Add auto close rule for test interfaces

This rule proxies calls to TestNetworkManager, keeps track of all
interfaces created by it, and closes them after running the test.

Test: builds
Change-Id: I01810b54929fea6e9c929a49bbf5e5268c6793af

staticlibs/testutils/devicetests/com/android/testutils/AutoCloseTestInterfaceRule.kt

@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2024 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.testutils
+
+import android.Manifest.permission.MANAGE_TEST_NETWORKS
+import android.content.Context
+import android.net.TestNetworkInterface
+import android.net.TestNetworkManager
+import org.junit.rules.TestRule
+import org.junit.runner.Description
+import org.junit.runners.model.Statement
+
+class AutoCloseTestInterfaceRule(
+        private val context: Context,
+    ) : TestRule {
+    private val tnm = runAsShell(MANAGE_TEST_NETWORKS) {
+        context.getSystemService(TestNetworkManager::class.java)!!
+    }
+    private val ifaces = ArrayList<TestNetworkInterface>()
+
+    fun createTapInterface(): TestNetworkInterface {
+        return runAsShell(MANAGE_TEST_NETWORKS) {
+            tnm.createTapInterface()
+        }.also {
+            ifaces.add(it)
+        }
+    }
+
+    private fun closeAllInterfaces() {
+        // TODO: wait on RTM_DELLINK before proceeding.
+        for (iface in ifaces) {
+            // ParcelFileDescriptor prevents the fd from being double closed.
+            iface.getFileDescriptor().close()
+        }
+    }
+
+    private inner class AutoCloseTestInterfaceRuleStatement(
+        private val base: Statement,
+        private val description: Description
+    ) : Statement() {
+        override fun evaluate() {
+            tryTest {
+                base.evaluate()
+            } cleanup {
+                closeAllInterfaces()
+            }
+        }
+    }
+
+    override fun apply(base: Statement, description: Description): Statement {
+        return AutoCloseTestInterfaceRuleStatement(base, description)
+    }
+}