/*
 * ====================================================================
 * 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.nio.protocol;

import java.io.IOException;
import java.net.SocketTimeoutException;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicBoolean;

import org.apache.http.ConnectionReuseStrategy;
import org.apache.http.ExceptionLogger;
import org.apache.http.HttpEntity;
import org.apache.http.HttpEntityEnclosingRequest;
import org.apache.http.HttpException;
import org.apache.http.HttpRequest;
import org.apache.http.HttpResponse;
import org.apache.http.HttpResponseFactory;
import org.apache.http.HttpStatus;
import org.apache.http.HttpVersion;
import org.apache.http.MethodNotSupportedException;
import org.apache.http.ProtocolException;
import org.apache.http.UnsupportedHttpVersionException;
import org.apache.http.annotation.Contract;
import org.apache.http.annotation.ThreadingBehavior;
import org.apache.http.concurrent.Cancellable;
import org.apache.http.entity.ContentType;
import org.apache.http.impl.DefaultConnectionReuseStrategy;
import org.apache.http.impl.DefaultHttpResponseFactory;
import org.apache.http.nio.ContentDecoder;
import org.apache.http.nio.ContentEncoder;
import org.apache.http.nio.NHttpConnection;
import org.apache.http.nio.NHttpServerConnection;
import org.apache.http.nio.NHttpServerEventHandler;
import org.apache.http.nio.entity.NStringEntity;
import org.apache.http.nio.reactor.SessionBufferStatus;
import org.apache.http.params.HttpParams;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.apache.http.protocol.HttpCoreContext;
import org.apache.http.protocol.HttpProcessor;
import org.apache.http.util.Args;
import org.apache.http.util.Asserts;

HttpAsyncService is a fully asynchronous HTTP server side protocol handler based on the non-blocking (NIO) I/O model. HttpAsyncServerProtocolHandler translates individual events fired through the NHttpServerEventHandler interface into logically related HTTP message exchanges. 
 Upon receiving an incoming request HttpAsyncService verifies the message for compliance with the server expectations using HttpAsyncExpectationVerifier, if provided, and then HttpAsyncRequestHandlerMapper is used to map the request to a particular HttpAsyncRequestHandler intended to handle the request with the given URI. The protocol handler uses the selected HttpAsyncRequestHandler instance to process the incoming request and to generate an outgoing response. 
 HttpAsyncService relies on HttpProcessor to generate mandatory protocol headers for all outgoing messages and apply common, cross-cutting message transformations to all incoming and outgoing messages, whereas individual HttpAsyncRequestHandlers are expected to implement application specific content generation and processing. 
 Individual HttpAsyncRequestHandlers do not have to submit a response immediately. They can defer transmission of an HTTP response back to the client without blocking the I/O thread by delegating the process of request handling to another service or a worker thread. HTTP response can be submitted as a later a later point of time once response content becomes available. 
Since:
4.2/**
 * {@code HttpAsyncService} is a fully asynchronous HTTP server side protocol
 * handler based on the non-blocking (NIO) I/O model.
 * {@code HttpAsyncServerProtocolHandler} translates individual events fired
 * through the {@link NHttpServerEventHandler} interface into logically related
 * HTTP message exchanges.
 * <p>
 * Upon receiving an incoming request {@code HttpAsyncService} verifies
 * the message for compliance with the server expectations using
 * {@link HttpAsyncExpectationVerifier}, if provided, and then
 * {@link HttpAsyncRequestHandlerMapper} is used to map the request
 * to a particular {@link HttpAsyncRequestHandler} intended to handle
 * the request with the given URI. The protocol handler uses the selected
 * {@link HttpAsyncRequestHandler} instance to process the incoming request
 * and to generate an outgoing response.
 * <p>
 * {@code HttpAsyncService} relies on {@link HttpProcessor} to generate
 * mandatory protocol headers for all outgoing messages and apply common,
 * cross-cutting message transformations to all incoming and outgoing messages,
 * whereas individual {@link HttpAsyncRequestHandler}s are expected
 * to implement application specific content generation and processing.
 * <p>
 * Individual {@link HttpAsyncRequestHandler}s do not have to submit a response
 * immediately. They can defer transmission of an HTTP response back to
 * the client without blocking the I/O thread by delegating the process of
 * request handling to another service or a worker thread. HTTP response can
 * be submitted as a later a later point of time once response content becomes
 * available.
 *
 * @since 4.2
 */
@SuppressWarnings("deprecation")
@Contract(threading = ThreadingBehavior.IMMUTABLE_CONDITIONAL)
public class HttpAsyncService implements NHttpServerEventHandler {

    static final String HTTP_EXCHANGE_STATE = "http.nio.http-exchange-state";

    private final HttpProcessor httpProcessor;
    private final ConnectionReuseStrategy connectionStrategy;
    private final HttpResponseFactory responseFactory;
    private final HttpAsyncRequestHandlerMapper handlerMapper;
    private final HttpAsyncExpectationVerifier expectationVerifier;
    private final ExceptionLogger exceptionLogger;

    
Creates new instance of HttpAsyncServerProtocolHandler. 
Params:
httpProcessor – HTTP protocol processor (required).
connStrategy – Connection re-use strategy (required).
responseFactory – HTTP response factory (required).
handlerResolver – Request handler resolver.
expectationVerifier – Request expectation verifier (optional).
params – HTTP parameters (required).
Deprecated:
(4.3) use HttpAsyncService(HttpProcessor, ConnectionReuseStrategy, HttpResponseFactory, HttpAsyncRequestHandlerMapper, HttpAsyncExpectationVerifier)/**
     * Creates new instance of {@code HttpAsyncServerProtocolHandler}.
     *
     * @param httpProcessor HTTP protocol processor (required).
     * @param connStrategy Connection re-use strategy (required).
     * @param responseFactory HTTP response factory (required).
     * @param handlerResolver Request handler resolver.
     * @param expectationVerifier Request expectation verifier (optional).
     * @param params HTTP parameters (required).
     *
     * @deprecated (4.3) use {@link HttpAsyncService#HttpAsyncService(HttpProcessor,
     *  ConnectionReuseStrategy, HttpResponseFactory, HttpAsyncRequestHandlerMapper,
     *    HttpAsyncExpectationVerifier)}
     */
    @Deprecated
    public HttpAsyncService(
            final HttpProcessor httpProcessor,
            final ConnectionReuseStrategy connStrategy,
            final HttpResponseFactory responseFactory,
            final HttpAsyncRequestHandlerResolver handlerResolver,
            final HttpAsyncExpectationVerifier expectationVerifier,
            final HttpParams params) {
        this(httpProcessor,
             connStrategy,
             responseFactory,
             new HttpAsyncRequestHandlerResolverAdapter(handlerResolver),
             expectationVerifier);
    }

    
Creates new instance of HttpAsyncServerProtocolHandler. 
Params:
httpProcessor – HTTP protocol processor (required).
connStrategy – Connection re-use strategy (required).
handlerResolver – Request handler resolver.
params – HTTP parameters (required).
Deprecated:
(4.3) use HttpAsyncService(HttpProcessor, ConnectionReuseStrategy, HttpResponseFactory, HttpAsyncRequestHandlerMapper, HttpAsyncExpectationVerifier)/**
     * Creates new instance of {@code HttpAsyncServerProtocolHandler}.
     *
     * @param httpProcessor HTTP protocol processor (required).
     * @param connStrategy Connection re-use strategy (required).
     * @param handlerResolver Request handler resolver.
     * @param params HTTP parameters (required).
     *
     * @deprecated (4.3) use {@link HttpAsyncService#HttpAsyncService(HttpProcessor,
     *   ConnectionReuseStrategy, HttpResponseFactory, HttpAsyncRequestHandlerMapper,
     *   HttpAsyncExpectationVerifier)}
     */
    @Deprecated
    public HttpAsyncService(
            final HttpProcessor httpProcessor,
            final ConnectionReuseStrategy connStrategy,
            final HttpAsyncRequestHandlerResolver handlerResolver,
            final HttpParams params) {
        this(httpProcessor,
             connStrategy,
             DefaultHttpResponseFactory.INSTANCE,
             new HttpAsyncRequestHandlerResolverAdapter(handlerResolver),
             null);
    }

    
Creates new instance of HttpAsyncServerProtocolHandler. 
Params:
httpProcessor – HTTP protocol processor.
connStrategy – Connection re-use strategy. If null DefaultConnectionReuseStrategy.INSTANCE will be used.
responseFactory – HTTP response factory. If null DefaultHttpResponseFactory.INSTANCE will be used.
handlerMapper – Request handler mapper.
expectationVerifier – Request expectation verifier. May be null.
Since:
4.3/**
     * Creates new instance of {@code HttpAsyncServerProtocolHandler}.
     *
     * @param httpProcessor HTTP protocol processor.
     * @param connStrategy Connection re-use strategy. If {@code null}
     *   {@link DefaultConnectionReuseStrategy#INSTANCE} will be used.
     * @param responseFactory HTTP response factory. If {@code null}
     *   {@link DefaultHttpResponseFactory#INSTANCE} will be used.
     * @param handlerMapper Request handler mapper.
     * @param expectationVerifier Request expectation verifier. May be {@code null}.
     *
     * @since 4.3
     */
    public HttpAsyncService(
            final HttpProcessor httpProcessor,
            final ConnectionReuseStrategy connStrategy,
            final HttpResponseFactory responseFactory,
            final HttpAsyncRequestHandlerMapper handlerMapper,
            final HttpAsyncExpectationVerifier expectationVerifier) {
        this(httpProcessor, connStrategy, responseFactory, handlerMapper, expectationVerifier, null);
    }

    
Creates new instance of HttpAsyncServerProtocolHandler. 
Params:
httpProcessor – HTTP protocol processor.
connStrategy – Connection re-use strategy. If null DefaultConnectionReuseStrategy.INSTANCE will be used.
responseFactory – HTTP response factory. If null DefaultHttpResponseFactory.INSTANCE will be used.
handlerMapper – Request handler mapper.
expectationVerifier – Request expectation verifier. May be null.
exceptionLogger – Exception logger. If null ExceptionLogger.NO_OP will be used. Please note that the exception logger will be only used to log I/O exception thrown while closing Closeable objects (such as HttpConnection).
Since:
4.4/**
     * Creates new instance of {@code HttpAsyncServerProtocolHandler}.
     *
     * @param httpProcessor HTTP protocol processor.
     * @param connStrategy Connection re-use strategy. If {@code null}
     *   {@link DefaultConnectionReuseStrategy#INSTANCE} will be used.
     * @param responseFactory HTTP response factory. If {@code null}
     *   {@link DefaultHttpResponseFactory#INSTANCE} will be used.
     * @param handlerMapper Request handler mapper.
     * @param expectationVerifier Request expectation verifier. May be {@code null}.
     * @param exceptionLogger Exception logger. If {@code null}
     *   {@link ExceptionLogger#NO_OP} will be used. Please note that the exception
     *   logger will be only used to log I/O exception thrown while closing
     *   {@link java.io.Closeable} objects (such as {@link org.apache.http.HttpConnection}).
     *
     * @since 4.4
     */
    public HttpAsyncService(
            final HttpProcessor httpProcessor,
            final ConnectionReuseStrategy connStrategy,
            final HttpResponseFactory responseFactory,
            final HttpAsyncRequestHandlerMapper handlerMapper,
            final HttpAsyncExpectationVerifier expectationVerifier,
            final ExceptionLogger exceptionLogger) {
        super();
        this.httpProcessor = Args.notNull(httpProcessor, "HTTP processor");
        this.connectionStrategy = connStrategy != null ? connStrategy :
                DefaultConnectionReuseStrategy.INSTANCE;
        this.responseFactory = responseFactory != null ? responseFactory :
                DefaultHttpResponseFactory.INSTANCE;
        this.handlerMapper = handlerMapper;
        this.expectationVerifier = expectationVerifier;
        this.exceptionLogger = exceptionLogger != null ? exceptionLogger : ExceptionLogger.NO_OP;
    }

    
Creates new instance of HttpAsyncServerProtocolHandler. 
Params:
httpProcessor – HTTP protocol processor.
handlerMapper – Request handler mapper.
Since:
4.3/**
     * Creates new instance of {@code HttpAsyncServerProtocolHandler}.
     *
     * @param httpProcessor HTTP protocol processor.
     * @param handlerMapper Request handler mapper.
     *
     * @since 4.3
     */
    public HttpAsyncService(
            final HttpProcessor httpProcessor,
            final HttpAsyncRequestHandlerMapper handlerMapper) {
        this(httpProcessor, null, null, handlerMapper, null);
    }

    
Creates new instance of HttpAsyncServerProtocolHandler. 
Params:
httpProcessor – HTTP protocol processor.
handlerMapper – Request handler mapper.
exceptionLogger – Exception logger. If null ExceptionLogger.NO_OP will be used. Please note that the exception logger will be only used to log I/O exception thrown while closing Closeable objects (such as HttpConnection).
Since:
4.4/**
     * Creates new instance of {@code HttpAsyncServerProtocolHandler}.
     *
     * @param httpProcessor HTTP protocol processor.
     * @param handlerMapper Request handler mapper.
     * @param exceptionLogger Exception logger. If {@code null}
     *   {@link ExceptionLogger#NO_OP} will be used. Please note that the exception
     *   logger will be only used to log I/O exception thrown while closing
     *   {@link java.io.Closeable} objects (such as {@link org.apache.http.HttpConnection}).
     *
     * @since 4.4
     */
    public HttpAsyncService(
            final HttpProcessor httpProcessor,
            final HttpAsyncRequestHandlerMapper handlerMapper,
            final ExceptionLogger exceptionLogger) {
        this(httpProcessor, null, null, handlerMapper, null, exceptionLogger);
    }

    @Override
    public void connected(final NHttpServerConnection conn) {
        final State state = new State();
        conn.getContext().setAttribute(HTTP_EXCHANGE_STATE, state);
    }

    @Override
    public void closed(final NHttpServerConnection conn) {
        final State state = (State) conn.getContext().removeAttribute(HTTP_EXCHANGE_STATE);
        if (state != null) {
            state.setTerminated();
            closeHandlers(state);
            final Cancellable cancellable = state.getCancellable();
            if (cancellable != null) {
                cancellable.cancel();
            }
        }
    }

    @Override
    public void exception(
            final NHttpServerConnection conn, final Exception cause) {
        log(cause);
        final State state = getState(conn);
        if (state == null) {
            shutdownConnection(conn);
            return;
        }
        state.setTerminated();
        closeHandlers(state, cause);
        final Cancellable cancellable = state.getCancellable();
        if (cancellable != null) {
            cancellable.cancel();
        }
        final Queue<PipelineEntry> pipeline = state.getPipeline();
        if (!pipeline.isEmpty()
                || conn.isResponseSubmitted()
                || state.getResponseState().compareTo(MessageState.INIT) > 0) {
            // There is not much that we can do if a response
            // has already been submitted or pipelining is being used.
            shutdownConnection(conn);
        } else {
            try {
                final Incoming incoming = state.getIncoming();
                final HttpRequest request = incoming != null ? incoming.getRequest() : null;
                final HttpContext context = incoming != null ? incoming.getContext() : new BasicHttpContext();
                final HttpAsyncResponseProducer responseProducer = handleException(cause, context);
                final HttpResponse response = responseProducer.generateResponse();
                final Outgoing outgoing = new Outgoing(request, response, responseProducer, context);
                state.setResponseState(MessageState.INIT);
                state.setOutgoing(outgoing);
                commitFinalResponse(conn, state);
            } catch (final Exception ex) {
                shutdownConnection(conn);
                closeHandlers(state);
                if (ex instanceof RuntimeException) {
                    throw (RuntimeException) ex;
                }
                log(ex);
            }
        }
    }

    @Override
    public void requestReceived(
            final NHttpServerConnection conn) throws IOException, HttpException {
        final State state = getState(conn);
        Asserts.notNull(state, "Connection state");
        Asserts.check(state.getRequestState() == MessageState.READY,
                "Unexpected request state %s", state.getRequestState());

        final HttpRequest request = conn.getHttpRequest();
        final HttpContext context = new BasicHttpContext();

        context.setAttribute(HttpCoreContext.HTTP_REQUEST, request);
        context.setAttribute(HttpCoreContext.HTTP_CONNECTION, conn);
        this.httpProcessor.process(request, context);

        final HttpAsyncRequestHandler<Object> requestHandler = getRequestHandler(request);
        final HttpAsyncRequestConsumer<Object> consumer = requestHandler.processRequest(request, context);
        consumer.requestReceived(request);

        final Incoming incoming = new Incoming(request, requestHandler, consumer, context);
        state.setIncoming(incoming);

        if (request instanceof HttpEntityEnclosingRequest) {

            // If 100-continue is expected make sure
            // there is no pending response data, no pipelined requests or buffered input
            if (((HttpEntityEnclosingRequest) request).expectContinue()
                        && state.getResponseState() == MessageState.READY
                        && state.getPipeline().isEmpty()
                        && !(conn instanceof SessionBufferStatus && ((SessionBufferStatus) conn).hasBufferedInput())) {

                state.setRequestState(MessageState.ACK_EXPECTED);
                final HttpResponse ack = this.responseFactory.newHttpResponse(HttpVersion.HTTP_1_1,
                        HttpStatus.SC_CONTINUE, context);
                if (this.expectationVerifier != null) {
                    conn.suspendInput();
                    conn.suspendOutput();
                    final HttpAsyncExchange httpAsyncExchange = new HttpAsyncExchangeImpl(
                            request, ack, state, conn, context);
                    this.expectationVerifier.verify(httpAsyncExchange, context);
                } else {
                    conn.submitResponse(ack);
                    state.setRequestState(MessageState.BODY_STREAM);
                }
            } else {
                state.setRequestState(MessageState.BODY_STREAM);
            }
        } else {
            // No request content is expected. Process request right away
            completeRequest(incoming, conn, state);
        }
    }

    @Override
    public void inputReady(
            final NHttpServerConnection conn,
            final ContentDecoder decoder) throws IOException, HttpException {
        final State state = getState(conn);
        Asserts.notNull(state, "Connection state");
        Asserts.check(state.getRequestState() == MessageState.BODY_STREAM,
                "Unexpected request state %s", state.getRequestState());

        final Incoming incoming = state.getIncoming();
        Asserts.notNull(incoming, "Incoming request");
        final HttpAsyncRequestConsumer<?> consumer = incoming.getConsumer();
        consumer.consumeContent(decoder, conn);
        if (decoder.isCompleted()) {
            completeRequest(incoming, conn, state);
        }
    }

    @Override
    public void responseReady(
            final NHttpServerConnection conn) throws IOException, HttpException {
        final State state = getState(conn);
        Asserts.notNull(state, "Connection state");
        Asserts.check(state.getResponseState() == MessageState.READY ||
                        state.getResponseState() == MessageState.INIT,
                "Unexpected response state %s", state.getResponseState());

        if (state.getRequestState() == MessageState.ACK_EXPECTED) {
            final Outgoing outgoing;
            synchronized (state) {
                outgoing = state.getOutgoing();
                if (outgoing == null) {
                    conn.suspendOutput();
                    return;
                }
            }
            final HttpResponse response = outgoing.getResponse();
            final int status = response.getStatusLine().getStatusCode();
            if (status == 100) {
                final HttpContext context = outgoing.getContext();
                final HttpAsyncResponseProducer responseProducer = outgoing.getProducer();
                try {
                    // Make sure 100 response has no entity
                    response.setEntity(null);
                    conn.requestInput();
                    state.setRequestState(MessageState.BODY_STREAM);
                    state.setOutgoing(null);
                    conn.submitResponse(response);
                    responseProducer.responseCompleted(context);
                } finally {
                    responseProducer.close();
                }
            } else if (status >= 400) {
                conn.resetInput();
                state.setRequestState(MessageState.READY);
                commitFinalResponse(conn, state);
            } else {
                throw new HttpException("Invalid response: " + response.getStatusLine());
            }
        } else {
            if (state.getResponseState() == MessageState.READY) {
                final Queue<PipelineEntry> pipeline = state.getPipeline();
                final PipelineEntry pipelineEntry = pipeline.poll();
                if (pipelineEntry == null) {
                    conn.suspendOutput();
                    return;
                }
                state.setResponseState(MessageState.INIT);
                final Object result = pipelineEntry.getResult();
                final HttpRequest request = pipelineEntry.getRequest();
                final HttpContext context = pipelineEntry.getContext();
                if (result != null) {
                    final HttpResponse response = this.responseFactory.newHttpResponse(HttpVersion.HTTP_1_1,
                            HttpStatus.SC_OK, context);
                    final HttpAsyncExchangeImpl httpExchange = new HttpAsyncExchangeImpl(
                            request, response, state, conn, context);
                    final HttpAsyncRequestHandler<Object> handler = pipelineEntry.getHandler();
                    conn.suspendOutput();
                    try {
                        handler.handle(result, httpExchange, context);
                    } catch (final RuntimeException ex) {
                        throw ex;
                    } catch (final Exception ex) {
                        pipeline.add(new PipelineEntry(
                            request,
                            null,
                            ex,
                            handler,
                            context));
                        state.setResponseState(MessageState.READY);
                        responseReady(conn);
                        return;
                    }
                } else {
                    final Exception exception = pipelineEntry.getException();
                    final HttpAsyncResponseProducer responseProducer = handleException(
                            exception != null ? exception : new HttpException("Internal error processing request"),
                            context);
                    final HttpResponse error = responseProducer.generateResponse();
                    state.setOutgoing(new Outgoing(request, error, responseProducer, context));
                }
            }
            if (state.getResponseState() == MessageState.INIT) {
                final Outgoing outgoing;
                synchronized (state) {
                    outgoing = state.getOutgoing();
                    if (outgoing == null) {
                        conn.suspendOutput();
                        return;
                    }
                }
                final HttpResponse response = outgoing.getResponse();
                final int status = response.getStatusLine().getStatusCode();
                if (status >= 200) {
                    commitFinalResponse(conn, state);
                } else {
                    throw new HttpException("Invalid response: " + response.getStatusLine());
                }
            }
        }
    }

    @Override
    public void outputReady(
            final NHttpServerConnection conn,
            final ContentEncoder encoder) throws HttpException, IOException {
        final State state = getState(conn);
        Asserts.notNull(state, "Connection state");
        Asserts.check(state.getResponseState() == MessageState.BODY_STREAM,
                "Unexpected response state %s", state.getResponseState());

        final Outgoing outgoing = state.getOutgoing();
        Asserts.notNull(outgoing, "Outgoing response");
        final HttpAsyncResponseProducer responseProducer = outgoing.getProducer();

        responseProducer.produceContent(encoder, conn);

        if (encoder.isCompleted()) {
            completeResponse(outgoing, conn, state);
        }
    }

    @Override
    public void endOfInput(final NHttpServerConnection conn) throws IOException {
        // Closing connection in an orderly manner and
        // waiting for output buffer to get flushed.
        // Do not want to wait indefinitely, though, in case
        // the opposite end is not reading
        if (conn.getSocketTimeout() <= 0) {
            conn.setSocketTimeout(1000);
        }
        conn.close();
    }

    @Override
    public void timeout(final NHttpServerConnection conn) throws IOException {
        final State state = getState(conn);
        if (state != null) {
            exception(conn, new SocketTimeoutException(
                    String.format("%,d milliseconds timeout on connection %s", conn.getSocketTimeout(), conn)));
        }
        if (conn.getStatus() == NHttpConnection.ACTIVE) {
            conn.close();
            if (conn.getStatus() == NHttpConnection.CLOSING) {
                // Give the connection some grace time to
                // close itself nicely
                conn.setSocketTimeout(250);
            }
        } else {
            conn.shutdown();
        }
    }

    private State getState(final NHttpConnection conn) {
        return (State) conn.getContext().getAttribute(HTTP_EXCHANGE_STATE);
    }

    
This method can be used to log I/O exception thrown while closing Closeable objects (such as HttpConnection). 
Params:
ex – I/O exception thrown by Closeable.close()/**
     * This method can be used to log I/O exception thrown while closing
     * {@link java.io.Closeable} objects (such as
     * {@link org.apache.http.HttpConnection}).
     *
     * @param ex I/O exception thrown by {@link java.io.Closeable#close()}
     */
    protected void log(final Exception ex) {
        this.exceptionLogger.log(ex);
    }

    private void shutdownConnection(final NHttpConnection conn) {
        try {
            conn.shutdown();
        } catch (final IOException ex) {
            log(ex);
        }
    }

    private void closeHandlers(final State state, final Exception ex) {
        final HttpAsyncRequestConsumer<Object> consumer =
                state.getIncoming() != null ? state.getIncoming().getConsumer() : null;
        if (consumer != null) {
            try {
                consumer.failed(ex);
            } finally {
                try {
                    consumer.close();
                } catch (final IOException ioex) {
                    log(ioex);
                }
            }
        }
        final HttpAsyncResponseProducer producer =
                state.getOutgoing() != null ? state.getOutgoing().getProducer() : null;
        if (producer != null) {
            try {
                producer.failed(ex);
            } finally {
                try {
                    producer.close();
                } catch (final IOException ioex) {
                    log(ioex);
                }
            }
        }
    }

    private void closeHandlers(final State state) {
        final HttpAsyncRequestConsumer<Object> consumer =
                state.getIncoming() != null ? state.getIncoming().getConsumer() : null;
        if (consumer != null) {
            try {
                consumer.close();
            } catch (final IOException ioex) {
                log(ioex);
            }
        }
        final HttpAsyncResponseProducer producer =
                state.getOutgoing() != null ? state.getOutgoing().getProducer() : null;
        if (producer != null) {
            try {
                producer.close();
            } catch (final IOException ioex) {
                log(ioex);
            }
        }
    }

    protected HttpAsyncResponseProducer handleException(
            final Exception ex, final HttpContext context) {
        String message = ex.getMessage();
        if (message == null) {
            message = ex.toString();
        }
        final HttpResponse response = this.responseFactory.newHttpResponse(HttpVersion.HTTP_1_1,
                toStatusCode(ex, context), context);
        return new ErrorResponseProducer(response,
                new NStringEntity(message, ContentType.DEFAULT_TEXT), false);
    }

    protected int toStatusCode(final Exception ex, final HttpContext context) {
        final int code;
        if (ex instanceof MethodNotSupportedException) {
            code = HttpStatus.SC_NOT_IMPLEMENTED;
        } else if (ex instanceof UnsupportedHttpVersionException) {
            code = HttpStatus.SC_HTTP_VERSION_NOT_SUPPORTED;
        } else if (ex instanceof ProtocolException) {
            code = HttpStatus.SC_BAD_REQUEST;
        } else if (ex instanceof SocketTimeoutException) {
            code = HttpStatus.SC_GATEWAY_TIMEOUT;
        } else {
            code = HttpStatus.SC_INTERNAL_SERVER_ERROR;
        }
        return code;
    }

    
This method can be used to handle callback set up happened after
response submission.
Params:
cancellable – Request cancellation callback.
context – Request context.
Since:
4.4/**
     * This method can be used to handle callback set up happened after
     * response submission.
     *
     * @param cancellable Request cancellation callback.
     * @param context Request context.
     *
     * @since 4.4
     */
    protected void handleAlreadySubmittedResponse(
            final Cancellable cancellable, final HttpContext context) {
        throw new IllegalStateException("Response already submitted");
    }

    
This method can be used to handle double response submission.
Params:
responseProducer – Response producer for second response.
context – Request context.
Since:
4.4/**
     * This method can be used to handle double response submission.
     *
     * @param responseProducer Response producer for second response.
     * @param context Request context.
     *
     * @since 4.4
     */
    protected void handleAlreadySubmittedResponse(
            final HttpAsyncResponseProducer responseProducer,
            final HttpContext context) {
        throw new IllegalStateException("Response already submitted");
    }

    private boolean canResponseHaveBody(final HttpRequest request, final HttpResponse response) {
        if (request != null && "HEAD".equalsIgnoreCase(request.getRequestLine().getMethod())) {
            return false;
        }
        final int status = response.getStatusLine().getStatusCode();
        return status >= HttpStatus.SC_OK
            && status != HttpStatus.SC_NO_CONTENT
            && status != HttpStatus.SC_NOT_MODIFIED
            && status != HttpStatus.SC_RESET_CONTENT;
    }

    private void completeRequest(
            final Incoming incoming,
            final NHttpServerConnection conn,
            final State state) throws IOException {
        state.setRequestState(MessageState.READY);
        state.setIncoming(null);

        final PipelineEntry pipelineEntry;
        final HttpAsyncRequestConsumer<?> consumer = incoming.getConsumer();
        try {
            final HttpContext context = incoming.getContext();
            consumer.requestCompleted(context);
            pipelineEntry = new PipelineEntry(
                    incoming.getRequest(),
                    consumer.getResult(),
                    consumer.getException(),
                    incoming.getHandler(),
                    context);
        } finally {
            consumer.close();
        }
        final Queue<PipelineEntry> pipeline = state.getPipeline();
        pipeline.add(pipelineEntry);
        if (state.getResponseState() == MessageState.READY) {
            conn.requestOutput();
        }
    }

    private void commitFinalResponse(
            final NHttpServerConnection conn,
            final State state) throws IOException, HttpException {
        final Outgoing outgoing = state.getOutgoing();
        Asserts.notNull(outgoing, "Outgoing response");
        final HttpRequest request = outgoing.getRequest();
        final HttpResponse response = outgoing.getResponse();
        final HttpContext context = outgoing.getContext();

        context.setAttribute(HttpCoreContext.HTTP_RESPONSE, response);
        this.httpProcessor.process(response, context);

        HttpEntity entity = response.getEntity();
        if (entity != null && !canResponseHaveBody(request, response)) {
            response.setEntity(null);
            entity = null;
        }

        conn.submitResponse(response);

        if (entity == null) {
            completeResponse(outgoing, conn, state);
        } else {
            state.setResponseState(MessageState.BODY_STREAM);
        }
    }

    private void completeResponse(
            final Outgoing outgoing,
            final NHttpServerConnection conn,
            final State state) throws IOException {
        final HttpContext context = outgoing.getContext();
        final HttpResponse response = outgoing.getResponse();
        final HttpAsyncResponseProducer responseProducer = outgoing.getProducer();
        try {
            responseProducer.responseCompleted(context);
            state.setOutgoing(null);
            state.setCancellable(null);
            state.setResponseState(MessageState.READY);
        } finally {
            responseProducer.close();
        }
        if (!this.connectionStrategy.keepAlive(response, context)) {
            conn.close();
        } else {
            conn.requestInput();
        }
    }

    @SuppressWarnings("unchecked")
    private HttpAsyncRequestHandler<Object> getRequestHandler(final HttpRequest request) {
        HttpAsyncRequestHandler<Object> handler = null;
        if (this.handlerMapper != null) {
            handler = (HttpAsyncRequestHandler<Object>) this.handlerMapper.lookup(request);
        }
        if (handler == null) {
            handler = NullRequestHandler.INSTANCE;
        }
        return handler;
    }

    static class Incoming {

        private final HttpRequest request;
        private final HttpAsyncRequestHandler<Object> handler;
        private final HttpAsyncRequestConsumer<Object> consumer;
        private final HttpContext context;

        Incoming(
                final HttpRequest request,
                final HttpAsyncRequestHandler<Object> handler,
                final HttpAsyncRequestConsumer<Object> consumer,
                final HttpContext context) {
            this.request = request;
            this.handler = handler;
            this.consumer = consumer;
            this.context = context;
        }

        public HttpRequest getRequest() {
            return this.request;
        }

        public HttpAsyncRequestHandler<Object> getHandler() {
            return this.handler;
        }

        public HttpAsyncRequestConsumer<Object> getConsumer() {
            return this.consumer;
        }

        public HttpContext getContext() {
            return this.context;
        }
    }

    static class Outgoing {

        private final HttpRequest request;
        private final HttpResponse response;
        private final HttpAsyncResponseProducer producer;
        private final HttpContext context;

        Outgoing(
                final HttpRequest request,
                final HttpResponse response,
                final HttpAsyncResponseProducer producer,
                final HttpContext context) {
            this.request = request;
            this.response = response;
            this.producer = producer;
            this.context = context;
        }

        public HttpRequest getRequest() {
            return this.request;
        }

        public HttpResponse getResponse() {
            return this.response;
        }

        public HttpAsyncResponseProducer getProducer() {
            return this.producer;
        }

        public HttpContext getContext() {
            return this.context;
        }
    }

    static class PipelineEntry {

        private final HttpRequest request;
        private final Object result;
        private final Exception exception;
        private final HttpAsyncRequestHandler<Object> handler;
        private final HttpContext context;

        PipelineEntry(
                final HttpRequest request,
                final Object result,
                final Exception exception,
                final HttpAsyncRequestHandler<Object> handler,
                final HttpContext context) {
            this.request = request;
            this.result = result;
            this.exception = exception;
            this.handler = handler;
            this.context = context;
        }

        public HttpRequest getRequest() {
            return this.request;
        }

        public Object getResult() {
            return this.result;
        }

        public Exception getException() {
            return this.exception;
        }

        public HttpAsyncRequestHandler<Object> getHandler() {
            return this.handler;
        }

        public HttpContext getContext() {
            return this.context;
        }

    }

    static class State {

        private final Queue<PipelineEntry> pipeline;
        private volatile boolean terminated;
        private volatile MessageState requestState;
        private volatile MessageState responseState;
        private volatile Incoming incoming;
        private volatile Outgoing outgoing;
        private volatile Cancellable cancellable;

        State() {
            super();
            this.pipeline = new ConcurrentLinkedQueue<PipelineEntry>();
            this.requestState = MessageState.READY;
            this.responseState = MessageState.READY;
        }

        public boolean isTerminated() {
            return this.terminated;
        }

        public void setTerminated() {
            this.terminated = true;
        }

        public MessageState getRequestState() {
            return this.requestState;
        }

        public void setRequestState(final MessageState state) {
            this.requestState = state;
        }

        public MessageState getResponseState() {
            return this.responseState;
        }

        public void setResponseState(final MessageState state) {
            this.responseState = state;
        }

        public Incoming getIncoming() {
            return this.incoming;
        }

        public void setIncoming(final Incoming incoming) {
            this.incoming = incoming;
        }

        public Outgoing getOutgoing() {
            return this.outgoing;
        }

        public void setOutgoing(final Outgoing outgoing) {
            this.outgoing = outgoing;
        }

        public Cancellable getCancellable() {
            return this.cancellable;
        }

        public void setCancellable(final Cancellable cancellable) {
            this.cancellable = cancellable;
        }

        public Queue<PipelineEntry> getPipeline() {
            return this.pipeline;
        }

        @Override
        public String toString() {
            final StringBuilder buf = new StringBuilder();
            buf.append("[incoming ");
            buf.append(this.requestState);
            if (this.incoming != null) {
                buf.append(" ");
                buf.append(this.incoming.getRequest().getRequestLine());
            }
            buf.append("; outgoing ");
            buf.append(this.responseState);
            if (this.outgoing != null) {
                buf.append(" ");
                buf.append(this.outgoing.getResponse().getStatusLine());
            }
            buf.append("]");
            return buf.toString();
        }

    }

    class HttpAsyncExchangeImpl implements HttpAsyncExchange {

        private final AtomicBoolean completed = new AtomicBoolean();
        private final HttpRequest request;
        private final HttpResponse response;
        private final State state;
        private final NHttpServerConnection conn;
        private final HttpContext context;

        public HttpAsyncExchangeImpl(
                final HttpRequest request,
                final HttpResponse response,
                final State state,
                final NHttpServerConnection conn,
                final HttpContext context) {
            super();
            this.request = request;
            this.response = response;
            this.state = state;
            this.conn = conn;
            this.context = context;
        }

        @Override
        public HttpRequest getRequest() {
            return this.request;
        }

        @Override
        public HttpResponse getResponse() {
            return this.response;
        }

        @Override
        public void setCallback(final Cancellable cancellable) {
            if (this.completed.get()) {
                handleAlreadySubmittedResponse(cancellable, context);
            } else if (this.state.isTerminated() && cancellable != null) {
                cancellable.cancel();
            } else {
                this.state.setCancellable(cancellable);
            }
        }

        @Override
        public void submitResponse(final HttpAsyncResponseProducer responseProducer) {
            Args.notNull(responseProducer, "Response producer");
            if (this.completed.getAndSet(true)) {
                handleAlreadySubmittedResponse(responseProducer, context);
            } else if (!this.state.isTerminated()) {
                final HttpResponse response = responseProducer.generateResponse();
                final Outgoing outgoing = new Outgoing(
                        this.request, response, responseProducer, this.context);

                synchronized (this.state) {
                    this.state.setOutgoing(outgoing);
                    this.state.setCancellable(null);
                    this.conn.requestOutput();
                }

            } else {
                try {
                    responseProducer.close();
                } catch (final IOException ex) {
                    log(ex);
                }
            }
        }

        @Override
        public void submitResponse() {
            submitResponse(new BasicAsyncResponseProducer(this.response));
        }

        @Override
        public boolean isCompleted() {
            return this.completed.get();
        }

        @Override
        public void setTimeout(final int timeout) {
            this.conn.setSocketTimeout(timeout);
        }

        @Override
        public int getTimeout() {
            return this.conn.getSocketTimeout();
        }

    }

    
Adaptor class to transition from HttpAsyncRequestHandlerResolver to HttpAsyncRequestHandlerMapper.
Deprecated:
Do not use./**
     * Adaptor class to transition from HttpAsyncRequestHandlerResolver to HttpAsyncRequestHandlerMapper.
     *
     * @deprecated Do not use.
     */
    @Deprecated
    private static class HttpAsyncRequestHandlerResolverAdapter implements HttpAsyncRequestHandlerMapper {

        private final HttpAsyncRequestHandlerResolver resolver;

        public HttpAsyncRequestHandlerResolverAdapter(final HttpAsyncRequestHandlerResolver resolver) {
            this.resolver = resolver;
        }

        @Override
        public HttpAsyncRequestHandler<?> lookup(final HttpRequest request) {
            return resolver.lookup(request.getRequestLine().getUri());
        }

    }

    
Gets the HttpResponseFactory for this service.
Returns:
 the HttpResponseFactory for this service.
Since:
4.4.8/**
     * Gets the HttpResponseFactory for this service.
     *
     * @return  the HttpResponseFactory for this service.
     * @since 4.4.8
     */
    public HttpResponseFactory getResponseFactory() {
      return responseFactory;
    }

    
Gets the HttpProcessor for this service.
Returns:
the HttpProcessor for this service.
Since:
4.4.9/**
     * Gets the HttpProcessor for this service.
     *
     * @return the HttpProcessor for this service.
     * @since 4.4.9
     */
    public HttpProcessor getHttpProcessor() {
        return httpProcessor;
    }

    
Gets the ConnectionReuseStrategy for this service.
Returns:
the ConnectionReuseStrategy for this service.
Since:
4.4.9/**
     * Gets the ConnectionReuseStrategy for this service.
     *
     * @return the ConnectionReuseStrategy for this service.
     * @since 4.4.9
     */
    public ConnectionReuseStrategy getConnectionStrategy() {
        return connectionStrategy;
    }

    
Gets the HttpAsyncRequestHandlerMapper for this service.
Returns:
the HttpAsyncRequestHandlerMapper for this service.
Since:
4.4.9/**
     * Gets the HttpAsyncRequestHandlerMapper for this service.
     *
     * @return the HttpAsyncRequestHandlerMapper for this service.
     * @since 4.4.9
     */
    public HttpAsyncRequestHandlerMapper getHandlerMapper() {
        return handlerMapper;
    }

    
Gets the HttpAsyncExpectationVerifier for this service.
Returns:
the HttpAsyncExpectationVerifier for this service.
Since:
4.4.9/**
     * Gets the HttpAsyncExpectationVerifier for this service.
     *
     * @return the HttpAsyncExpectationVerifier for this service.
     * @since 4.4.9
     */
    public HttpAsyncExpectationVerifier getExpectationVerifier() {
        return expectationVerifier;
    }

    
Gets the ExceptionLogger for this service.
Returns:
the ExceptionLogger for this service.
Since:
4.4.9/**
     * Gets the ExceptionLogger for this service.
     *
     * @return the ExceptionLogger for this service.
     * @since 4.4.9
     */
    public ExceptionLogger getExceptionLogger() {
        return exceptionLogger;
    }

}