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Using XML CDATA nodes to send files via a Web Service

, 26 Jul 2005
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Using XML CDATA nodes to send files via a web service.

Introduction

There was a need to have a web service send a file. The documented way to do this is through WSE (Web Service Extension), which is an add-on to the .NET Framework to do things with web services like attachments. Using two CodeProject articles, I added zipping the file and encoding the file using Base64. Then I placed the encoded file into a CDATA node in an XML document.

Background

As I looked into sending a file via a web service, I was not pleased with the amount of work that had to be done to attach a file using WSE. So I started to look for other options. One of my co-workers suggested using a CDATA node in an XML document. As I looked into the CDATA node, it seemed like it might be a good fit. The CDATA node is for storing blob data in an XML file. It is marked so that it ignores what is between the CDATA nodes. I decided to zip the file to reduce the size of the XML file I would be sending. The problem is that zipping a file produces some characters that cause problems with the XML file. So, that leads us to base64 encoding. I found two code project articles to help me with zipping files with Sharpziplib and base64 encoding that would fit into what I needed.

The code

After having some discussion with my co-workers, we decided on an XML structure that looks like this:

<FILES>
  <FILE FileName="file.txt"><CDATA></CDATA></File>
  <FILE FileName="file2.txt"><CDATA></CDATA></File>
</FILES>

where we could add as many file nodes in the XML document as we wanted. Here is the code to create that XML doc:

public static XmlDocument GetFileXml(String[] Files)
{
  //We are returning an XML Doc
  XmlDocument tmpXmlDoc = new XmlDocument();

  //Create the root node...
  tmpXmlDoc.LoadXml("<FILES></FILES>");

  //Loop through the WorkItemFiles 
  //array and create the file nodes
  for (Int32 i=0;i<=Files.Length-1;i++)
  {
    //The File node
    XmlElement tmpFile = 
          tmpXmlDoc.CreateElement("File");
    //Add the filename attribute to it...
    XmlAttribute tmpA = 
          tmpXmlDoc.CreateAttribute("FileName");
    //Find the last \ to pull off the filename.
    tmpA.Value = 
        Files[i].Substring(Files[i].LastIndexOf(@"\")+1);
    tmpFile.Attributes.Append(tmpA);

    //Read in the File
    Byte[] myCompressed;

    //Compress the file
    myCompressed = 
        CompressionHelper.CompressFile(Files[i]);

        //Next encode the compressed stream 
        //so that we don't blow the 
        //CData node in the XML
    Char[] myEncoded;
    Base64Encoder myBE;
    myBE = new Base64Encoder(myCompressed);
    myEncoded = myBE.GetEncoded();

    //A StringBuilder is the fastest way 
    //to get a string from a byte array
    StringBuilder myStr = new StringBuilder();
    myStr.Append(myEncoded);

    //create CData child appened 
    //to the file node...
    tmpFile.AppendChild(tmpXmlDoc.CreateCDataSection(
                                       myStr.ToString()));

    //Add the file node to the xml doc...
    tmpXmlDoc.DocumentElement.AppendChild(tmpFile);
  } // for

  return tmpXmlDoc;
}

Next, we call the web service to get the XML document. Then, we parse through the XML file and extract and save the documents from the CDATA nodes.

public static void GetFiles(XmlNode inXml, String FilePath)
{
  XmlNodeList myFile;

  myFile = inXml.SelectNodes("/File");

  //This Loops through the File nodes
  for (Int32 j=0;j<=myFile.Count-1;j++)
  {
    //The first child is the CDATA node
    XmlNode myCData = (XmlNode)(myFile.Item(j)).FirstChild;

    //Grab the Filename attribute
    String FileName = 
      ((XmlNode)(myFile.Item(j))).Attributes.Item(0).InnerText;

    //This is the actual data that is in the CDATA
    Char[] theFile;
    theFile = new Char[myCData.InnerText.Length];

    for (Int32 i=0;i<=myCData.InnerText.Length-1;i++)
    {
        theFile[i] = myCData.InnerText[i];

    }//for i
    //Delete the file if it exists
    if (File.Exists(FilePath+FileName))
    {
        File.Delete(FilePath+FileName);
    }

    //next we need to switch from base64 
    //encoding to our zip compressed
    Byte[] myDecoder;
    Base64Decoder myBD = new Base64Decoder(theFile);
    myDecoder = myBD.GetDecoded();

    //Finally we decompress the file and 
    //save it where it is supose to go
    CompressionHelper.DecompressFile(myDecoder,
                                  FilePath+FileName);


  } //for j
}

Conclusion

I would like to thank my co-worker Steve Rowe for his help and guidance in coming to this solution. I would also like to thank Uwe Keim for his shareziplib article and wchvic for his base64 article. Hopefully, others will find this article helpful in their solutions.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

kubben
Web Developer
United States United States
I started my programmer career over 18 years ago doing COBOL and SAS on a MVS mainframe. It didn't take long for me to move into windows programming. I started my windows programming in Delphi (Pascal) with a Microsoft SQL server back end. I started working with vb.net when the beta 2 came out in 2001. After spending most of my programming life as a windows programmer I started to check out asp.net in 2004. I achieved my MCSD.net in April 2005. I have done a lot of MS SQL database stuff. I have a lot of experience with Window Service and Web services as well. I spent three years as a consultant programing in C#. I really enjoyed it and found the switch between vb.net and C# to be mostly syntax. In my current position I am programming in both vb.net and C#. Lately I have been using VS2012 and writing a Windows 8 app. You can search for the app it is called ConvertIT.
 
On a personal note I am a born again Christian, if anyone has any questions about what it means to have a right relationship with God or if you have questions about who Jesus Christ is, send me an e-mail. ben.kubicek[at]netzero[dot]com You need to replace the [at] with @ and [dot] with . for the email to work. My relationship with God gives purpose and meaning to my life.

Comments and Discussions

 
Questionreference.cs Pinmemberimpeesa_016-Jan-09 16:30 
AnswerRe: reference.cs Pinmemberkubben7-Jan-09 2:32 
Generalfedex web service with axapta Pinmemberadsfdsdsfds14-Nov-08 9:18 
GeneralRe: fedex web service with axapta Pinmemberkubben14-Nov-08 9:21 
QuestionHow diffirence PinmemberHoanglkKHTN17-Jul-06 22:46 
AnswerRe: How diffirence Pinmemberkubben18-Jul-06 2:02 
hoanglk,
 
Thanks for you post. For smaller sized things you could send just a string. The application I wrote this for has really large files. 100MB or more at times. So it was helpful to compress the file down and send it. Also if you have a file and what you want on the other side is a file, then it probably makes more sense to send a file.
 
Just so you know the latest release of the web service extensions did a really nice job of making it easier to send files with a web service. The only down side is you have to install the web service extentions. It isn't a bit deal to install, it is just that normally it is not installed.
 
Thanks,
Ben
GeneralFile progressbar Pinmemberlogikonline6-Aug-05 2:14 
GeneralRe: File progressbar Pinmemberkubben6-Aug-05 2:43 
Generalw3c, WS-* Pinmemberian mariano3-Aug-05 3:04 
GeneralRe: w3c, WS-* Pinmemberkubben3-Aug-05 8:21 
GeneralWSE/DIME solution Pinmember..::Hubert::..2-Aug-05 21:45 
GeneralRe: WSE/DIME solution Pinmemberkubben3-Aug-05 8:17 
GeneralRe: WSE/DIME solution Pinmember..::Hubert::..3-Aug-05 21:02 
GeneralRe: WSE/DIME solution Pinmemberkubben4-Aug-05 3:32 
GeneralAttention!!!!! Pinmemberilnar2-Aug-05 19:29 
GeneralRe: Attention!!!!! Pinmemberkubben3-Aug-05 8:19 

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