ByteArray: immutable byte array wrapper

This is used for AesKey, and can be used for more.

core/src/main/java/org/bitcoinj/base/internal/ByteArray.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright by the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.bitcoinj.base.internal;
+
+import java.util.Arrays;
+
+/**
+ * An effectively-immutable byte array.
+ */
+public class ByteArray implements Comparable<ByteArray> {
+    protected final byte[] bytes;
+
+    /**
+     * Wrapper for a {@code byte[]}
+     * @param bytes byte data to wrap
+     */
+    public ByteArray(byte[] bytes) {
+        // Make defensive copy, so we are effectively immutable
+        this.bytes = new byte[bytes.length];
+        System.arraycopy(bytes, 0, this.bytes, 0, bytes.length);
+    }
+
+    /**
+     * @return the key bytes
+     */
+    public byte[] bytes() {
+        return bytes;
+    }
+
+    /**
+     * @return the bytes as a hex-formatted string
+     */
+    public String formatHex() {
+        return ByteUtils.formatHex(bytes);
+    }
+
+    /**
+     * {@inheritDoc}
+     * @return {@inheritDoc}
+     */
+    @Override
+    public int hashCode() {
+        return Arrays.hashCode(bytes);
+    }
+
+    /**
+     * {@inheritDoc}
+     * @param o {@inheritDoc}
+     * @return {@inheritDoc}
+     */
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        ByteArray other = (ByteArray) o;
+        return Arrays.equals(this.bytes, other.bytes);
+    }
+
+    /**
+     * {@inheritDoc}
+     * <p>For {@link ByteArray} this is a byte-by-byte, unsigned comparison.
+     * @param o {@inheritDoc}
+     * @return {@inheritDoc}
+     */
+    @Override
+    public int compareTo(ByteArray o) {
+        return ByteUtils.arrayUnsignedComparator().compare(bytes, o.bytes);
+    }
+}

core/src/main/java/org/bitcoinj/crypto/AesKey.java

@@ -16,6 +16,7 @@
 
 package org.bitcoinj.crypto;
 
+import org.bitcoinj.base.internal.ByteArray;
 import org.bouncycastle.crypto.params.KeyParameter;
 
 /**
@@ -27,24 +28,13 @@ import org.bouncycastle.crypto.params.KeyParameter;
  *  If for some reason you have code that uses the Bouncy Castle {@link KeyParameter} type and need to convert
  *  to or from {@code AesKey}, you can temporarily use {@link #ofKeyParameter(KeyParameter)} or {@link #toKeyParameter()}
  */
-public class AesKey {
+public class AesKey extends ByteArray {
-    private final byte[] bytes;
-
     /**
      * Wrapper for a {@code byte[]} containing an AES Key
      * @param keyBytes implementation-dependent AES Key bytes
      */
     public AesKey(byte[] keyBytes) {
-        // Make defensive copy, so AesKey is effectively immutable
+        super(keyBytes);
-        this.bytes = new byte[keyBytes.length];
-        System.arraycopy(keyBytes, 0, this.bytes, 0, keyBytes.length);
-    }
-
-    /**
-     * @return The key bytes
-     */
-    public byte[] bytes() {
-        return bytes;
     }
 
     /**

core/src/test/java/org/bitcoinj/base/internal/ByteArrayTest.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright by the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.bitcoinj.base.internal;
+
+import junitparams.JUnitParamsRunner;
+import junitparams.Parameters;
+import nl.jqno.equalsverifier.EqualsVerifier;
+import nl.jqno.equalsverifier.Warning;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+
+@RunWith(JUnitParamsRunner.class)
+public class ByteArrayTest {
+
+    @Test
+    public void testImmutability() {
+        byte[] bytes = new byte[]{0x00};
+        ByteArray ba = new ByteArray(bytes);
+        // Modify original array
+        bytes[0] = (byte) 0xFF;
+
+        // Verify ByteArray not modified (due to defensive copy)
+        assertNotEquals(ba.bytes, bytes);
+    }
+
+    @Test
+    public void equalsContract() {
+        EqualsVerifier.forClass(ByteArray.class)
+                .suppress(Warning.NULL_FIELDS)
+                .suppress(Warning.TRANSIENT_FIELDS)
+                .usingGetClass()
+                .verify();
+    }
+
+    @Test
+    @Parameters(method = "bytesToHexStringVectors")
+    public void formatHexValid(byte[] bytes, String expectedHexString) {
+        ByteArray ba = new ByteArray(bytes);
+        assertEquals("incorrect hex formatted string", expectedHexString, ba.formatHex());
+    }
+
+    // Two-way test vectors (can be used to validate mapping in both directions)
+    private Object[] bytesToHexStringVectors() {
+        return new Object[]{
+                new Object[]{ new byte[] {}, ""},
+                new Object[]{ new byte[] {0x00}, "00"},
+                new Object[]{ new byte[] {(byte) 0xff}, "ff"},
+                new Object[]{ new byte[] {(byte) 0xab, (byte) 0xcd, (byte) 0xef}, "abcdef"}
+        };
+    }
+}