Add boilerplate to represent interface states in state machine

Adds empty boilerplate states to represent ethernet interface states
(currently tracked in NetworkInterfaceState) in a StateMachine.

Test: TH
Change-Id: I1041dc577a9c41b44272dfd534abe705220ff3e0

service-t/src/com/android/server/ethernet/EthernetInterfaceStateMachine.java

@@ -0,0 +1,87 @@
+/*
+ * 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.server.ethernet;
+
+import android.os.Handler;
+
+import com.android.internal.util.State;
+import com.android.net.module.util.SyncStateMachine;
+import com.android.net.module.util.SyncStateMachine.StateInfo;
+
+import java.util.ArrayList;
+import java.util.List;
+
+class EthernetInterfaceStateMachine extends SyncStateMachine {
+    /** Interface is in tethering mode. */
+    private class TetheringState extends State {
+
+    }
+
+    /** Link is down */
+    private class DisconnectedState extends State {
+
+    }
+
+    /** Parent states of all states that do not cause a NetworkOffer to be extended. */
+    private class NetworkOfferExtendedState extends State {
+
+    }
+
+    /** Link is up, network offer is extended */
+    private class StoppedState extends State {
+    }
+
+    /** Network is needed, start provisioning */
+    private class ProvisioningState extends State {
+
+    }
+
+    /** Network is needed */
+    private class RunningState extends State {
+
+    }
+
+    private final TetheringState mTetheringState = new TetheringState();
+    private final DisconnectedState mDisconnectedState = new DisconnectedState();
+    private final NetworkOfferExtendedState mOfferExtendedState = new NetworkOfferExtendedState();
+    private final StoppedState mStoppedState = new StoppedState();
+    private final ProvisioningState mProvisioningState = new ProvisioningState();
+    private final RunningState mRunningState = new RunningState();
+
+    public EthernetInterfaceStateMachine(String iface, Handler handler) {
+        super(EthernetInterfaceStateMachine.class.getSimpleName() + "." + iface,
+                handler.getLooper().getThread());
+
+        // Tethering mode is special as the interface is configured by Tethering, rather than the
+        // ethernet module.
+        final List<StateInfo> states = new ArrayList<>();
+        states.add(new StateInfo(mTetheringState, null));
+
+        // CHECKSTYLE:OFF IndentationCheck
+        // Initial state
+        states.add(new StateInfo(mDisconnectedState, null));
+        states.add(new StateInfo(mOfferExtendedState, null));
+            states.add(new StateInfo(mStoppedState, mOfferExtendedState));
+            states.add(new StateInfo(mProvisioningState, mOfferExtendedState));
+            states.add(new StateInfo(mRunningState, mOfferExtendedState));
+        // CHECKSTYLE:ON IndentationCheck
+
+        // TODO: set initial state to TetheringState if a tethering interface has been requested and
+        // this is the first interface to be added.
+        start(mDisconnectedState);
+    }
+}