I've written about COM binary arrays before in a previous post. The issue is that when you make a COM call to retrieve a binary result from a COM object the result gets returned as byte[*] type rather than byte[].
To demonstrate imagine you have a simple COM client that returns a binary result as a SafeArray of bytes. The following dumbed down example is a FoxPro method in COM published component where an object is returned that contains a ByteResult property that holds binary data:
************************************************************************
* SendBinaryFile
****************************************
FUNCTION SendBinaryFile(lcPath)
LOCAL lvBinary, lcBinary, loResult as ServiceResult
TRY
*** Grab the file from disk into a string
lcBinary = FILETOSTR(lcPath)
*** Turn the string to binary - over COM this turns into a SAFEARRAY
lvBinary = CREATEBINARY(lcBinary) && OR CAST(lcBinary as Q)
*** Return value is standard Service Response object
loResult = CREATEOBJECT("ServiceResult")
*** Attach the binary response to the ServiceResult
loResult.ByteResult = lvBinary
CATCH TO loException
loResult = this.ErrorToServiceResult(loException,20)
ENDTRY
RETURN loResult
ENDFUNC
The interesting part in relation to this post is the binary result which in this case is the content of a file. Internally FoxPro treats binary values as strings since it's stuck with ANSI codepages, so string can easily contain binary data. However FoxPro cannot return that string as a binary value over COM. In order to return a binary value the value needs to be explicitly converted using CREATEBINARY() or CAST(val as Q) which turns it into a SAFEARRAY when passed back over COM. This binary value is then assigned to a ServiceResult object that returns actual result value(s) back to the .NET Web Service which in turn publishes these values through the Service interface.
Read more: Rick Strahl blog
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