Separate method for Base64 length calc. Added offset method in RawSkin

common/src/main/java/org/geysermc/floodgate/util/Base64Utils.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2019-2020 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.floodgate.util;
+
+public class Base64Utils {
+    public static int getEncodedLength(int length) {
+        if (length <= 0) {
+            return -1;
+        }
+        return 4 * ((length + 2) / 3);
+    }
+}

common/src/main/java/org/geysermc/floodgate/util/RawSkin.java

@@ -45,13 +45,18 @@ public final class RawSkin {
     }
 
     public static RawSkin decode(byte[] data) throws InvalidFormatException {
+        return decode(data, 0);
+    }
+
+    public static RawSkin decode(byte[] data, int offset) throws InvalidFormatException {
+        // offset is an amount of bytes before the Base64 starts
         if (data == null) {
             return null;
         }
 
-        int maxEncodedLength = 4 * (((64 * 64 * 4 + 9) + 2) / 3);
+        int maxEncodedLength = Base64Utils.getEncodedLength(64 * 64 * 4 + 9);
         // if the RawSkin is longer then the max Java Edition skin length
-        if (data.length > maxEncodedLength) {
+        if ((data.length - offset) > maxEncodedLength) {
             throw new InvalidFormatException(format(
                     "Encoded data cannot be longer then %s bytes! Got %s",
                     maxEncodedLength, data.length
@@ -59,7 +64,7 @@ public final class RawSkin {
         }
 
         // if the encoded data doesn't even contain the width, height (8 bytes, 2 ints) and isAlex
-        if (data.length < 4 * ((9 + 2) / 3)) {
+        if ((data.length - offset) < Base64Utils.getEncodedLength(9)) {
             throw new InvalidFormatException("Encoded data must be at least 16 bytes long!");
         }