Throw InvalidDatabaseException on bad ctrl byte

Previously, we would throw an ArrayIndexOutOfBoundsException.

Closes #68.

CHANGELOG.md

@@ -6,6 +6,10 @@ CHANGELOG
 
 * IMPORTANT: Java 8 is now required. If you need Java 7 support, please
   continue using 1.3.1 or earlier.
+* The decoder will now throw an `InvalidDatabaseException` on an invalid
+  control byte in the data section rather than an
+  `ArrayIndexOutOfBoundsException`. Reported by Edwin Delgado H. GitHub
+  #68.
 
 1.3.1 (2020-03-03)
 ------------------

src/main/java/com/maxmind/db/Decoder.java

@@ -49,16 +49,19 @@ enum Type {
         // the speed by about 5000 requests per second on my machine.
         final static Type[] values = Type.values();
 
-        static Type get(int i) {
+        static Type get(int i) throws InvalidDatabaseException {
+            if (i >= Type.values.length) {
+                throw new InvalidDatabaseException("The MaxMind DB file's data section contains bad data");
+            }
             return Type.values[i];
         }
 
-        private static Type get(byte b) {
+        private static Type get(byte b) throws InvalidDatabaseException {
             // bytes are signed, but we want to treat them as unsigned here
             return Type.get(b & 0xFF);
         }
 
-        static Type fromControlByte(int b) {
+        static Type fromControlByte(int b) throws InvalidDatabaseException {
             // The type is encoded in the first 3 bits of the byte.
             return Type.get((byte) ((0xFF & b) >>> 5));
         }

src/test/java/com/maxmind/db/DecoderTest.java

@@ -1,8 +1,5 @@
 package com.maxmind.db;
 
-import static org.junit.Assert.assertArrayEquals;
-import static org.junit.Assert.assertEquals;
-
 import java.io.File;
 import java.io.IOException;
 import java.io.RandomAccessFile;
@@ -23,6 +20,10 @@
 import com.fasterxml.jackson.databind.node.FloatNode;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.Assert.*;
+
 @SuppressWarnings({"boxing", "static-method"})
 public class DecoderTest {
 
@@ -415,6 +416,19 @@ public void testArrays() throws IOException {
         DecoderTest.testTypeDecoding(Decoder.Type.ARRAY, DecoderTest.arrays());
     }
 
+    @Test
+    public void testInvalidControlByte() throws IOException {
+        try (FileChannel fc = DecoderTest.getFileChannel(new byte[]{0x0, 0xF})) {
+            MappedByteBuffer mmap = fc.map(MapMode.READ_ONLY, 0, fc.size());
+
+            Decoder decoder = new Decoder(new CHMCache(), mmap, 0);
+            InvalidDatabaseException ex = assertThrows(
+                    InvalidDatabaseException.class,
+                    () -> decoder.decode(0));
+            assertThat(ex.getMessage(), containsString("The MaxMind DB file's data section contains bad data"));
+        }
+    }
+
     private static <T> void testTypeDecoding(Decoder.Type type, Map<T, byte[]> tests)
             throws IOException {