Add JniUtil to identify jni library by package name

Bug: 205088391
Test: atest NetworkStaticLibTests
Change-Id: I4ace7803f246bb396f53d878064fec1204e7c1ef

staticlibs/Android.bp

@@ -103,6 +103,7 @@ java_library {
         "device/com/android/net/module/util/BpfMap.java",
         "device/com/android/net/module/util/HexDump.java",
         "device/com/android/net/module/util/Ipv6Utils.java",
+        "device/com/android/net/module/util/JniUtil.java",
         "device/com/android/net/module/util/Struct.java",
         "device/com/android/net/module/util/netlink/*.java",
         "device/com/android/net/module/util/structs/*.java",

staticlibs/device/com/android/net/module/util/JniUtil.java

@@ -0,0 +1,35 @@
+/*
+ * 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.net.module.util;
+
+/**
+ * Utilities for modules to use jni.
+ */
+public final class JniUtil {
+    /**
+     * The method to find jni library accroding to the giving package name.
+     *
+     * The jni library name would be packageName + _jni.so. E.g.
+     * com_android_networkstack_tethering_util_jni for tethering,
+     * com_android_connectivity_util_jni for connectivity.
+     */
+    public static String getJniLibraryName(final Package pkg) {
+        final String libPrefix = pkg.getName().replaceAll("\\.", "_");
+
+        return libPrefix + "_jni";
+    }
+}

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

@@ -0,0 +1,38 @@
+/*
+ * 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.net.module.util
+
+import androidx.test.filters.SmallTest
+import androidx.test.runner.AndroidJUnit4
+import kotlin.test.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(AndroidJUnit4::class)
+@SmallTest
+public final class JniUtilTest {
+    private val TEST_JAVA_UTIL_NAME = "java_util_jni"
+    private val TEST_ORG_JUNIT_NAME = "org_junit_jni"
+
+    @Test
+    fun testGetJniLibraryName() {
+        assertEquals(TEST_JAVA_UTIL_NAME,
+                JniUtil.getJniLibraryName(java.util.Set::class.java.getPackage()))
+        assertEquals(TEST_ORG_JUNIT_NAME,
+                JniUtil.getJniLibraryName(org.junit.Before::class.java.getPackage()))
+    }
+}