W3C home > Mailing lists > Public > www-dom@w3.org > January to March 2002

DOMInputSource.inputStream in L3 Load/Save problematic (at least for COM)

From: Arnold, Curt <Curt.Arnold@hyprotech.com>
Date: Thu, 14 Feb 2002 10:43:52 -0700
Message-ID: <70E215722F6AD511820A000103D141D40AA7B8@thor.aeathtl.com>
To: "'www-dom@w3.org'" <www-dom@w3.org>
The DOMInputSource.byteStream attribute is defined as returning a binding
dependent type that represents a byte of streams (aka a DOMInputStream not
DOMInputSource as appears in the interface definition).

In the Java binding this would be fairly straight forward as:

public interface DOMInputSource {
     java.io.InputStream getByteStream();
...
} 

If you trying to define a COM interface, you would be tempted to try:

[propget]
HRESULT byteStream([retval,out] IStream** byteStream);

IStream is not an Automation-compatible type, so using it as a return type
makes the entire interface unusable from scripting languages and Visual
Basic.

As a fall back, you might try to either return the IStream as a variant
which may keep the interface usable, however automation clients can't do
anything with return value from byteStream.  Otherwise, you now have to
define an automation compatible wrapper object for IStream.

However, all of that is unnecessary since the calling code has no need to
interact with the DOMInputSource.  It is just there so the eventual call to
parse() can get at the byte stream.

The whole thing can be avoided if DOMInputSource only provides the
additional information necessary to interpret the stream and DOMInputSource
and a binding specific stream interface are both implemented on the object.

In Java this would be something like:

public interface DOMInputSource {
	/*   return null if encoding declaration in stream should be used.
           Otherwise ignore encoding declaration in stream.    
           Typically null for streams from URL sources, "UTF-16" for streams
               from String's.
      */
	String getEncoding();
	/*   URI used to interpret relative URI.  May have no connection
			to the location used to create the InputStream  */
	String getBaseURI();
}

And in an implementation something like:

public class MyURLSource implements InputStream, DOMInputSource {
}

In COM, the object would implement both IStream and DOMInputSource.

This design would allow non-script implementations to implement their own
custom classes for arbitrary input streams.  Script implementations should
have access to standard source implementations through create functions on
DocumentLS such as:

public interface DocumentLS {
   DOMInputSource createURLSource(String url, String baseURI);
   DOMInputSource createStringSource(String source, String baseURI);
}

createPublicIDSource() and createSystemIDSource() would not seem to be
necessary since the resolution will either result in a URL and which can be
passed to createURLSource() or can be captured in a String and can be passed
to createStringSource().  Non script languages could also use a custom
object implementing both DOMInputSource and the platform appropriate stream
type.
Received on Thursday, 14 February 2002 12:43:31 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Friday, 22 June 2012 06:13:55 GMT