[DFDL-WG] String literal syntax for hexBinary ?? - Re: String literals - various usage patterns thereof

[Steve Hanson]

Mike

This is where the XPath constructors come into play.

<element name="myHexBin" type="xs:hexBinary" dfdl:inputValueCalc="{ 
xs:hexBinary(...) }"/>

These (plus the special fn:dateTime() constructor that DFDL adds) allow 
the correct types to be created.
 
Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848



From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     Steve Hanson/UK/IBM at IBMGB
Cc:     dfdl-wg at ogf.org
Date:   18/04/2012 17:37
Subject:        String literal syntax for hexBinary ?? - Re: String 
literals - various usage patterns thereof



What is the DFDL string literal syntax for a hexBinary type value?

E.g.,  I want a hex binary whose value is the 4 bytes described by this 
hex: DE AD BE EF.

<element name="myHexBin" type="xs:hexBinary" dfdl:inputValueCalc="{ ... 
}"/>

So, what can one syntactically put, for literal constant values, in the 
input value calculation expression? 

Note that this is legal pure (non-DFDL) XSD (I think)

<element name="aHexBin" type="xs:hexBinary" fixed="DeadBeef"/>

That is, the fixed/default are allowed and one specifies these values as 
just strings of hex digits. Notice no special escaping or anything. You 
just use a string that just so happens to contain hex digits.

I think there are three possibilites
(a) we allow "DEADBEEF" i.e., because the type of the expression is 
hexBinary, a string is cast to hexBinary by interpreting it as hex 
nibbles. 
(b) we require a special kind of string literal - a bytes-only string 
literal, so for example: "%#rDE;%#rAD;%#rBE;%#rEF;" is the way you create 
4 bytes. If you just put characters, then that's a processing error - like 
a cast failure. Only raw-bytes allowed.
(c) Anything you return from the expression is converted to a hexBinary by 
unparsing it to bytes (using current properties), then using the bytes as 
the hexBinary data. So you could have an expression that returns a double, 
and that would create 8 bytes if representation="binary".  In this case 
the decimal number 3735928559 (hex 0xdeadbeef) as a binary bigEndian int 
would produce the 4 bytes I want.










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