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The RabbitMQ Java client library allows Java applications to interface with RabbitMQ.

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// Copyright (c) 2007-Present Pivotal Software, Inc.  All rights reserved.
//
// This software, the RabbitMQ Java client library, is triple-licensed under the
// Mozilla Public License 1.1 ("MPL"), the GNU General Public License version 2
// ("GPL") and the Apache License version 2 ("ASL"). For the MPL, please see
// LICENSE-MPL-RabbitMQ. For the GPL, please see LICENSE-GPL2.  For the ASL,
// please see LICENSE-APACHE2.
//
// This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND,
// either express or implied. See the LICENSE file for specific language governing
// rights and limitations of this software.
//
// If you have any questions regarding licensing, please contact us at
// [email protected].


package com.rabbitmq.client;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.TimeoutException;
import java.util.function.Function;

import com.rabbitmq.client.impl.MethodArgumentReader;
import com.rabbitmq.client.impl.MethodArgumentWriter;
import com.rabbitmq.client.impl.ValueReader;
import com.rabbitmq.client.impl.ValueWriter;
import com.rabbitmq.utility.BlockingCell;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Convenience class which manages simple RPC-style communication.
 * The class is agnostic about the format of RPC arguments / return values.
 * It simply provides a mechanism for sending a message to an exchange with a given routing key,
 * and waiting for a response.
*/
public class RpcClient {

    private static final Logger LOGGER = LoggerFactory.getLogger(RpcClient.class);

    /** Channel we are communicating on */
    private final Channel _channel;
    /** Exchange to send requests to */
    private final String _exchange;
    /** Routing key to use for requests */
    private final String _routingKey;
    /** Queue where the server should put the reply */
    private final String _replyTo;
    /** timeout to use on call responses */
    private final int _timeout;
    /** NO_TIMEOUT value must match convention on {@link BlockingCell#uninterruptibleGet(int)} */
    protected final static int NO_TIMEOUT = -1;
    /** Whether to publish RPC requests with the mandatory flag or not. */
    private final boolean _useMandatory;

    public final static Function DEFAULT_REPLY_HANDLER = reply -> {
        if (reply instanceof ShutdownSignalException) {
            ShutdownSignalException sig = (ShutdownSignalException) reply;
            ShutdownSignalException wrapper =
                    new ShutdownSignalException(sig.isHardError(),
                            sig.isInitiatedByApplication(),
                            sig.getReason(),
                            sig.getReference());
            wrapper.initCause(sig);
            throw wrapper;
        } else if (reply instanceof UnroutableRpcRequestException) {
            throw (UnroutableRpcRequestException) reply;
        } else {
            return (Response) reply;
        }
    };

    private final Function _replyHandler;

    /** Map from request correlation ID to continuation BlockingCell */
    private final Map> _continuationMap = new HashMap>();
    /** Contains the most recently-used request correlation ID */
    private int _correlationId;

    /** Consumer attached to our reply queue */
    private DefaultConsumer _consumer;

    /**
     * Construct a {@link RpcClient} with the passed-in {@link RpcClientParams}.
     *
     * @param params
     * @throws IOException
     * @see RpcClientParams
     * @since 5.6.0
     */
    public RpcClient(RpcClientParams params) throws
            IOException {
        _channel = params.getChannel();
        _exchange = params.getExchange();
        _routingKey = params.getRoutingKey();
        _replyTo = params.getReplyTo();
        if (params.getTimeout() < NO_TIMEOUT) {
            throw new IllegalArgumentException("Timeout argument must be NO_TIMEOUT(-1) or non-negative.");
        }
        _timeout = params.getTimeout();
        _useMandatory = params.shouldUseMandatory();
        _replyHandler = params.getReplyHandler();
        _correlationId = 0;

        _consumer = setupConsumer();
        if (_useMandatory) {
            this._channel.addReturnListener(returnMessage -> {
                synchronized (_continuationMap) {
                    String replyId = returnMessage.getProperties().getCorrelationId();
                    BlockingCell blocker = _continuationMap.remove(replyId);
                    if (blocker == null) {
                        // Entry should have been removed if request timed out,
                        // log a warning nevertheless.
                        LOGGER.warn("No outstanding request for correlation ID {}", replyId);
                    } else {
                        blocker.set(new UnroutableRpcRequestException(returnMessage));
                    }
                }
            });
        }
    }

    /**
     * Construct a new RpcClient that will communicate on the given channel, sending
     * requests to the given exchange with the given routing key.
     *
     * Causes the creation of a temporary private autodelete queue. The name of this queue can be specified.
     * @param channel the channel to use for communication
     * @param exchange the exchange to connect to
     * @param routingKey the routing key
     * @param replyTo the queue where the server should put the reply
     * @param timeout milliseconds before timing out on wait for response
     * @throws IOException if an error is encountered
     * @deprecated use {@link RpcClient#RpcClient(RpcClientParams)} instead, will be removed in 6.0.0
     */
    @Deprecated
    public RpcClient(Channel channel, String exchange, String routingKey, String replyTo, int timeout) throws
            IOException {
        this(new RpcClientParams()
            .channel(channel).exchange(exchange).routingKey(routingKey)
            .replyTo(replyTo).timeout(timeout)
            .useMandatory(false)
        );
    }

    /**
     * Construct a new RpcClient that will communicate on the given channel, sending
     * requests to the given exchange with the given routing key.
     *
     * Causes the creation of a temporary private autodelete queue.
     * The name of the queue can be provided (only relevant for RabbitMQ servers
     * that do not support Direct Reply-to.
     *
     * Waits forever for responses (that is, no timeout).
     * @param channel the channel to use for communication
     * @param exchange the exchange to connect to
     * @param routingKey the routing key
     * @param replyTo the queue where the server should put the reply
     * @throws IOException if an error is encountered
     * @deprecated use {@link RpcClient#RpcClient(RpcClientParams)} instead, will be removed in 6.0.0
     */
    @Deprecated
    public RpcClient(Channel channel, String exchange, String routingKey, String replyTo) throws IOException {
        this(channel, exchange, routingKey, replyTo, NO_TIMEOUT);
    }

    /**
     * Construct a new RpcClient that will communicate on the given channel, sending
     * requests to the given exchange with the given routing key.
     *
     * Direct Reply-to will be used
     * for response propagation.
     *
     * Waits forever for responses (that is, no timeout).
     * @param channel the channel to use for communication
     * @param exchange the exchange to connect to
     * @param routingKey the routing key
     * @throws IOException if an error is encountered
     * @deprecated use {@link RpcClient#RpcClient(RpcClientParams)} instead, will be removed in 6.0.0
     */
    @Deprecated
    public RpcClient(Channel channel, String exchange, String routingKey) throws IOException {
        this(channel, exchange, routingKey, "amq.rabbitmq.reply-to", NO_TIMEOUT);
    }


    /**
     * 

* Construct a new RpcClient that will communicate on the given channel, sending * requests to the given exchange with the given routing key. *

* * Causes the creation of a temporary private autodelete queue. The name of this queue will be * "amq.rabbitmq.reply-to". * @param channel the channel to use for communication * @param exchange the exchange to connect to * @param routingKey the routing key * @param timeout milliseconds before timing out on wait for response * @throws IOException if an error is encountered * @deprecated use {@link RpcClient#RpcClient(RpcClientParams)} instead, will be removed in 6.0.0 */ @Deprecated public RpcClient(Channel channel, String exchange, String routingKey, int timeout) throws IOException { this(channel, exchange, routingKey, "amq.rabbitmq.reply-to", timeout); } /** * Private API - ensures the RpcClient is correctly open. * @throws IOException if an error is encountered */ public void checkConsumer() throws IOException { if (_consumer == null) { throw new EOFException("RpcClient is closed"); } } /** * Public API - cancels the consumer, thus deleting the temporary queue, and marks the RpcClient as closed. * @throws IOException if an error is encountered */ public void close() throws IOException { if (_consumer != null) { _channel.basicCancel(_consumer.getConsumerTag()); _consumer = null; } } /** * Registers a consumer on the reply queue. * @throws IOException if an error is encountered * @return the newly created and registered consumer */ protected DefaultConsumer setupConsumer() throws IOException { DefaultConsumer consumer = new DefaultConsumer(_channel) { @Override public void handleShutdownSignal(String consumerTag, ShutdownSignalException signal) { synchronized (_continuationMap) { for (Entry> entry : _continuationMap.entrySet()) { entry.getValue().set(signal); } _consumer = null; } } @Override public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException { synchronized (_continuationMap) { String replyId = properties.getCorrelationId(); BlockingCell blocker =_continuationMap.remove(replyId); if (blocker == null) { // Entry should have been removed if request timed out, // log a warning nevertheless. LOGGER.warn("No outstanding request for correlation ID {}", replyId); } else { blocker.set(new Response(consumerTag, envelope, properties, body)); } } } }; _channel.basicConsume(_replyTo, true, consumer); return consumer; } public void publish(AMQP.BasicProperties props, byte[] message) throws IOException { _channel.basicPublish(_exchange, _routingKey, _useMandatory, props, message); } public Response doCall(AMQP.BasicProperties props, byte[] message) throws IOException, TimeoutException { return doCall(props, message, _timeout); } public Response doCall(AMQP.BasicProperties props, byte[] message, int timeout) throws IOException, ShutdownSignalException, TimeoutException { checkConsumer(); BlockingCell k = new BlockingCell(); String replyId; synchronized (_continuationMap) { _correlationId++; replyId = "" + _correlationId; props = ((props==null) ? new AMQP.BasicProperties.Builder() : props.builder()) .correlationId(replyId).replyTo(_replyTo).build(); _continuationMap.put(replyId, k); } publish(props, message); Object reply; try { reply = k.uninterruptibleGet(timeout); } catch (TimeoutException ex) { // Avoid potential leak. This entry is no longer needed by caller. _continuationMap.remove(replyId); throw ex; } return _replyHandler.apply(reply); } public byte[] primitiveCall(AMQP.BasicProperties props, byte[] message) throws IOException, ShutdownSignalException, TimeoutException { return primitiveCall(props, message, _timeout); } public byte[] primitiveCall(AMQP.BasicProperties props, byte[] message, int timeout) throws IOException, ShutdownSignalException, TimeoutException { return doCall(props, message, timeout).getBody(); } /** * Perform a simple byte-array-based RPC roundtrip. * @param message the byte array request message to send * @return the byte array response received * @throws ShutdownSignalException if the connection dies during our wait * @throws IOException if an error is encountered * @throws TimeoutException if a response is not received within the configured timeout */ public byte[] primitiveCall(byte[] message) throws IOException, ShutdownSignalException, TimeoutException { return primitiveCall(null, message); } /** * Perform a simple byte-array-based RPC roundtrip * * Useful if you need to get at more than just the body of the message * * @param message the byte array request message to send * @return The response object is an envelope that contains all of the data provided to the `handleDelivery` consumer * @throws ShutdownSignalException if the connection dies during our wait * @throws IOException if an error is encountered * @throws TimeoutException if a response is not received within the configured timeout */ public Response responseCall(byte[] message) throws IOException, ShutdownSignalException, TimeoutException { return responseCall(message, _timeout); } /** * Perform a simple byte-array-based RPC roundtrip * * Useful if you need to get at more than just the body of the message * * @param message the byte array request message to send * @param timeout milliseconds before timing out on wait for response * @return The response object is an envelope that contains all of the data provided to the `handleDelivery` consumer * @throws ShutdownSignalException if the connection dies during our wait * @throws IOException if an error is encountered * @throws TimeoutException if a response is not received within the configured timeout */ public Response responseCall(byte[] message, int timeout) throws IOException, ShutdownSignalException, TimeoutException { return doCall(null, message, timeout); } /** * Perform a simple string-based RPC roundtrip. * @param message the string request message to send * @return the string response received * @throws ShutdownSignalException if the connection dies during our wait * @throws IOException if an error is encountered * @throws TimeoutException if a timeout occurs before the response is received */ @SuppressWarnings("unused") public String stringCall(String message) throws IOException, ShutdownSignalException, TimeoutException { byte[] request; try { request = message.getBytes(StringRpcServer.STRING_ENCODING); } catch (IOException _e) { request = message.getBytes(); } byte[] reply = primitiveCall(request); try { return new String(reply, StringRpcServer.STRING_ENCODING); } catch (IOException _e) { return new String(reply); } } /** * Perform an AMQP wire-protocol-table based RPC roundtrip

* * There are some restrictions on the values appearing in the table:
* they must be of type {@link String}, {@link LongString}, {@link Integer}, {@link java.math.BigDecimal}, {@link Date}, * or (recursively) a {@link Map} of the enclosing type. * * @param message the table to send * @return the table received * @throws ShutdownSignalException if the connection dies during our wait * @throws IOException if an error is encountered * @throws TimeoutException if a timeout occurs before a response is received */ public Map mapCall(Map message) throws IOException, ShutdownSignalException, TimeoutException { ByteArrayOutputStream buffer = new ByteArrayOutputStream(); MethodArgumentWriter writer = new MethodArgumentWriter(new ValueWriter(new DataOutputStream(buffer))); writer.writeTable(message); writer.flush(); byte[] reply = primitiveCall(buffer.toByteArray()); MethodArgumentReader reader = new MethodArgumentReader(new ValueReader(new DataInputStream(new ByteArrayInputStream(reply)))); return reader.readTable(); } /** * Perform an AMQP wire-protocol-table based RPC roundtrip, first * constructing the table from an array of alternating keys (in * even-numbered elements, starting at zero) and values (in * odd-numbered elements, starting at one)
* Restrictions on value arguments apply as in {@link RpcClient#mapCall(Map)}. * * @param keyValuePairs alternating {key, value, key, value, ...} data to send * @return the table received * @throws ShutdownSignalException if the connection dies during our wait * @throws IOException if an error is encountered * @throws TimeoutException if a timeout occurs before a response is received */ public Map mapCall(Object[] keyValuePairs) throws IOException, ShutdownSignalException, TimeoutException { Map message = new HashMap(); for (int i = 0; i < keyValuePairs.length; i += 2) { message.put((String) keyValuePairs[i], keyValuePairs[i + 1]); } return mapCall(message); } /** * Retrieve the channel. * @return the channel to which this client is connected */ public Channel getChannel() { return _channel; } /** * Retrieve the exchange. * @return the exchange to which this client is connected */ public String getExchange() { return _exchange; } /** * Retrieve the routing key. * @return the routing key for messages to this client */ public String getRoutingKey() { return _routingKey; } /** * Retrieve the continuation map. * @return the map of objects to blocking cells for this client */ public Map> getContinuationMap() { return _continuationMap; } /** * Retrieve the correlation id. * @return the most recently used correlation id */ public int getCorrelationId() { return _correlationId; } /** * Retrieve the consumer. * @return an interface to the client's consumer object */ public Consumer getConsumer() { return _consumer; } /** * The response object is an envelope that contains all of the data provided to the `handleDelivery` consumer */ public static class Response { protected String consumerTag; protected Envelope envelope; protected AMQP.BasicProperties properties; protected byte[] body; public Response() { } public Response( final String consumerTag, final Envelope envelope, final AMQP.BasicProperties properties, final byte[] body) { this.consumerTag = consumerTag; this.envelope = envelope; this.properties = properties; this.body = body; } public String getConsumerTag() { return consumerTag; } public Envelope getEnvelope() { return envelope; } public AMQP.BasicProperties getProperties() { return properties; } public byte[] getBody() { return body; } } }