From 43510a529117b03de3dd983c1baaa241d6cf2b57 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Fri, 29 Jul 2022 17:57:52 +0000
Subject: [PATCH] ArrayUtils: add concat() for byte arrays

Concatenating byte arrays is a common thing that needs to be done,
especially in the locksettings package, so add a utility method for it.

Test: atest com.android.internal.util.ArrayUtilsTest
Merged-In: I099c83155456139729f4d73f5873a172590ee7e9
Change-Id: I099c83155456139729f4d73f5873a172590ee7e9
(cherry picked from commit 4dd9540f0e1d157b233a4c0d27c7f350b93f18c0)
---
 .../com/android/internal/util/ArrayUtils.java | 31 ++++++++++--
 .../android/internal/util/ArrayUtilsTest.java | 50 +++++++++++++++++++
 2 files changed, 77 insertions(+), 4 deletions(-)

diff --git a/core/java/com/android/internal/util/ArrayUtils.java b/core/java/com/android/internal/util/ArrayUtils.java
index 19228bc290e5a..d192ad932a623 100644
--- a/core/java/com/android/internal/util/ArrayUtils.java
+++ b/core/java/com/android/internal/util/ArrayUtils.java
@@ -39,8 +39,7 @@ import java.util.Set;
 import java.util.function.IntFunction;
 
 /**
- * ArrayUtils contains some methods that you can call to find out
- * the most efficient increments by which to grow arrays.
+ * Static utility methods for arrays that aren't already included in {@link java.util.Arrays}.
  */
 public class ArrayUtils {
     private static final int CACHE_SIZE = 73;
@@ -341,10 +340,11 @@ public class ArrayUtils {
     }
 
     /**
-     * Combine multiple arrays into a single array.
+     * Returns the concatenation of the given arrays.  Only works for object arrays, not for
+     * primitive arrays.  See {@link #concat(byte[]...)} for a variant that works on byte arrays.
      *
      * @param kind The class of the array elements
-     * @param arrays The arrays to combine
+     * @param arrays The arrays to concatenate.  Null arrays are treated as empty.
      * @param <T> The class of the array elements (inferred from kind).
      * @return A single array containing all the elements of the parameter arrays.
      */
@@ -390,6 +390,29 @@ public class ArrayUtils {
         return (T[]) Array.newInstance(kind, 0);
     }
 
+    /**
+     * Returns the concatenation of the given byte arrays.  Null arrays are treated as empty.
+     */
+    public static @NonNull byte[] concat(@Nullable byte[]... arrays) {
+        if (arrays == null) {
+            return new byte[0];
+        }
+        int totalLength = 0;
+        for (byte[] a : arrays) {
+            if (a != null) {
+                totalLength += a.length;
+            }
+        }
+        final byte[] result = new byte[totalLength];
+        int pos = 0;
+        for (byte[] a : arrays) {
+            if (a != null) {
+                System.arraycopy(a, 0, result, pos, a.length);
+                pos += a.length;
+            }
+        }
+        return result;
+    }
 
     /**
      * Adds value to given array if not already present, providing set-like
diff --git a/core/tests/utiltests/src/com/android/internal/util/ArrayUtilsTest.java b/core/tests/utiltests/src/com/android/internal/util/ArrayUtilsTest.java
index 61f06bd515174..c66a743d8f530 100644
--- a/core/tests/utiltests/src/com/android/internal/util/ArrayUtilsTest.java
+++ b/core/tests/utiltests/src/com/android/internal/util/ArrayUtilsTest.java
@@ -207,4 +207,54 @@ public class ArrayUtilsTest extends TestCase {
 
         assertArrayEquals(expectation, ArrayUtils.concat(String.class, array1, array2, array3));
     }
+
+    public void testConcat_zeroByteArrays() {
+        // empty varargs array
+        assertArrayEquals(new byte[] {}, ArrayUtils.concat());
+        // null varargs array
+        assertArrayEquals(new byte[] {}, ArrayUtils.concat((byte[][]) null));
+    }
+
+    public void testConcat_oneByteArray() {
+        assertArrayEquals(new byte[] { 1, 2 }, ArrayUtils.concat(new byte[] { 1, 2 }));
+    }
+
+    public void testConcat_oneEmptyByteArray() {
+        assertArrayEquals(new byte[] {}, ArrayUtils.concat((byte[]) null));
+        assertArrayEquals(new byte[] {}, ArrayUtils.concat(new byte[] {}));
+    }
+
+    public void testConcat_twoByteArrays() {
+        assertArrayEquals(new byte[] { 1 }, ArrayUtils.concat(new byte[] { 1 }, new byte[] {}));
+        assertArrayEquals(new byte[] { 1 }, ArrayUtils.concat(new byte[] {}, new byte[] { 1 }));
+        assertArrayEquals(new byte[] { 1, 2 },
+                ArrayUtils.concat(new byte[] { 1 }, new byte[] { 2 }));
+        assertArrayEquals(new byte[] { 1, 2, 3, 4 },
+                ArrayUtils.concat(new byte[] { 1, 2 }, new byte[] { 3, 4 }));
+    }
+
+    public void testConcat_twoEmptyByteArrays() {
+        assertArrayEquals(new byte[] {}, ArrayUtils.concat((byte[]) null, null));
+        assertArrayEquals(new byte[] {}, ArrayUtils.concat(new byte[] {}, null));
+        assertArrayEquals(new byte[] {}, ArrayUtils.concat((byte[]) null, new byte[] {}));
+        assertArrayEquals(new byte[] {}, ArrayUtils.concat(new byte[] {}, new byte[] {}));
+    }
+
+    public void testConcat_threeByteArrays() {
+        byte[] array1 = { 1, 2 };
+        byte[] array2 = { 3, 4 };
+        byte[] array3 = { 5, 6 };
+        byte[] expectation = { 1, 2, 3, 4, 5, 6 };
+
+        assertArrayEquals(expectation, ArrayUtils.concat(array1, array2, array3));
+    }
+
+    public void testConcat_threeByteArraysWithNull() {
+        byte[] array1 = { 1, 2 };
+        byte[] array2 = null;
+        byte[] array3 = { 5, 6 };
+        byte[] expectation = { 1, 2, 5, 6 };
+
+        assertArrayEquals(expectation, ArrayUtils.concat(array1, array2, array3));
+    }
 }