Internet DRAFT - draft-ietf-acap-motd-dataset
draft-ietf-acap-motd-dataset
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Network Working Group Ryan Troll
Document: draft-ietf-acap-motd-dataset-00.txt Carnegie Mellon
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ACAP Message of the Day Dataset Class
<draft-ietf-acap-motd-dataset-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. 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 inappropriate to use Internet- Drafts as
reference material or to cite them other than as "work in progress."
To view the list Internet-Draft Shadow Directories, see
http://www.ietf.org/shadow.html.
Distribution of this memo is unlimited.
Abstract
The Application Configuration Access Protocol [ACAP] is designed to
support remote storage and access of common application option,
configuration and preference information. Once such piece of
information is the "Message of the Day" greeting, used by system
administrators to communicate important information to all users
when they begin to use a system. This document describes a common
format for storing MOTD information in ACAP, how site administrators
may configure their ACAP MOTD service to allow multiple groups
within the site to provide custom MOTD information, and how a client
should access and use this information.
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Table of Contents
Status of this Memo ............................................... 1
Abstract .......................................................... 1
1. Introduction .................................................. 3
1.1. Conventions Used in the Document ........................ 3
1.2. Terminology ............................................. 3
2. ACAP MOTD Dataset Prefix ...................................... 4
3. ACAP MOTD Hierarchy ........................................... 4
4. ACAP MOTD Attributes .......................................... 4
4.1. Basic Attributes ........................................ 4
4.2. Specific Attributes ..................................... 5
4.3. Common ABNF ............................................. 6
4.4. MOTD Entry Naming Scheme ................................ 6
5. Client MOTD Behaviour ......................................... 7
5.1. Advanced Client Behaviour ............................... 8
5.1.1. Example: Subscribe ................................ 8
5.1.2. Example: Unsubscribe .............................. 8
5.1.3. Example: Prune .................................... 9
6. Server Configuration .......................................... 9
7. Design Issues ................................................. 10
8. Security Considerations ....................................... 10
9. Acknowledgments ............................................... 10
10. Copyright .................................................... 10
11. References ................................................... 11
12. Author's Address ............................................. 11
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1. Introduction
Multi-user systems offer a small "Message of the Day" (MOTD)
greeting to all users that sign onto the system, informing them of
any changes made to the system, scheduled outages, etc. As systems
become more distributed, the ability to make announcements to all
users becomes substantially harder. Additionally, distributed
systems may now fall under the management of multiple administrative
domains, and each domain may wish to notify its users of upcoming
events.
The ACAP MOTD dataset class specifies a way to store small messages
in ACAP. The MOTD dataset structure also leverages ACAP's
inheritance capabilities to allow users to "subscribe" to MOTD
providers.
MOTD clients will allow users to view any existing MOTDs, mark MOTDs
as read, and notify users when new MOTD entries are posted.
Advanced MOTD clients will also allow users to subscribe or
unsubscribe from MOTD providers, as well as prune any old message
information. Administrative clients will create MOTDs.
1.1. Conventions Used in the Document
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 [KEYWORDS].
Dataset names will use the string "{group-name}" to indicate that
any group name may be used, and "{user-name}" to indicate that any
user name, may be used in that part of the name.
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
1.2. Terminology
Subscription
A user may wish to view MOTD information from a variety of
administrative sources. This is accomplished by creating sub-
datasets within the user's MOTD hierarchy (/motd/user/{user-
name}) with a specific name. This sub-dataset inherits entries
from the administrative MOTD repository.
MOTD Provider
A MOTD provider is an administrative organization that wishes to
provide MOTD information to clients. Each provider MUST have a
group dataset within the ACAP hierarchy, under
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/motd/group/{group-name}.
2. ACAP MOTD Dataset Prefix
Datasets whose names begin with "/motd" are assumed to contain MOTD
entries as defined in this document.
3. ACAP MOTD Hierarchy
MOTD entries will be stored by administrators in either the
/motd/site dataset, or the appropriate /motd/group/{group-name}
dataset. The dataset /motd/user/{user-name} will inherit entries
directly from /motd/site, giving all users access to the default,
site-wide MOTD entries.
Additionally, users will be able to create sub-datasets under
/motd/user/{user-name}, which will be configured to inherit from one
of the datasets under /motd/group. This sub-dataset indicates a
subscription to a MOTD provider.
4. ACAP MOTD Attributes
Attributes are specified using Augmented Backus-Naur Form [ABNF].
All attributes are single-valued.
The ABNF defines the content of the attribute values prior to their
encoding as an ACAP string. Clients MUST conform to the syntax when
generating these attributes, but MUST NOT assume that the attribute
values will conform to this syntax on access. Servers MUST NOT
enforce the syntax.
4.1. Basic Attributes
These attributes are defined in ACAP [ACAP] and have meaning in all
dataset classes. This section describes how they are used in a MOTD
dataset.
entry
The "entry" attribute is a unique string used to identify and
entry within the MOTD dataset. MOTD entries MUST follow the
entry naming scheme defined below.
subdataset
The "subdataset" attribute indicates there is another MOTD
dataset underneath the current dataset. This is used to specify
MOTD subscriptions and their locations. Entries that contain
this attribute are not actually messages, and MUST not be
displayed by a MOTD viewer client. However, the client MAY use
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this information to display what subscription a MOTD came from.
dataset.inherit
The "dataset.inherit" attribute specifies what dataset this
dataset inherits from. Inheritance is used in every MOTD
dataset under /motd/user. All base user MOTD datasets
(/motd/user/{user-name}) have this attribute set to
"/motd/site". Subscriptions have this attribute set to the path
of the subscribed to MOTD provider.
For more information on inheritance, consult [ACAP], section
5.1.
4.2. Specific Attributes
These attributes are specific to the MOTD dataset class.
motd.ExpirationDate
The "motd.ExpirationDate" attribute contains the date this MOTD
entry becomes invalid. This field is present only to aid MOTD
administrators, and MAY be ignored by clients when displaying
the MOTD. It is optional.
motd.ExpirationDate = motd-datetime
; specified in Common ABNF
motd.Title
The "motd.Title" attribute contains a short (less than 80
characters) title for the MOTD entry. All MOTD entries MUST
have the title attribute set when they are created. However,
clients MUST NOT assume that all MOTD entries have this field,
as purged entries MAY leave blank entries in the hierarchy.
This is described in detail below.
motd.Title = 1*TEXT-UTF8-CHAR
; Length <= 80 chars XXXXX
motd.Body
The "motd.Body" attribute contains the actual text of the MOTD.
As with "motd.Title", this attribute MUST be set when the entry
is created, but clients MUST NOT assume that this field is
present.
motd.Body = 1*TEXT-UTF8-CHAR
motd.Seen
The "motd.Seen" attribute indiciates whether or not the user has
marked the message as seen. The contents of this attribute is
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the time at which the user marked the entry as seen.
motd.Seen = motd-datetime
; specified in Common ABNF
4.3. Common ABNF
The following [ABNF] rules are used above:
motd-datetime = time-year time-month time-day time-hour
time-minute time-second time-subsecond
;; Timestamp in UTC
time-day = 2DIGIT ;; 01-31
time-hour = 2DIGIT ;; 00-23
time-minute = 2DIGIT ;; 00-59
time-month = 2DIGIT ;; 01-12
time-second = 2DIGIT ;; 00-60
time-subsecond = *DIGIT
time-year = 4DIGIT
4.4. MOTD Entry Naming Scheme
MOTD entry names MUST be the creation time of the entry, using the
UTC encoding scheme described above. If multiple entries are being
written at the same time (IE: from different administrative
clients), all entries MUST delay a random amount of time, and then
try again. This time information is informative, and used as a
uniquifier within the dataset. It MAY also be displayed by clients
to show when the MOTD entry was created.
When subdatasets are created to provide subscription information,
the entry name MUST be "sub-{group-name}", where "{group-name}" is
the name of the group this subscription is for, if the group is
present under /motd/group. If the MOTD provider is on an external
source, the dataset entry name MUST be "ext-{name}", where the
choice of "{name}" is up to the user. If a conflict arises with
something already in use, the client MUST choose another name.
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5. Client MOTD Behaviour
When fetching all available MOTDs, clients will search the user's
MOTD dataset with a depth of 2, excluding entries that have already
been seen.
C: . SEARCH "/motd/~" DEPTH 2 RETURN ("*") NOT EQUAL "motd.Seen"
"i;octet" NIL
S: . ENTRY "/motd/~/19990222130000" (("entry" "19990222130000")
("modtime" "19990222130000") ("motd.Title" "Cyrus Server
Unavailable") ("motd.Body" "The Cyrus EMail Server will be
unavailable on Feb 23rd from 3AM to 6AM EST."))
S: . ENTRY "/motd/~/sub-asg/19990222125700" (("entry" "19990222125700")
("modtime" "19990222125700") ("motd.Title" "New Calendar
Clients") ("motd.Body" "The new calendar clients are available
via http://calendar.andrew.cmu.edu/."))
S: . REFER "/motd/~/ext-whatever"
"acap://some.server.org/motd/group/whatever"
S: . MODTIME "19990222133450"
S: . OK "SEARCH Complete"
The client MUST follow any referrals returned by the server, by
performing a search of depth 1, and ignoring any subdatasets that
are present in the remote store. (There SHOULD NOT be any
subdatasets present, as referrals are only used to indicate a remote
MOTD provider the user has subscribed to.)
All entries that are returned SHOULD be displayed to the user.
Clients can view entries that have been marked as seen by removing
the seen restriction in the search. However, when doing this, the
client MUST ignore any entries that have no title. These entries
represent seen messages that were previously removed from the
server. The ACAP server administrator will remove this at a later
date.
C: . SEARCH "/motd/~" DEPTH 2 RETURN ("*") ALL
S: . ENTRY "/motd/~/19990222130000" (("entry" "19990222130000")
("modtime" "19990222130000") ("motd.Title" "Cyrus Server
Unavailable") ("motd.Body" "The Cyrus EMail Server will be
unavailable on Feb 23rd from 3AM to 6AM EST."))
S: . ENTRY "/motd/~/sub-asg/19990222125700" (("entry" "19990222125700")
("modtime" "19990222125700") ("motd.Title" "New Calendar
Clients") ("motd.Body" "The new calendar clients are available
via http://calendar.andrew.cmu.edu/."))
S: . ENTRY "/motd/~/19990222100000" (("entry" "19990222100000")
("modtime" "19990222100000") ("motd.Seen" "19990221173200"))
S: . REFER "/motd/~/ext-whatever"
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"acap://some.server.org/motd/group/whatever"
S: . MODTIME "19990222133500"
S: . OK "SEARCH Complete"
By using ACAP search contexts and notifications, clients MAY keep
informed of any pertinent MOTD changes.
5.1. Advanced Client Behaviour
By searching /motd/group, advanced MOTD clients MAY see what MOTD
services are available. Clients may subscribe to a service by
creating an entry within the user's MOTD hierarchy
(/motd/user/{user-name}). This entry MUST indicate a subdataset
relative to the root by setting the entry's "subdataset" attribute
to ".". The client MUST then create the subdataset, and configure
it to inherit from the appropriate group dataset.
Advanced clients will also be able to locate and prune all entries
that are no longer pertinent within the user's data store. This
will remove the partial entries that were left around when
administrators removed MOTDs that the user had marked as seen.
5.1.1. Example: Subscribe
First, the client would search the ACAP hierarchy to see what MOTD
groups are available:
C: . SEARCH "/motd/group" RETURN () ALL
S: . ENTRY "compserv"
S: . ENTRY "asg"
S: . MODTIME "19990222133600"
S: . OK "SEARCH Complete"
If the user decides to subscribe to the "compserv" MOTD group, the
client MUST create the dataset "/motd/~/link-compserv", and set the
"dataset.inherit" attribute to "/motd/group/compserv".
C: . STORE ("/motd/~/link-compserv"
"dataset.inherit" "/motd/group/compserv"
"subdataset" ".")
S: . OK "STORE Complete"
5.1.2. Example: Unsubscribe
A client may view current subscriptions by performing the following
ACAP search:
C: . SEARCH "/motd/~" RETURN () NOT EQUAL "subdataset"
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"i;octet" NIL
S: . ENTRY "link-compserv"
S: . MODTIME "19990222133700"
S: . OK "SEARCH Complete"
In order to unsubscribe from a MOTD provider, the client MUST remove
the subdataset entry. To unsubscribe from the "compserv" MOTD
provider, both the entry and the dataset /motd/user/{user-
name}/link-compserv MUST be removed.
C: . STORE ("/motd/~/link-compserv" "entry" NIL)
S: . OK "STORE Complete"
5.1.3. Example: Prune
A client MAY find all of the existing entries that should be pruned
by performing the following ACAP search:
C: . SEARCH "/motd/~" DEPTH 2 RETURN ("entry") AND EQUAL "motd.Title"
"i;octet" NIL EQUAL "subdataset" "i;octet" NIL
S: . ENTRY "/motd/~/19990222130000" ("entry" "19990222130000")
S: . ENTRY "/motd/~/sub-asg/19990222125700" ("entry" "19990222125700")
S: . ENTRY "/motd/~/19990222100000" ("entry" "19990222100000")
S: . MODTIME "19990222164000"
S: . OK "SEARCH Complete"
All of the returned entries do not have titles, and are not
subdataset identifiers. They may all be removed.
C: . STORE ("/motd/~/19990222130000" "entry" NIL)
S: . OK "STORE Complete"
C: . STORE ("/motd/~/sub-asg/199902212700" "entry" NIL)
S: . OK "STORE Complete"
C: . STORE ("/motd/~/19990222100000" "entry" NIL)
S: . OK "STORE Complete"
6. Server Configuration
Administrators of ACAP servers that provide MOTD service must make
sure that each initial "/motd/user/{user-name}" dataset is
configured to inherit from "/motd/site".
Admins MUST make sure that the ACLs are set correctly on all MOTD
datasets. "Anyone" MUST be given "r" access to "/motd/site".
Finally, admins may want to go through and prune the entire /motd
hierarchy, per the instructions defined above.
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7. Design Issues
The MOTD dataset class was designed with the following ideas in
mind:
Multiple administrative domains MUST be able to provide MOTD
information,
Users MUST be able to specify what administrative domains they
would like to receive MOTD information from, and
Users MUST be able to both mark MOTD information as read, and be
able to go back and view messages that were marked as seen, but
are still being provided.
The current specification meets all of these needs.
8. Security Considerations
It is important to make sure that access controls are set correctly
on all MOTD datasets. Incorrect ACLs will result in users not being
able to see all messages, or malicious users introducing false
messages.
9. Acknowledgments
Many thanks to Rob Earhart, for his numerous technical discussions
about ACAP.
10. Copyright
Copyright (C) The Internet Society 1999. All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
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revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
11. References
[ABNF] D. Crocker, P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997
<ftp://ds.internic.net/rfc/rfc2234.txt>
[ACAP] C. Newman, J. G. Myers, "Application Configuration Access
Protocol", RFC 2244, November 1997
<ftp://ds.internic.net/rfc/rfc2244.txt>
[KEYWORDS] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997
<ftp://ds.internic.net/rfc/rfc2119.txt>
12. Author's Address
Ryan Troll
Computing Services
Carnegie Mellon
5000 Forbes Avenue
Pittsburgh, PA 15213
Phone: (412) 268-8691
EMail: ryan@andrew.cmu.edu
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