protected override void PreInvoke(IExecutionContext executionContext)
        {
            var request = executionContext.RequestContext.OriginalRequest;
            var config = executionContext.RequestContext.ClientConfig;

            var copySnapshotRequest = request as CopySnapshotRequest;
            if (copySnapshotRequest != null)
            {
                if (string.IsNullOrEmpty(copySnapshotRequest.DestinationRegion))
                {
                    copySnapshotRequest.DestinationRegion = AWS4Signer.DetermineSigningRegion(config, "ec2", alternateEndpoint: null);
                }
                if (string.IsNullOrEmpty(copySnapshotRequest.SourceRegion))
                {
                    throw new AmazonEC2Exception("SourceRegion is required to perform the copy snapshot.");
                }

                var endpoint = RegionEndpoint.GetBySystemName(copySnapshotRequest.SourceRegion);
                if(endpoint == null)
                {
                    throw new AmazonEC2Exception(string.Format(CultureInfo.InvariantCulture, "No endpoint for region {0}.", copySnapshotRequest.SourceRegion));
                }

                // Make sure the presigned URL is currently null so we don't attempt to generate
                // a presigned URL with a presigned URL.
                copySnapshotRequest.PresignedUrl = null;

                // Marshall this request but switch to the source region and make it a GET request.
                var marshaller = new CopySnapshotRequestMarshaller();
                var irequest = marshaller.Marshall(copySnapshotRequest);
                irequest.UseQueryString = true;
                irequest.HttpMethod = "GET";
                irequest.Parameters.Add("X-Amz-Expires", AWS4PreSignedUrlSigner.MaxAWS4PreSignedUrlExpiry.ToString(CultureInfo.InvariantCulture));
                irequest.Endpoint = new Uri("https://" +  endpoint.GetEndpointForService(config.RegionEndpointServiceName).Hostname);

                // Create presigned URL.
                var metrics = new RequestMetrics();
                var immutableCredentials = _credentials.GetCredentials();

                if (immutableCredentials.UseToken)
                {
                    irequest.Parameters["X-Amz-Security-Token"] = immutableCredentials.Token;
                }

                var signingResult = AWS4PreSignedUrlSigner.SignRequest(irequest,
                                                                       config,
                                                                       metrics,
                                                                       immutableCredentials.AccessKey,
                                                                       immutableCredentials.SecretKey,
                                                                       "ec2",
                                                                       copySnapshotRequest.SourceRegion);

                var authorization = "&" + signingResult.ForQueryParameters;                
                var url = AmazonServiceClient.ComposeUrl(irequest);

                copySnapshotRequest.PresignedUrl = url.AbsoluteUri + authorization;
            }
        }

        public void CopySnapshotMarshallTest()
        {
            var operation = service_model.FindOperation("CopySnapshot");

            var request = InstantiateClassGenerator.Execute<CopySnapshotRequest>();
            var marshaller = new CopySnapshotRequestMarshaller();
            var internalRequest = marshaller.Marshall(request);
            var validator = new AWSQueryValidator(internalRequest.Parameters, request, service_model, operation);
            validator.Validate();


            var payloadResponse = new XmlSampleGenerator(service_model, operation).Execute();
            var context = new XmlUnmarshallerContext(Utils.CreateStreamFromString(payloadResponse), false, null);
            var response = CopySnapshotResponseUnmarshaller.Instance.Unmarshall(context)
                as CopySnapshotResponse;   
            InstantiateClassGenerator.ValidateObjectFullyInstantiated(response);       
        }

        /// <summary>
        /// Initiates the asynchronous execution of the CopySnapshot operation.
        /// </summary>
        /// 
        /// <param name="request">Container for the necessary parameters to execute the CopySnapshot operation.</param>
        /// <param name="cancellationToken">
        ///     A cancellation token that can be used by other objects or threads to receive notice of cancellation.
        /// </param>
        /// <returns>The task object representing the asynchronous operation.</returns>
        public Task<CopySnapshotResponse> CopySnapshotAsync(CopySnapshotRequest request, System.Threading.CancellationToken cancellationToken = default(CancellationToken))
        {
            var marshaller = new CopySnapshotRequestMarshaller();
            var unmarshaller = CopySnapshotResponseUnmarshaller.Instance;

            return InvokeAsync<CopySnapshotRequest,CopySnapshotResponse>(request, marshaller, 
                unmarshaller, cancellationToken);
        }

        /// <summary>
        /// Copies a point-in-time snapshot of an EBS volume and stores it in Amazon S3. You can
        /// copy the snapshot within the same region or from one region to another. You can use
        /// the snapshot to create EBS volumes or Amazon Machine Images (AMIs). The snapshot is
        /// copied to the regional endpoint that you send the HTTP request to.
        /// 
        ///  
        /// <para>
        /// Copies of encrypted EBS snapshots remain encrypted. Copies of unencrypted snapshots
        /// remain unencrypted, unless the <code>Encrypted</code> flag is specified during the
        /// snapshot copy operation. By default, encrypted snapshot copies use the default AWS
        /// Key Management Service (KMS) master key; however, you can specify a non-default master
        /// key with the <code>KmsKeyId</code> parameter.
        /// </para>
        ///  
        /// <para>
        /// For more information, see <a href="http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-copy-snapshot.html">Copying
        /// an Amazon EBS Snapshot</a> in the <i>Amazon Elastic Compute Cloud User Guide</i>.
        /// </para>
        /// </summary>
        /// <param name="request">Container for the necessary parameters to execute the CopySnapshot service method.</param>
        /// 
        /// <returns>The response from the CopySnapshot service method, as returned by EC2.</returns>
        public CopySnapshotResponse CopySnapshot(CopySnapshotRequest request)
        {
            var marshaller = new CopySnapshotRequestMarshaller();
            var unmarshaller = CopySnapshotResponseUnmarshaller.Instance;

            return Invoke<CopySnapshotRequest,CopySnapshotResponse>(request, marshaller, unmarshaller);
        }

        /// <summary>
        /// Initiates the asynchronous execution of the CopySnapshot operation.
        /// </summary>
        /// 
        /// <param name="request">Container for the necessary parameters to execute the CopySnapshot operation on AmazonEC2Client.</param>
        /// <param name="callback">An AsyncCallback delegate that is invoked when the operation completes.</param>
        /// <param name="state">A user-defined state object that is passed to the callback procedure. Retrieve this object from within the callback
        ///          procedure using the AsyncState property.</param>
        /// 
        /// <returns>An IAsyncResult that can be used to poll or wait for results, or both; this value is also needed when invoking EndCopySnapshot
        ///         operation.</returns>
        public IAsyncResult BeginCopySnapshot(CopySnapshotRequest request, AsyncCallback callback, object state)
        {
            var marshaller = new CopySnapshotRequestMarshaller();
            var unmarshaller = CopySnapshotResponseUnmarshaller.Instance;

            return BeginInvoke<CopySnapshotRequest>(request, marshaller, unmarshaller,
                callback, state);
        }

 IAsyncResult invokeCopySnapshot(CopySnapshotRequest copySnapshotRequest, AsyncCallback callback, object state, bool synchronized)
 {
     IRequest irequest = new CopySnapshotRequestMarshaller().Marshall(copySnapshotRequest);
     var unmarshaller = CopySnapshotResponseUnmarshaller.GetInstance();
     AsyncResult result = new AsyncResult(irequest, callback, state, synchronized, signer, unmarshaller);
     Invoke(result);
     return result;
 }

        /// <summary>
        /// <para>Copies a point-in-time snapshot of an Amazon EBS volume and stores it in Amazon S3. You can copy the snapshot within the same region
        /// or from one region to another. You can use the snapshot to create Amazon EBS volumes or Amazon Machine Images (AMIs).</para> <para>For more
        /// information, see <a href="http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-copy-snapshot.html">Copying an Amazon EBS Snapshot</a> in
        /// the <i>Amazon Elastic Compute Cloud User Guide</i> .</para>
        /// </summary>
        /// 
        /// <param name="copySnapshotRequest">Container for the necessary parameters to execute the CopySnapshot service method on AmazonEC2.</param>
        /// 
        /// <returns>The response from the CopySnapshot service method, as returned by AmazonEC2.</returns>
        /// <param name="cancellationToken">
        ///     A cancellation token that can be used by other objects or threads to receive notice of cancellation.
        /// </param>
		public Task<CopySnapshotResponse> CopySnapshotAsync(CopySnapshotRequest copySnapshotRequest, CancellationToken cancellationToken = default(CancellationToken))
        {
            var marshaller = new CopySnapshotRequestMarshaller();
            var unmarshaller = CopySnapshotResponseUnmarshaller.GetInstance();
            return Invoke<IRequest, CopySnapshotRequest, CopySnapshotResponse>(copySnapshotRequest, marshaller, unmarshaller, signer, cancellationToken);
        }

        /// <summary>
        /// Initiates the asynchronous execution of the CopySnapshot operation.
        /// <seealso cref="Amazon.EC2.IAmazonEC2.CopySnapshot"/>
        /// </summary>
        /// 
        /// <param name="request">Container for the necessary parameters to execute the CopySnapshot operation.</param>
        /// <param name="cancellationToken">
        ///     A cancellation token that can be used by other objects or threads to receive notice of cancellation.
        /// </param>
        /// <returns>The task object representing the asynchronous operation.</returns>
		public async Task<CopySnapshotResponse> CopySnapshotAsync(CopySnapshotRequest request, CancellationToken cancellationToken = default(CancellationToken))
        {
            var marshaller = new CopySnapshotRequestMarshaller();
            var unmarshaller = CopySnapshotResponseUnmarshaller.GetInstance();
            var response = await Invoke<IRequest, CopySnapshotRequest, CopySnapshotResponse>(request, marshaller, unmarshaller, signer, cancellationToken)
                .ConfigureAwait(continueOnCapturedContext: false);
            return response;
        }

 IAsyncResult invokeCopySnapshot(CopySnapshotRequest copySnapshotRequest, AsyncCallback callback, object state, bool synchronized)
 {
     var marshaller = new CopySnapshotRequestMarshaller();
     var unmarshaller = CopySnapshotResponseUnmarshaller.GetInstance();
     var result = Invoke<IRequest, CopySnapshotRequest>(copySnapshotRequest, callback, state, synchronized, marshaller, unmarshaller, this.signer);
     return result;
 }