Multiple Flat File Schemas Disassembler

The problem with Flat File Disassembler is that doesn't allow multiple Document Schemas as XML Disassembler does.

In the BizTalk SDK, there is a sample pipeline component that allows this feature (see the project inside \Microsoft BizTalk Server 2006\SDK\Samples\Pipelines\SchemaResolverComponent\SchemaResolverFlatFileDasm), but this component only recognizes different documents if them have a Tag Identifier in the first two characters.

My problem was a bit different. The difference between documents is in a concrete position:

DOCUMENT DATA MESSAGE TYPE 65 DOCUMENT DETAIL

The info about wich is the flat file schema is inside the message (in previous sample, was 65 the identifier).

I have modified the SDK sample Pipeline Component to select the correct schema with the info inside the different messages.

First of all, I added two new properties: StartPosition and ReadLength. StartPosition indicates where the identifier characters starts. ReadLength is the identifier's length.

private int startPosition = 0;
private int readLength = 0;

public int StartPosition
{
   get
   {
      return startPosition;
   }
   set
   {
      startPosition = value;
   }
}

public int ReadLength
{
   get
   {
      return readLength;
   }
   set
   {
      readLength = value;
   }
}

Second step is to implement the IPersistPropertyBag, to save and load this properties:

public void Load(IPropertyBag propertyBag, int errorLog)
{
   object property = null;

   propertyBag.Read("StartPosition", out property, errorLog);
   if (property != null)
      StartPosition = (int)property;

   propertyBag.Read("ReadLength", out property, errorLog);
   if (property != null)
      ReadLength = (int)property;
}

public void Save(IPropertyBag propertyBag, bool clearDirty, bool saveAllProperties)
{
   object ptrVar = StartPosition;
   propertyBag.Write("StartPosition", ref ptrVar);
   ptrVar = ReadLength;
   propertyBag.Write("ReadLength", ref ptrVar);
}

Third and last step is modify the Probe method, that reads the message stream, at the StartPosition position ReadLength characters:

public bool Probe(IPipelineContext pContext, IBaseMessage pInMsg)
{
   if (null == pContext)
      throw new ArgumentNullException("pContext");

   if (null == pInMsg)
      throw new ArgumentNullException("pInMsg");
                
   if (null == pInMsg.BodyPart || null == pInMsg.BodyPart.GetOriginalDataStream())
      return false;

   ReadOnlySeekableStream stream = new ReadOnlySeekableStream(pInMsg.BodyPart.GetOriginalDataStream());
   Stream sourceStream = pInMsg.BodyPart.GetOriginalDataStream();

   if (!sourceStream.CanSeek)
   {
      ReadOnlySeekableStream seekableStream = new ReadOnlySeekableStream(sourceStream);

      pInMsg.BodyPart.Data = seekableStream;

      sourceStream = pInMsg.BodyPart.Data;
   }

   long position = sourceStream.Position;

   char[] identifier = new char[ReadLength];
   try
   {
      StreamReader reader = new StreamReader(sourceStream);
      reader.BaseStream.Position = StartPosition;
      if (reader.Read(identifier, 0, identifier.Length) < identifier.Length)
         return false;

   }
   finally
   {
      sourceStream.Position = position;
   }

   string messageType = GetMessageType(new string(identifier));

   if (null == messageType)
      return false;

   IDocumentSpec documentSpec = pContext.GetDocumentSpecByType(messageType);

   pInMsg.Context.Write(DOCUMENT_SPEC_NAME_PROPERTY_NAME, XML_NORM_NAMESPACE_URI, documentSpec.DocSpecStrongName);

   return disassembler.Probe(pContext, pInMsg);
}

At last, GetMessageType method in SDK sample, hard-coded the schemas DocumentSpec. We can modify this method to retrieve this information from a config file or SSO as config store.