RFC 2017 (rfc2017) - Page 3 of 5

Definition of the URL MIME External-Body Access-Type

RFC 2017                    URL Access-Type                 October 1996


3.1.  Syntax and Use of the URL parameter

   Using the ANBF notations and definitions of RFC 822 and RFC 1521, the
   syntax of the URL parameter Is as follows:

     URL-parameter :=  URL-word *(*LWSP-char URL-word) 

     URL-word := token
                 ; Must not exceed 40 characters in length

   The syntax of an actual URL string is given in RFC 1738.  URL strings
   can be of any length and can contain arbitrary character content.
   This presents problems when URLs are embedded in MIME body part
   headers that are wrapped according to RFC 822 rules. For this reason
   they are transformed into a URL-parameter for inclusion in a
   message/external-body content-type specification as follows:

    (1)   A check is made to make sure that all occurrences of
          SPACE, CTLs, double quotes, backslashes, and 8-bit
          characters in the URL string are already encoded using
          the URL encoding scheme specified in RFC 1738. Any
          unencoded occurrences of these characters must be
          encoded.  Note that the result of this operation is
          nothing more than a different representation of the
          original URL.

    (2)   The resulting URL string is broken up into substrings
          of 40 characters or less.

    (3)   Each substring is placed in a URL-parameter string as a
          URL-word, separated by one or more spaces.  Note that
          the enclosing quotes are always required since all URLs
          contain one or more colons, and colons are tspecial
          characters [RFC 1521].

   Extraction of the URL string from the URL-parameter is even simpler:
   The enclosing quotes and any linear whitespace are removed and the
   remaining material is the URL string.













Freed, et. al.              Standards Track