DTD removal and string replacement

I want to strip a DTD declaration in an XML instance in the Receive pipeline component and add some schema declarations to the root node –

From –

[color=indigo:e6d3c3f283][code:1:e6d3c3f283]<!DOCTYPE ONIXmessage SYSTEM \"http://www.editeur.org/onix/2.0/short/onix-international.dtd\">
<ONIXmessage>

To –

<ONIXmessage xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns=”http://CompanyName.ProjectName.Schemas\">[/code:1:e6d3c3f283][/color:e6d3c3f283]
I could do it like this

[size=9:e6d3c3f283][color=darkblue:e6d3c3f283][code:1:e6d3c3f283]public IBaseMessage Execute(IPipelineContext pc, IBaseMessage inmsg)

{

IBaseMessagePart bodyPart = inmsg.BodyPart;

if (bodyPart!=null)

{

Stream originalStrm = bodyPart.Data;

originalStrm = bodyPart.GetOriginalDataStream();

byte[] buffer = new byte[originalStrm.Length];

originalStrm.Read(buffer,0,Convert.ToInt32(originalStrm.Length));

string xmlString = Encoding.UTF8.GetString(buffer);

// Do replace here

Stream strm = new MemoryStream(ConvertToBytes(xmlString));

bodyPart.Data = strm;

pc.ResourceTracker.AddResource( strm );

}

return inmsg;

}[/code:1:e6d3c3f283][/color:e6d3c3f283][/size:e6d3c3f283]
But I dont want to read the full message into a string as the message could be in 100s of MBs.

The ideal would be either to do a replace on a stream (not possible in .NET in my knowledge) or read in the first 1000 chars in which the DTD surely resides

[code:1:e6d3c3f283]string contents = originalStrm.Read(buffer,0, 1000); [color=olive]//the part I need to replace will be present in the first 1000 chars[/color].[/code:1:e6d3c3f283]

But then how to prepend this stream before the rest of the stream into the memorystream which gets assigned to the bodyPart.Data?

[color=darkblue:e6d3c3f283][code:1:e6d3c3f283]
object originalFileNameObj = inmsg.Context.Read(\"ReceivedFileName\",@\"http://schemas.microsoft.com/BizTalk/2003/file-properties\");
string strReceivedFileName;
if (originalFileNameObj != null)
{
strReceivedFileName = Path.GetFileName(originalFileNameObj.ToString());
StreamWriter sw = File.CreateText(strReceivedFileName);
sw.Write(contents);
sw.Close();
}[/code:1:e6d3c3f283]
[/color:e6d3c3f283]
Cant concatenate streams in .NET either (to my knowledge).

Only dirty solution left is to resave the file with a StreamWriter

[color=darkblue:e6d3c3f283][code:1:e6d3c3f283]object originalFileNameObj = inmsg.Context.Read(\"ReceivedFileName\",@\"http://schemas.microsoft.com/BizTalk/2003/file-properties\");
string strReceivedFileName;
if (originalFileNameObj != null)
{
strReceivedFileName = Path.GetFileName(originalFileNameObj.ToString());
StreamWriter sw = File.CreateText(strReceivedFileName);
sw.Write(contents);
sw.Close();[/code:1:e6d3c3f283]}[/color:e6d3c3f283]
The problem with this is – I have to read in the full message into a string and I may not have write permissions on the FTP directory where this is received.

Also – I cannot use a Streaming XPath reader because of this reason
http://www.thescripts.com/forum/thread176011.html
(somehow on hitting an ONIXMessage DTD, the .NET XmlReader breaks)

Anyone have any better ideas than I do?

thanks in advance!