As per Relevance of the word parameter, we have this rfc below:
Network Working Group N.
Request for Comments: 2017 Innosoft
Category: Standards Track K.
University of
A. Cargille, WG
October 1996
Definition of the
MIME External-Body Access-
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
1.
This memo defines a new access-type for message/external-body
parts for Uniform Resource Locators (URLs). URLs provide schemes
access external objects via a growing number of protocols,
HTTP, Gopher, and TELNET. An initial set of URL schemes are
in RFC 1738.
2.
The Multipurpose Internet Message Extensions (MIME) define a
whereby an object can contain a reference or pointer to some form
data rather than the actual data itself. This facility is embodied
the message/external-body media type defined in RFC 1521. Use
this facility is growing as a means of conserving bandwidth
large objects are sent to large mailing lists
Each message/external-body reference must specify a mechanism
the actual data can be retrieved. These mechanisms are called
types, and RFC 1521 defines an initial set of access types: "FTP",
"ANON-FTP", "TFTP", "LOCAL-FILE", and "MAIL-SERVER".
Freed, et. al. Standards Track [Page 1]
RFC 2017 URL Access-Type October 1996
Uniform Resource Locators, or URLs, also provide a means by
remote data can be retrieved automatically. Each URL string
with a scheme specification, which in turn specifies how
remaining string is to be used in conjunction with some protocol
retrieve the data. However, URL schemes exist for protocol
that have no corresponding MIME message/external-body access type
Registering an access type for URLs therefore
message/external-body with access to the retrieval mechanisms of
that are not currently available as access types. It also
access to any future mechanisms for which URL schemes are developed
This access type is only intended for use with URLs that
retreive something. Other URL mechansisms, e.g. mailto, may not
used in this context
3. Definition of the URL Access-
The URL access-type is defined as follows
(1) The name of the access-type is URL
(2) A new message/external-body content-type parameter
used to actually store the URL string. The name of
parameter is also "URL", and this parameter
mandatory for this access-type. The syntax and use
this parameter is specified in the next section
(3) The phantom body area of the message/external-body
not used and should be left blank
For example, the following message illustrates how the URL access
type is used
Content-type: message/external-body; access-type=URL
URL="http://www.foo.com/file
Content-type: text/
Content-Transfer-Encoding:
THIS IS NOT REALLY THE BODY
Freed, et. al. Standards Track [Page 2]
RFC 2017 URL Access-Type October 1996
3.1. Syntax and Use of the URL
Using the ANBF notations and definitions of RFC 822 and RFC 1521,
syntax of the URL parameter Is as follows
URL-parameter := <"> URL-word *(*LWSP-char URL-word) <">
URL-word :=
; Must not exceed 40 characters in
The syntax of an actual URL string is given in RFC 1738. URL
can be of any length and can contain arbitrary character content
This presents problems when URLs are embedded in MIME body
headers that are wrapped according to RFC 822 rules. For this
they are transformed into a URL-parameter for inclusion in
message/external-body content-type specification as follows
(1) A check is made to make sure that all occurrences
SPACE, CTLs, double quotes, backslashes, and 8-
characters in the URL string are already encoded
the URL encoding scheme specified in RFC 1738.
unencoded occurrences of these characters must
encoded. Note that the result of this operation
nothing more than a different representation of
original URL
(2) The resulting URL string is broken up into
of 40 characters or less
(3) Each substring is placed in a URL-parameter string as
URL-word, separated by one or more spaces. Note
the enclosing quotes are always required since all
contain one or more colons, and colons are
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
remaining material is the URL string
Freed, et. al. Standards Track [Page 3]
RFC 2017 URL Access-Type October 1996
The following example shows how a long URL is handled
Content-type: message/external-body; access-type=URL
URL="ftp://ftp.deepdirs.org/1/2/3/4/5/6/7/
8/9/10/11/12/13/14/15/16/17/18/20/21/
file.html
Content-type: text/
Content-Transfer-Encoding:
THIS IS NOT REALLY THE BODY
Some URLs may provide access to multiple versions of the same
in different formats. The HTTP URL mechanism has this capability,
example. However, applications may not expect to receive
whose type doesn't agree with that expressed in
message/external-body, and may in fact have already made
choices based on this information
Due to these considerations, the following restriction is imposed
When URLs are used in the context of an access-type only
versions of an object whose content-type agrees with that
by the inner message/external-body header can be retrieved and used
4. Security
The security considerations of using URLs in the context of a
access-type are no different from the concerns that arise from
use in other contexts. The specific security
associated with each type of URL are discussed in the URL's
document
Note that the Content-MD5 field can be used in conjunction with
message/external-body access-type to provide an integrity check.
insures that the referenced object really is what the
originator intended it to be. This is not a signature service
should not be confused with one, but nevetheless is quite useful
many situations
5.
The authors are grateful for the feedback and review provided by
Beck and John Klensin
Freed, et. al. Standards Track [Page 4]
RFC 2017 URL Access-Type October 1996
6.
[RFC-822]
Crocker, D., "Standard for the Format of ARPA
Text Messages", STD 11, RFC 822, UDEL, August 1982.
[RFC-1521]
Borenstein, N. and N. Freed, "MIME (
Internet Mail Extensions): Mechanisms for Specifying
Describing the Format of Internet Message Bodies",
1521, Bellcore, Innosoft, September, 1993.
[RFC-1590]
Postel, J., "Media Type Registration Procedure",
1590, USC/Information Sciences Institute, March 1994.
[RFC-1738]
Berners-Lee, T., Masinter, L., and M. McCahill, "
Resource Locators (URL)", December 1994.
7. Authors'
Ned
Innosoft International, Inc
1050 East Garvey Avenue
West Covina, CA 91790
Phone: +1 818 919 3600
Fax: +1 818 919 3614
EMail: ned@innosoft.
Keith
Computer Science Dept
University of
107 Ayres
Knoxville, TN 37996-1301
EMail: moore@cs.utk.
Freed, et. al. Standards Track [Page 5]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
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