| /* |
| * Copyright (C) 2019 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.internal.net.utils; |
| |
| /** |
| * SimpleStateMachine provides a minimal, synchronous state machine framework. |
| * |
| * <p>This state machine is of limited functionality, but sufficient for implementation of simple |
| * protocols. Due to the limited functionality, it is also easy to read and maintain. |
| * |
| * SimpleStateMachine defaults to the null state. Implementers should immediately transition |
| * to their default state when instantiated. |
| * |
| * @param <T> The input message type. |
| * @param <R> The result type. For SimpleStateMachines without a return value, use {@link |
| * java.lang.Void} |
| */ |
| public abstract class SimpleStateMachine<T, R> { |
| protected final SimpleState mNullState = |
| new SimpleState() { |
| public R process(T msg) { |
| throw new IllegalStateException("Process called on null state"); |
| } |
| }; |
| |
| protected SimpleState mState = mNullState; |
| |
| // Non-static to allow for compiler verification of T, R from SimpleStateMachine |
| protected abstract class SimpleState { |
| public abstract R process(T msg); |
| } |
| |
| /** |
| * Processes the given message based on the current {@link SimpleState} |
| * |
| * @param msg The message to be processed by the current state |
| * @return The result of the processing by the current state |
| */ |
| public R process(T msg) { |
| return mState.process(msg); |
| } |
| |
| /** |
| * Transitions to a new state |
| * |
| * @param newState The {@link SimpleState} that the {@link SimpleStateMachine} should |
| * transition to |
| * @throws IllegalArgumentException if newState is null |
| */ |
| protected void transitionTo(SimpleState newState) { |
| if (newState == null) { |
| throw new IllegalArgumentException("SimpleState value must be non-null."); |
| } |
| |
| mState = newState; |
| } |
| |
| /** |
| * Transitions to a new state, and lets the new state process the given message |
| * |
| * @param newState The {@link SimpleState} that the {@link SimpleStateMachine} should transition |
| * to. This state will immediately be requested to process the given message. |
| * @param msg The message that should be processed by the new state |
| * @return The result of the processing by the new state |
| * @throws IllegalArgumentException if newState is null |
| */ |
| protected R transitionAndProcess(SimpleState newState, T msg) { |
| transitionTo(newState); |
| return mState.process(msg); |
| } |
| } |