byte) (((c2 << 6) | c3) & mask);
         }
-        return buffer;
+        return retVal;
     }
 }

src/test/java/com/pusher/client/util/Base64Test.java

@@ -0,0 +1,27 @@
+package com.pusher.client.util;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import org.junit.Test;
+
+public class Base64Test {
+
+    @Test
+    public void decodeValidChars() {
+        String validChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+        assertThat(Base64.decode(validChars)).isNotEmpty();
+    }
+
+    // https://en.wikipedia.org/wiki/Base64#URL_applications
+    @Test(expected = IllegalArgumentException.class)
+    public void failDecodingMinusChar() {
+        Base64.decode("-");
+    }
+
+    // https://en.wikipedia.org/wiki/Base64#URL_applications
+    @Test(expected = IllegalArgumentException.class)
+    public void failDecodingUnderscoreChar() {
+        Base64.decode("_");
+    }
+
+}