Network Working Group C. Newman
Request for Comments: 2244 Innosoft
Category: Standards Track J. G. Myers
Netscape
November 1997
ACAP -- Application Configuration Access Protocol
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society 1997. All Rights Reserved.
Abstract
The Application Configuration Access Protocol (ACAP) is designed to
support remote storage and access of program option, configuration
and preference information. The data store model is designed to
allow a client relatively simple access to interesting data, to allow
new information to be easily added without server re-configuration,
and to promote the use of both standardized data and custom or
proprietary data. Key features include "inheritance" which can be
used to manage default values for configuration settings and access
control lists which allow interesting personal information to be
shared and group information to be restricted.
Newman & Myers Standards Track [Page i]RFC 2244 ACAP November 1997
Table of Contents
Status of this Memo ............................................... i
Copyright Notice .................................................. i
Abstract .......................................................... i
ACAP Protocol Specification ....................................... 1
1. Introduction ............................................. 1
1.1. Conventions Used in this Document ........................ 1
1.2. ACAP Data Model .......................................... 1
1.3. ACAP Design Goals ........................................ 1
1.4. Validation ............................................... 2
1.5. Definitions .............................................. 2
1.6. ACAP Command Overview .................................... 4
2. Protocol Framework ....................................... 4
2.1. Link Level ............................................... 4
2.2. Commands and Responses ................................... 4
2.2.1. Client Protocol Sender and Server Protocol Receiver ...... 4
2.2.2. Server Protocol Sender and Client Protocol Receiver ...... 5
2.3. Server States ............................................ 6
2.3.1. Non-Authenticated State .................................. 6
2.3.2. Authenticated State ...................................... 6
2.3.3. Logout State ............................................. 6
2.4. Operational Considerations ............................... 7
2.4.1. Untagged Status Updates .................................. 7
2.4.2. Response when No Command in Progress ..................... 7
2.4.3. Auto-logout Timer ........................................ 7
2.4.4. Multiple Commands in Progress ............................ 8
2.5. Server Command Continuation Request ...................... 8
2.6. Data Formats ............................................. 8
2.6.1. Atom ..................................................... 9
2.6.2. Number ................................................... 9
2.6.3. String ................................................... 9
2.6.3.1. 8-bit and Binary Strings ................................. 10
2.6.4. Parenthesized List ....................................... 10
2.6.5. NIL ...................................................... 10
3. Protocol Elements ........................................ 10
3.1. Entries and Attributes ................................... 10
3.1.1. Predefined Attributes .................................... 11
3.1.2. Attribute Metadata ....................................... 12
3.2. ACAP URL scheme .......................................... 13
3.2.1. ACAP URL User Name and Authentication Mechanism .......... 13
3.2.2. Relative ACAP URLs ....................................... 14
3.3. Contexts ................................................. 14
Newman & Myers Standards Track [Page ii]RFC 2244 ACAP November 1997
3.4. Comparators .............................................. 15
3.5. Access Control Lists (ACLs) .............................. 17
3.6. Server Response Codes .................................... 18
4. Namespace Conventions .................................... 21
4.1. Dataset Namespace ........................................ 21
4.2. Attribute Namespace ...................................... 21
4.3. Formal Syntax for Dataset and Attribute Namespace ........ 22
5. Dataset Management ....................................... 23
5.1. Dataset Inheritance ...................................... 23
5.2. Dataset Attributes ....................................... 24
5.3. Dataset Creation ......................................... 25
5.4. Dataset Class Capabilities ............................... 25
5.5. Dataset Quotas ........................................... 26
6. Command and Response Specifications ...................... 26
6.1. Initial Connection ....................................... 26
6.1.1. ACAP Untagged Response ................................... 26
6.2. Any State ................................................ 27
6.2.1. NOOP Command ............................................. 27
6.2.2. LANG Command ............................................. 28
6.2.3. LANG Intermediate Response ............................... 28
6.2.4. LOGOUT Command ........................................... 29
6.2.5. OK Response .............................................. 29
6.2.6. NO Response .............................................. 29
6.2.7. BAD Response ............................................. 30
6.2.8. BYE Untagged Response .................................... 30
6.2.9. ALERT Untagged Response .................................. 31
6.3. Non-Authenticated State .................................. 31
6.3.1. AUTHENTICATE Command ..................................... 31
6.4. Searching ................................................ 33
6.4.1. SEARCH Command ........................................... 33
6.4.2. ENTRY Intermediate Response .............................. 37
6.4.3. MODTIME Intermediate Response ............................ 38
6.4.4. REFER Intermediate Response .............................. 38
6.4.5. Search Examples .......................................... 38
6.5. Contexts ................................................. 39
6.5.1. FREECONTEXT Command ...................................... 39
6.5.2. UPDATECONTEXT Command .................................... 40
6.5.3. ADDTO Untagged Response .................................. 40
6.5.4. REMOVEFROM Untagged Response ............................. 41
6.5.5. CHANGE Untagged Response ................................. 41
6.5.6. MODTIME Untagged Response ................................ 42
6.6. Dataset modification ..................................... 42
6.6.1. STORE Command ............................................ 42
6.6.2. DELETEDSINCE Command ..................................... 45
6.6.3. DELETED Intermediate Response ............................ 45
6.7. Access Control List Commands ............................. 45
6.7.1. SETACL Command ........................................... 46
6.7.2. DELETEACL Command ........................................ 46
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RFC 2244 ACAP November 1997
6.7.3. MYRIGHTS Command ......................................... 47
6.7.4. MYRIGHTS Intermediate Response ........................... 47
6.7.5. LISTRIGHTS Command ....................................... 47
6.7.6. LISTRIGHTS Intermediate Response ......................... 48
6.8. Quotas ................................................... 48
6.8.1. GETQUOTA Command ......................................... 48
6.8.3. QUOTA Untagged Response .................................. 49
6.9. Extensions ............................................... 49
7. Registration Procedures .................................. 49
7.1. ACAP Capabilities ........................................ 50
7.2. ACAP Response Codes ...................................... 50
7.3. Dataset Classes .......................................... 51
7.4. Vendor Subtree ........................................... 51
8. Formal Syntax ............................................ 52
9. Multi-lingual Considerations ............................. 61
10. Security Considerations .................................. 62
11. Acknowledgments .......................................... 63
12. Authors' Addresses ....................................... 63
Appendices ........................................................ 64
A. References ............................................... 64
B. ACAP Keyword Index ....................................... 66
C. Full Copyright Statement
Newman & Myers Standards Track [Page iv]
RFC 2244 ACAP November 1997
ACAP Protocol Specification
1. Introduction
1.1. Conventions Used in this Document
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. If such lines are wrapped without a new "C:" or
"S:" label, then the wrapping is for editorial clarity and is not
part of the command.
The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT",
and "MAY" in this document are to be interpreted as described in "Key
words for use in RFCs to Indicate Requirement Levels" [KEYWORDS].
1.2. ACAP Data Model
An ACAP server exports a hierarchical tree of entries. Each level of
the tree is called a dataset, and each dataset is made up of a list
of entries. Each entry has a unique name and may contain any number
of named attributes. Each attribute within an entry may be single
valued or multi-valued and may have associated metadata to assist
access and interpretation of the value.
The rules with which a client interprets the data within a portion of
ACAP's tree of entries are called a dataset class.
1.3. ACAP Design Goals
ACAP's primary purpose is to allow users access to their
configuration data from multiple network-connected computers. Users
can then sit down in front of any network-connected computer, run any
ACAP-enabled application and have access to their own configuration
data. Because it is hoped that many applications will become ACAP-
enabled, client simplicity was preferred to server or protocol
simplicity whenever reasonable.
ACAP is designed to be easily manageable. For this reason, it
includes "inheritance" which allows one dataset to inherit default
attributes from another dataset. In addition, access control lists
are included to permit delegation of management and quotas are
included to control storage. Finally, an ACAP server which is
conformant to this base specification should be able to support most
dataset classes defined in the future without requiring a server
reconfiguration or upgrade.
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RFC 2244 ACAP November 1997
ACAP is designed to operate well with a client that only has
intermittent access to an ACAP server. For this reason, each entry
has a server maintained modification time so that the client may
detect changes. In addition, the client may ask the server for a
list of entries which have been removed since it last accessed the
server.
ACAP presumes that a dataset may be potentially large and/or the
client's network connection may be slow, and thus offers server
sorting, selective fetching and change notification for entries
within a dataset.
As required for most Internet protocols, security, scalability and
internationalization were important design goals.
Given these design goals, an attempt was made to keep ACAP as simple
as possible. It is a traditional Internet text based protocol which
massively simplifies protocol debugging. It was designed based on
the successful IMAP [IMAP4] protocol framework, with a few
refinements.
1.4. Validation
By default, any value may be stored in any attribute for which the
user has appropriate permission and quota. This rule is necessary to
allow the addition of new simple dataset classes without
reconfiguring or upgrading the server.
In some cases, such as when the value has special meaning to the
server, it is useful to have the server enforce validation by
returning the INVALID response code to a STORE command. These cases
MUST be explicitly identified in the dataset class specification
which SHOULD include specific fixed rules for validation. Since a
given ACAP server may be unaware of any particular dataset class
specification, clients MUST NOT depend on the presence of enforced
validation on the server.
1.5. Definitions
access control list (ACL)
A set of identifier, rights pairs associated with an object. An
ACL is used to determine which operations a user is permitted to
perform on that object. See section 3.5.
attribute
A named value within an entry. See section 3.1.
Newman & Myers Standards Track [Page 2]RFC 2244 ACAP November 1997
comparator
A named function which can be used to perform one or more of
three comparison operations: ordering, equality and substring
matching. See section 3.4.
context
An ordered subset of entries in a dataset, created by a SEARCH
command with a MAKECONTEXT modifier. See section 3.3.
dataset
One level of hierarchy in ACAP's tree of entries.
dataset class specification
The rules which allow a client to interpret the data within a
portion of ACAP's tree of entries.
entry
A set of attributes with a unique entry name. See section 3.1.
metadata
Information describing an attribute, its value and any access
controls associated with that attribute. See section 3.1.2.
NIL This represents the non-existence of a particular data item.
NUL A control character encoded as 0 in US-ASCII [US-ASCII].
octet
An 8-bit value. On most modern computer systems, an octet is
one byte.
SASL Simple Authentication and Security Layer [SASL].
UTC Universal Coordinated Time as maintained by the Bureau
International des Poids et Mesures (BIPM).
UTF-8
An 8-bit transformation format of the Universal Character Set
[UTF8]. Note that an incompatible change was made to the coded
character set referenced by [UTF8], so for the purpose of this
document, UTF-8 refers to the UTF-8 encoding as defined by
version 2.0 of Unicode [UNICODE-2], or ISO 10646 [ISO-10646]
including amendments one through seven.
Newman & Myers Standards Track [Page 3]RFC 2244 ACAP November 1997
1.6. ACAP Command Overview
The AUTHENTICATE, NOOP, LANG and LOGOUT commands provide basic
protocol services. The SEARCH command is used to select, sort, fetch
and monitor changes to attribute values and metadata. The
UPDATECONTEXT and FREECONTEXT commands are also used to assist in
monitoring changes in attribute values and metadata. The STORE
command is used to add, modify and delete entries and attributes.
The DELETEDSINCE command is used to assist a client in
re-synchronizing a cache with the server. The GETQUOTA, SETACL,
DELETEACL, LISTRIGHTS and MYRIGHTS commands are used to examine
storage quotas and examine or modify access permissions.
2. Protocol Framework
2.1. Link Level
The ACAP protocol assumes a reliable data stream such as provided by
TCP. When TCP is used, an ACAP server listens on port 674.
2.2. Commands and Responses
An ACAP session consists of the establishment of a client/server
connection, an initial greeting from the server, and client/server
interactions. These client/server interactions consist of a client
command, server data, and a server completion result.
ACAP is a text-based line-oriented protocol. In general,
interactions transmitted by clients and servers are in the form of
lines; that is, sequences of characters that end with a CRLF. The
protocol receiver of an ACAP client or server is either reading a
line, or is reading a sequence of octets with a known count (a
literal) followed by a line. Both clients and servers must be
capable of handling lines of arbitrary length.
2.2.1. Client Protocol Sender and Server Protocol Receiver
The client command begins an operation. Each client command is
prefixed with a identifier (an alphanumeric string of no more than 32
characters, e.g., A0001, A0002, etc.) called a "tag". A different
tag SHOULD be generated by the client for each command.
There are two cases in which a line from the client does not
represent a complete command. In one case, a command argument is
quoted with an octet count (see the description of literal in section
2.6.3); in the other case, the command arguments require server
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RFC 2244 ACAP November 1997
feedback (see the AUTHENTICATE command). In some of these cases, the
server sends a command continuation request if it is ready for the
next part of the command. This response is prefixed with the token
"+".
Note: If, instead, the server detected an error in a
command, it sends a BAD completion response with tag
matching the command (as described below) to reject the
command and prevent the client from sending any more of the
command.
It is also possible for the server to send a completion or
intermediate response for some other command (if multiple
commands are in progress), or untagged data. In either
case, the command continuation request is still pending;
the client takes the appropriate action for the response,
and reads another response from the server.
The ACAP server reads a command line from the client, parses the
command and its arguments, and transmits server data and a server
command completion result.
2.2.2. Server Protocol Sender and Client Protocol Receiver
Data transmitted by the server to the client come in four forms:
command continuation requests, command completion results,
intermediate responses, and untagged responses.
A command continuation request is prefixed with the token "+".
A command completion result indicates the success or failure of the
operation. It is tagged with the same tag as the client command
which began the operation. Thus, if more than one command is in
progress, the tag in a server completion response identifies the
command to which the response applies. There are three possible
server completion responses: OK (indicating success), NO (indicating
failure), or BAD (indicating protocol error such as unrecognized
command or command syntax error).
An intermediate response returns data which can only be interpreted
within the context of a command in progress. It is tagged with the
same tag as the client command which began the operation. Thus, if
more than one command is in progress, the tag in an intermediate
response identifies the command to which the response applies. A
tagged response other than "OK", "NO", or "BAD" is an intermediate
response.
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An untagged response returns data or status messages which may be
interpreted outside the context of a command in progress. It is
prefixed with the token "*". Untagged data may be sent as a result
of a client command, or may be sent unilaterally by the server.
There is no syntactic difference between untagged data that resulted
from a specific command and untagged data that were sent
unilaterally.
The protocol receiver of an ACAP client reads a response line from
the server. It then takes action on the response based upon the
first token of the response, which may be a tag, a "*", or a "+" as
described above.
A client MUST be prepared to accept any server response at all times.
This includes untagged data that it may not have requested.
This topic is discussed in greater detail in the Server Responses
section.
2.3. Server States
An ACAP server is in one of three states. Most commands are valid in
only certain states. It is a protocol error for the client to
attempt a command while the server is in an inappropriate state for
that command. In this case, a server will respond with a BAD command
completion result.
2.3.1. Non-Authenticated State
In non-authenticated state, the user must supply authentication
credentials before most commands will be permitted. This state is
entered when a connection starts.
2.3.2. Authenticated State
In authenticated state, the user is authenticated and most commands
will be permitted. This state is entered when acceptable
authentication credentials have been provided.
2.3.3. Logout State
In logout state, the session is being terminated, and the server will
close the connection. This state can be entered as a result of a
client request or by unilateral server decision.
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RFC 2244 ACAP November 1997
+--------------------------------------+
|initial connection and server greeting|
+--------------------------------------+
|| (1) || (2)
VV ||
+-----------------+ ||
|non-authenticated| ||
+-----------------+ ||
|| (4) || (3) ||
|| VV ||
|| +----------------+ ||
|| | authenticated | ||
|| +----------------+ ||
|| || (4) ||
VV VV VV
+--------------------------------------+
| logout and close connection |
+--------------------------------------+
(1) connection (ACAP greeting)
(2) rejected connection (BYE greeting)
(3) successful AUTHENTICATE command
(4) LOGOUT command, server shutdown, or connection closed
2.4. Operational Considerations
2.4.1. Untagged Status Updates
At any time, a server can send data that the client did not request.
2.4.2. Response when No Command in Progress
Server implementations are permitted to send an untagged response
while there is no command in progress. Server implementations that
send such responses MUST deal with flow control considerations.
Specifically, they must either (1) verify that the size of the data
does not exceed the underlying transport's available window size, or
(2) use non-blocking writes.
2.4.3. Auto-logout Timer
If a server has an inactivity auto-logout timer, that timer MUST be
of at least 30 minutes duration. The receipt of ANY command from the
client during that interval MUST suffice to reset the auto-logout
timer.
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2.4.4. Multiple Commands in Progress
The client is not required to wait for the completion result of a
command before sending another command, subject to flow control
constraints on the underlying data stream. Similarly, a server is
not required to process a command to completion before beginning
processing of the next command, unless an ambiguity would result
because of a command that would affect the results of other commands.
If there is such an ambiguity, the server executes commands to
completion in the order given by the client.
2.5. Server Command Continuation Request
The command continuation request is indicated by a "+" token instead
of a tag. This indicates that the server is ready to accept the
continuation of a command from the client.
This response is used in the AUTHENTICATE command to transmit server
data to the client, and request additional client data. This
response is also used if an argument to any command is a
synchronizing literal (see section 2.6.3).
The client is not permitted to send the octets of a synchronizing
literal unless the server indicates that it expects it. This permits
the server to process commands and reject errors on a line-by-line
basis, assuming it checks for non-synchronizing literals at the end
of each line. The remainder of the command, including the CRLF that
terminates a command, follows the octets of the literal. If there
are any additional command arguments the literal octets are followed
by a space and those arguments.
Example: C: A099 FREECONTEXT {10}
S: + "Ready for additional command text"
C: FRED
C: FOOB
S: A099 OK "FREECONTEXT completed"
C: A044 BLURDYBLOOP {102856}
S: A044 BAD "No such command as 'BLURDYBLOOP'"
2.6. Data Formats
ACAP uses textual commands and responses. Data in ACAP can be in one
of five forms: atom, number, string, parenthesized list or NIL.
Newman & Myers Standards Track [Page 8]RFC 2244 ACAP November 1997
2.6.1. Atom
An atom consists of one to 1024 non-special characters. It must
begin with a letter. Atoms are used for protocol keywords.
2.6.2. Number
A number consists of one or more digit characters, and represents a
numeric value. Numbers are restricted to the range of an unsigned
32-bit integer: 0 < number < 4,294,967,296.
2.6.3. String
A string is in one of two forms: literal and quoted string. The
literal form is the general form of string. The quoted string form
is an alternative that avoids the overhead of processing a literal at
the cost of restrictions of what may be in a quoted string.
A literal is a sequence of zero or more octets (including CR and LF),
prefix-quoted with an octet count in the form of an open brace ("{"),
the number of octets, close brace ("}"), and CRLF. In the case of
literals transmitted from server to client, the CRLF is immediately
followed by the octet data.
There are two forms of literals transmitted from client to server.
The form where the open brace ("{") and number of octets is
immediately followed by a close brace ("}") and CRLF is called a
synchronizing literal. When sending a synchronizing literal, the
client must wait to receive a command continuation request before
sending the octet data (and the remainder of the command). The other
form of literal, the non-synchronizing literal, is used to transmit a
string from client to server without waiting for a command
continuation request. The non-synchronizing literal differs from the
synchronizing literal by having a plus ("+") between the number of
octets and the close brace ("}") and by having the octet data
immediately following the CRLF.
A quoted string is a sequence of zero to 1024 octets excluding NUL,
CR and LF, with double quote (<">) characters at each end.
The empty string is represented as "" (a quoted string with zero
characters between double quotes), as {0} followed by CRLF (a
synchronizing literal with an octet count of 0), or as {0+} followed
by a CRLF (a non-synchronizing literal with an octet count of 0).
Note: Even if the octet count is 0, a client transmitting a
synchronizing literal must wait to receive a command
continuation request.
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2.6.3.1. 8-bit and Binary Strings
Most strings in ACAP are restricted to UTF-8 characters and may not
contain NUL octets. Attribute values MAY contain any octets
including NUL.
2.6.4. Parenthesized List
Data structures are represented as a "parenthesized list"; a sequence
of data items, delimited by space, and bounded at each end by
parentheses. A parenthesized list can contain other parenthesized
lists, using multiple levels of parentheses to indicate nesting.
The empty list is represented as () -- a parenthesized list with no
members.
2.6.5. NIL
The special atom "NIL" represents the non-existence of a particular
data item that is represented as a string or parenthesized list, as
distinct from the empty string "" or the empty parenthesized list ().
3. Protocol Elements
This section defines data formats and other protocol elements used
throughout the ACAP protocol.
3.1. Entries and Attributes
Within a dataset, each entry name is made up of zero or more UTF-8
characters other than slash ("/"). A slash separated list of
entries, one at each level of the hierarchy, forms the full path to
an entry.
Each entry is made up of a set of attributes. Each attribute has a
hierarchical name in UTF-8, with each component of the name separated
by a period (".").
The value of an attribute is either single or multi-valued. A single
value is NIL (has no value), or a string of zero or more octets. A
multi-value is a list of zero or more strings, each of zero or more
octets.
Attribute names are not permitted to contain asterisk ("*") or
percent ("%") and MUST be valid UTF-8 strings which do not contain
NUL. Invalid attribute names result in a BAD response. Entry names
Newman & Myers Standards Track [Page 10]RFC 2244 ACAP November 1997
are not permitted to begin with "." or contain slash ("/") and MUST
be valid UTF-8 strings which do not contain NUL. Invalid entry names
in the entry field of a command result in a BAD response.
Use of non-visible UTF-8 characters in attribute and entry names is
discouraged.
3.1.1. Predefined Attributes
Attribute names which do not contain a dot (".") are reserved for
standardized attributes which have meaning in any dataset. The
following attributes are defined by the ACAP protocol.
entry
Contains the name of the entry. MUST be single valued.
Attempts to use illegal or multi-valued values for the entry
attribute are protocol errors and MUST result in a BAD
completion response. This is a special case.
modtime
Contains the date and time any read-write metadata in the entry
was last modified. This value MUST be in UTC, MUST be
automatically updated by the server.
The value consists of 14 or more US-ASCII digits. The first
four indicate the year, the next two indicate the month, the
next two indicate the day of month, the next two indicate the
hour (0 - 23), the next two indicate the minute, and the next
two indicate the second. Any further digits indicate fractions
of a second.
The time, particularly fractions of a second, need not be
accurate. It is REQUIRED, however, that any two entries in a
dataset changed by successive modifications have strictly
ascending modtime values. In addition, each STORE command
within a dataset (including simultaneous stores from different
connections) MUST use different modtime values.
This attribute has enforced validation, so any attempt to STORE
a value in this attribute MAY result in a NO response with an
INVALID response code.
subdataset
If this attribute is set, it indicates the existence of a sub-
dataset of this entry.
Newman & Myers Standards Track [Page 11]RFC 2244 ACAP November 1997
The value consists of a list of relative ACAP URLs (see section
3.2) which may be used to locate the sub-dataset. The base URL
is the full path to the entry followed by a slash ("/"). The
value "." indicates a subdataset is located directly under this
one. Multiple values indicate replicated copies of the
subdataset.
For example, if the dataset "/folder/site/" has an entry
"public-folder" with a subdataset attribute of ".", then there
exists a dataset "/folder/site/public-folder/". If the value of
the subdataset attribute was instead
"//other.acap.domain//folder/site/public-folder/", that would
indicate the dataset is actually located on a different ACAP
server.
A dataset can be created by storing a "subdataset" attribute
including ".", and a sub-hierarchy of datasets is deleted by
storing a NIL value to the "subdataset" attribute on the entry
in the parent dataset.
This attribute has enforced syntax validation. Specifically, if
an attempt is made to STORE a non-list value (other than NIL),
an empty list, or one of the values does not follow the URL
syntax rules [BASIC-URL, REL-URL], then this will result in a NO
response with an INVALID response code.
3.1.2. Attribute Metadata
Each attribute is made up of metadata items which describe that
attribute, its value and any associated access controls. Metadata
items may be either read-only, in which case the client is never
permitted to modify the item, or read-write, in which case the client
may modify the item if the access control list (ACL) permits.
The following metadata items are defined in this specification:
acl The access control list for the attribute, if one exists. If
the attribute does not have an ACL, NIL is returned.
Read-write. See section 3.5 for the contents of an ACL.
attribute
The attribute name. Read-only.
myrights
The set of rights that the client has to the attribute.
Read-only. See section 3.5 for the possible rights.
Newman & Myers Standards Track [Page 12]RFC 2244 ACAP November 1997
size This is the length of the value. In the case of a
multi-value, this is a list of lengths for each of the values.
Read-only.
value The value. For a multi-value, this is a list of single
values. Read-write.
Additional items of metadata may be defined in extensions to this
protocol. Servers MUST respond to unrecognized metadata by returning
a BAD command completion result.
3.2. ACAP URL scheme
ACAP URLs are used within the ACAP protocol for the "subdataset"
attribute, referrals and inheritance. They provide a convenient
syntax for referring to other ACAP datasets. The ACAP URL follows
the common Internet scheme syntax as defined in [BASIC-URL] except
that plaintext passwords are not permitted. If :<port> is omitted,
the port defaults to 674.
An ACAP URL has the following general form:
url-acap = "acap://" url-server "/" url-enc-entry [url-filter]
[url-extension]
The <url-server> element includes the hostname, and optional user
name, authentication mechanism and port number. The <url-enc-entry>
element contains the name of an entry path encoded according to the
rules in [BASIC-URL].
The <url-filter> element is an optional list of interesting attribute
names. If omitted, the URL refers to all attributes of the named
entry. The <url-extension> element is reserved for extensions to
this URL scheme.
Note that unsafe or reserved characters such as " " or "?" MUST be
hex encoded as described in the URL specification [BASIC-URL]. Hex
encoded octets are interpreted according to UTF-8 [UTF8].
3.2.1. ACAP URL User Name and Authentication Mechanism
A user name and/or authentication mechanism may be supplied. They
are used in the "AUTHENTICATE" command after making the connection to
the ACAP server. If no user name or authentication mechanism is
supplied, then the SASL ANONYMOUS [SASL-ANON] mechanism is used by
default. If an authentication mechanism is supplied without a user
Newman & Myers Standards Track [Page 13]RFC 2244 ACAP November 1997
name, then one SHOULD be obtained from the specified mechanism or
requested from the user as appropriate. If a user name is supplied
without an authentication mechanism then ";AUTH=*" is assumed.
The ";AUTH=" authentication parameter is interpreted as described in
the IMAP URL Scheme [IMAP-URL].
Note that if unsafe or reserved characters such as " " or ";" are
present in the user name or authentication mechanism, they MUST be
encoded as described in the URL specification [BASIC-URL].
3.2.2. Relative ACAP URLs
Because ACAP uses "/" as the hierarchy separator for dataset paths,
it works well with the relative URL rules defined in the relative URL
specification [REL-URL].
The <aauth> grammar element is considered part of the user name for
purposes of resolving relative ACAP URLs.
The base URL for a relative URL stored in an attribute's value is
formed by taking the path to the dataset containing that attribute,
appending a "/" followed by the entry name of the entry containing
that attribute followed by "/".
3.3. Contexts
A context is subset of entries in a dataset or datasets, created by a
SEARCH command with a MAKECONTEXT modifier. Context names are
client-generated strings and must not start with the slash ('/')
character.
When a client creates a context, it may request automatic
notification of changes. A client may also request enumeration of
entries within a context. Enumeration simplifies the implementation
of a "virtual scrollbar" by the client.
A context exists only within the ACAP session in which it was
created. When the connection is closed, all contexts associated with
that connection are automatically discarded. A server is required to
support at least 100 active contexts within a session. If the server
supports a larger limit it must advertise it in a CONTEXTLIMIT
capability.
Newman & Myers Standards Track [Page 14]RFC 2244 ACAP November 1997
3.4. Comparators
A comparator is a named function which takes two input values and can
be used to perform one or more of four comparison operations:
ordering, equality, prefix and substring matching.
The ordering operation is used both for the SORT search modifier and
the COMPARE and COMPARESTRICT search keys. Ordering comparators can
determine the ordinal precedence of any two values. When used for
ordering, a comparator's name can be prefixed with "+" or "-" to
indicate that the ordering should be normal order or reversed order
respectively. If no prefix is included, "+" is assumed.
For the purpose of ordering, a comparator may designate certain
values as having an undefined ordinal precedence. Such values always
collate with equal value after all other values regardless of whether
normal or reversed ordering is used. Unless the comparator
definition specifies otherwise, multi-values and NIL values have an
undefined ordinal precedence.
The equality operation is used for the EQUAL search modifier, and
simply determines if the two values are considered equal under the
comparator function. When comparing a single value to a multi-value,
the two are considered equal if any one of the multiple values is
equal to the single value.
The prefix match operation is used for the PREFIX search modifier,
and simply determines if the search value is a prefix of the item
being searched. In the case of prefix search on a multi-value, the
match is successful if the value is a prefix of any one of the
multiple values.
The substring match operation is used for the SUBSTRING search
modifier, and simply determines if search value is a substring of the
item being searched. In the case of substring search on a multi-
value, the match is successful if the value is a substring of any one
of the multiple values.
Rules for naming and registering comparators will be defined in a
future specification. Servers MUST respond to unknown or improperly
used comparators with a BAD command completion result.
Newman & Myers Standards Track [Page 15]
RFC 2244 ACAP November 1997
The following comparators are defined by this standard and MUST be
implemented:
i;octet
Operations: Ordering, Equality, Prefix match, Substring match
For collation, the i;octet comparator interprets the value of
an attribute as a series of unsigned octets with ordinal
values from 0 to 255. When ordering two strings, each octet
pair is compared in sequence until the octets are unequal or
the end of the string is reached. When collating two strings
where the shorter is a prefix of the longer, the shorter
string is interpreted as having a smaller ordinal value. The
"i;octet" or "+i;octet" forms collate smaller ordinal values
earlier, and the "-i;octet" form collates larger ordinal
values earlier.
For the equality function, two strings are equal if they are
the same length and contain the same octets in the same
order. NIL is equal only to itself.
For non-binary, non-nil single values, i;octet ordering is
equivalent to the ANSI C [ISO-C] strcmp() function applied to
C string representations of the values. For non-binary,
non-nil single values, i;octet substring match is equivalent
to the ANSI C strstr() function applied to the C string
representations of the values.
i;ascii-casemap
Operations: Ordering, Equality, Prefix match, Substring match
The i;ascii-casemap comparator first applies a mapping to the
attribute values which translates all US-ASCII letters to
uppercase (octet values 0x61 to 0x7A are translated to octet
values 0x41 to 0x5A respectively), then applies the i;octet
comparator as described above. With this function the values
"hello" and "HELLO" have the same ordinal value and are
considered equal.
i;ascii-numeric
Operations: Ordering, Equality
The i;ascii-numeric comparator interprets strings as decimal
positive integers represented as US-ASCII digits. All values
which do not begin with a US-ASCII digit are considered equal
with an ordinal value higher than all non-NIL single-valued
Newman & Myers Standards Track [Page 16]RFC 2244 ACAP November 1997
attributes. Otherwise, all US-ASCII digits (octet values
0x30 to 0x39) are interpreted starting from the beginning of
the string to the first non-digit or the end of the string.
3.5. Access Control Lists (ACLs)
An access control list is a set of identifier, rights pairs used to
restrict access to a given dataset, attribute or attribute within an
entry. An ACL is represented by a multi-value with each value
containing an identifier followed by a tab character followed by the
rights. The syntax is defined by the "acl" rule in the formal syntax
in section 8.
Identifier is a UTF-8 string. The identifier "anyone" is reserved to
refer to the universal identity (all authentications, including
anonymous). All user name strings accepted by the AUTHENTICATE
command to authenticate to the ACAP server are reserved as
identifiers for the corresponding user. Identifiers starting with a
slash ("/") character are reserved for authorization groups which
will be defined in a future specification. Identifiers MAY be
prefixed with a dash ("-") to indicate a revocation of rights. All
other identifiers have implementation-defined meanings.
Rights is a string listing a (possibly empty) set of alphanumeric
characters, each character listing a set of operations which is being
controlled. Letters are reserved for "standard" rights, listed
below. The set of standard rights may only be extended by a
standards-track or IESG approved experimental RFC. Digits are
reserved for implementation or site defined rights. The currently
defined standard rights are:
x - search (use EQUAL search key with i;octet comparator)
r - read (access with SEARCH command)
w - write (modify with STORE command)
i - insert (perform STORE on a previously NIL value)
a - administer (perform SETACL or STORE on ACL attribute/metadata)
An implementation may force rights to always or never be granted. In
particular, implementations are expected to grant implicit read and
administer rights to a user's personal dataset storage in order to
avoid denial of service problems. Rights are never tied, unlike the
IMAP ACL extension [IMAP-ACL].
It is possible for multiple identifiers in an access control list to
apply to a given user (or other authentication identity). For
example, an ACL may include rights to be granted to the identifier
matching the user, one or more implementation-defined identifiers
Newman & Myers Standards Track [Page 17]RFC 2244 ACAP November 1997
matching groups which include the user, and/or the identifier
"anyone". These rights are combined by taking the union of all
positive rights which apply to a given user and subtracting the union
of all negative rights which apply to that user. A client MAY avoid
this calculation by using the MYRIGHTS command and metadata items.
Each attribute of each entry of a dataset may potentially have an
ACL. If an attribute in an entry does not have an ACL, then access
is controlled by a default ACL for that attribute in the dataset, if
it exists. If there is no default ACL for that attribute in the
dataset, access is controlled by a default ACL for that dataset. The
default ACL for a dataset must exist.
In order to perform any access or manipulation on an entry in a
dataset, the client must have 'r' rights on the "entry" attribute of
the entry. Implementations should take care not to reveal via error
messages the existence of an entry for which the client does not have
'r' rights. A client does not need access to the "subdataset"
attribute of the parent dataset in order to access the contents of a
dataset.
Many of the ACL commands and responses include an "acl object"
parameter, for specifying what the ACL applies to. This is a
parenthesized list. The list contains just the dataset name when
referring to the default ACL for a dataset. The list contains a
dataset name and an attribute name when referring to the default ACL
for an attribute in a dataset. The list contains a dataset name, an
attribute name, and an entry name when referring to the ACL for an
attribute of an entry of a dataset.
3.6. Server Response Codes
An OK, NO, BAD, ALERT or BYE response from the server MAY contain a
response code to describe the event in a more detailed machine
parsable fashion. A response code consists of data inside
parentheses in the form of an atom, possibly followed by a space and
arguments. Response codes are defined when there is a specific
action that a client can take based upon the additional information.
In order to support future extension, the response code is
represented as a slash-separated hierarchy with each level of
hierarchy representing increasing detail about the error. Clients
MUST tolerate additional hierarchical response code detail which they
don't understand.
The currently defined response codes are:
Newman & Myers Standards Track [Page 18]
RFC 2244 ACAP November 1997
AUTH-TOO-WEAK
This response code is returned on a tagged NO result from an
AUTHENTICATE command. It indicates that site security policy
forbids the use of the requested mechanism for the specified
authentication identity.
ENCRYPT-NEEDED
This response code is returned on a tagged NO result from an
AUTHENTICATE command. It indicates that site security policy
requires the use of a strong encryption mechanism for the
specified authentication identity and mechanism.
INVALID
This response code indicates that a STORE command included
data which the server implementation does not permit. It
MUST NOT be used unless the dataset class specification for
the attribute in question explicitly permits enforced server
validation. The argument is the attribute which was invalid.
MODIFIED
This response code indicates that a conditional store failed
because the modtime on the entry is later than the modtime
specified with the STORE command UNCHANGEDSINCE modifier.
The argument is the entry which had been modified.
NOEXIST
This response code indicates that a search or NOCREATE store
failed because a specified dataset did not exist. The
argument is the dataset which does not exist.
PERMISSION
A command failed due to insufficient permission based on the
access control list or implicit rights. The argument is the
acl-object which caused the permission failure.
QUOTA
A STORE or SETACL command which would have increased the size
of the dataset failed due to insufficient quota.
REFER
This response code may be returned in a tagged NO response to
any command that takes a dataset name as a parameter. It has
one or more arguments with the syntax of relative URLs. It
is a referral, indicating that the command should be retried
using one of the relative URLs.
Newman & Myers Standards Track [Page 19]RFC 2244 ACAP November 1997
SASL This response code can occur in the tagged OK response to a
successful AUTHENTICATE command and includes the optional
final server response data from the server as specified by
SASL [SASL].
TOOMANY
This response code may be returned in a tagged OK response to
a SEARCH command which includes the LIMIT modifier. The
argument returns the total number of matching entries.
TOOOLD
The modtime specified in the DELETEDSINCE command is too old,
so deletedsince information is no longer available.
TRANSITION-NEEDED
This response code occurs on a NO response to an AUTHENTICATE
command. It indicates that the user name is valid, but the
entry in the authentication database needs to be updated in
order to permit authentication with the specified mechanism.
This can happen if a user has an entry in a system
authentication database such as Unix /etc/passwd, but does
not have credentials suitable for use by the specified
mechanism.
TRYLATER
A command failed due to a temporary server failure. The
client MAY continue using local information and try the
command later.
TRYFREECONTEXT
This response code may be returned in a tagged NO response to
a SEARCH command which includes the MAKECONTEXT modifier. It
indicates that a new context may not be created due to the
server's limit on the number of existing contexts.
WAYTOOMANY
This response code may be returned in a tagged NO response to
a SEARCH command which includes a HARDLIMIT search modifier.
It indicates that the SEARCH would have returned more entries
than the HARDLIMIT permitted.
Additional response codes MUST be registered with IANA according
to the proceedures in section 7.2. Client implementations MUST
tolerate response codes that they do not recognize.
Newman & Myers Standards Track [Page 20]RFC 2244 ACAP November 1997
4. Namespace Conventions
4.1. Dataset Namespace
The dataset namespace is a slash-separated hierarchy. The first
component of the dataset namespace is a dataset class. Dataset
classes MUST have a vendor prefix (vendor.<vendor/product>) or be
specified in a standards track or IESG approved experimental RFC.
See section 7.3 for the registration template.
The second component of the dataset name is "site", "group", "host",
or "user" referring to server-wide data, administrative group data,
per-host data and per-user data respectively.
For "group", "host", and "user" areas, the third component of the
path is the group name, the fully qualified host domain name, or the
user name. A path of the form "/<dataset-class>/~/" is a convenient
abbreviation for "/<dataset-class>/user/<current-user>/".
Dataset names which begin with "/byowner/" are reserved as an
alternate view of the namespace. This provides a way to see all the
dataset classes which a particular owner uses. For example,
"/byowner/~/<dataset-class>/" is an alternate name for
"/<dataset-class>/~/". Byowner provides a way to view a list of
dataset classes owned by a given user; this is done using the dataset
"/byowner/user/<current-user>/" with the NOINHERIT SEARCH modifier.
The dataset "/" may be used to find all dataset classes visible to
the current user. A dataset of the form "/<dataset-class>/user/" may
be used to find all users which have made a dataset or entry of that
class visible to the current user.
The formal syntax for a dataset name is defined by the "dataset-name"
rule in section 4.3.
4.2. Attribute Namespace
Attribute names which do not contain a dot (".") are reserved for
standardized attributes which have meaning in any dataset. In order
to simplify client implementations, the attribute namespace is
intended to be unique across all datasets. To achieve this,
attribute names are prefixed with the dataset class name followed by
a dot ("."). Attributes which affect management of the dataset are
prefixed with "dataset.". In addition, a subtree of the "vendor."
attribute namespace may be registered with IANA according to the
rules in section 7.4. ACAP implementors are encouraged to help
define interoperable dataset classes specifications rather than using
the private attribute namespace.
Newman & Myers Standards Track [Page 21]RFC 2244 ACAP November 1997
Some users or sites may wish to add their own private attributes to
certain dataset classes. In order to enable this, the "user.<user-
name>." and "site." subtrees of the attribute namespace are reserved
for user-specific and site-specific attributes respectively and will
not be standardized. Such attributes are not interoperable so are
discouraged in favor of defining standard attributes. A future
extension is expected to permit discovery of syntax for user or
site-specific attributes. Clients wishing to support display of user
or site-specific attributes should display the value of any non-NIL
single-valued "user.<user-name>." or "site." attribute which has
valid UTF-8 syntax.
The formal syntax for an attribute name is defined by the
"attribute-name" rule in the next section.
4.3. Formal Syntax for Dataset and Attribute Namespace
The naming conventions for datasets and attributes are defined by the
following ABNF. Note that this grammar is not part of the ACAP
protocol syntax in section 8, as dataset names and attribute names
are encoded as strings within the ACAP protocol.
attribute-dacl = "dataset.acl" *("." name-component)
attribute-dset = dataset-std 1*("." name-component)
;; MUST be defined in a dataset class specification
attribute-name = attribute-std / attr-site / attr-user / vendor-name
attribute-std = "entry" / "subdataset" / "modtime" /
"dataset.inherit" / attribute-dacl / attribute-dset
attr-site = "site" 1*("." name-component)
attr-user = "user." name-component 1*("." name-component)
byowner = "/byowner/" owner "/"
[dataset-class "/" dataset-sub]
dataset-class = dataset-std / vendor-name
dataset-normal = "/" [dataset-class "/"
(owner-prefix / dataset-tail)]
dataset-name = byowner / dataset-normal
Newman & Myers Standards Track [Page 22]RFC 2244 ACAP November 1997
dataset-std = name-component
;; MUST be registered with IANA and the spec MUST
;; be published as a standards track or
;; IESG-approved experimental RFC
dataset-sub = *(dname-component "/")
;; The rules for this portion of the namespace may
;; be further restricted by the dataset class
;; specification.
dataset-tail = owner "/" dataset-sub
dname-component = 1*UTF8-CHAR
;; MUST NOT begin with "." or contain "/"
name-component = 1*UTF8-CHAR
;; MUST NOT contain ".", "/", "%", or "*"
owner = "site" / owner-host / owner-group /
owner-user / "~"
owner-group = "group/" dname-component
owner-host = "host/" dname-component
owner-prefix = "group/" / "host/" / "user/"
owner-user = "user/" dname-component
vendor-name = vendor-token *("." name-component)
vendor-token = "vendor." name-component
;; MUST be registered with IANA
5. Dataset Management
The entry with an empty name ("") in the dataset is used to hold
management information for the dataset as a whole.
5.1. Dataset Inheritance
It is possible for one dataset to inherit data from another. The
dataset from which the data is inherited is called the base dataset.
Data in the base dataset appears in the inheriting dataset, except
when overridden by a STORE to the inheriting dataset.
Newman & Myers Standards Track [Page 23]RFC 2244 ACAP November 1997
The base dataset is usually a system-wide or group-wide set of
defaults. A system-wide dataset usually has one inheriting dataset
per user, allowing each user to add to or modify the defaults as
appropriate.
An entry which exists in both the inheriting and base dataset
inherits a modtime equal to the greater of the two modtimes. An
attribute in such an entry is inherited from the base dataset if it
was never modified by a STORE command in the inheriting dataset or if
DEFAULT was stored to that attribute. This permits default entries
to be amended rather than replaced in the inheriting dataset.
The "subdataset" attribute is not directly inherited. If the base
dataset includes a "subdataset" attribute and the inheriting dataset
does not, then the "subdataset" attribute will inherit a virtual
value of a list containing a ".". The subdataset at that node is
said to be a "virtual" dataset as it is simply a virtual copy of the
appropriate base dataset with all "subdataset" attributes changed to
a list containing a ".". A virtual dataset is not visible if
NOINHERIT is specified on the SEARCH command.
Servers MUST support at least two levels of inheritance. This
permits a user's dataset such as "/options/user/fred/common" to
inherit from a group dataset such as "/options/group/dinosaur
operators/common" which in turn inherits from a server-wide dataset
such as "/options/site/common".
5.2. Dataset Attributes
The following attributes apply to management of the dataset when
stored in the "" entry of a dataset. These attributes are not
inherited.
dataset.acl
This holds the default access control list for the dataset.
This attribute is validated, so an invalid access control list
in a STORE command will result in a NO response with an INVALID
response code.
dataset.acl.<attribute>
This holds the default access control list for an attribute
within the dataset. This attribute is validated, so an invalid
access control list in a STORE command will result in a NO
response with an INVALID response code.
dataset.inherit
This holds the name of a dataset from which to inherit according
to the rules in the previous section. This attribute MAY refer
Newman & Myers Standards Track [Page 24]RFC 2244 ACAP November 1997
to a non-existent dataset, in which case nothing is inherited.
This attribute is validated, so illegal dataset syntax or an
attempt to store a multi-value will result in a NO response with
an INVALID response code.
5.3. Dataset Creation
When a dataset is first created (by storing a "." in the subdataset
attribute or storing an entry in a previously non-existent dataset),
the dataset attributes are initialized with the values from the
parent dataset in the "/byowner/" hierarchy. In the case of the
"dataset.inherit" attribute, the appropriate hierarchy component is
added. For example, given the following entry (note that \t refers
to the US-ASCII horizontal tab character):
entry path "/byowner/user/joe/"
dataset.acl ("joe\txrwia" "fred\txr")
dataset.inherit "/byowner/site"
If a new dataset class "/byowner/user/joe/new" is created, it will
have the following dataset attributes:
entry path "/byowner/user/joe/new/"
dataset.acl ("joe\txrwia" "fred\txr")
dataset.inherit "/byowner/site/new"
Note that the dataset "/byowner/user/joe/new/" is equivalent to
"/new/user/joe/".
5.4. Dataset Class Capabilities
Certain dataset classes or dataset class features may only be useful
if there is an active updating client or integrated server support
for the feature. The dataset class "capability" is reserved to allow
clients or servers to advertise such features. The "entry" attribute
within this dataset class is the name of the dataset class whose
features are being described. The attributes are prefixed with
"capability.<dataset-class>." and are defined by the appropriate
dataset class specification.
Since it is possible for an unprivileged user to run an active client
for himself, a per-user capability dataset is useful. The dataset
"/capability/~/" holds information about all features available to
the user (via inheritance), and the dataset "/capability/site/" holds
information about all features supported by the site.
Newman & Myers Standards Track [Page 25]RFC 2244 ACAP November 1997
5.5. Dataset Quotas
Management and scope of quotas is implementation dependent. Clients
can check the applicable quota limit and usage (in bytes) with the
GETQUOTA command. Servers can notify the client of a low quota
situation with the QUOTA untagged response.
6. Command and Response Specifications
ACAP commands and responses are described in this section. Commands
are organized first by the state in which the command is permitted,
then by a general category of command type.
Command arguments, identified by "Arguments:" in the command
descriptions below, are described by function, not by syntax. The
precise syntax of command arguments is described in the Formal Syntax
section.
Some commands cause specific server data to be returned; these are
identified by "Data:" in the command descriptions below. See the
response descriptions in the Responses section for information on
these responses, and the Formal Syntax section for the precise syntax
of these responses. It is possible for server data to be transmitted
as a result of any command; thus, commands that do not specifically
require server data specify "no specific data for this command"
instead of "none".
The "Result:" in the command description refers to the possible
tagged status responses to a command, and any special interpretation
of these status responses.
6.1. Initial Connection
Upon session startup, the server sends one of two untagged responses:
ACAP or BYE. The untagged BYE response is described in section
6.2.8.
6.1.1. ACAP Untagged Response
Data: capability list
The untagged ACAP response indicates the session is ready to
accept commands and contains a space-separated listing of
capabilities that the server supports. Each capability is
represented by a list containing the capability name optionally
followed by capability specific string arguments.
Newman & Myers Standards Track [Page 26]RFC 2244 ACAP November 1997
ACAP capability names MUST be registered with IANA according to
the rules in section 7.1.
Client implementations SHOULD NOT require any capability name
beyond those defined in this specification, and MUST tolerate any
unknown capability names. A client implementation MAY be
configurable to require SASL mechanisms other than CRAM-MD5
[CRAM-MD5] for site security policy reasons.
The following initial capabilities are defined:
CONTEXTLIMIT
The CONTEXTLIMIT capability has one argument which is a
number describing the maximum number of contexts the server
supports per connection. The number 0 indicates the server
has no limit, otherwise this number MUST be greater than
100.
IMPLEMENTATION
The IMPLEMENTATION capability has one argument which is a
string describing the server implementation. ACAP clients
MUST NOT alter their behavior based on this value. It is
intended primarily for debugging purposes.
SASL The SASL capability includes a list of the authentication
mechanisms supported by the server. See section 6.3.1.
Example: S: * ACAP (IMPLEMENTATION "ACME v3.5")
(SASL "CRAM-MD5") (CONTEXTLIMIT "200")
6.2. Any State
The following commands and responses are valid in any state.
6.2.1. NOOP Command
Arguments: none
Data: no specific data for this command (but see below)
Result: OK - noop completed
BAD - command unknown or arguments invalid
The NOOP command always succeeds. It does nothing. It can be
used to reset any inactivity auto-logout timer on the server.
Example: C: a002 NOOP
Newman & Myers Standards Track [Page 27]RFC 2244 ACAP November 1997
S: a002 OK "NOOP completed"
6.2.2. LANG Command
Arguments: list of language preferences
Data: intermediate response: LANG
Result: OK - lang completed
NO - no matching language available
BAD - command unknown or arguments invalid
One or more arguments are supplied to indicate the client's
preferred languages [LANG-TAGS] for error messages. The server
will match each client preference in order against its internal
table of available error string languages. For a client
preference to match a server language, the client's language tag
MUST be a prefix of the server's tag and match up to a "-" or the
end of string. If a match is found, the server returns an
intermediate LANG response and an OK response. The LANG response
indicates the actual language selected and appropriate comparators
for use with the languages listed in the LANG command.
If no LANG command is issued, all error text strings MUST be in
the registered language "i-default" [CHARSET-LANG-POLICY],
intended for an international audience.
Example: C: A003 LANG "fr-ca" "fr" "en-ca" "en-uk"
S: A003 LANG "fr-ca" "i;octet" "i;ascii-numeric"
"i;ascii-casemap" "en;primary" "fr;primary"
S: A003 OK "Bonjour"
6.2.3. LANG Intermediate Response
Data: language for error responses
appropriate comparators
The LANG response indicates the language which will be used for
error responses and the comparators which are appropriate for the
languages listed in the LANG command. The comparators SHOULD be
in approximate order from most efficient (usually "i;octet") to
most appropriate for human text in the preferred language.
Newman & Myers Standards Track [Page 28]RFC 2244 ACAP November 1997
6.2.4. LOGOUT Command
Arguments: none
Data: mandatory untagged response: BYE
Result: OK - logout completed
BAD - command unknown or arguments invalid
The LOGOUT command informs the server that the client is done with
the session. The server must send a BYE untagged response before
the (tagged) OK response, and then close the network connection.
Example: C: A023 LOGOUT
S: * BYE "ACAP Server logging out"
S: A023 OK "LOGOUT completed"
(Server and client then close the connection)
6.2.5. OK Response
Data: optional response code
human-readable text
The OK response indicates an information message from the server.
When tagged, it indicates successful completion of the associated
command. The human-readable text may be presented to the user as
an information message. The untagged form indicates an
information-only message; the nature of the information MAY be
indicated by a response code.
Example: S: * OK "Master ACAP server is back up"
6.2.6. NO Response
Data: optional response code
human-readable text
The NO response indicates an operational error message from the
server. When tagged, it indicates unsuccessful completion of the
associated command. The untagged form indicates a warning; the
command may still complete successfully. The human-readable text
describes the condition.
Example: C: A010 SEARCH "/addressbook/" DEPTH 3 RETURN ("*")
EQUAL "entry" "+i;octet" "bozo"
S: * NO "Master ACAP server is down, your data may
Newman & Myers Standards Track [Page 29]RFC 2244 ACAP November 1997
be out of date."
S: A010 OK "search done"
...
C: A222 STORE ("/folder/site/comp.mail.misc"
"folder.creation-time" "19951206103412")
S: A222 NO (PERMISSION ("/folder/site/")) "Permission
denied"
6.2.7. BAD Response
Data: optional response code
human-readable text
The BAD response indicates an error message from the server. When
tagged, it reports a protocol-level error in the client's command;
the tag indicates the command that caused the error. The untagged
form indicates a protocol-level error for which the associated
command can not be determined; it may also indicate an internal
server failure. The human-readable text describes the condition.
Example: C: ...empty line...
S: * BAD "Empty command line"
C: A443 BLURDYBLOOP
S: A443 BAD "Unknown command"
C: A444 NOOP Hello
S: A444 BAD "invalid arguments"
6.2.8. BYE Untagged Response
Data: optional response code
human-readable text
The untagged BYE response indicates that the server is about to
close the connection. The human-readable text may be displayed to
the user in a status report by the client. The BYE response may
be sent as part of a normal logout sequence, or as a panic
shutdown announcement by the server. It is also used by some
server implementations as an announcement of an inactivity auto-
logout.
This response is also used as one of two possible greetings at
session startup. It indicates that the server is not willing to
accept a session from this client.
Example: S: * BYE "Auto-logout; idle for too long"
Newman & Myers Standards Track [Page 30]RFC 2244 ACAP November 1997
6.2.9. ALERT Untagged Response
Data: optional response code
human-readable text
The human-readable text contains a special human generated alert
message that MUST be presented to the user in a fashion that calls
the user's attention to the message. This is intended to be used
for vital messages from the server administrator to the user, such
as a warning that the server will soon be shut down for
maintenance.
Example: S: * ALERT "This ACAP server will be shut down in
10 minutes for system maintenance."
6.3. Non-Authenticated State
In non-authenticated state, the AUTHENTICATE command establishes
authentication and enters authenticated state. The AUTHENTICATE
command provides a general mechanism for a variety of authentication
techniques.
Server implementations may allow non-authenticated access to certain
information by supporting the SASL ANONYMOUS [SASL-ANON] mechanism.
Once authenticated (including as anonymous), it is not possible to
re-enter non-authenticated state.
Only the any-state commands (NOOP, LANG and LOGOUT) and the
AUTHENTICATE command are valid in non-authenticated state.
6.3.1. AUTHENTICATE Command
Arguments: SASL mechanism name
optional initial response
Data: continuation data may be requested
Result: OK - authenticate completed, now in authenticated state
NO - authenticate failure: unsupported authentication
mechanism, credentials rejected
BAD - command unknown or arguments invalid,
authentication exchange cancelled
Newman & Myers Standards Track [Page 31]RFC 2244 ACAP November 1997
The AUTHENTICATE command indicates a SASL [SASL] authentication
mechanism to the server. If the server supports the requested
authentication mechanism, it performs an authentication protocol
exchange to authenticate and identify the user. Optionally, it
also negotiates a security layer for subsequent protocol
interactions. If the requested authentication mechanism is not
supported, the server rejects the AUTHENTICATE command by sending
a tagged NO response.
The authentication protocol exchange consists of a series of
server challenges and client answers that are specific to the
authentication mechanism. A server challenge consists of a
command continuation request with the "+" token followed by a
string. The client answer consists of a line consisting of a
string. If the client wishes to cancel an authentication
exchange, it should issue a line with a single unquoted "*". If
the server receives such an answer, it must reject the
AUTHENTICATE command by sending a tagged BAD response.
The optional initial-response argument to the AUTHENTICATE command
is used to save a round trip when using authentication mechanisms
that are defined to send no data in the initial challenge. When
the initial-response argument is used with such a mechanism, the
initial empty challenge is not sent to the client and the server
uses the data in the initial-response argument as if it were sent
in response to the empty challenge. If the initial-response
argument to the AUTHENTICATE command is used with a mechanism that
sends data in the initial challenge, the server rejects the
AUTHENTICATE command by sending a tagged NO response.
The service name specified by this protocol's profile of SASL is
"acap".
If a security layer is negotiated through the SASL authentication
exchange, it takes effect immediately following the CRLF that
concludes the authentication exchange for the client, and the CRLF
of the tagged OK response for the server.
All ACAP implementations MUST implement the CRAM-MD5 SASL
mechanism [CRAM-MD5], although they MAY offer a configuration
option to disable it if site security policy dictates. The
example below is the same example described in the CRAM-MD5
specification.
If an AUTHENTICATE command fails with a NO response, the client
may try another authentication mechanism by issuing another
AUTHENTICATE command. In other words, the client may request
authentication types in decreasing order of preference.
Newman & Myers Standards Track [Page 32]RFC 2244 ACAP November 1997
Example: S: * ACAP (IMPLEMENTATION "Blorfysoft v3.5")
(SASL "CRAM-MD5" "KERBEROS_V4")
C: A001 AUTHENTICATE "CRAM-MD5"
S: + "<1896.697170952@postoffice.reston.mci.net>"
C: "tim b913a602c7eda7a495b4e6e7334d3890"
S: A001 OK "CRAM-MD5 authentication successful"
6.4. Searching
This section describes the SEARCH command, for retrieving data from
datasets.
6.4.1. SEARCH Command
Arguments: dataset or context name
optional list of modifiers
search criteria
Data: intermediate responses: ENTRY, MODTIME, REFER
untagged responses: ADDTO, REMOVEFROM, CHANGE, MODTIME
Result: OK - search completed
NO - search failure: can't perform search
BAD - command unknown or arguments invalid
The SEARCH command identifies a subset of entries in a dataset and
returns information on that subset to the client. Inherited
entries and attributes are included in the search unless the
NOINHERIT search modifier is included or the user does not have
permission to read the attributes in the base dataset.
The first argument to SEARCH identifies what is to be searched.
If the string begins with a slash ("/"), it is the name of a
dataset to be searched, otherwise it is a name of a context that
was created by a SEARCH command given previously in the session.
A successful SEARCH command MAY result in intermediate ENTRY
responses and MUST result in a MODTIME intermediate response.
Following that are zero or more modifiers to the search. Each
modifier may be specified at most once. The defined modifiers
are:
Newman & Myers Standards Track [Page 33]RFC 2244 ACAP November 1997
DEPTH number
The SEARCH command will traverse the dataset tree up to the
specified depth. ENTRY responses will include the full path
to the entry. A value of "0" indicates that the search
should traverse the entire tree. A value of "1" is the
default and indicates only the specified dataset should be
searched. If a dataset is traversed which is not located on
the current server, then a REFER intermediate response is
returned for that subtree and the search continues.
HARDLIMIT number
If the SEARCH command would result in more than number
entries, the SEARCH fails with a NO completion result with a
WAYTOOMANY response code.
LIMIT number number
Limits the number of intermediate ENTRY responses that the
search may generate. The first numeric argument specifies
the limit, the second number specifies the number of entries
to return if the number of matches exceeds the limit. If the
limit is exceeded, the SEARCH command still succeeds,
returning the total number of matches in a TOOMANY response
code in the tagged OK response.
MAKECONTEXT [ENUMERATE] [NOTIFY] context
Causes the SEARCH command to create a context with the name
given in the argument to refer to the matching entries. If
the SEARCH is successful, the context name may then be given
as an argument to subsequent SEARCH commands to search the
set of matching entries. If a context with the specified
name already exists, it is first freed. If a new context may
not be created due to the server's limit on the number of
existing contexts, the command fails, returning a
TRYFREECONTEXT response code in the NO completion response.
The optional "ENUMERATE" and "NOTIFY" arguments may be
included to request enumeration of the context (for virtual
scroll bars) or change notifications for the context. If
"NOTIFY" is not requested, the context represents a snapshot
of the entries at the time the SEARCH was issued.
ENUMERATE requests that the contents of the context be
ordered according to the SORT modifier and that sequential
numbers, starting with one, be assigned to the entries in the
context. This permits the RANGE modifier to be used to fetch
portions of the ordered context.
Newman & Myers Standards Track [Page 34]RFC 2244 ACAP November 1997
NOTIFY requests that the server send untagged ADDTO,
REMOVEFROM, CHANGE, and MODTIME responses while the context
created by this SEARCH command exists. The server MAY issue
untagged ADDTO, REMOVEFROM, CHANGE and MODTIME notifications
for a context at any time between the issuing of the SEARCH
command with MAKECONTEXT NOTIFY and the completion of a
FREECONTEXT command for the context. Notifications are only
issued for changes which occur after the server receives the
SEARCH command which created the context. After issuing a
sequence of ADDTO, REMOVEFROM or CHANGE notifications, the
server MUST issue an untagged MODTIME notification indicating
that the client has all updates to the entries in the context
up to and including the given modtime value. Servers are
permitted a reasonable delay to batch change notifications
before sending them to the client.
The position arguments of the ADDTO, REMOVEFROM and CHANGE
notifications are 0 if ENUMERATE is not requested.
NOINHERIT
This causes the SEARCH command to operate without
inheritance. It can be used to tell which values are
explicit overrides. If MAKECONTEXT is also specified, the
created context is also not affected by inheritance.
RETURN (metadata...)
Specifies what is to be returned in intermediate ENTRY
responses. If this modifier is not specified, no
intermediate ENTRY responses are returned.
Inside the parentheses is an optional list of attributes,
each optionally followed by a parenthesized list of metadata.
If the parenthesized list of metadata is not specified, it
defaults to "(value)".
An attribute name with a trailing "*" requests all attributes
with that prefix. A "*" by itself requests all attributes.
If the parenthesized list of metadata is not specified for an
attribute with a trailing "*", it defaults to "(attribute
value)". Results matching such an attribute pattern are
grouped in parentheses.
Following the last intermediate ENTRY response, the server
returns a single intermediate MODTIME response.
Newman & Myers Standards Track [Page 35]RFC 2244 ACAP November 1997
SORT (attribute comparator ...)
Specifies the order in which any resulting ENTRY replies are
to be returned to the client. The SORT modifier takes as an
argument a parenthesized list of one or more
attribute/comparator pairs. Attribute lists the attribute to
sort on, comparator specifies the name of the collation rule
to apply to the values of the attribute. Successive
attribute/comparator pairs are used to order two entries only
when all preceding pairs indicate the two entries collate the
same.
If the SORT modifier is used in conjunction with the
MAKECONTEXT modifier, the SORT modifier specifies the
ordering of entries in the created context.
If no SORT modifier is specified, or none of the
attribute/comparator pairs indicates an order for the two
entries, the server uses the order of the entries that exists
in the context or dataset being searched.
Following the modifiers is the search criteria. Searching
criteria consist of one or more search keys. Search keys may be
combined using the AND, and OR search keys. For example, the
criteria (the newline is for readability and not part of the
criteria):
AND COMPARE "modtime" "+i;octet" "19951206103400"
COMPARE "modtime" "-i;octet" "19960112000000"
refers to all entries modified between 10:34 December 6 1995 and
midnight January 12, 1996 UTC.
The currently defined search keys are as follows.
ALL This matches all entries.
AND search-key1 search-key2
Entries that match both search keys.
COMPARE attribute comparator value
Entries for which the value of the specified attribute
collates using the specified comparator the same or later
than the specified value.
COMPARESTRICT attribute comparator value
Entries for which the specified attribute collates using the
specified comparator later than the specified value.
Newman & Myers Standards Track [Page 36]RFC 2244 ACAP November 1997
EQUAL attribute comparator value
Entries for which the value of the attribute is equal to the
specified value using the specified comparator.
NOT search-key
Entries that do not match the specified search key.
OR search-key1 search-key2
Entries that match either search key.
PREFIX attribute comparator value
Entries which begin with the specified value using the
specified comparator. If the specified comparator doesn't
support substring matching, a BAD response is returned.
RANGE start end time
Entries which are within the specified range of the
enumerated context's ordering. The lowest-ordered entry in
the context is assigned number one, the next lowest entry is
assigned number two, and so on. The numeric arguments
specify the lowest and highest numbers to match. The time
specifies that the client has processed notifications for the
context up to the specified time. If the context has been
modified since then, the server MUST either return a NO with
a MODIFIED response code, or return the results that the
SEARCH would have returned if none of the changes since that
time had been made.
RANGE is only permitted on enumerated contexts. If RANGE is
used with a dataset or non-enumerated context, the server
MUST return a BAD response.
SUBSTRING attribute comparator value
Entries which contain the specified value, using the
specified comparator. If the specified comparator doesn't
support substring matching, a BAD response is returned.
6.4.2. ENTRY Intermediate Response
Data: entry name
entry data
The ENTRY intermediate response occurs as a result of a SEARCH or
STORE command. This is the means by which dataset entries are
returned to the client.
Newman & Myers Standards Track [Page 37]RFC 2244 ACAP November 1997
The ENTRY response begins with the entry name, if a SEARCH command
without the DEPTH modifier was issued, or the entry path in other
cases. This is followed by a set of zero or more items, one for
each metadata item in the RETURN search modifier. Results
matching an attribute pattern or returning multiple metadata items
are grouped in parentheses.
6.4.3. MODTIME Intermediate Response
Data: modtime value
The MODTIME intermediate response occurs as a result of a SEARCH
command. It indicates that the just created context or the
previously returned ENTRY responses include all updates to the
returned entries up to and including the modtime value in the
argument.
6.4.4. REFER Intermediate Response
Data: dataset path
relative ACAP URLs
The REFER intermediate response occurs as a result of a
multi-level SEARCH where one of the levels is located on a
different server. The response indicates the dataset which is not
located on the current server and one or more relative ACAP URLs
for where that dataset may be found.
6.4.5. Search Examples
Here are some SEARCH command exchanges between the client and server:
C: A046 SEARCH "/addressbook/" DEPTH 3 RETURN ("addressbook.Alias"
"addressbook.Email" "addressbook.List") OR NOT EQUAL
"addressbook.Email" "i;octet" NIL NOT EQUAL
"addressbook.List" "i;octet" NIL
S: A046 ENTRY "/addressbook/user/joe/A0345" "fred"
"fred@stone.org" NIL
S: A046 ENTRY "/addressbook/user/fred/A0537" "joe" "joe@stone.org"
NIL
S: A046 ENTRY "/addressbook/group/Dinosaur Operators/A423"
"saurians" NIL "1"
S: A046 MODTIME "19970728105252"
S: A046 OK "SEARCH completed"
C: A047 SEARCH "/addressbook/user/fred/" RETURN ("*") EQUAL "entry"
"i;octet" "A0345"
S: A047 ENTRY "A0345" (("modtime" "19970728102226")
Newman & Myers Standards Track [Page 38]RFC 2244 ACAP November 1997
("addressbook.Alias" "fred") ("addressbook.Email"
"fred@stone.org") ("addressbook.CommonName"
"Fred Flintstone") ("addressbook.Surname" "Flintstone")
("addressbook.GivenName" "Fred"))
S: A047 MODTIME "19970728105258"
S: A047 OK "SEARCH completed"
C: A048 SEARCH "/options/~/vendor.example/" RETURN
("option.value"("size" "value" "myrights"))
SORT ("entry" "i;octet") COMPARE "modtime" "i;octet"
"19970727123225"
S: A048 ENTRY "blurdybloop" (5 "ghoti" "rwia")
S: A048 ENTRY "buckybits" (2 "10" "rwia")
S: A048 ENTRY "windowSize" (7 "100x100" "rwia")
S: A048 MODTIME "19970728105304"
S: A048 OK "SEARCH completed"
C: A049 SEARCH "/addressbook/~/public" RETURN ("addressbook.Alias"
"addressbook.Email") MAKECONTEXT ENUMERATE "blob" LIMIT 100 1
SORT ("addressbook.Alias" "i;octet") NOT EQUAL
"addressbook.Email" NIL
S: A049 ENTRY "A437" "aaguy" "aaguy@stone.org"
S: A049 MODTIME "19970728105308"
S: A049 OK (TOOMANY 347) "Context 'blob' created"
C: A050 SEARCH "blob" RANGE 2 2 "19970728105308" ALL
S: A050 ENTRY "A238" "abguy" "abguy@stone.org"
S: A050 MODTIME "19970728105310"
S: A050 OK "SEARCH Completed"
6.5. Contexts
The following commands use contexts created by a SEARCH command with
a MAKECONTEXT modifier.
6.5.1. FREECONTEXT Command
Arguments: context name
Data: no specific data for this command
Result: OK - freecontext completed
NO - freecontext failure: no such context
BAD - command unknown or arguments invalid
Newman & Myers Standards Track [Page 39]RFC 2244 ACAP November 1997
The FREECONTEXT command causes the server to free all state
associated with the named context. The context may no longer be
searched and the server will no longer issue any untagged
responses for the context. The context is no longer counted
against the server's limit on the number of contexts.
Example: C: A683 FREECONTEXT "blurdybloop"
S: A683 OK "Freecontext completed"
6.5.2. UPDATECONTEXT Command
Arguments: list of context names
Data: untagged responses: ADDTO REMOVEFROM CHANGE MODTIME
Result: OK - Updatecontext completed: all updates completed
NO - Updatecontext failed: no such context
not a notify context
BAD - command unknown or arguments invalid
The UPDATECONTEXT command causes the server to ensure that the
client is notified of all changes known to the server for the
contexts listed as arguments up to the current time. The contexts
listed in the arguments must have been previously given to a
successful SEARCH command with a MAKECONTEXT NOTIFY modifier. A
MODTIME untagged response MUST be returned if any read-write
metadata in the context changed since the last MODTIME for that
context. This includes metadata which is not listed in the RETURN
modifier for the context.
While a server may issue untagged ADDTO, REMOVEFROM, CHANGE, and
MODTIME at any time, the UPDATECONTEXT command is used to "prod"
the server to send any notifications it has not sent yet.
The UPDATECONTEXT command SHOULD NOT be used to poll for updates.
Example: C: Z4S9 UPDATECONTEXT "blurdybloop" "blarfl"
S: Z4S9 OK "client has been notified of all changes"
6.5.3. ADDTO Untagged Response
Data: context name
entry name
position
metadata list
Newman & Myers Standards Track [Page 40]RFC 2244 ACAP November 1997
The untagged ADDTO response informs the client that an entry has
been added to a context. The response includes the position
number of the added entry (the first entry in the context is
numbered 1) and those metadata contained in the entry which match
the RETURN statement when the context was created.
For enumerated contexts, the ADDTO response implicitly adds one to
the position of all members of the context which had position
numbers that were greater than or equal to the ADDTO position
number. For non-enumerated contexts, the position field is always
0.
Example: S: * ADDTO "blurdybloop" "fred" 15
("addressbook.Email" "fred@stone.org")
6.5.4. REMOVEFROM Untagged Response
Data: context name
entry name
old position
The untagged REMOVEFROM response informs the client that an entry
has been removed from a context. The response includes the
position number that the removed entry used to have (the first
entry in the context is numbered 1).
For enumerated contexts, the REMOVEFROM response implicitly
subtracts one from the position numbers of all members of the
context which had position numbers greater than the REMOVEFROM
position number. For non-enumerated contexts, the position field
is always 0.
Example: S: * REMOVEFROM "blurdybloop" "fred" 15
6.5.5. CHANGE Untagged Response
Data: context name
entry name
old position
new position
metadata list
The untagged CHANGE response informs the client that an entry in a
context has either changed position in the context or has changed
the values of one or more of the attributes specified in the
RETURN modifier when the context was created.
Newman & Myers Standards Track [Page 41]RFC 2244 ACAP November 1997
The response includes the previous and current position numbers of
the entry (which are 0 if ENUMERATE was not specified on the
context) and the attribute metadata requested in the RETURN
modifier when the context was created.
For enumerated contexts, the CHANGE response implicitly changes
the position numbers of all entries which had position numbers
between the old and new position. If old position is less than
new position, than one is subtracted from all entries which had
position numbers in that range. Otherwise one is added to all
entries which had position numbers in that range. If the old
position and new position are the same, then no implicit position
renumbering occurs.
CHANGE responses are not issued for entries which have changed
position implicitly due to another ADDTO, REMOVEFROM or CHANGE
response.
Example: S: * CHANGE "blurdybloop" "fred" 15 10
("addressbook.Email" "fred@stone.org")
6.5.6. MODTIME Untagged Response
Data: context name
modtime value
The untagged MODTIME response informs the client that it has
received all updates to entries in the context which have modtime
values less than or equal to the modtime value in the argument.
Example: S: * MODTIME mycontext "19970320162338"
6.6. Dataset modification
The following commands and responses handle modification of datasets.
Newman & Myers Standards Track [Page 42]RFC 2244 ACAP November 1997
6.6.1. STORE Command
Arguments: entry store list
Data: intermediate responses: ENTRY
Result: OK - store completed
NO - store failure: can't store that name
UNCHANGEDSINCE specified and entry changed
BAD - command unknown or arguments invalid
invalid UTF-8 syntax in attribute name
Creates, modifies, or deletes the named entries in the named
datasets. The values of metadata not specified in the command are
not changed. Setting the "value" metadata of an attribute to NIL
removes that attribute from the entry. Setting the "value" of the
"entry" attribute to NIL removes that entry from the dataset and
cancels inheritance for the entire entry. Setting the "value" of
the "entry" attribute to DEFAULT removes that entry from the
inheriting dataset and reverts the entry and its attributes to
inherited values, if any. Changing the value of the "entry"
attribute renames the entry.
Storing DEFAULT to the "value" metadata of an attribute is
equivalent to storing NIL, except that inheritance is enabled for
that attribute. If a non-NIL value is inherited then an ENTRY
intermediate response is generated to notify the client of the
this change. The ENTRY response includes the entry-path and the
attribute name and value metadata for each attribute which
reverted to a non-NIL inherited setting.
Storing NIL to the "value" metadata of an attribute MAY be treated
equivalent to storing DEFAULT to that "value" if there is a NIL
value in the base dataset.
The STORE command is followed by one or more entry store lists.
Each entry store list begins with an entry path followed by STORE
modifiers, followed by zero or more attribute store items. Each
attribute store item is made up of the attribute name followed by
NIL (to remove the attribute's value), DEFAULT (to revert the item
to any inherited value), a single value (to set the attribute's
single value), or a list of metadata items to modify. The
following STORE modifiers may be specified:
Newman & Myers Standards Track [Page 43]RFC 2244 ACAP November 1997
NOCREATE
By default, the server MUST create any datasets necessary to
store the entry, including multiple hierarchy levels. If
NOCREATE is specified, the STORE command will fail with a
NOEXIST error unless the parent dataset already exists.
UNCHANGEDSINCE
If the "modtime" of the entry is later than the
unchangedsince time, then the store fails with a MODIFIED
response code. Use of UNCHANGEDSINCE with a time of
"00000101000000" will always fail if the entry exists.
Clients writing to a shared dataset are encouraged to use
UNCHANGEDSINCE when modifying an existing entry.
The server MUST either make all the changes specified in a single
STORE command or make none of them. If successful, the server
MUST update the "modtime" attribute for every entry which was
changed.
It is illegal to list any metadata item within an attribute twice,
any attribute within an entry twice or any entry path twice. The
server MUST return a BAD response if this happens.
The server MAY re-order the strings in a multi-value on STORE and
MAY remove duplicate strings. However, SEARCH MUST return multi-
values and the associated size list metadata in a consistant
order.
Example: C: A342 STORE ("/addressbook/user/fred/ABC547"
"addressbook.TelephoneNumber" "555-1234"
"addressbook.CommonName" "Barney Rubble"
"addressbook.AlternateNames" ("value"
("Barnacus Rubble" "Coco Puffs Thief"))
"addressbook.Email" NIL)
S: A342 OK "Store completed"
C: A343 STORE ("/addressbook/user/joe/ABD42"
UNCHANGEDSINCE "19970320162338"
"user.joe.hair-length" "10 inches")
S: A343 NO (MODIFIED) "'ABD42' has been changed
by somebody else."
C: A344 STORE ("/addressbook/group/Developers/ACD54"
"entry" NIL)
S: A344 OK "Store completed"
C: A345 STORE ("/option/~/common/SMTPserver"
"option.value" DEFAULT)
S: A345 ENTRY "/option/~/common/SMTPserver"
Newman & Myers Standards Track [Page 44]RFC 2244 ACAP November 1997
"option.value" "smtp.server.do.main"
S: A345 OK "Store completed"
C: A347 STORE ("/addressbook/~/" "dataset.inherit"
"/addressbook/group/Developers")
S: A347 OK "Store completed"
6.6.2. DELETEDSINCE Command
Arguments: dataset name
time
Data: intermediate response: DELETED
Result: OK - DELETEDSINCE completed
NO - DELETEDSINCE failure: can't read dataset
date too far in the past
BAD - command unknown or arguments invalid
The DELETEDSINCE command returns in intermediate DELETED replies
the names of entries that have been deleted from the named dataset
since the given time.
Servers may impose a limit on the number or age of deleted entry
names they keep track of. If the server does not have information
going back to the specified time, the command fails, returning a
TOOOLD response code in the tagged NO response.
Example: C: Z4S9 DELETEDSINCE "/folder/site/" 19951205103412
S: Z4S9 DELETED "blurdybloop"
S: Z4S9 DELETED "anteaters"
S: Z4S9 OK "DELETEDSINCE completed"
C: Z4U3 DELETEDSINCE "/folder/site/" 19951009040854
S: Z4U3 NO (TOOOLD) "Don't have that information"
6.6.3. DELETED Intermediate Response
Data: entry name
The intermediate DELETED response occurs as a result of a
DELETEDSINCE command. It returns an entry that has been deleted
from the dataset specified in the DELETEDSINCE command.
6.7. Access Control List Commands
The commands in this section are used to manage access control lists.
Newman & Myers Standards Track [Page 45]RFC 2244 ACAP November 1997
6.7.1. SETACL Command
Arguments: acl object
authentication identifier
access rights
Data: no specific data for this command
Result: OK - setacl completed
NO - setacl failure: can't set acl
BAD - command unknown or arguments invalid
The SETACL command changes the access control list on the
specified object so that the specified identifier is granted the
permissions enumerated in rights. If the object did not
previously have an access control list, one is created.
Example: C: A123 SETACL ("/addressbook/~/public/") "anyone" "r"
S: A123 OK "Setacl complete"
C: A124 SETACL ("/folder/site/") "B1FF" "rwa"
S: A124 NO (PERMISSION ("/folder/site/")) "'B1FF' not
permitted to modify access rights
for '/folder/site/'"
6.7.2. DELETEACL Command
Arguments: acl object
optional authentication identifier
Data: no specific data for this command
Result: OK - deleteacl completed
NO - deleteacl failure: can't delete acl
BAD - command unknown or arguments invalid
If given the optional identifier argument, the DELETEACL command
removes any portion of the access control list on the specified
object for the specified identifier.
If not given the optional identifier argument, the DELETEACL
command removes the ACL from the object entirely, causing access
to be controlled by a higher-level default ACL. This form of the
DELETEACL command is not permitted on the default ACL for a
dataset and servers MUST return a BAD.
Newman & Myers Standards Track [Page 46]RFC 2244 ACAP November 1997
Example: C: A223 DELETEACL ("/addressbook/~/public") "anyone"
S: A223 OK "Deleteacl complete"
C: A224 DELETEACL ("/folder/site")
S: A224 BAD "Can't delete ACL from dataset"
C: A225 DELETEACL ("/addressbook/user/fred"
"addressbook.Email" "barney")
S: A225 OK "Deleteacl complete"
6.7.3. MYRIGHTS Command
Arguments: acl object
Data: intermediate responses: MYRIGHTS
Result: OK - myrights completed
NO - myrights failure: can't get rights
BAD - command unknown or arguments invalid
The MYRIGHTS command returns the set of rights that the client has
to the given dataset or dataset attribute.
Example: C: A003 MYRIGHTS ("/folder/site")
S: A003 MYRIGHTS "r"
S: A003 OK "Myrights complete"
6.7.4. MYRIGHTS Intermediate Response
Data: rights
The MYRIGHTS response occurs as a result of a MYRIGHTS command.
The argument is the set of rights that the client has for the
object referred to in the MYRIGHTS command.
6.7.5. LISTRIGHTS Command
Arguments: acl object
authentication identifier
Data: untagged responses: LISTRIGHTS
Result: OK - listrights completed
NO - listrights failure: can't get rights list
BAD - command unknown or arguments invalid
Newman & Myers Standards Track [Page 47]RFC 2244 ACAP November 1997
The LISTRIGHTS command takes an object and an identifier and
returns information about what rights the current user may revoke
or grant to that identifier in the ACL for that object.
Example: C: a001 LISTRIGHTS ("/folder/~/") "smith"
S: a001 LISTRIGHTS "xra" "w" "i"
S: a001 OK Listrights completed
C: a005 LISTRIGHTS ("/folder/site/archive/imap") "anyone"
S: a005 LISTRIGHTS "" "x" "r" "w" "i"
S: a005 OK Listrights completed
6.7.6. LISTRIGHTS Intermediate Response
Data: required rights
list of optional rights
The LISTRIGHTS response occurs as a result of a LISTRIGHTS
command. The first argument is a string containing the (possibly
empty) set of rights the identifier will always be granted on the
dataset or attribute.
Following this are zero or more strings each containing a single
right which the current user may revoke or grant to the identifier
in the dataset or attribute.
The same right MUST NOT be listed more than once in the LISTRIGHTS
response.
6.8. Quotas
The section defines the commands and responses relating to quotas.
6.8.1. GETQUOTA Command
Arguments: dataset
Data: untagged responses: QUOTA
Result: OK - Quota information returned
NO - Quota failure: can't access resource limit
no resource limit
BAD - command unknown or arguments invalid
Newman & Myers Standards Track [Page 48]RFC 2244 ACAP November 1997
The GETQUOTA command takes the name of a dataset, and returns in
an untagged QUOTA response the name of the dataset, quota limit in
bytes that applies to that dataset and the quota usage within that
limit. The scope of a quota limit is implementation dependent.
Example: C: A043 GETQUOTA "/option/user/fred/common"
S: * QUOTA "/option/user/fred/common" 1048576 2475
S: A043 OK "Getquota completed"
6.8.3. QUOTA Untagged Response
Data: dataset
quota limit in bytes
amount of quota limit used
extension data
The QUOTA untagged response is generated as a result of a GETQUOTA
command or MAY be generated by the server in response to a SEARCH
or STORE command to warn about high usage of a quota. It includes
the name of the applicable dataset, the quota limit in bytes, the
quota usage and some optional extension data. Clients MUST
tolerate the extension data as its use is reserved for a future
extension.
6.9. Extensions
In order to simplify the process of extending the protocol, clients
MUST tolerate unknown server responses which meet the syntax of
response-extend. In addition, clients MUST tolerate unknown server
response codes which meet the syntax of resp-code-ext. Availability
of new commands MUST be announced via a capability on the initial
greeting line and such commands SHOULD meet the syntax of
command-extend.
Servers MUST respond to unknown commands with a BAD command
completion result. Servers MUST skip over non-synchronizing literals
contained in an unknown command. This may be done by assuming the
unknown command matches the command-extend syntax, or by reading a
line at a time and checking for the non-synchronizing literal syntax
at the end of the line.
7. Registration Procedures
ACAP's usefulness comes from providing a structured storage model for
all sorts of configuration data. However, for its potential to be
achieved, it is important that the Internet community strives for the
following goals:
Newman & Myers Standards Track [Page 49]RFC 2244 ACAP November 1997
(1) Standardization. It is very important to standardize dataset
classes. The authors hope that ACAP achieves the success that SNMP
has seen with the definition of numerous standards track MIBs.
(2) Community Review. In the absence of standardization, it is
important to get community review on a proposal to improve its
engineering quality. Community review is strongly recommended prior
to registration. The ACAP implementors mailing list
<ietf-acap@andrew.cmu.edu> should be used for this purpose.
(3) Registration. Registration serves a two-fold purpose. First it
prevents use of the same name for different purposes, and second it
provides a one-stop list which can be used to locate existing
extensions or dataset classes to prevent duplicate work.
The following registration templates may be used to register ACAP
protocol elements with the Internet Assigned Numbers Authority
(IANA).
7.1. ACAP Capabilities
New ACAP capabilities MUST be registered prior to use. Careful
consideration should be made before extending the protocol, as it can
lead to complexity or interoperability problems. Review of proposals
on the acap implementors mailing list is strongly encouraged prior to
registration.
To: iana@iana.org
Subject: Registration of ACAP capability
Capability name:
Capability keyword:
Capability arguments:
Published Specification(s):
(Optional, but strongly encouraged)
Person and email address to contact for further information:
7.2. ACAP Response Codes
ACAP response codes are registered on a first come, first served
basis. Review of proposals on the acap implementors mailing list is
strongly encouraged prior to registration.
Newman & Myers Standards Track [Page 50]
RFC 2244 ACAP November 1997
To: iana@iana.org
Subject: Registration of ACAP response code
Response Code:
Arguments (use ABNF to specify syntax):
Purpose:
Published Specification(s):
(Optional, but strongly encouraged)
Person and email address to contact for further information:
7.3. Dataset Classes
A dataset class provides a core set of attributes for use in a
specified hierarchy. It may also define rules for the dataset
hierarchy underneath that class. Dataset class specifications must
be standards track or IESG approved experimental RFCs.
To: iana@iana.org
Subject: Registration of ACAP dataset class
Dataset class name/attribute prefix:
Purpose:
Published Specification(s):
(Standards track or IESG approved experimental RFC)
Person and email address to contact for further information:
7.4. Vendor Subtree
Vendors may reserve a portion of the ACAP namespace for private use.
Dataset class names beginning with "vendor.<company/product name>."
are reserved for use by that company or product. In addition, all
attribute names beginning with "vendor.<company/product name>." are
reserved for use by that company or product once registered.
Registration is on a first come, first served basis. Whenever
possible, private attributes and dataset classes should be avoided in
favor of improving interoperable dataset class definitions.
Newman & Myers Standards Track [Page 51]
RFC 2244 ACAP November 1997
To: iana@iana.org
Subject: Registration of ACAP vendor subtree
Private Prefix: vendor.<company/product name>.
Person and email address to contact for further information:
(company names and addresses should be included when appropriate)
8. Formal Syntax
The following syntax specification uses the augmented Backus-Naur
Form (BNF) notation as specified in [ABNF]. This uses the ABNF core
rules as specified in Appendix A of the ABNF specification [ABNF].
Except as noted otherwise, all alphabetic characters are
case-insensitive. The use of upper or lower case characters to
define token strings is for editorial clarity only. Implementations
MUST accept these strings in a case-insensitive fashion.
The "initial-greeting" rule below defines the initial ACAP greeting
from the server. The "command" rule below defines the syntax for
commands sent by the client. The "response" rule below defines the
syntax for responses sent by the server.
ATOM-CHAR = "!" / %x23-27 / %x2A-5B / %x5D-7A / %x7C-7E
;; Any CHAR except ATOM-SPECIALS
ATOM-SPECIALS = "(" / ")" / "{" / SP / CTL / QUOTED-SPECIALS
CHAR = %x01-7F
DIGIT-NZ = %x31-39
; non-zero digits ("1" - "9")
QUOTED-CHAR = SAFE-UTF8-CHAR / "\" QUOTED-SPECIALS
QUOTED-SPECIALS = <"> / "\"
SAFE-CHAR = %x01-09 / %x0B-0C / %x0E-21 /
%x23-5B / %x5D-7F
;; any TEXT-CHAR except QUOTED-SPECIALS
SAFE-UTF8-CHAR = SAFE-CHAR / UTF8-2 / UTF8-3 / UTF8-4 /
UTF8-5 / UTF8-6
TAG-CHAR = %x21 / %x23-27 / %x2C-5B / %x5D-7A / %x7C-7E
;; Any ATOM-CHAR except "*" or "+"
Newman & Myers Standards Track [Page 52]RFC 2244 ACAP November 1997
TEXT-CHAR = %x01-09 / %x0B-0C / %x0E-7F
;; any CHAR except CR and LF
TEXT-UTF8-CHAR = SAFE-UTF8-CHAR / QUOTED-SPECIALS
UTF8-1 = %x80-BF
UTF8-2 = %xC0-DF UTF8-1
UTF8-3 = %xE0-EF 2UTF8-1
UTF8-4 = %xF0-F7 3UTF8-1
UTF8-5 = %xF8-FB 4UTF8-1
UTF8-6 = %xFC-FD 5UTF8-1
UTF8-CHAR = TEXT-UTF8-CHAR / CR / LF
acl = "(" [acl-identrights *(SP acl-identrights)] ")"
*(SPACE acl-identrights)] ")"
acl-identifier = string-utf8
;; MUST NOT contain HTAB
acl-identrights = string-utf8
;; The identifier followed by a HTAB,
;; followed by the rights.
acl-delobject = "(" dataset SP attribute [SP entry-name] ")"
acl-object = "(" dataset [SP attribute [SP entry-name]] ")"
acl-rights = quoted
atom = ALPHA *1023ATOM-CHAR
attribute = string-utf8
;; dot-separated attribute name
;; MUST NOT contain "*" or "%"
attribute-store = attribute SP (value-nildef /
"(" 1*(metadata-write-q SP value-store) ")")
;; MUST NOT include the same metadata twice
auth-type = <"> auth-type-name <">
Newman & Myers Standards Track [Page 53]RFC 2244 ACAP November 1997
auth-type-name = iana-token
;; as defined in SASL [SASL]
command = tag SP (command-any / command-auth /
command-nonauth) CRLF
;; Modal based on state
command-authent = "AUTHENTICATE" SP auth-type
[SP string] *(CRLF string)
command-any = "NOOP" / command-lang / "LOGOUT" /
command-extend
command-auth = command-delacl / command-dsince /
command-freectx / command-getquota /
command-lrights / command-myrights /
command-search / command-setacl /
command-store
;; only valid in authenticated state
command-delacl = "DELETEACL" SP acl-delobject [SP acl-identifier]
command-dsince = "DELETEDSINCE" SP dataset SP time
command-extend = extend-token [SP extension-data]
command-freectx = "FREECONTEXT" SP context
command-getquota = "GETQUOTA" SP dataset
command-lang = "LANG" *(SP lang-tag)
command-lrights = "LISTRIGHTS" SP acl-object
command-myrights = "MYRIGHTS" SP acl-object
command-nonauth = command-authent
;; only valid in non-authenticated state
command-search = "SEARCH" SP (dataset / context)
*(SP search-modifier) SP search-criteria
;; MUST NOT include same search-modifier twice
command-setacl = "SETACL" SP acl-object SP acl-identifier
SP acl-rights
command-store = "STORE" SP store-entry-list
Newman & Myers Standards Track [Page 54]RFC 2244 ACAP November 1997
comparator = <"> comparator-name <">
comparator-name = ["+" / "-"] iana-token
context = string-utf8
;; MUST NOT begin with slash ("/")
dataset = string-utf8
;; slash-separated dataset name
;; begins with slash
entry = entry-name / entry-path
entry-name = string-utf8
;; entry name MUST NOT contain slash
;; MUST NOT begin with "."
entry-path = string-utf8
;; slash-separated path to entry
;; begins with slash
entry-relative = string-utf8
;; potentially relative path to entry
extend-token = atom
;; MUST be defined by a standards track or
;; IESG approved experimental protocol extension
extension-data = extension-item *(SP extension-item)
extension-item = extend-token / string / number /
"(" [extension-data] ")"
iana-token = atom
;; MUST be registered with IANA
initial-greeting = "*" SP "ACAP" *(SP "(" init-capability ")") CRLF
init-capability = init-cap-context / init-cap-extend /
init-cap-implem / init-cap-sasl
init-cap-context = "CONTEXTLIMIT" SP string
init-cap-extend = iana-token [SP string-list]
init-cap-implem = "IMPLEMENTATION" SP string
init-cap-sasl = "SASL" SP string-list
Newman & Myers Standards Track [Page 55]RFC 2244 ACAP November 1997
lang-tag = <"> Language-Tag <">
;; Language-Tag rule is defined in [LANG-TAGS]
literal = "{" number [ "+" ] "}" CRLF *OCTET
;; The number represents the number of octets
;; MUST be literal-utf8 except for values
literal-utf8 = "{" number [ "+" ] "}" CRLF *UTF8-CHAR
;; The number represents the number of octets
;; not the number of characters
metadata = attribute [ "(" metadata-type-list ")" ]
;; attribute MAY end in "*" as wildcard.
metadata-list = metadata *(SP metadata)
metadata-type = "attribute" / "myrights" / "size" /
"count" / metadata-write
metadata-type-q = <"> metadata-type <">
metadata-type-list = metadata-type-q *(SP metadata-type-q)
metadata-write = "value" / "acl"
metadata-write-q = <"> metadata-write <">
nil = "NIL"
number = *DIGIT
;; A 32-bit unsigned number.
;; (0 <= n < 4,294,967,296)
nz-number = DIGIT-NZ *DIGIT
;; A 32-bit unsigned non-zero number.
;; (0 < n < 4,294,967,296)
position = number
;; "0" if context is not enumerated
;; otherwise this is non-zero
quota-limit = number
quota-usage = number
quoted = <"> *QUOTED-CHAR <">
;; limited to 1024 octets between the <">s
Newman & Myers Standards Track [Page 56]RFC 2244 ACAP November 1997
response = response-addto / response-alert / response-bye /
response-change / response-cont /
response-deleted / response-done /
response-entry / response-extend /
response-listr / response-lang /
response-mtimei / response-mtimeu /
response-myright / response-quota /
response-refer / response-remove / response-stat
response-addto = "*" SP "ADDTO" SP context SP entry-name
SP position SP return-data-list
response-alert = "*" SP "ALERT" SP resp-body CRLF
;; Client MUST display alert text to user
response-bye = "*" SP "BYE" SP resp-body CRLF
;; Server will disconnect condition
response-change = "*" SP "CHANGE" SP context SP entry-name
SP position SP position SP return-data-list
response-cont = "+" SP string
response-deleted = tag SP "DELETED" SP entry-name
response-done = tag SP resp-cond-state CRLF
response-entry = tag SP "ENTRY" SP entry SP return-data-list
response-extend = (tag / "*") SP extend-token [SP extension-data]
response-lang = "*" SP "LANG" SP lang-tag 1*(SP comparator)
response-listr = tag SP "LISTRIGHTS" SP acl-rights
*(SP acl-rights)
response-mtimei = tag SP "MODTIME" SP time
response-mtimeu = "*" SP "MODTIME" SP context SP time
response-myright = tag SP "MYRIGHTS" SP acl-rights
response-quota = "*" SP "QUOTA" SP dataset SP quota-limit
SP quota-usage [SP extension-data]
response-refer = tag SP "REFER" SP dataset
1*(SP <"> url-relative <">)
Newman & Myers Standards Track [Page 57]RFC 2244 ACAP November 1997
response-remove = "*" SP "REMOVEFROM" SP context SP
entry-name SP position
response-stat = "*" SP resp-cond-state CRLF
resp-body = ["(" resp-code ")" SP] quoted
resp-code = "AUTH-TOO-WEAK" / "ENCRYPT-NEEDED" /
resp-code-inval / resp-code-mod /
resp-code-noexist / resp-code-perm / "QUOTA" /
resp-code-refer / resp-code-sasl /
resp-code-toomany / "TOOOLD" /
"TRANSITION-NEEDED" / "TRYFREECONTEXT" /
"TRYLATER" / "WAYTOOMANY" / resp-code-ext
resp-code-ext = iana-token [SP extension-data]
;; unknown codes MUST be tolerated by the client
resp-code-inval = "INVALID" 1*(SP entry-path SP attribute)
resp-code-mod = "MODIFIED" SP entry-path
resp-code-noexist = "NOEXIST" SP dataset
resp-code-perm = "PERMISSION" SP acl-object
resp-code-refer = "REFER" 1*(SP <"> url-relative <">)
resp-code-sasl = "SASL" SP string
resp-code-toomany = "TOOMANY" SP nz-number
resp-cond-state = ("OK" / "NO" / "BAD") SP resp-body
;; Status condition
return-attr-list = "(" return-metalist *(SP return-metalist) ")"
;; occurs when "*" in RETURN pattern on SEARCH
return-data = return-metadata / return-metalist /
return-attr-list
return-data-list = return-data *(SP return-data)
return-metalist = "(" return-metadata *(SP return-metadata) ")"
;; occurs when multiple metadata items requested
return-metadata = nil / string / value-list / acl
Newman & Myers Standards Track [Page 58]RFC 2244 ACAP November 1997
searchkey-equal = "EQUAL" SP attribute SP comparator SP value-nil
searchkey-comp = "COMPARE" SP attribute SP comparator SP value
searchkey-prefix = "PREFIX" SP attribute SP comparator SP value
searchkey-range = "RANGE" SP nz-number SP nz-number SP time
searchkey-strict = "COMPARESTRICT" SP attribute SP comparator
SP value
searchkey-substr = "SUBSTRING" SP attribute SP comparator SP value
searchmod-depth = "DEPTH" SP number
searchmod-hard = "HARDLIMIT" SP nz-number
searchmod-limit = "LIMIT" SP number SP number
searchmod-make = "MAKECONTEXT" [SP "ENUMERATE"]
[SP "NOTIFY"] SP context
searchmod-ninh = "NOINHERIT"
searchmod-return = "RETURN" SP "(" [metadata-list] ")"
searchmod-sort = "SORT" SP "(" sort-list ")"
search-criteria = "ALL" / searchkey-equal / searchkey-comp /
searchkey-strict / searchkey-range /
searchkey-prefix / searchkey-substr /
"NOT" SP search-criteria /
"OR" SP search-criteria SP search-criteria /
"AND" SP search-criteria SP search-criteria
search-modifier = searchmod-depth / searchmod-hard /
searchmod-limit / searchmod-make /
searchmod-ninh / searchmod-return /
searchmod-sort
sort-list = sort-item *(SP sort-item)
sort-item = attribute SP comparator
store-entry = "(" entry-path *(SP store-modifier)
*(SP attribute-store) ")"
;; MUST NOT include same store-modifier twice
;; MUST NOT include same attribute twice
Newman & Myers Standards Track [Page 59]RFC 2244 ACAP November 1997
store-entry-list = store-entry *(SP store-entry)
;; MUST NOT include same entry twice
store-modifier = store-mod-unchang / store-mod-nocreate
store-mod-nocreate = "NOCREATE"
store-mod-unchang = "UNCHANGEDSINCE" SP time
string = quoted / literal
string-list = string *(SP string)
string-utf8 = quoted / literal-utf8
tag = 1*32TAG-CHAR
time = <"> 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
value = string
value-list = "(" [value *(SP value)] ")"
value-nil = value / nil
value-nildef = value-nil / "DEFAULT"
value-store = value-nildef / value-list / acl
url-acap = "acap://" url-server "/" url-enc-entry
[url-filter] [url-extension]
;; url-enc-entry interpreted relative to "/"
Newman & Myers Standards Track [Page 60]RFC 2244 ACAP November 1997
url-attr-list = url-enc-attr *("&" url-enc-attr)
url-auth = ";AUTH=" ("*" / url-enc-auth)
url-achar = uchar / "&" / "=" / "~"
;; See RFC 1738 for definition of "uchar"
url-char = uchar / "=" / "~" / ":" / "@" / "/"
;; See RFC 1738 for definition of "uchar"
url-enc-attr = 1*url-char
;; encoded version of attribute name
url-enc-auth = 1*url-achar
;; encoded version of auth-type-name above
url-enc-entry = 1*url-char
;; encoded version of entry-relative above
url-enc-user = *url-achar
;; encoded version of login userid
url-extension = *("?" 1*url-char)
url-filter = "?" url-attr-list
url-relative = url-acap / [url-enc-entry] [url-filter]
;; url-enc-entry is relative to base URL
url-server = [url-enc-user [url-auth] "@"] hostport
;; See RFC 1738 for definition of "hostport"
9. Multi-lingual Considerations
The IAB charset workshop [IAB-CHARSET] came to a number of
conclusions which influenced the design of ACAP. The decision to use
UTF-8 as the character encoding scheme was based on that work. The
LANG command to negotiate a language for error messages is also
included.
Section 3.4.5 of the IAB charset workshop report states that there
should be a way to identify the natural language for human readable
strings. Several promising proposals have been made for use within
ACAP, but no clear consensus on a single method is apparent at this
stage. The following rules are likely to permit the addition of
multi-lingual support in the future:
Newman & Myers Standards Track [Page 61]RFC 2244 ACAP November 1997
(1) A work in progress called Multi-Lingual String Format (MLSF)
proposes a layer on top of UTF-8 which uses otherwise illegal UTF-8
sequences to store language tags. In order to permit its addition to
a future version of this standard, client-side UTF-8 interpreters
MUST be able to silently ignore illegal multi-byte UTF-8 characters,
and treat illegal single-byte UTF-8 characters as end of string
markers. Servers, for the time being, MUST be able to silently
accept illegal UTF-8 characters, except in attribute names and entry
names. Clients MUST NOT send illegal UTF-8 characters to the server
unless a future standard changes this rule.
(2) There is a proposal to add language tags to Unicode. To support
this, servers MUST be able to store UTF-8 characters of up to 20 bits
of data.
(3) The metadata item "language" is reserved for future use.
10. Security Considerations
The AUTHENTICATE command uses SASL [SASL] to provide basic
authentication, authorization, integrity and privacy services. This
is described in section 6.3.1.
When the CRAM-MD5 mechanism is used, the security considerations for
the CRAM-MD5 SASL mechanism [CRAM-MD5] apply. The CRAM-MD5 mechanism
is also susceptible to passive dictionary attacks. This means that
if an authentication session is recorded by a passive observer, that
observer can try common passwords through the CRAM-MD5 mechanism and
see if the results match. This attack is reduced by using hard to
guess passwords. Sites are encouraged to educate users and have the
password change service test candidate passwords against a
dictionary. ACAP implementations of CRAM-MD5 SHOULD permit passwords
of at least 64 characters in length.
ACAP protocol transactions are susceptible to passive observers or
man in the middle attacks which alter the data, unless the optional
encryption and integrity services of the AUTHENTICATE command are
enabled, or an external security mechanism is used for protection.
It may be useful to allow configuration of both clients and servers
to refuse to transfer sensitive information in the absence of strong
encryption.
ACAP access control lists provide fine grained authorization for
access to attributes. A number of related security issues are
described in section 3.5.
ACAP URLs have the same security considerations as IMAP URLs
[IMAP-URL].
Newman & Myers Standards Track [Page 62]
RFC 2244 ACAP November 1997
ACAP clients are encouraged to consider the security problems
involved with a lab computer situation. Specifically, a client cache
of ACAP configuration information MUST NOT allow access by an
unauthorized user. One way to assure this is for an ACAP client to
be able to completely flush any non-public cached configuration data
when a user leaves.
As laptop computers can be easily stolen and a cache of configuration
data may contain sensitive information, a disconnected mode ACAP
client may wish to encrypt and password protect cached configuration
information.
11. Acknowledgments
Many thanks to the follow people who have contributed to ACAP over
the past four years: Wallace Colyer, Mark Crispin, Jack DeWinter, Rob
Earhart, Ned Freed, Randy Gellens, Terry Gray, J. S. Greenfield,
Steve Dorner, Steve Hole, Steve Hubert, Dave Roberts, Bart Schaefer,
Matt Wall and other participants of the IETF ACAP working group.
12. Authors' Addresses
Chris Newman
Innosoft International, Inc.
1050 Lakes Drive
West Covina, CA 91790 USA
Email: chris.newman@innosoft.com
John Gardiner Myers
Netscape Communications
501 East Middlefield Road
Mail Stop MV-029
Mountain View, CA 94043
Email: jgmyers@netscape.com
Newman & Myers Standards Track [Page 63]
RFC 2244 ACAP November 1997
Appendices
A. References
[ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd,
November 1997.
<ftp://ds.internic.net/rfc/rfc2234.txt>
[BASIC-URL] Berners-Lee, Masinter, McCahill, "Uniform Resource
Locators (URL)", RFC 1738, CERN, Xerox Coproration, University of
Minnesota, December 1994.
<ftp://ds.internic.net/rfc/rfc1738.txt>
[CHARSET-LANG-POLICY] Alvestrand, "IETF Policy on Character Sets and
Languages", work in progress.
[CRAM-MD5] Klensin, Catoe, Krumviede, "IMAP/POP AUTHorize Extension
for Simple Challenge/Response", RFC 2195, MCI, September 1997.
<ftp://ds.internic.net/rfc/rfc2195.txt>
[IAB-CHARSET] Weider, Preston, Simonsen, Alvestrand, Atkinson,
Crispin, Svanberg, "The Report of the IAB Character Set Workshop held
29 February - 1 March, 1996", RFC 2130, April 1997.
<ftp://ds.internic.net/rfc/rfc2130.txt>
[IMAP4] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 2060, University of Washington, December 1996.
<ftp://ds.internic.net/rfc/rfc2060.txt>
[IMAP-ACL] Myers, J., "IMAP4 ACL extension", RFC 2086, Carnegie
Mellon, January 1997.
<ftp://ds.internic.net/rfc/rfc2086.txt>
[IMAP-URL] Newman, "IMAP URL Scheme", RFC 2192, Innosoft, July 1997.
<ftp://ds.internic.net/rfc/rfc2192.txt>
[ISO-10646] ISO/IEC 10646-1:1993(E) "Information Technology--
Universal Multiple-octet Coded Character Set (UCS)." See also
amendments 1 through 7, plus editorial corrections.
Newman & Myers Standards Track [Page 64]RFC 2244 ACAP November 1997
[ISO-C] "Programming languages -- C", ISO/IEC 9899:1990,
International Organization for Standardization. This is effectively
the same as ANSI C standard X3.159-1989.
[KEYWORDS] Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, Harvard University, March 1997.
<ftp://ds.internic.net/rfc/rfc2119.txt>
[LANG-TAGS] Alvestrand, H., "Tags for the Identification of
Languages", RFC 1766.
<ftp://ds.internic.net/rfc/rfc1766.txt>
[REL-URL] Fielding, "Relative Uniform Resource Locators", RFC 1808,
UC Irvine, June 1995.
<ftp://ds.internic.net/rfc/rfc1808.txt>
[SASL] Myers, J., "Simple Authentication and Security Layer (SASL)",
RFC 2222, Netscape Communications, October 1997.
<ftp://ds.internic.net/rfc/rfc2222.txt>
[SASL-ANON] Newman, C., "Anonymous SASL Mechanism", RFC 2245,
November 1997.
[UNICODE-2] The Unicode Consortium, "The Unicode Standard, Version
2.0", Addison-Wesley, 1996. ISBN 0-201-48345-9.
[US-ASCII] "USA Standard Code for Information Interchange," X3.4.
American National Standards Institute: New York (1968).
[UTF8] Yergeau, F. "UTF-8, a transformation format of Unicode and ISO
10646", RFC 2044, Alis Technologies, October 1996.
<ftp://ds.internic.net/rfc/rfc2044.txt>
Newman & Myers Standards Track [Page 65]RFC 2244 ACAP November 1997
B. ACAP Keyword Index
ACAP (untagged response) ................................... 26
ADDTO (untagged response) .................................. 40
ALERT (untagged response) .................................. 31
ALL (search keyword) ....................................... 36
AND (search keyword) ....................................... 36
AUTH-TOO-WEAK (response code) .............................. 19
AUTHENTICATE (command) ..................................... 31
BAD (response) ............................................. 30
BYE (untagged response) .................................... 30
CHANGE (untagged response) ................................. 41
COMPARE (search keyword) ................................... 36
COMPARESTRICT (search keyword) ............................. 36
CONTEXTLIMIT (ACAP capability) ............................. 27
DELETEACL (command) ........................................ 46
DELETED (intermediate response) ............................ 45
DELETEDSINCE (command) ..................................... 45
DEPTH (search modifier) .................................... 34
ENCRYPT-NEEDED (response code) ............................. 19
ENTRY (intermediate response) .............................. 37
EQUAL (search keyword) ..................................... 37
FREECONTEXT (command) ...................................... 39
GETQUOTA (command) ......................................... 48
HARDLIMIT (search modifier) ................................ 34
IMPLEMENTATION (ACAP capability) ........................... 27
INVALID (response code) .................................... 19
LANG (command) ............................................. 28
LANG (intermediate response) ............................... 28
LIMIT (search modifier) .................................... 34
LISTRIGHTS (command) ....................................... 47
LISTRIGHTS (intermediate response) ......................... 48
LOGOUT (command) ........................................... 29
MAKECONTEXT (search modifier) .............................. 34
MODIFIED (response code) ................................... 19
MODTIME (intermediate response) ............................ 38
MODTIME (untagged response) ................................ 42
MYRIGHTS (command) ......................................... 47
MYRIGHTS (intermediate response) ........................... 47
NO (response) .............................................. 29
NOCREATE (store modifier) .................................. 44
NOEXIST (response code) .................................... 19
NOINHERIT (search modifier) ................................ 35
NOOP (command) ............................................. 27
NOT (search keyword) ....................................... 37
OK (response) .............................................. 29
OR (search keyword) ........................................ 37
PERMISSION (response code) ................................. 19
Newman & Myers Standards Track [Page 66]RFC 2244 ACAP November 1997
PREFIX (search keyword) .................................... 37
QUOTA (response code) ...................................... 19
QUOTA (untagged response) .................................. 49
RANGE (search keyword) ..................................... 37
REFER (intermediate response) .............................. 38
REFER (response code) ...................................... 19
REMOVEFROM (untagged response) ............................. 41
RETURN (search modifier) ................................... 35
SASL (ACAP capability) ..................................... 27
SASL (response code) ....................................... 20
SEARCH (command) ........................................... 33
SETACL (command) ........................................... 46
SORT (search modifier) ..................................... 36
STORE (command) ............................................ 42
SUBSTRING (search keyword) ................................. 37
TOOMANY (response code) .................................... 20
TOOOLD (response code) ..................................... 20
TRANSITION-NEEDED (response code) .......................... 20
TRYFREECONTEXT (response code) ............................. 20
TRYLATER (response code) ................................... 20
UNCHANGEDSINCE (store modifier) ............................ 44
UPDATECONTEXT (command) .................................... 40
WAYTOOMANY (response code) ................................. 20
acl (attribute metadata) ................................... 12
anyone (ACL identifier) .................................... 17
attribute (attribute metadata) ............................. 12
dataset.acl (dataset attribute) ............................ 24
dataset.acl.<attribute> (dataset attribute) ................ 24
dataset.inherit (dataset attribute) ........................ 24
entry (predefined attribute) ............................... 11
i;ascii-casemap (comparator) ............................... 16
i;ascii-numeric (comparator) ............................... 16
i;octet (comparator) ....................................... 16
modtime (predefined attribute) ............................. 11
myrights (attribute metadata) .............................. 12
size (attribute metadata) .................................. 13
subdataset (predefined attribute) .......................... 11
value (attribute metadata) ................................. 13
Newman & Myers Standards Track [Page 67]RFC 2244 ACAP November 1997
C. Full Copyright Statement
Copyright (C) The Internet Society 1997. 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 implmentation 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
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.
Newman & Myers Standards Track [Page 68]
