src/main/csharp/Transport/ResponseCorrelator.cs

/*
 * 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.
 */

using System;
using System.Threading;
using System.Collections;

using Apache.NMS.Stomp.Commands;

namespace Apache.NMS.Stomp.Transport
{
	/// <summary>
	/// A Transport that correlates asynchronous send/receive messages into single request/response.
	/// </summary>
    public class ResponseCorrelator : TransportFilter
    {
        private readonly IDictionary requestMap = Hashtable.Synchronized(new Hashtable());
        private int nextCommandId;
        private Exception error;

        public ResponseCorrelator(ITransport next) : base(next)
        {
        }

        protected override void OnException(ITransport sender, Exception command)
        {
            Dispose(command);
            base.OnException(sender, command);
        }

        internal int GetNextCommandId()
        {
            return Interlocked.Increment(ref nextCommandId);
        }

        public override void Oneway(Command command)
        {
            command.CommandId = GetNextCommandId();
            command.ResponseRequired = false;
            
            next.Oneway(command);
        }

        public override FutureResponse AsyncRequest(Command command)
        {
            int commandId = GetNextCommandId();

            command.CommandId = commandId;
            command.ResponseRequired = true;
            FutureResponse future = new FutureResponse();
            Exception priorError = null;
            lock(requestMap.SyncRoot) 
            {
                priorError = this.error;
                if(priorError == null) 
                {
                    requestMap[commandId] = future;
                }
            }
    
            if(priorError != null) 
            {
                BrokerError brError = new BrokerError();
                brError.Message = priorError.Message;
                ExceptionResponse response = new ExceptionResponse();
                response.Exception = brError;
                future.Response = response;
                throw priorError;
            }
            
            next.Oneway(command);

            return future;
        }

        public override Response Request(Command command, TimeSpan timeout)
        {
            FutureResponse future = AsyncRequest(command);
            future.ResponseTimeout = timeout;
            Response response = future.Response;

            if(response != null && response is ExceptionResponse)
            {
                ExceptionResponse er = response as ExceptionResponse;
                BrokerError brokerError = er.Exception;

                if(brokerError == null)
                {
                    throw new BrokerException();
                }
                else
                {
                    throw new BrokerException(brokerError);
                }
            }

            return response;
        }

        protected override void OnCommand(ITransport sender, Command command)
        {
            if(command is Response)
            {
                Response response = (Response) command;
                int correlationId = response.CorrelationId;
                FutureResponse future = (FutureResponse) requestMap[correlationId];

                if(future != null)
                {
                    requestMap.Remove(correlationId);
                    future.Response = response;

                    if(response is ExceptionResponse)
                    {
                        ExceptionResponse er = response as ExceptionResponse;
                        BrokerError brokerError = er.Exception;
                        BrokerException exception = new BrokerException(brokerError);
                        this.exceptionHandler(this, exception);
                    }
                }
                else
                {
                    if(Tracer.IsDebugEnabled)
                    {
                        Tracer.Debug("Unknown response ID: " + response.CommandId + " for response: " + response);
                    }
                }
            }
            else
            {
                this.commandHandler(sender, command);
            }
        }
        
        public override void Stop()
        {
            this.Dispose(new IOException("Stopped"));
            base.Stop();
        }
        
        private void Dispose(Exception error)
        {
            ArrayList requests = null;
            
            lock(requestMap.SyncRoot) 
            {
                if(this.error == null) 
                {
                    this.error = error;
                    requests = new ArrayList(requestMap.Values);
                    requestMap.Clear();
                }
            }
            
            if(requests != null)
            {
                foreach(FutureResponse future in requests)
                {
                    BrokerError brError = new BrokerError();
                    brError.Message = error.Message;
                    ExceptionResponse response = new ExceptionResponse();
                    response.Exception = brError;
                    future.Response = response;
                }
            }
        }

    }
}