[DFDL-WG] String literal syntax for hexBinary ?? - Re: String literals - various usage patterns thereof
Tim Kimber
KIMBERT at uk.ibm.com
Thu Apr 19 04:35:08 EDT 2012
I'm pretty sure that the rules are:
- DFDL expressions must not *contain* DFDL String Literals. They must be
valid XPath 2.0 expressions except that the list of allowable function
names includes the DFDL extension functions.
- A DFDL expression is sometimes allowed to *return* a DFDL String
Literal. In this case, the returned value is an xs:string that conforms to
the DFDL String Literal syntax. But that does not apply to your example
because the dfdl:inputValueCalc must return a value ( an XML value ) that
is valid for the type of the element.
I think that corresponds to your answer a) ; 'DEADBEEF' is a valid
xs:hexBinary lexical value.
regards,
Tim Kimber, Common Transformation Team,
Hursley, UK
Internet: kimbert at uk.ibm.com
Tel. 01962-816742
Internal tel. 246742
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Steve Hanson/UK/IBM at IBMGB
Cc: dfdl-wg at ogf.org
Date: 19/04/2012 07:42
Subject: [DFDL-WG] String literal syntax for hexBinary ?? - Re:
String literals - various usage patterns thereof
Sent by: dfdl-wg-bounces at ogf.org
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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