Stefano Ricciardi » WCF

File Transfer with WCF: Part III

stefanoricciardi — Thu, 02 Sep 2010 12:08:55 +0000

This is the third post on a small series about transferring large files with WCF using streaming :

I am closing this series of posts by sharing a skeleton for the client side handling of the uploaded and downloaded files. Please note that the following are excerpt from a larger context and so will not compile in your environment as is: they are only intended to give a rough idea of how the files can be handled.

Download

 private void IssueDownloadRequest(string localFile, string serviceUrl, FileDownloadMessage request)
{
    this.service = this.proxy.OpenProxy(serviceUrl);

    try
    {
        using (FileDownloadReturnMessage response = this.service.DownloadFile(request))
        {
            if (response != null && response.FileByteStream != null)
            {
                SaveFile(response.FileByteStream, localFile);
            }
        }

        this.proxy.CloseProxy(this.service);
    }
    catch (Exception e)
    {
        throw new FileTransferProxyException("Error while downloading the file", e);
    }
    finally
    {
        // we expect the stream returned from the server to be closed by the
        // server itself so nothing to be done with it here. Just abort
        // the proxy if needed.
        this.proxy.AbortProxyIfNeeded(this.service);
    }
}

private static void SaveFile(Stream saveFile, string localFilePath)
{
    const int bufferSize = 65536; // 64K

    using (FileStream outfile = new FileStream(localFilePath, FileMode.Create))
    {
        byte[] buffer = new byte[bufferSize];
        int bytesRead = saveFile.Read(buffer, 0, bufferSize);

        while (bytesRead > 0)
        {
            outfile.Write(buffer, 0, bytesRead);
            bytesRead = saveFile.Read(buffer, 0, bufferSize);
        }
    }
}

Upload

public void UploadFile(string localFileName, string serviceUrl, FileTypeEnum fileType)
{
    this.service = this.proxy.OpenProxy(serviceUrl);
    try
    {
        using (Stream fileStream = new FileStream(localFileName, FileMode.Open, FileAccess.Read))
        {
            var request = new FileUploadMessage();
            string remoteFileName = null;
            if (fileType == FileTypeEnum.Generic)
            {
                // we are using the service as a "FTP on WCF"
                // give the remote file the same name as the local one
                remoteFileName = Path.GetFileName(localFileName);
            }

            var fileMetadata = new FileMetaData(localFileName, remoteFileName, fileType);
            request.MetaData = fileMetadata;
            request.FileByteStream = fileStream;

            this.service.UploadFile(request);
            this.proxy.CloseProxy(this.service);
        }
    }
    catch (IOException)
    {
        throw new FileTransferProxyException("Unable to open the file to upload");
    }
    catch (Exception e)
    {
        throw new FileTransferProxyException(e.Message);
    }
    finally
    {
        this.proxy.AbortProxyIfNeeded(this.service);
    }
 }

Making WCF Serializer Work with Circular References

stefanoricciardi — Thu, 22 Oct 2009 12:07:43 +0000

The Problem of Circular References

Recently I had to model a tree-like structure using a variation of the GoF composite design pattern and to pass this class to a WCF service for further processing.

The class has circular reference as described by the following drawing:

Therefore off I went to naively create my DataContract along the following lines:

[DataContract(Namespace = "http://schemas.acme.it/2009/10"]
public class Node
{
	[DataMember(Name="Children", Order=2)]
    private IList children;

    [DataMember(Name="Id", Order=0)]
    public string Id { get; set; }

    [DataMember(Name="Parent", Order=1)]
    public Node Parent { get; set; }

    public Node()
    {
        children = new List()
    }

    public void AddChild(Node node)
    {
        this.children.Add(node);
        node.Parent = this;
    }

    public IList Children
    {
        get
        {
            IList result = new List(this.children);
            foreach (Node child in this.children)
            {
                foreach (Node innerChild in child.Children)
                {
                result.Add(innerChild);
                }
            }

            return result;
        }
    }
}

Unfortunately at run time I was greeted by the following exception:
Object graph for type 'System.Collections.Generic.List`1[[Node ...]]' contains cycles and cannot be serialized if reference tracking is disabled..

The Solution

Reading around I realized that up until some time ago you had to implement your own DataContractSerializer (see for example this post by Sowmy Srinivasan).

Luckily, it turns out that with NET 3.5 SP1 everything is much simpler: you just have to use the IsReference parameter in the DataContract attribute, as follows:

[DataContract(Namespace = "http://schemas.acme.it/2009/10", IsReference=true)]
public class Node
{
    // everything same as in the example above.
}

The Catch

For some reason, if you turn on the IsReference attribute, then you cannot set the IsRequired attribute to true on any DataMember of the DataContract. The reason is somehow explained here.

Technorati Tags: Programming, C#, WCF, SOA

File Transfer with WCF: Part II

stefanoricciardi — Fri, 02 Oct 2009 12:23:22 +0000

This is the second post on a small series about transferring large files with WCF using streaming :

A few readers of my previous post on File Transfer with WCF have asked to share the implementation of the UploadFile and DownloadFile methods.

While I can’t share the complete implemention of the service for obvious Intellectual Property reasons, I will outline the basic steps involved in implementing the service. Please refer to my previous post for the details on the DataContracts and OperationContracts involved here.

NOTE: I have extracted these portions from the actual code. I cannot verify this to work as-is, but it should give you a head-start to complete your own service. You should also add your own error checking, and any pre or post-download and/or pre or post-upload processing as required by the business.

Download

public FileDownloadReturnMessage DownloadFile(FileDownloadMessage request)
{
    // parameters validation omitted for clarity
    string localFileName = request.MetaData.LocalFileName;

    try
    {
        string basePath = ConfigurationSettings.AppSettings["FileTransferPath"];
        string serverFileName = Path.Combine(basePath, request.MetaData.RemoteFileName);

        Stream fs = new FileStream(serverFileName, FileMode.Open);

        return new FileDownloadReturnMessage(new FileMetaData(localFileName, serverFileName), fs);
    }
    catch (IOException e)
    {
        throw new FaultException(e);
    }
}

Upload

public void UploadFile(FileUploadMessage request)
{
    // parameters validation omitted for clarity
    try
    {
        string basePath = ConfigurationSettings.AppSettings["FileTransferPath"];
        string serverFileName = Path.Combine(basePath, request.MetaData.RemoteFileName);

        using (FileStream outfile = new FileStream(serverFileName, FileMode.Create))
        {
            const int bufferSize = 65536; // 64K

            Byte[] buffer = new Byte[bufferSize];
            int bytesRead = request.FileByteStream.Read(buffer, 0, bufferSize);

            while (bytesRead > 0)
            {
                outfile.Write(buffer, 0, bytesRead);
                bytesRead = request.FileByteStream.Read(buffer, 0, bufferSize);
            }
        }
    }
    catch (IOException e)
    {
        throw new FaultException(e);
    }
}

Technorati Tags: Programming, C#, WCF, SOA

File Transfer with WCF

stefanoricciardi — Fri, 28 Aug 2009 12:43:14 +0000

This is the first post on a small series about transferring large files with WCF using streaming :

WCF streaming is helpful in all those cases when you need to move a lot of data between the client and the service in a way that keeps memory consumption under control (see Large Data and Streaming on MSDN for more details if you are not familiar with the topic).

Streaming does impose some restrictions. Among them is that your operations can only have one input and/or output parameter and they can only be only one of the following:

a Stream
a Message
a class implementing IXmlSerializable

I wanted to expose a very simple service to upload and download files through WCF. And because I wanted to be able to pass both the file content as a stream and at least the file name, I could not just use a Stream but had to resort to using Messages: the headers would convey the file information (such as the file type) and the body the content of the file itself through a stream.

I therefore defined the service as follows:

    [ServiceContract(Namespace = "http://schemas.acme.it/2009/04")]
    public interface IFileTransferService
    {
        [OperationContract(IsOneWay = true)]
        void UploadFile(FileUploadMessage request);
        [OperationContract(IsOneWay = false)]
        FileDownloadReturnMessage DownloadFile(FileDownloadMessage request);
    }

    [MessageContract]
    public class FileUploadMessage
    {
        [MessageHeader(MustUnderstand = true)]
        public FileMetaData Metadata;
        [MessageBodyMember(Order = 1)]
        public Stream FileByteStream;
    }

    [MessageContract]
    public class FileDownloadMessage
    {
        [MessageHeader(MustUnderstand = true)]
        public FileMetaData FileMetaData;
    }

   [MessageContract]
    public class FileDownloadReturnMessage
    {
        public FileDownloadReturnMessage(FileMetaData metaData, Stream stream)
        {
            this.DownloadedFileMetadata = metaData;
            this.FileByteStream = stream;
        }

        [MessageHeader(MustUnderstand = true)]
        public FileMetaData DownloadedFileMetadata;
        [MessageBodyMember(Order = 1)]
        public Stream FileByteStream;
    }

   [DataContract(Namespace = "http://schemas.acme.it/2009/04")]
    public class FileMetaData
    {
        public FileMetaData(
            string localFileName,
            string remoteFileName)
        {
            this.LocalFileName = localFileName;
            this.RemoteFileName = remoteFileName;
            this.FileType = FileTypeEnum.Generic;
        }

        public FileMetaData(
            string localFileName,
            string remoteFileName,
            FileTypeEnum fileType)
        {
            this.LocalFileName = localFileName;
            this.RemoteFileName = remoteFileName;
            this.FileType = fileType;
        }

        [DataMember(Name="FileType", Order=0, IsRequired=true)]
        public FileTypeEnum FileType;
        [DataMember(Name="localFilename", Order=1, IsRequired=false)]
        public string LocalFileName;
        [DataMember(Name = "remoteFilename", Order = 2, IsRequired = false)]
        public string RemoteFileName;
    }

    public class FileTransferService : IFileTransferService
    {
        public void UploadFile(FileUploadMessage request)
        {
             // implementation here
        }

        public FileDownloadReturnMessage DownloadFile(FileDownloadMessage request)
        {
             // implementation here
        }
    }

I am omitting the details of the implementation, they are pretty straightforward (if you are interested, I will gladly share it. UPDATE: I have put the basic scheleton of the server implementation is a separate post).

And this is how the service was configured on the server side within the web.config.

This is the base of the plumbing that it’s needed to create the service.

While I was developing it, I have lost quite some time for an error which was really obscure to decipher:
Server Error in ‘/’ Application. Operation ‘UploadFile’ in contract ‘IFileTransferService’ uses a MessageContract that has SOAP headers. SOAP headers are not supported by the None MessageVersion.

Googling and binging around I found almost no relevant information on the topic, so I was pretty on my own.

I thought the problem was in the HTTP binding that I was using (maybe it was not compatible with SOAP headers?). Unfortunately the HTTP binding did not have any way to specify a different MessageVersion. So I ended up creating a custom binding, like the following, but that didn’t help either:

I made several other attempts with no luck. I then tried self hosting the service and that did work. Then I was certain that it was something with the web hosting. Tried IIS6, IIS7, etc… Same exception all the time.

To make a long story short, at the end, while reducing my web.config to the bare bones, I found the culprit: it was the name of the service in the service configuration.

Instead of writing:

I had written by mistake:

Talk about meaningful error messages!

See more at File Transfer with WCF II

Technorati Tags: Programming, C#, WCF, SOA