RFCs in HTML Format

RFC 1873

              Message/External-Body Content-ID Access Type

1. Introduction

   Consider a MIME multipart entity several of whose body parts contain
   the same data (body) but different parameters or Content-* headers.
   Representing those body parts without duplicating the data in each
   one promotes efficient use of resources (bandwidth and storage
   space).  To achieve these benefits an access-type is defined that
   permits one message part to refer to another one in the same message.

Levinson & Clark              Experimental                      [Page 1]

RFC 1873 Access Type Content-ID December 1995 2. The Content-ID Access Type 2.1 Registration Information MIME access-type name: content-id Required parameters: none Optional parameters: none Published specification: this document Person & email address to contact for further information: Ed Levinson <ELevinson@accurate.com> Additional requirements: The content-id header of the access-type=content-id MIME entity must match (be identical to) exactly one content-id in the same message, excluding other access-type=content-id entities. Thus, the content-id access type can only occur within a multipart message and can refer to another body part anywhere in the same message. A MIME User Agent (MUA) constructs the resultant MIME body part as described below. We call the access-type=content-id MIME entity the referring body part and the MIME body part to which it refers, the one with the matching content-id, the referenced body part. The MIME entity that results from content-id access type consists of: (a) the referenced body part's content-type header, (b) the referring body part's headers except its content-type header, (c) any headers in the referenced body part not in the referring one, (d) the line separating the headers from the body, and (e) the referenced body part's body. Levinson & Clark Experimental [Page 2]
RFC 1873 Access Type Content-ID December 1995 2.2 Example Usage The following example shows a message that consists of two identical images. MIME-Version: 1.0 Content-Type: Multipart/Mixed; boundary=tiger-lily --tiger-lily Content-Type: image/jpeg Content-ID: <950323.1552@XIson.com> AAAcdb... --tiger-lily Content-type: Message/External-Body; access-type=content-id Content-ID: <950323.1552@XIson.com> Content-Description: This body part is duplicated by reference --tiger-lily-- The equivalent MIME entity for the second body part is: --tiger-lily Content-Type: image/jpeg Content-ID: <950323.1552@XIson.com> Content-Description: This body part is duplicated by reference AAAcdb... --tiger-lily 3. Security Considerations The content-id access-type does not impact the security of messages or systems. The referenced MIME entity may have security implications. Levinson & Clark Experimental [Page 3]
RFC 1873 Access Type Content-ID December 1995 4. References [822] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, August 1982. [SGML] ISO 8879:1988, Information processing -- Text and office systems -- Standard Generalized Markup Language (SGML). [MIME] Borenstein, N., and N. Freed, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, Bellcore, Innosoft, September 1993.

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