IPP> OPS - Proposal to go back to precluding 'out-of-band' values with values

IPP> OPS - Proposal to go back to precluding 'out-of-band' values with values

IPP> OPS - Proposal to go back to precluding 'out-of-band' values with values

Hastings, Tom N hastings at cp10.es.xerox.com
Tue Mar 21 20:24:22 EST 2000


After hearing the problems with existing parsers on extending IPP to allow
new out-of-band values to have a non-zero value, it appears prudent to
abandon such an extension.  Please send comments to the mailing list.  We
will also discuss, tomorrow, Wednesday, 3/22, on the IPP telecon.

Instead, lets replace the proposed 'any-value' out-of-band value which had
an attribute syntax value with a simpler 'custom' out-of-band value which
MUST have a zero length.  The 'custom' out-of-band value (as with the
'any-value') is used in a Get-Printer-Supported-Values response for as one
of the values of a requested "xxx-supported" attribute to indicate that the
System Administrator can set custom values using the
"Set-Printer-Attributes" operation.


Here is the suggested updates to the "Job and Printer Set Operations"
document:

15.1	Changes to the March 8, 2000 version to make the March 21, 2000
version
The following changes have been made to the March 8, 2000 version to make
the March 21, 2000 version as a result of the IPP WG telecons and mailing
list discussion:
1.	Changed the name of the 'any-value' out-of-band value to 'custom'.
Removed the idea of encoding the attribute syntax that the 'custom'
out-of-band value goes with.  Instead, the spec for the attribute defines
whether or not the 'custom' out-of-band value can be used.
2.	Clarified that the 'custom' out-of-band value can be used in
combination with other values of an "xxx-supported" Printer attribute.
3.	Clarified that an implementation is not prevented from supporting
some 'name' attribute values for "xxx-supported" out-of-the-box, if desired.
But these values would be returned in a Get-Printer-Supported-Values
response, such like keywords are. 
  



8.3	'custom' out-of-band attribute value
The 'custom' out-of-band attribute value MAY be used as one of the values of
an "xxx-supported" Printer attribute to indicate that the client can supply
custom values in a request.  The client MUST supply any such values in the
particular attribute syntax explicitly defined for that attribute. 
See section 4.3 in this document for an example definition of the usage of
the 'custom' out-of-band attribute value in any "xxx-supported" attribute
returned in a Get-Printer-Supported-Values response.

8.3.1	Encoding of the 'custom' out-of-band attribute value
The encoding of the 'custom' out-of-band attribute value is 0x17 (see
[ipp-pro]).  The value-length MUST be 0 and the value empty.  


1.1	Get-Printer-Supported-Values Operation
This OPTIONAL operation allows a client to request the values that the
Printer allows in the Set-Printer-Attributes operation for "xxx-supported"
attributes.  If the Printer supports the Set-Printer-Attributes operation
AND some of its "xxx-supported" Printer attributes are settable, then the
Printer MUST also support this operation.  This operation has identical
request/response attributes to the Get-Printer-Attributes operation in
IPP/1.1 [ipp-mod].  The operation also behaves identically to the
Get-Printer-Attributes operation in IPP/1.1 [ipp-mod] with the following
exceptions: 
1.	The Get-Printer-Supported-Values operation supports only
"xxx-supported" attributes.
2.	The Get-Printer-Attributes operation returns the current value of
specified attributes while the Get-Printer-Supported-Values operation
returns values that permit a client to determine what values of
"xxx-supported" attributes the Printer supports in the
Set-Printer-Attributes operation. 
3.	If an implementation does not support setting an attribute that is
requested, it MUST NOT return that attribute in the Printer Attributes Group
of the Get-Printer-Supported-Values response.  Furthermore, in such a case,
as in the Get-Printer-Attributes response, the Unsupported Attributes Group
of the response NEED NOT contain the "requested-attributes" operation
attribute with any supplied values (attribute keywords) that were requested
by the client but are not supported or are not settable by the IPP Printer.
4.	The Get-Printer-Supported-Values operation does not return any
values for any "xxx-supported" attributes that were configured by the System
Administrator using the Set-Printer-Attributes operation.  Instead, if the
Set-Printer-Attributes operation allows the System Administrator to
customize the Printer's "xxx-supported" attribute by adding arbitrary values
of a specified attribute syntax, then the Get-Printer-Supported-Values
operation MUST return the 'custom' out-of-band attribute value (see section
8.3) as one of the values of the "xxx-supported" attribute.  In other words,
the 'custom' out-of-band attribute value indicates that the Printer
implementation supports clients setting arbitrary values for that
"xxx-supported" attribute as long as the value is of the attribute syntax
defined for that attribute.
For example, if the Get-Printer-Supported-Values operation returns several
keywords as the value of the "media-supported" attribute, then the
Set-Printer-Attributes operation MUST accept any of these keywords as values
for the "media-supported" attribute.  If the Get-Printer-Supported-Values
operation returns a 'custom' out-of-band attribute value as one of the
values of the "media-supported" attribute, then the Set-Printer-Attributes
operation MUST accept any value whose attribute syntax is 'name' as values
for the "media-supported" attribute. 
The Get-Printer-Supported-Values MAY return the 'custom' out-of-band
attribute value for any IPP/1.1 or extension Job Template attribute if the
implementation supports allowing the System Administrator to add values to
the "xxx-supported" attribute using the Set-Printer-Attributes operation.
In this case, the Printer MUST accept any value of the correct attribute
syntax in a Set-Printer-Attributes operation that is setting that attribute.
For "xxx-supported" attributes that are defined with a choice of attribute
syntaxes, such as 'keyword | name', it is the 'name' attribute syntax that
the System Administrator can use to add new values, not the 'keyword'
attribute syntax.  For IPP/1.1 this requirement includes the following Job
Template attributes:
		media-supported
		job-hold-until-supported
		job-sheets-supported
For "xxx-supported" attributes that are defined to have only a single
attribute syntax, the 'custom' out-of-band value indicates that the Printer
will accept any value of that attribute syntax in a Set-Printer-Attributes
request for that "xxx-supported" attribute. 
If the 'custom' out-of-band attribute value is not one of the values of an
"xxx-supported" attribute returned in a Get-Printer-Supported-Values
response, then the Printer MUST NOT allow the Set-Printer-Attributes
operation for that attribute to contain a value that is not one of the
explicit values returned in a Get-Printer-Supported-Values response.
See Appendix B for a full list of values returned by this operation.

Send any comments to the mailing list.
Thanks,
Tom




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