Add BluetoothAddress.java.

Test: Unit Test.

Bug: 200231384
Change-Id: I69b55d0ead9ec5f6b7f2884847611c4e9b95a9c9
diff --git a/nearby/service/Android.bp b/nearby/service/Android.bp
index 25beee6..4982d1f 100644
--- a/nearby/service/Android.bp
+++ b/nearby/service/Android.bp
@@ -39,8 +39,8 @@
         "error_prone_annotations",
     ],
     static_libs: [
-        "guava",
         "androidx.annotation_annotation",
+        "guava",
     ],
     sdk_version: "system_server_current",
 
diff --git a/nearby/service/java/com/android/server/nearby/common/bluetooth/fastpair/BluetoothAddress.java b/nearby/service/java/com/android/server/nearby/common/bluetooth/fastpair/BluetoothAddress.java
new file mode 100644
index 0000000..9bb5a86
--- /dev/null
+++ b/nearby/service/java/com/android/server/nearby/common/bluetooth/fastpair/BluetoothAddress.java
@@ -0,0 +1,105 @@
+/*
+ * Copyright 2021 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.server.nearby.common.bluetooth.fastpair;
+
+import static com.google.common.io.BaseEncoding.base16;
+
+import android.bluetooth.BluetoothAdapter;
+import android.bluetooth.BluetoothDevice;
+import android.content.Context;
+import android.provider.Settings;
+
+import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
+
+import com.google.common.base.Ascii;
+import com.google.common.io.BaseEncoding;
+
+import java.util.Locale;
+
+/** Utils for dealing with Bluetooth addresses. */
+public final class BluetoothAddress {
+
+    private static final BaseEncoding ENCODING = base16().upperCase().withSeparator(":", 2);
+
+    @VisibleForTesting
+    static final String SECURE_SETTINGS_KEY_BLUETOOTH_ADDRESS = "bluetooth_address";
+
+    /**
+     * @return The string format used by e.g. {@link android.bluetooth.BluetoothDevice}. Upper case.
+     *     Example: "AA:BB:CC:11:22:33"
+     */
+    public static String encode(byte[] address) {
+        return ENCODING.encode(address);
+    }
+
+    /**
+     * @param address The string format used by e.g. {@link android.bluetooth.BluetoothDevice}.
+     *     Case-insensitive. Example: "AA:BB:CC:11:22:33"
+     */
+    public static byte[] decode(String address) {
+        return ENCODING.decode(address.toUpperCase(Locale.US));
+    }
+
+    /**
+     * Get public bluetooth address.
+     *
+     * @param context a valid {@link Context} instance.
+     */
+    public static @Nullable byte[] getPublicAddress(Context context) {
+        String publicAddress =
+                Settings.Secure.getString(
+                        context.getContentResolver(), SECURE_SETTINGS_KEY_BLUETOOTH_ADDRESS);
+        return publicAddress != null && BluetoothAdapter.checkBluetoothAddress(publicAddress)
+                ? decode(publicAddress)
+                : null;
+    }
+
+    /**
+     * Hides partial information of Bluetooth address.
+     * ex1: input is null, output should be empty string
+     * ex2: input is String(AA:BB:CC), output should be AA:BB:CC
+     * ex3: input is String(AA:BB:CC:DD:EE:FF), output should be XX:XX:XX:XX:EE:FF
+     * ex4: input is String(Aa:Bb:Cc:Dd:Ee:Ff), output should be XX:XX:XX:XX:EE:FF
+     * ex5: input is BluetoothDevice(AA:BB:CC:DD:EE:FF), output should be XX:XX:XX:XX:EE:FF
+     */
+    public static String maskBluetoothAddress(@Nullable Object address) {
+        if (address == null) {
+            return "";
+        }
+
+        if (address instanceof String) {
+            String originalAddress = (String) address;
+            String upperCasedAddress = Ascii.toUpperCase(originalAddress);
+            if (!BluetoothAdapter.checkBluetoothAddress(upperCasedAddress)) {
+                return originalAddress;
+            }
+            return convert(upperCasedAddress);
+        } else if (address instanceof BluetoothDevice) {
+            return convert(((BluetoothDevice) address).getAddress());
+        }
+
+        // For others, returns toString().
+        return address.toString();
+    }
+
+    private static String convert(String address) {
+        return "XX:XX:XX:XX:" + address.substring(12);
+    }
+
+    private BluetoothAddress() {}
+}
diff --git a/nearby/tests/Android.bp b/nearby/tests/Android.bp
index 67a3b83..76b3683 100644
--- a/nearby/tests/Android.bp
+++ b/nearby/tests/Android.bp
@@ -35,6 +35,7 @@
         "androidx.test.rules",
         "framework-nearby-pre-jarjar",
         "platform-test-annotations",
+        "service-nearby",
         "truth-prebuilt",
     ],
     test_suites: [
diff --git a/nearby/tests/src/com/android/server/nearby/common/bluetooth/fastpair/BluetoothAddressTest.java b/nearby/tests/src/com/android/server/nearby/common/bluetooth/fastpair/BluetoothAddressTest.java
new file mode 100644
index 0000000..36ebb7e
--- /dev/null
+++ b/nearby/tests/src/com/android/server/nearby/common/bluetooth/fastpair/BluetoothAddressTest.java
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2021 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.server.nearby.common.bluetooth.fastpair;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.bluetooth.BluetoothAdapter;
+import android.platform.test.annotations.Presubmit;
+
+import androidx.test.filters.SmallTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Unit tests for {@link BluetoothAddress}. */
+@Presubmit
+@SmallTest
+@RunWith(AndroidJUnit4.class)
+public class BluetoothAddressTest {
+
+    @Test
+    public void maskBluetoothAddress_whenInputIsNull() {
+        assertThat(BluetoothAddress.maskBluetoothAddress(null)).isEqualTo("");
+    }
+
+    @Test
+    public void maskBluetoothAddress_whenInputStringNotMatchFormat() {
+        assertThat(BluetoothAddress.maskBluetoothAddress("AA:BB:CC")).isEqualTo("AA:BB:CC");
+    }
+
+    @Test
+    public void maskBluetoothAddress_whenInputStringMatchFormat() {
+        assertThat(BluetoothAddress.maskBluetoothAddress("AA:BB:CC:DD:EE:FF"))
+                .isEqualTo("XX:XX:XX:XX:EE:FF");
+    }
+
+    @Test
+    public void maskBluetoothAddress_whenInputStringContainLowerCaseMatchFormat() {
+        assertThat(BluetoothAddress.maskBluetoothAddress("Aa:Bb:cC:dD:eE:Ff"))
+                .isEqualTo("XX:XX:XX:XX:EE:FF");
+    }
+
+    @Test
+    public void maskBluetoothAddress_whenInputBluetoothDevice() {
+        assertThat(
+                BluetoothAddress.maskBluetoothAddress(
+                        BluetoothAdapter.getDefaultAdapter().getRemoteDevice("FF:EE:DD:CC:BB:AA")))
+                .isEqualTo("XX:XX:XX:XX:BB:AA");
+    }
+}