Add ByteUtils for byte utility functions

Bug: 254155029
Test: atest NetworkStaticLibTests
Change-Id: I996ead6f23698313828e844672de5917efdfce69

staticlibs/framework/com/android/net/module/util/ByteUtils.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * 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 com.android.net.module.util;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+
+/**
+ * Byte utility functions.
+ * @hide
+ */
+public class ByteUtils {
+    /**
+     * Returns the index of the first appearance of the value {@code target} in {@code array}.
+     *
+     * @param array an array of {@code byte} values, possibly empty
+     * @param target a primitive {@code byte} value
+     * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
+     *     such index exists.
+     */
+    public static int indexOf(@NonNull byte[] array, @Nullable byte target) {
+        return indexOf(array, target, 0, array.length);
+    }
+
+    private static int indexOf(byte[] array, byte target, int start, int end) {
+        for (int i = start; i < end; i++) {
+            if (array[i] == target) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    /**
+     * Returns the values from each provided array combined into a single array. For example, {@code
+     * concat(new byte[] {a, b}, new byte[] {}, new byte[] {c}} returns the array {@code {a, b, c}}.
+     *
+     * @param arrays zero or more {@code byte} arrays
+     * @return a single array containing all the values from the source arrays, in order
+     */
+    public static byte[] concat(@NonNull byte[]... arrays) {
+        int length = 0;
+        for (byte[] array : arrays) {
+            length += array.length;
+        }
+        byte[] result = new byte[length];
+        int pos = 0;
+        for (byte[] array : arrays) {
+            System.arraycopy(array, 0, result, pos, array.length);
+            pos += array.length;
+        }
+        return result;
+    }
+}

staticlibs/tests/unit/src/com/android/net/module/util/ByteUtilsTests.kt

@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * 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 com.android.net.module.util
+
+import com.android.net.module.util.ByteUtils.indexOf
+import com.android.net.module.util.ByteUtils.concat
+import org.junit.Test
+import kotlin.test.assertContentEquals
+import kotlin.test.assertEquals
+import kotlin.test.assertNotSame
+
+class ByteUtilsTests {
+    private val EMPTY = byteArrayOf()
+    private val ARRAY1 = byteArrayOf(1)
+    private val ARRAY234 = byteArrayOf(2, 3, 4)
+
+    @Test
+    fun testIndexOf() {
+        assertEquals(-1, indexOf(EMPTY, 1))
+        assertEquals(-1, indexOf(ARRAY1, 2))
+        assertEquals(-1, indexOf(ARRAY234, 1))
+        assertEquals(0, indexOf(byteArrayOf(-1), -1))
+        assertEquals(0, indexOf(ARRAY234, 2))
+        assertEquals(1, indexOf(ARRAY234, 3))
+        assertEquals(2, indexOf(ARRAY234, 4))
+        assertEquals(1, indexOf(byteArrayOf(2, 3, 2, 3), 3))
+    }
+
+    @Test
+    fun testConcat() {
+        assertContentEquals(EMPTY, concat())
+        assertContentEquals(EMPTY, concat(EMPTY))
+        assertContentEquals(EMPTY, concat(EMPTY, EMPTY, EMPTY))
+        assertContentEquals(ARRAY1, concat(ARRAY1))
+        assertNotSame(ARRAY1, concat(ARRAY1))
+        assertContentEquals(ARRAY1, concat(EMPTY, ARRAY1, EMPTY))
+        assertContentEquals(byteArrayOf(1, 1, 1), concat(ARRAY1, ARRAY1, ARRAY1))
+        assertContentEquals(byteArrayOf(1, 2, 3, 4), concat(ARRAY1, ARRAY234))
+    }
+}