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/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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 org.apache.coyote;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.concurrent.atomic.AtomicLong;

import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.net.AbstractEndpoint.Handler.SocketState;
import org.apache.tomcat.util.res.StringManager;
import org.apache.tomcat.util.security.PrivilegedGetTccl;
import org.apache.tomcat.util.security.PrivilegedSetTccl;

/**
 * Manages the state transitions for async requests.
 *
 * 
 * The internal states that are used are:
 * DISPATCHED       - Standard request. Not in Async mode.
 * STARTING         - ServletRequest.startAsync() has been called from
 *                    Servlet.service() but service() has not exited.
 * STARTED          - ServletRequest.startAsync() has been called from
 *                    Servlet.service() and service() has exited.
 * READ_WRITE_OP    - Performing an asynchronous read or write.
 * MUST_COMPLETE    - ServletRequest.startAsync() followed by complete() have
 *                    been called during a single Servlet.service() method. The
 *                    complete() will be processed as soon as Servlet.service()
 *                    exits.
 * COMPLETE_PENDING - ServletRequest.startAsync() has been called from
 *                    Servlet.service() but, before service() exited, complete()
 *                    was called from another thread. The complete() will
 *                    be processed as soon as Servlet.service() exits.
 * COMPLETING       - The call to complete() was made once the request was in
 *                    the STARTED state.
 * TIMING_OUT       - The async request has timed out and is waiting for a call
 *                    to complete() or dispatch(). If that isn't made, the error
 *                    state will be entered.
 * MUST_DISPATCH    - ServletRequest.startAsync() followed by dispatch() have
 *                    been called during a single Servlet.service() method. The
 *                    dispatch() will be processed as soon as Servlet.service()
 *                    exits.
 * DISPATCH_PENDING - ServletRequest.startAsync() has been called from
 *                    Servlet.service() but, before service() exited, dispatch()
 *                    was called from another thread. The dispatch() will
 *                    be processed as soon as Servlet.service() exits.
 * DISPATCHING      - The dispatch is being processed.
 * MUST_ERROR       - ServletRequest.startAsync() has been called from
 *                    Servlet.service() but, before service() exited, an I/O
 *                    error occurred on another thread. The container will
 *                    perform the necessary error handling when
 *                    Servlet.service() exits.
 * ERROR            - Something went wrong.
 *
 *
 * The valid state transitions are:
 *
 *                  post()                                        dispatched()
 *    |-------»------------------»---------|    |-------«-----------------------«-----|
 *    |                                    |    |                                     |
 *    |                                    |    |        post()                       |
 *    |               post()              \|/  \|/       dispatched()                 |
 *    |           |-----»----------------»DISPATCHED«-------------«-------------|     |
 *    |           |                          | /|\ |                            |     |
 *    |           |              startAsync()|  |--|timeout()                   |     |
 *    ^           |                          |                                  |     |
 *    |           |        complete()        |                  dispatch()      ^     |
 *    |           |   |--«---------------«-- | ---«--MUST_ERROR--»-----|        |     |
 *    |           |   |                      |         /|\             |        |     |
 *    |           ^   |                      |          |              |        |     |
 *    |           |   |                      |    /-----|error()       |        |     |
 *    |           |   |                      |   /                     |        ^     |
 *    |           |  \|/  ST-complete()     \|/ /   ST-dispatch()     \|/       |     |
 *    |    MUST_COMPLETE«--------«--------STARTING--------»---------»MUST_DISPATCH    |
 *    |                                    / | \                                      |
 *    |                                   /  |  \                                     |
 *    |                    OT-complete() /   |   \    OT-dispatch()                   |
 *    |   COMPLETE_PENDING«------«------/    |    \-------»---------»DISPATCH_PENDING |
 *    |        |      /|\                    |                       /|\ |            |
 *    |        |       |                     |                        |  |post()      |
 *    |        |       |OT-complete()        |           OT-dispatch()|  |            |
 *    |        |       |---------«-------«---|---«--\                 |  |            |
 *    |        |                             |       \                |  |            |
 *    |        |         /-------«-------«-- | --«---READ_WRITE--»----|  |            |
 *    |        |        / ST-complete()      |        /  /|\  \          |            |
 *    |        |       /                     | post()/   /     \         |            |
 *    |        |      /                      |      /   /       \        |            |
 *    |        |     /                       |     /   /         \       |            |
 *    |        |    /                        |    /   /           \      |            |
 *    |        |   /                         |   |   /             \     |            |
 *    |        |  /                          |   |  /  ST-dispatch()\    |            |
 *    |        |  |                          |   | |                 \   |            |
 *    |  post()|  |  timeout()         post()|   | |asyncOperation()  \  |  timeout() |
 *    |        |  |  |--|                    |   | |                  |  |    |--|    |
 *    |       \|/\|/\|/ |     complete()    \|/ \|/|   dispatch()    \|/\|/  \|/ |    |
 *    |--«-----COMPLETING«--------«----------STARTED--------»---------»DISPATCHING----|
 *            /|\  /|\                       | /|\ |                       /|\ /|\
 *             |    |                        |  |--|                        |   |
 *             |    |               timeout()|  post()                      |   |
 *             |    |                        |                              |   |
 *             |    |       complete()      \|/         dispatch()          |   |
 *             |    |------------«-------TIMING_OUT--------»----------------|   |
 *             |                                                                |
 *             |            complete()                     dispatch()           |
 *             |---------------«-----------ERROR--------------»-----------------|
 *
 *
 * Notes: * For clarity, the transitions to ERROR which are valid from every state apart from
 *          STARTING are not shown.
 *        * All transitions may happen on either the Servlet.service() thread (ST) or on any
 *          other thread (OT) unless explicitly marked.
 * 
*/ class AsyncStateMachine { private static final Log log = LogFactory.getLog(AsyncStateMachine.class); private static final StringManager sm = StringManager.getManager(AsyncStateMachine.class); private enum AsyncState { DISPATCHED(false, false, false, false), STARTING(true, true, false, false), STARTED(true, true, false, false), MUST_COMPLETE(true, true, true, false), COMPLETE_PENDING(true, true, false, false), COMPLETING(true, false, true, false), TIMING_OUT(true, true, false, false), MUST_DISPATCH(true, true, false, true), DISPATCH_PENDING(true, true, false, false), DISPATCHING(true, false, false, true), READ_WRITE_OP(true, true, false, false), MUST_ERROR(true, true, false, false), ERROR(true, true, false, false); private final boolean isAsync; private final boolean isStarted; private final boolean isCompleting; private final boolean isDispatching; AsyncState(boolean isAsync, boolean isStarted, boolean isCompleting, boolean isDispatching) { this.isAsync = isAsync; this.isStarted = isStarted; this.isCompleting = isCompleting; this.isDispatching = isDispatching; } boolean isAsync() { return isAsync; } boolean isStarted() { return isStarted; } boolean isDispatching() { return isDispatching; } boolean isCompleting() { return isCompleting; } } private volatile AsyncState state = AsyncState.DISPATCHED; private volatile long lastAsyncStart = 0; /* * Tracks the current generation of async processing for this state machine. The generation is incremented every * time async processing is started. The primary purpose of this is to enable Tomcat to detect and prevent attempts * to process an event for a previous generation with the current generation as processing such an event usually * ends badly: e.g. CVE-2018-8037. */ private final AtomicLong generation = new AtomicLong(0); /* * Error processing should only be triggered once per async generation. This field tracks whether the async * processing has entered the error state during this async cycle. * * Guarded by this */ private boolean hasProcessedError = false; // Need this to fire listener on complete private AsyncContextCallback asyncCtxt = null; private final AbstractProcessor processor; AsyncStateMachine(AbstractProcessor processor) { this.processor = processor; } boolean isAsync() { return state.isAsync(); } boolean isAsyncDispatching() { return state.isDispatching(); } boolean isAsyncStarted() { return state.isStarted(); } boolean isAsyncTimingOut() { return state == AsyncState.TIMING_OUT; } boolean isAsyncError() { return state == AsyncState.ERROR; } boolean isCompleting() { return state.isCompleting(); } /** * Obtain the time that this connection last transitioned to async processing. * * @return The time (as returned by {@link System#currentTimeMillis()}) that this connection last transitioned to * async */ long getLastAsyncStart() { return lastAsyncStart; } long getCurrentGeneration() { return generation.get(); } synchronized void asyncStart(AsyncContextCallback asyncCtxt) { if (state == AsyncState.DISPATCHED) { generation.incrementAndGet(); updateState(AsyncState.STARTING); // Note: In this instance, caller is responsible for calling // asyncCtxt.incrementInProgressAsyncCount() as that allows simpler // error handling. this.asyncCtxt = asyncCtxt; lastAsyncStart = System.currentTimeMillis(); } else { throw new IllegalStateException(sm.getString("asyncStateMachine.invalidAsyncState", "asyncStart()", state)); } } synchronized void asyncOperation() { if (state == AsyncState.STARTED) { updateState(AsyncState.READ_WRITE_OP); } else { throw new IllegalStateException( sm.getString("asyncStateMachine.invalidAsyncState", "asyncOperation()", state)); } } /* * Async has been processed. Whether or not to enter a long poll depends on current state. For example, as per * SRV.2.3.3.3 can now process calls to complete() or dispatch(). */ synchronized SocketState asyncPostProcess() { if (state == AsyncState.COMPLETE_PENDING) { clearNonBlockingListeners(); updateState(AsyncState.COMPLETING); return SocketState.ASYNC_END; } else if (state == AsyncState.DISPATCH_PENDING) { clearNonBlockingListeners(); updateState(AsyncState.DISPATCHING); return SocketState.ASYNC_END; } else if (state == AsyncState.STARTING || state == AsyncState.READ_WRITE_OP) { updateState(AsyncState.STARTED); return SocketState.LONG; } else if (state == AsyncState.MUST_COMPLETE || state == AsyncState.COMPLETING) { asyncCtxt.fireOnComplete(); updateState(AsyncState.DISPATCHED); asyncCtxt.decrementInProgressAsyncCount(); return SocketState.ASYNC_END; } else if (state == AsyncState.MUST_DISPATCH) { updateState(AsyncState.DISPATCHING); return SocketState.ASYNC_END; } else if (state == AsyncState.DISPATCHING) { asyncCtxt.fireOnComplete(); updateState(AsyncState.DISPATCHED); asyncCtxt.decrementInProgressAsyncCount(); return SocketState.ASYNC_END; } else if (state == AsyncState.STARTED) { // This can occur if an async listener does a dispatch to an async // servlet during onTimeout return SocketState.LONG; } else { throw new IllegalStateException( sm.getString("asyncStateMachine.invalidAsyncState", "asyncPostProcess()", state)); } } synchronized boolean asyncComplete() { Request request = processor.getRequest(); if ((request == null || !request.isRequestThread()) && (state == AsyncState.STARTING || state == AsyncState.READ_WRITE_OP)) { updateState(AsyncState.COMPLETE_PENDING); return false; } clearNonBlockingListeners(); boolean triggerDispatch = false; if (state == AsyncState.STARTING || state == AsyncState.MUST_ERROR) { // Processing is on a container thread so no need to transfer // processing to a new container thread updateState(AsyncState.MUST_COMPLETE); } else if (state == AsyncState.STARTED) { updateState(AsyncState.COMPLETING); // A dispatch to a container thread is always required. // If on a non-container thread, need to get back onto a container // thread to complete the processing. // If on a container thread the current request/response are not the // request/response associated with the AsyncContext so need a new // container thread to process the different request/response. triggerDispatch = true; } else if (state == AsyncState.READ_WRITE_OP || state == AsyncState.TIMING_OUT || state == AsyncState.ERROR) { // Read/write operations can happen on or off a container thread but // while in this state the call to listener that triggers the // read/write will be in progress on a container thread. // Processing of timeouts and errors can happen on or off a // container thread (on is much more likely) but while in this state // the call that triggers the timeout will be in progress on a // container thread. // The socket will be added to the poller when the container thread // exits the AbstractConnectionHandler.process() method so don't do // a dispatch here which would add it to the poller a second time. updateState(AsyncState.COMPLETING); } else { throw new IllegalStateException( sm.getString("asyncStateMachine.invalidAsyncState", "asyncComplete()", state)); } return triggerDispatch; } synchronized boolean asyncTimeout() { if (state == AsyncState.STARTED) { updateState(AsyncState.TIMING_OUT); return true; } else if (state == AsyncState.COMPLETING || state == AsyncState.DISPATCHING || state == AsyncState.DISPATCHED) { // NOOP - App called complete() or dispatch() between the the // timeout firing and execution reaching this point return false; } else { throw new IllegalStateException( sm.getString("asyncStateMachine.invalidAsyncState", "asyncTimeout()", state)); } } synchronized boolean asyncDispatch() { Request request = processor.getRequest(); if ((request == null || !request.isRequestThread()) && (state == AsyncState.STARTING || state == AsyncState.READ_WRITE_OP)) { updateState(AsyncState.DISPATCH_PENDING); return false; } clearNonBlockingListeners(); boolean triggerDispatch = false; if (state == AsyncState.STARTING || state == AsyncState.MUST_ERROR) { // Processing is on a container thread so no need to transfer // processing to a new container thread updateState(AsyncState.MUST_DISPATCH); } else if (state == AsyncState.STARTED) { updateState(AsyncState.DISPATCHING); // A dispatch to a container thread is always required. // If on a non-container thread, need to get back onto a container // thread to complete the processing. // If on a container thread the current request/response are not the // request/response associated with the AsyncContext so need a new // container thread to process the different request/response. triggerDispatch = true; } else if (state == AsyncState.READ_WRITE_OP || state == AsyncState.TIMING_OUT || state == AsyncState.ERROR) { // Read/write operations can happen on or off a container thread but // while in this state the call to listener that triggers the // read/write will be in progress on a container thread. // Processing of timeouts and errors can happen on or off a // container thread (on is much more likely) but while in this state // the call that triggers the timeout will be in progress on a // container thread. // The socket will be added to the poller when the container thread // exits the AbstractConnectionHandler.process() method so don't do // a dispatch here which would add it to the poller a second time. updateState(AsyncState.DISPATCHING); } else { throw new IllegalStateException( sm.getString("asyncStateMachine.invalidAsyncState", "asyncDispatch()", state)); } return triggerDispatch; } synchronized void asyncDispatched() { if (state == AsyncState.DISPATCHING || state == AsyncState.MUST_DISPATCH) { updateState(AsyncState.DISPATCHED); asyncCtxt.decrementInProgressAsyncCount(); } else { throw new IllegalStateException( sm.getString("asyncStateMachine.invalidAsyncState", "asyncDispatched()", state)); } } synchronized boolean asyncError() { Request request = processor.getRequest(); boolean containerThread = (request != null && request.isRequestThread()); if (log.isTraceEnabled()) { log.trace(sm.getString("asyncStateMachine.asyncError.start")); } clearNonBlockingListeners(); if (state == AsyncState.STARTING) { updateState(AsyncState.MUST_ERROR); } else { if (hasProcessedError) { if (log.isTraceEnabled()) { log.trace(sm.getString("asyncStateMachine.asyncError.skip")); } return false; } hasProcessedError = true; if (state == AsyncState.DISPATCHED) { // Async error handling has moved processing back into an async // state. Need to increment in progress count as it will decrement // when the async state is exited again. asyncCtxt.incrementInProgressAsyncCount(); updateState(AsyncState.ERROR); } else { updateState(AsyncState.ERROR); } } // Return true for non-container threads to trigger a dispatch return !containerThread; } synchronized void asyncRun(Runnable runnable) { if (state == AsyncState.STARTING || state == AsyncState.STARTED || state == AsyncState.READ_WRITE_OP) { // Execute the runnable using a container thread from the // Connector's thread pool. Use a wrapper to prevent a memory leak ClassLoader oldCL; Thread currentThread = Thread.currentThread(); if (Constants.IS_SECURITY_ENABLED) { PrivilegedAction pa = new PrivilegedGetTccl(currentThread); oldCL = AccessController.doPrivileged(pa); } else { oldCL = currentThread.getContextClassLoader(); } try { if (Constants.IS_SECURITY_ENABLED) { PrivilegedAction pa = new PrivilegedSetTccl(currentThread, this.getClass().getClassLoader()); AccessController.doPrivileged(pa); } else { currentThread.setContextClassLoader(this.getClass().getClassLoader()); } processor.execute(runnable); } finally { if (Constants.IS_SECURITY_ENABLED) { PrivilegedAction pa = new PrivilegedSetTccl(currentThread, oldCL); AccessController.doPrivileged(pa); } else { currentThread.setContextClassLoader(oldCL); } } } else { throw new IllegalStateException(sm.getString("asyncStateMachine.invalidAsyncState", "asyncRun()", state)); } } synchronized boolean isAvailable() { if (asyncCtxt == null) { // Async processing has probably been completed in another thread. // Trigger a timeout to make sure the Processor is cleaned up. return false; } return asyncCtxt.isAvailable(); } synchronized void recycle() { // Use lastAsyncStart to determine if this instance has been used since // it was last recycled. If it hasn't there is no need to recycle again // which saves the relatively expensive call to notifyAll() if (lastAsyncStart == 0) { return; } // Ensure in case of error that any non-container threads that have been // paused are unpaused. notifyAll(); asyncCtxt = null; state = AsyncState.DISPATCHED; lastAsyncStart = 0; hasProcessedError = false; } private void clearNonBlockingListeners() { processor.getRequest().listener = null; processor.getRequest().getResponse().listener = null; } private synchronized void updateState(AsyncState newState) { if (log.isTraceEnabled()) { log.trace(sm.getString("asyncStateMachine.stateChange", state, newState)); } state = newState; } }




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