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]
