A critique of XML-RPC

John Cowan cowan at locke.ccil.org
Sun Feb 7 03:42:46 GMT 1999

I have read the XML-RPC specification
at http://www.scripting.com/frontier5/xml/code/rpc.html with great
interest.  I have the following issues with it:

1) There is no support for internationalization, despite the
support present in XML.  Since the MIME type is text/xml
(as opposed to application/xml), the character encoding is
US-ASCII unless overridden.  No mention is made of support for
character references like † (DOUBLE DAGGER).

I would suggest supporting either "text/xml; charset='utf-8'".
In addition, the references to "ASCII" in the spec should be changed.

2) There is no support for integers longer than 32 bits.

I suggest allowing <int> values to be arbitrarily large, reserving
the <i4> tag for 32-bit signed values.  This would be an upward
compatible extension for senders; receivers would have to check
whether <int> data was in fact within the 32-bit signed range
if backward compatibility is desired.

3) Floats are fairly useless because no rules exist for setting limits.

I suggest that no receiver be allowed to reject a value which can be
represented in 32-bit IEEE floats: between 1e-149 and 1e104, positive
or negative, or zero.

4) The statement that "A string can be used to encode binary data"
cannot be true, because arbitrary binary data cannot appear in XML
documents: there is no way to represent bytes of value 0-8, 11-12, or
14-31.  This is only a documentation consideration, as the base64
element does allow the representation of arbitrary binary data.

5) The very limited fault struct means that more complex exceptions
such as Java, Python, or C++ support must be flattened into strings
for return to the client, even though XML-RPC has ways of encoding more
complex objects.

I suggest allowing a struct within a fault object.

John Cowan					cowan at ccil.org
		e'osai ko sarji la lojban.

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