[Search] [txt|pdf|bibtex] [Tracker] [WG] [Email] [Nits]

Versions: 00 01                                                         
Network Working Group                                         R. Earhart
Internet Draft: ACAP-TYPE-EXT                            Carnegie Mellon
Document: draft-ietf-acap-type-ext-00.txt                     April 1997
Expire in six months


                          ACAP TYPE Extension

Status of this Memo

  This document is an Internet-Draft.  Internet-Drafts are working
  documents of the Internet Engineering Task Force (IETF), its areas,
  and its working groups.  Note that other groups may also distribute
  working documents as Internet-Drafts.

  Internet-Drafts are draft documents valid for a maximum of six months.
  and may be updated, replaced, or obsoleted by other documents at any
  time.  It is not appropriate to use Internet-Drafts as reference
  material or to cite them other than as "work in progress".

  To learn the current status of any Internet-Draft, please check the
  1id-abstracts.txt listing contained in the Internet-Drafts Shadow
  Directories on ftp.is.co.za (Africa), ftp.nordu.net (Europe),
  munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
  ftp.isi.edu (US West Coast).

  This document suggests a proposed protocol for the Internet community,
  and requests discussion and suggestions for improvements.
  Distribution of this draft is unlimited.

  The protocol discussed in this document is experimental and subject to
  change.  Persons planning on either implementing or using this
  protocol are STRONGLY URGED to get in touch with the author before
  embarking on such a project.


1.   Abstract

  The Application Configuration Access Protocol [ACAP] defines rough
  typing information in the form of an attribute naming convention.
  This extension to ACAP allows a MIME content-type/subtype with
  parameters to be associated with a given piece of data, providing
  knowledgeable clients with useful information in a way which maintains
  compatability with innocent clients and servers.


2.   Conventions Used in this Document




Earhart                                                         [Page 1]


Internet DRAFT            ACAP TYPE Extension             April 23, 1997


  In examples, "C:" and "S:" indicate lines sent by the client and
  server respectively.

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  document are to be interpreted as described in RFC 2119.


3.   Specification

  The TYPE extension may be used with any ACAP server which returns
  "TYPE" as one of the supported capabilities in the initial untagged
  ACAP response.

  Servers that support the TYPE extension define a new item of metadata
  on attributes, called "type".  This metadata is Read-Write, is
  protected by the same ACL that protects the rest of the attribute, and
  contains the MIME content-type/subtype of the "value" metadata
  associated with the attribute, along with any associated parameters.

  The content-type of all data stored in attributes whose name does not
  end in ".bin" MUST be "text", and the charset parameter (if specified)
  MUST be "utf8" or a subset of utf8.

  Changing the "type" metadata of an attribute in an entry MUST also
  update the entry's "modtime" attribute.

  "text/plain" is a valid type, and means exactly what it does in MIME
  -- "text/plain; charset=us-ascii"; utf8 is only implied on attributes
  that do not end in ".bin" in the absence of the type extension (when
  no type is available, and the client must assume that any
  syntactically valid utf8 value may be present).


3.1. Client Issues

  A client MAY request the "type" metadata from any server which
  supports the TYPE extension.  This SHOULD NOT be taken as
  authoritative; the associated "value" metadata might not in fact be
  syntactically legal for the given type.  Nevertheless, the type MAY be
  used as a hint to indicate how the data should be treated or
  displayed.

  A client MAY STORE into the "type" metadata of an attribute to
  indicate the type of the associated "value" metadata.  The type stored
  MUST be a legal MIME type, the "value" metadata MUST be a legal value
  for that type.




Earhart                                                         [Page 2]


Internet DRAFT            ACAP TYPE Extension             April 23, 1997


  If a server does not implement the TYPE extension, clients MAY assume
  that the type of the value associated with a given attribute is
  "text/plain; charset=utf8" if the attribute name does not end with
  ".bin"; otherwise, a client MAY assume that the type is
  "application/octet-stream".


3.2. Server Issues

  Servers recieving a STORE command for a "type" metadata MUST ensure
  that the type is a legally formatted MIME type; if it is not, servers
  MUST return a tagged BAD response.

  Servers MUST also ensure that the content-type stored for an attribute
  whose name does not end with ".bin" is "text", and that the charset
  parameter is either not specified or specified as "utf8"; if either of
  these conditions is not met, the server MUST return a tagged BAD
  response.

  Servers MAY parse the "value" metadata and ensure that it conforms to
  the specified type; if it does not, servers SHOULD return a tagged NO
  response.

  Servers MUST NOT reject STOREs to "type" metadata merely because they
  lack knowledge of the specified type.

  If a server recieves a request to STORE into the "value" metadata of
  an attribute without an accompanying value for the "type" metadata,
  the server MUST behave as though the "type" metadata were being set to
  "text/plain; charset=utf8" if the attribute name does not end with
  ".bin"; otherwise, the server MUST behave as though the type were
  being set to "application/octet-stream".

  Note that this implies that the server MUST NOT reject a STORE into a
  value that would be a legal store if this extension were not in place
  -- a STORE without a supplied type MUST cause the type to change to
  the most general type available given the restrictions imposed by the
  base protocol on the types of data that a given attribute may assume.

  Storing a NIL into a "type" metadata MUST be treated as storing
  "text/plain; charset=utf8" if the attribute does not end in ".bin", or
  "application/octet-stream" if it does.

  The server MAY change the charset specified in a "type" metadata
  element to a more specific charset, as specified by [MIME-IMB].  For
  instance, when the value consists solely of us-ascii characters, the
  server MAY report the charset as being us-ascii (or just omit the
  charset parameter altogether, as us-ascii is the default charset for



Earhart                                                         [Page 3]


Internet DRAFT            ACAP TYPE Extension             April 23, 1997


  the "text/plain" type), instead of the more general utf8.


4.   Examples

  Example:  C: A001 Store ("/user/rob/people/kelly"
               "people.name" "Joe"
               "people.description" "<bold>richtext</bold>"
               "people.description" ("type") "text/richtext"
               "people.icon.bin" {1024+}
               <icon data> "people.icon.bin" ("type") "image/png")
            S: A001 OK "Store completed"

            (where <icon data> stands for the 1024 bytes of data that
            make up the image/png object being stored).


5.   Formal Syntax

  The following syntax specification uses the same notation as is used
  in [ACAP].  It describes the format of the data that may be stored as
  "type" metadata.

  metadata-type ::=  type "/" subtype *(";" SPACE parameter)
            ;; type, subtype, and parameter as defined in [MIME-IMB]
            ;; free insertion of linear-white-space is not permitted.


6.   References

  [RFC 2119] Bradner, "Key words for use in RFCs to Indicate Requirement
  Levels", RFC 2119.

  [ACAP] Myers, J., and Newman, C., "Application Configuration Access
  Protocol (ACAP)", Work in Progress of the IETF ACAP WG, draft-ietf-
  acap-spec-??.txt.  Check Internet Drafts listing for latest version.

  [MIME-IMB] Freed, N., and Borenstein, N., "Multipurpose Internet Mail
  Extensions (MIME) Part One: Format of Internet Message Bodies", RFC
  2045.

  [UTF-8] Yergeau, F., "UTF-8, a transformation format of Unicode and
  ISO 10646", RFC 2044.


7.   Security Considerations

  Clients SHOULD NOT automatically launch potentially unsafe helper



Earhart                                                         [Page 4]


Internet DRAFT            ACAP TYPE Extension             April 23, 1997


  applications to view data.


8.   Author's Address

  Robert H. Earhart
  Carnegie Mellon
  5000 Forbes Ave.
  Pittsburgh PA, 15213-3890

  Email: earhart+@cmu.edu








































Earhart                                                         [Page 5]