draft-ietf-imapext-i18n-13.txt   draft-ietf-imapext-i18n-14.txt 
Network Working Group Chris Newman Network Working Group Chris Newman
Internet-Draft Sun Microsystems Internet-Draft Sun Microsystems
Intended Status: Proposed Standard Arnt Gulbrandsen Intended Status: Proposed Standard Arnt Gulbrandsen
Oryx Mail Systems GmhH Oryx Mail Systems GmhH
Alexey Melnikov Alexey Melnikov
Isode Limited Isode Limited
November 14, 2007 December 8, 2007
Internet Message Access Protocol Internationalization Internet Message Access Protocol Internationalization
draft-ietf-imapext-i18n-13.txt draft-ietf-imapext-i18n-14.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
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Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
Internet Message Access Protocol (IMAP) version 4rev1 has basic Internet Message Access Protocol (IMAP) version 4rev1 has basic
support for non-ASCII characters in mailbox names and search support for non-ASCII characters in mailbox names and search
substrings. It also supports non-ASCII message headers and content substrings. It also supports non-ASCII message headers and content
encoded as specified by Multipurpose Internet Mail Extensions encoded as specified by Multipurpose Internet Mail Extensions
(MIME). This specification defines a collection of IMAP extensions (MIME). This specification defines a collection of IMAP extensions
Internet-draft November 2007 Internet-draft December 2007
which improve international support including comparator negotiation which improve international support including comparator negotiation
for search, sort and thread, language negotiation for international for search, sort and thread, language negotiation for international
error text, and translations for namespace prefixes. error text, and translations for namespace prefixes.
Table of Contents Table of Contents
1. Conventions Used in this Document . . . . . . . . . . . . . . 2 1. Conventions Used in this Document . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . 3 3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . 3
3.1 LANGUAGE Extension Requirements . . . . . . . . . . . . . . . 3 3.1 LANGUAGE Extension Requirements . . . . . . . . . . . . . . . 3
3.2 LANGUAGE Command . . . . . . . . . . . . . . . . . . . . . . 4 3.2 LANGUAGE Command . . . . . . . . . . . . . . . . . . . . . . 4
3.3 LANGUAGE Response . . . . . . . . . . . . . . . . . . . . . . 6 3.3 LANGUAGE Response . . . . . . . . . . . . . . . . . . . . . . 6
3.4 TRANSLATION Extension to the NAMESPACE Response . . . . . . . 6 3.4 TRANSLATION Extension to the NAMESPACE Response . . . . . . . 6
3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6 3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6
4. COMPARATOR Extension . . . . . . . . . . . . . . . . . . . . 7 4. I18NLEVEL=1 and I18NLEVEL=2 Extensions . . . . . . . . . . . 7
4.1 COMPARATOR Extension Requirements . . . . . . . . . . . . . . 8 4.1 Introduction and Overview . . . . . . . . . . . . . . . . . . 8
4.2 Comparators and Charsets . . . . . . . . . . . . . . . . . . 9 4.2 Requirements common to both I18NLEVEL=1 and I18NLEVEL=2 . . .
4.3 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . 9 4.3 I18NLEVEL=1 Extension Requirements . . . . . . . . . . . . . 8
4.4 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10 4.4 I18NLEVEL=2 Extension Requirements . . . . . . . . . . . . . 8
4.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 10 4.5 Compatibility Notes
4.6 Comparators and Charsets . . . . . . . . . . . . . . . . . . 9
4.7 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . 9
4.8 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10
4.9 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Other IMAP Internationalization Issues . . . . . . . . . . . 11 5. Other IMAP Internationalization Issues . . . . . . . . . . . 11
5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11 5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11
5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 11 5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 11
5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 11 5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. Relevant Standards for i18n IMAP Implementations . . . . . . 13 9. Relevant Standards for i18n IMAP Implementations . . . . . . 13
Normative References . . . . . . . . . . . . . . . . . . . . 13 Normative References . . . . . . . . . . . . . . . . . . . . 13
Informative References . . . . . . . . . . . . . . . . . . . 14 Informative References . . . . . . . . . . . . . . . . . . . 14
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Conventions Used in This Document Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
The formal syntax use the Augmented Backus-Naur Form (ABNF) The formal syntax use the Augmented Backus-Naur Form (ABNF)
[RFC4234] notation including the core rules defined in Appendix A. [RFC4234] notation including the core rules defined in Appendix A.
The UTF8-related productions are defined in [RFC3629]. The UTF8-related productions are defined in [RFC3629].
Internet-draft December 2007
In examples, "C:" and "S:" indicate lines sent by the client and In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. If a single "C:" or "S:" label applies to server respectively. If a single "C:" or "S:" label applies to
multiple lines, then the line breaks between those lines are for multiple lines, then the line breaks between those lines are for
Internet-draft November 2007
editorial clarity only and are not part of the actual protocol editorial clarity only and are not part of the actual protocol
exchange. exchange.
2. Introduction 2. Introduction
This specification defines two IMAP4rev1 [RFC3501] extensions to This specification defines two IMAP4rev1 [RFC3501] extensions to
enhance international support. These extensions can be advertised enhance international support. These extensions can be advertised
and implemented separately. and implemented separately.
The LANGUAGE extension allows the client to request a suitable The LANGUAGE extension allows the client to request a suitable
language for protocol error messages and in combination with the language for protocol error messages and in combination with the
NAMESPACE extension [RFC2342] enables namespace translations. NAMESPACE extension [RFC2342] enables namespace translations.
The COMPARATOR extension allows the client to request a suitable The I18NLEVEL=2 extension allows the client to request a suitable
collation which will modify the behavior of the base specification's collation which will modify the behavior of the base specification's
SEARCH command as well as the SORT and THREAD extensions [SORT]. SEARCH command as well as the SORT and THREAD extensions [SORT].
This leverages the collation registry [RFC4790]. This leverages the collation registry [RFC4790].
3. LANGUAGE Extension 3. LANGUAGE Extension
IMAP allows server responses to include human-readable text that in IMAP allows server responses to include human-readable text that in
many cases needs to be presented to the user. But that text is many cases needs to be presented to the user. But that text is
limited to US-ASCII by the IMAP specification [RFC3501] in order to limited to US-ASCII by the IMAP specification [RFC3501] in order to
preserve backwards compatibility with deployed IMAP implementations. preserve backwards compatibility with deployed IMAP implementations.
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3.1 LANGUAGE Extension Requirements 3.1 LANGUAGE Extension Requirements
IMAP servers that support this extension MUST list the keyword IMAP servers that support this extension MUST list the keyword
LANGUAGE in their CAPABILITY response as well as in the greeting LANGUAGE in their CAPABILITY response as well as in the greeting
CAPABILITY data. CAPABILITY data.
A server that advertises this extension MUST use the language "i- A server that advertises this extension MUST use the language "i-
default" as described in [RFC2277] as its default language until default" as described in [RFC2277] as its default language until
another supported language is negotiated by the client. A server another supported language is negotiated by the client. A server
MUST include "i-default" as one of its supported languages.
Clients and servers that support this extension MUST also support Internet-draft December 2007
Internet-draft November 2007 MUST include "i-default" as one of its supported languages.
Clients and servers that support this extension MUST also support
the NAMESPACE extension [RFC2342]. the NAMESPACE extension [RFC2342].
The LANGUAGE command is valid in all states. Clients are urged to The LANGUAGE command is valid in all states. Clients are urged to
issue LANGUAGE before authentication, since some servers send issue LANGUAGE before authentication, since some servers send
valuable user information as part of authentication (e.g. "password valuable user information as part of authentication (e.g. "password
is correct, but expired"). is correct, but expired").
3.2 LANGUAGE Command 3.2 LANGUAGE Command
Arguments: Optional language range arguments. Arguments: Optional language range arguments.
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If a language range does not match a known language tag exactly but If a language range does not match a known language tag exactly but
does match a language by the rules of [RFC4647], the server MUST does match a language by the rules of [RFC4647], the server MUST
send an untagged LANGUAGE response indicating the language selected. send an untagged LANGUAGE response indicating the language selected.
If there aren't any arguments, the server SHOULD send an untagged If there aren't any arguments, the server SHOULD send an untagged
LANGUAGE response listing the languages it supports. If the server LANGUAGE response listing the languages it supports. If the server
is unable to enumerate the list of languages it supports it MAY is unable to enumerate the list of languages it supports it MAY
return a tagged NO response to the enumeration request. return a tagged NO response to the enumeration request.
Internet-draft December 2007
< The server defaults to using English i-default responses until < The server defaults to using English i-default responses until
the user explicitly changes the language. > the user explicitly changes the language. >
Internet-draft November 2007
C: A001 LOGIN KAREN PASSWORD C: A001 LOGIN KAREN PASSWORD
S: A001 OK LOGIN completed S: A001 OK LOGIN completed
< Client requested MUL language, which no server supports. > < Client requested MUL language, which no server supports. >
C: A002 LANGUAGE MUL C: A002 LANGUAGE MUL
S: A002 NO Unsupported language MUL S: A002 NO Unsupported language MUL
< A LANGUAGE command with no arguments is a request to enumerate < A LANGUAGE command with no arguments is a request to enumerate
the list of languages the server supports. > the list of languages the server supports. >
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C: D001 LANGUAGE FR C: D001 LANGUAGE FR
S: D001 NO Diese Sprache ist nicht unterstuetzt S: D001 NO Diese Sprache ist nicht unterstuetzt
C: D002 LANGUAGE DE-IT C: D002 LANGUAGE DE-IT
S: * LANGUAGE (DE-IT) S: * LANGUAGE (DE-IT)
S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Mailboxen/"))) "TRANSLATION" ("Gemeinsame Mailboxen/")))
S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
C: D003 LANGUAGE "default" C: D003 LANGUAGE "default"
S: * LANGUAGE (DE) S: * LANGUAGE (DE)
S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
< Server does not speak French, but does speak English. User Internet-draft December 2007
Internet-draft November 2007 S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
< Server does not speak French, but does speak English. User
speaks Canadian French and Canadian English. > speaks Canadian French and Canadian English. >
C: E001 LANGUAGE FR-CA EN-CA C: E001 LANGUAGE FR-CA EN-CA
S: * LANGUAGE (EN) S: * LANGUAGE (EN)
S: E001 OK Now speaking English S: E001 OK Now speaking English
3.3 LANGUAGE Response 3.3 LANGUAGE Response
Contents: A list of one or more language tags. Contents: A list of one or more language tags.
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Folders" to its only Shared Namespace. Since a client will often Folders" to its only Shared Namespace. Since a client will often
display these prefixes to the user, the server includes a display these prefixes to the user, the server includes a
translation of them that can be presented to the user. translation of them that can be presented to the user.
C: A001 LANGUAGE DE-IT C: A001 LANGUAGE DE-IT
S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Mailboxen/"))) "TRANSLATION" ("Gemeinsame Mailboxen/")))
S: A001 OK LANGUAGE-Befehl ausgefuehrt S: A001 OK LANGUAGE-Befehl ausgefuehrt
3.5 Formal Syntax Internet-draft December 2007
Internet-draft November 2007 3.5 Formal Syntax
The following syntax specification inherits ABNF [RFC4234] rules The following syntax specification inherits ABNF [RFC4234] rules
from IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the from IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the
Identifying Languages [RFC4646], UTF-8 [RFC3629] and Collected Identifying Languages [RFC4646], UTF-8 [RFC3629] and Collected
Extensions to IMAP4 ABNF [RFC4466]. Extensions to IMAP4 ABNF [RFC4466].
command-any =/ language-cmd command-any =/ language-cmd
; LANGUAGE command is valid in all states ; LANGUAGE command is valid in all states
language-cmd = "LANGUAGE" *(SP lang-range-quoted) language-cmd = "LANGUAGE" *(SP lang-range-quoted)
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resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR
*(UTF8-TEXT-CHAR / "[") *(UTF8-TEXT-CHAR / "[")
; After the server is changed to a language other than ; After the server is changed to a language other than
; i-default, this resp-text rule replaces the resp-text ; i-default, this resp-text rule replaces the resp-text
; rule from [RFC3501]. ; rule from [RFC3501].
UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4 UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4
; UTF-8 excluding 7-bit control characters and "[" ; UTF-8 excluding 7-bit control characters and "["
4. COMPARATOR Extension 4. I18NLEVEL=1 and I18NLEVEL=2 Extensions
4.1 Introduction and Overview
IMAP4rev1 [RFC3501] includes the SEARCH command which can be used to IMAP4rev1 [RFC3501] includes the SEARCH command which can be used to
locate messages matching criteria including human-readable text. locate messages matching criteria including human-readable text.
The SORT extension [SORT] to IMAP allows the client to ask the The SORT extension [SORT] to IMAP allows the client to ask the
Internet-draft December 2007
server to determine the order of messages based on criteria server to determine the order of messages based on criteria
including human-readable text. These mechanisms require the ability including human-readable text. These mechanisms require the ability
to support non-English search and sort functions. to support non-English search and sort functions.
This section defines an IMAP extension to negotiate use of Section 4 defines two IMAP extensions for internationalizing IMAP
SEARCH, SORT and THREAD [SORT] using the comparator framework
[RFC4790].
Internet-draft November 2007 The I18NLEVEL=1 extension updates SEARCH/SORT/THREAD to use
i;unicode-casemap comparator, as defined in [UCM]. See Sections 4.2
and 4.3 for more details.
comparators [RFC4790] to internationalize IMAP SEARCH, SORT and The I18NLEVEL=2 extension is a superset of the I18NLEVEL=1
THREAD. The IMAP extension consists of a new command to determine extension. It adds to I18NLEVEL=1 extension the ability to determine
or change the active comparator and a new response to indicate the the active comparator (see definition below) and negotiate use of
active comparator and possibly other available comparators. comparators using the COMPARATOR command. It also adds the
COMPARATOR response that indicates the active comparator and
possibly other available comparators. See Sections 4.2 and 4.4 for
more details.
4.2 Requirements common to both I18NLEVEL=1 and I18NLEVEL=2
The term "default comparator" refers to the comparator which is used The term "default comparator" refers to the comparator which is used
by SEARCH and SORT absent any negotiation using the COMPARATOR by SEARCH and SORT absent any negotiation using the COMPARATOR (see
command. The term "active comparator" refers to the comparator Section 4.7) command. The term "active comparator" refers to the
which will be used within a session e.g. by SEARCH and SORT. The comparator which will be used within a session e.g. by SEARCH and
COMPARATOR command is used to change the active comparator. SORT. The COMPARATOR command is used to change the active
comparator.
The active comparator applies to the following SEARCH keys: "BCC", The active comparator applies to the following SEARCH keys: "BCC",
"BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER". If the "BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER". If the
server also advertises the "SORT" extension, then the active server also advertises the "SORT" extension, then the active
comparator applies to the following SORT keys: "CC", "FROM", comparator applies to the following SORT keys: "CC", "FROM",
"SUBJECT" and "TO". If the server advertises THREAD=ORDEREDSUBJECT, "SUBJECT" and "TO". If the server advertises THREAD=ORDEREDSUBJECT,
then the active comparator applies to the ORDEREDSUBJECT threading then the active comparator applies to the ORDEREDSUBJECT threading
algorithm. If the server advertises THREAD=REFERENCES, then the algorithm. If the server advertises THREAD=REFERENCES, then the
active comparator applies to the subject field comparisons done by active comparator applies to the subject field comparisons done by
REFERENCES threading algorithm. Future extensions may choose to REFERENCES threading algorithm. Future extensions may choose to
apply the active comparator to their SEARCH keys. apply the active comparator to their SEARCH keys.
For SORT and THREAD, the pre-processing necessary to extract the For SORT and THREAD, the pre-processing necessary to extract the
base subject text from a Subject header occurs prior to the base subject text from a Subject header occurs prior to the
application of a comparator. application of a comparator.
4.1 COMPARATOR Extension Requirements A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
implement the i;unicode-casemap comparator, as defined in [UCM].
IMAP servers that support this extension MUST list the keyword Internet-draft December 2007
COMPARATOR in their CAPABILITY data once IMAP enters authenticated
A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
support UTF-8 as a SEARCH charset.
4.3 I18NLEVEL=1 Extension Requirements
IMAP servers that satisfies all requirements specified in sections
4.2 and 4.6 (and doesn't support/advertise any other I18NLEVEL=<n>
extension, where n > 1) MUST list the keyword I18NLEVEL=1 in their
CAPABILITY data once IMAP enters authenticated state, and MAY list
that keyword in other states.
4.4 I18NLEVEL=2 Extension Requirements
IMAP servers that satisfies all requirements specified in sections
4.2, 4.4, 4.6-4.9 (and doesn't support/advertise any other
I18NLEVEL=<n> extension, where n > 2) MUST list the keyword
I18NLEVEL=2 in their CAPABILITY data once IMAP enters authenticated
state, and MAY list that keyword in other states. state, and MAY list that keyword in other states.
A server that advertises this extension MUST implement the A server that advertises this extension MUST implement the
i;unicode-casemap comparator, as defined in [UCM]. It MAY implement i;unicode-casemap comparator, as defined in [UCM]. It MAY implement
other comparators from the IANA registry established by [RFC4790]. other comparators from the IANA registry established by [RFC4790].
See also section 4.5 of this document.
A server that advertises this extension SHOULD use i;unicode-casemap A server that advertises this extension SHOULD use i;unicode-casemap
as the default comparator. The selection of the default comparator as the default comparator. (Note that i;unicode-casemap is the
MAY be adjustable by the server administrator, and MAY be sensitive default comparator for I18NLEVEL=1, but not necessarily the default
to the current user. Once the IMAP connection enters authenticated for I18NLEVEL=2.) The selection of the default comparator MAY be
state, the default comparator MUST remain static for the remainder adjustable by the server administrator, and MAY be sensitive to the
of that connection. current user. Once the IMAP connection enters authenticated state,
the default comparator MUST remain static for the remainder of that
A server that advertises this extension MUST support UTF-8 as a connection.
SEARCH charset.
The COMPARATOR command is valid in authenticated and selected
Internet-draft November 2007
states.
Note that since SEARCH uses the substring operation, IMAP servers Note that since SEARCH uses the substring operation, IMAP servers
can only implement collations that offer the substring operation can only implement collations that offer the substring operation
(see [RFC4790 section 4.2.2). Since SORT uses ordering operation (see [RFC4790 section 4.2.2). Since SORT uses ordering operation
(and by implication equality), IMAP servers which advertise the SORT (and by implication equality), IMAP servers which advertise the SORT
extension can only implement collations that offer all three extension can only implement collations that offer all three
operations (see [RFC4790] sections 4.2.2-4). operations (see [RFC4790] sections 4.2.2-4).
If the active collation does not provide the operations needed by an If the active collation does not provide the operations needed by an
IMAP command, the server MUST respond with a tagged BAD. IMAP command, the server MUST respond with a tagged BAD.
4.2 Comparators and Character Encodings 4.5 Compatibility Notes
Internet-draft December 2007
Several server implementations deployed prior to the publication of
this specification comply with I18NLEVEL=1 (see section 4.3), but do
not advertise that. Other legacy servers use the i;ascii-casemap
(see [RFC4790]) comparator.
There is no good way for a client to know which comparator that a
legacy server uses. If the client has to assume the worst, it may
end up doing expensive local operations to obtain i;unicode-casemap
comparisons even though the server implements it.
Legacy server implementations which comply with I18NLEVEL=1 should
be updated to advertise I18NLEVEL=1. All server implementations
should eventually be updated to comply with the I18NLEVEL=2
extension.
4.6 Comparators and Character Encodings
RFC 3501, section 6.4.4 says: RFC 3501, section 6.4.4 says:
In all search keys that use strings, a message matches In all search keys that use strings, a message matches
the key if the string is a substring of the field. The the key if the string is a substring of the field. The
matching is case-insensitive. matching is case-insensitive.
When performing the SEARCH operation, the active comparator is When performing the SEARCH operation, the active comparator is
applied instead of the case-insensitive matching specified above. applied instead of the case-insensitive matching specified above.
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etc.), the collation of this message is undefined by this etc.), the collation of this message is undefined by this
specification, and is handled in an implementation-dependent specification, and is handled in an implementation-dependent
manner. manner.
(b) The decoded text from (a) MUST be converted to the charset (b) The decoded text from (a) MUST be converted to the charset
expected by the active comparator. expected by the active comparator.
(c) For the substring operation: (c) For the substring operation:
If step (b) failed (e.g., the text is in an unknown charset, If step (b) failed (e.g., the text is in an unknown charset,
contains a sequence which is not valid according in that contains a sequence which is not valid according in that
Internet-draft December 2007
charset, etc.), the original decoded text from (a) (i.e., charset, etc.), the original decoded text from (a) (i.e.,
before the charset conversion attempt) is collated using the before the charset conversion attempt) is collated using the
i;octet comparator (see [RFC4790]). i;octet comparator (see [RFC4790]).
Internet-draft November 2007
If step (b) was successful, the converted text from (b) is If step (b) was successful, the converted text from (b) is
collated according to the active comparator. collated according to the active comparator.
For the ordering operation: For the ordering operation:
All strings that were successfully converted by step (b) are All strings that were successfully converted by step (b) are
separated from all strings that failed step (b). Strings in separated from all strings that failed step (b). Strings in
each group are collated independently. All strings that fail each group are collated independently. All strings that fail
step (b) are collated (after applying step (a)) using the step (b) are collated (after applying step (a)) using the
i;octet comparator (see [RFC4790]). All strings successfully i;octet comparator (see [RFC4790]). All strings successfully
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comparator returns the "undefined" result (see section 4.2.3 of comparator returns the "undefined" result (see section 4.2.3 of
[RFC4790]) for either the text specified in the SEARCH command or [RFC4790]) for either the text specified in the SEARCH command or
the message text, then the operation is repeated on the result of the message text, then the operation is repeated on the result of
step (a) using the i;octet comparator. step (a) using the i;octet comparator.
The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate
the following together: strings encoded using unknown or invalid the following together: strings encoded using unknown or invalid
character encodings, strings in unrecognized charsets, and invalid character encodings, strings in unrecognized charsets, and invalid
input (as defined by the active collation). input (as defined by the active collation).
4.3 COMPARATOR Command 4.7 COMPARATOR Command
Arguments: Optional comparator order arguments. Arguments: Optional comparator order arguments.
Response: A possible COMPARATOR response (see Section 4.4). Response: A possible COMPARATOR response (see Section 4.8).
Result: OK - Command completed Result: OK - Command completed
NO - No matching comparator found NO - No matching comparator found
BAD - arguments invalid BAD - arguments invalid
The COMPARATOR command is valid in authenticated and selected
states.
The COMPARATOR command is used to determine or change the active The COMPARATOR command is used to determine or change the active
Internet-draft December 2007
comparator. When issued with no arguments, it results in a comparator. When issued with no arguments, it results in a
COMPARATOR response indicating the currently active comparator. COMPARATOR response indicating the currently active comparator.
When issued with one or more comparator argument, it changes the When issued with one or more comparator argument, it changes the
active comparator as directed. (If more than one installed active comparator as directed. (If more than one installed
comparator is matched by an argument, the first argument wins.) The comparator is matched by an argument, the first argument wins.) The
COMPARATOR response lists all matching comparators if more than one COMPARATOR response lists all matching comparators if more than one
Internet-draft November 2007
matches the specified patterns. matches the specified patterns.
The argument "default" refers to the server's default comparator. The argument "default" refers to the server's default comparator.
Otherwise each argument is an collation specification as defined in Otherwise each argument is an collation specification as defined in
the Internet Application Protocol Comparator Registry [RFC4790]. the Internet Application Protocol Comparator Registry [RFC4790].
< The client requests activating a Czech comparator if possible, < The client requests activating a Czech comparator if possible,
or else a generic international comparator which it considers or else a generic international comparator which it considers
suitable for Czech. The server picks the first supported suitable for Czech. The server picks the first supported
comparator. > comparator. >
C: A001 COMPARATOR "cz;*" i;basic C: A001 COMPARATOR "cz;*" i;basic
S: * COMPARATOR i;basic S: * COMPARATOR i;basic
S: A001 OK Will use i;basic for collation S: A001 OK Will use i;basic for collation
4.4 COMPARATOR Response 4.8 COMPARATOR Response
Contents: The active comparator. Contents: The active comparator.
An optional list of available matching comparators An optional list of available matching comparators
The COMPARATOR response occurs as a result of a COMPARATOR command. The COMPARATOR response occurs as a result of a COMPARATOR command.
The first argument in the comparator response is the name of the The first argument in the comparator response is the name of the
active comparator. The second argument is a list of comparators active comparator. The second argument is a list of comparators
which matched any of the arguments to the COMPARATOR command and is which matched any of the arguments to the COMPARATOR command and is
present only if more than one match is found. present only if more than one match is found.
4.5 Formal Syntax 4.9 Formal Syntax
The following syntax specification inherits ABNF [RFC4234] rules The following syntax specification inherits ABNF [RFC4234] rules
from IMAP4rev1 [RFC3501], and Internet Application Protocol from IMAP4rev1 [RFC3501], and Internet Application Protocol
Comparator Registry [RFC4790]. Comparator Registry [RFC4790].
command-auth =/ comparator-cmd command-auth =/ comparator-cmd
resp-text-code =/ "BADCOMPARATOR" / "BADMATCH" resp-text-code =/ "BADCOMPARATOR" / "BADMATCH"
comparator-cmd = "COMPARATOR" *(SP comp-order-quoted) comparator-cmd = "COMPARATOR" *(SP comp-order-quoted)
response-payload =/ comparator-data response-payload =/ comparator-data
Internet-draft December 2007
comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "(" comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "("
comp-id-quoted *(SP comp-id-quoted) ")"] comp-id-quoted *(SP comp-id-quoted) ")"]
comp-id-quoted = astring comp-id-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
; follows the collation-id rule from [RFC4790] ; follows the collation-id rule from [RFC4790]
Internet-draft November 2007
comp-order-quoted = astring comp-order-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
; follows the collation-order rule from [RFC4790] ; follows the collation-order rule from [RFC4790]
comp-sel-quoted = astring comp-sel-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
; follows the collation-selected rule from [RFC4790] ; follows the collation-selected rule from [RFC4790]
4.6 UNICASEMAP Extension Requirements
An IMAP server that implements the i;unicode-casemap comparator
[UCM] and satisfies all requirements specified in sections 4, 4.1
and 4.2 of this document, but doesn't implement the COMPARATOR
command and response, SHOULD advertise the UNICASEMAP capability in
the CAPABILITY response.
5. Other IMAP Internationalization Issues 5. Other IMAP Internationalization Issues
The following sections provide an overview of various other IMAP The following sections provide an overview of various other IMAP
internationalization issues. These issues are not resolved by this internationalization issues. These issues are not resolved by this
specification, but could be resolved by other standards work, such specification, but could be resolved by other standards work, such
as that being done by the EAI group (see [IMAP-EAI]). as that being done by the EAI group (see [IMAP-EAI]).
5.1 Unicode Userids and Passwords 5.1 Unicode Userids and Passwords
IMAP4rev1 presently restricts the userid and password fields of the IMAP4rev1 currently restricts the userid and password fields of the
LOGIN command to US-ASCII. The "userid" and "password" fields of the LOGIN command to US-ASCII. The "userid" and "password" fields of the
IMAP LOGIN command are restricted to US-ASCII only until a future IMAP LOGIN command are restricted to US-ASCII only until a future
standards track RFC states otherwise. Servers are encouraged to standards track RFC states otherwise. Servers are encouraged to
validate both fields to make sure they conform to the formal syntax validate both fields to make sure they conform to the formal syntax
of UTF-8 and to reject the LOGIN command if that syntax is violated. of UTF-8 and to reject the LOGIN command if that syntax is violated.
Servers MAY reject the use of any 8-bit in the "userid" or Servers MAY reject the use of any 8-bit in the "userid" or
"password" field. "password" field.
When AUTHENTICATE is used, some servers may support userids and When AUTHENTICATE is used, some servers may support userids and
passwords in Unicode [RFC3490] since SASL (see [RFC4422]) allows passwords in Unicode [RFC3490] since SASL (see [RFC4422]) allows
that. However, such userids cannot be used as part of email that. However, such userids cannot be used as part of email
addresses. addresses.
5.2 UTF-8 Mailbox Names 5.2 UTF-8 Mailbox Names
The modified UTF-7 mailbox naming convention described in section The modified UTF-7 mailbox naming convention described in section
5.1.3 of RFC 3501 is best viewed as an transition from the status 5.1.3 of RFC 3501 is best viewed as an transition from the status
quo in 1996 when modified UTF-7 was first specified. At that time, quo in 1996 when modified UTF-7 was first specified. At that time,
Internet-draft November 2007
there was widespread unofficial use of local character sets such as there was widespread unofficial use of local character sets such as
ISO-8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant ISO-8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant
Internet-draft December 2007
non-interoperability. non-interoperability.
The requirements in section 5.1 of RFC 3501 are very important if The requirements in section 5.1 of RFC 3501 are very important if
we're ever going to be able to deploy UTF-8 mailbox names. Servers we're ever going to be able to deploy UTF-8 mailbox names. Servers
are encouraged to enforce them. are encouraged to enforce them.
5.3 UTF-8 Domains, Addresses and Mail Headers 5.3 UTF-8 Domains, Addresses and Mail Headers
There is now an IETF standard for Internationalizing Domain Names in There is now an IETF standard for Internationalizing Domain Names in
Applications [RFC3490]. While IMAP clients are free to support this Applications [RFC3490]. While IMAP clients are free to support this
standard, an argument can be made that it would be helpful to simple standard, an argument can be made that it would be helpful to simple
clients if the IMAP server could perform this conversion (the same clients if the IMAP server could perform this conversion (the same
argument would apply to MIME header encoding [RFC2047]). However, argument would apply to MIME header encoding [RFC2047]). However,
it would be unwise to move forward with such work until the work in it would be unwise to move forward with such work until the work in
progress to define the format of international email addresses is progress to define the format of international email addresses is
complete. complete.
6. IANA Considerations 6. IANA Considerations
The IANA is requested to add LANGUAGE, COMPARATOR and UNICASEMAP to The IANA is requested to add LANGUAGE, I18NLEVEL=1 and I18NLEVEL=2
the IMAP4 Capabilities Registry. [Note to IANA: to the IMAP4 Capabilities Registry. [Note to IANA:
http://www.iana.org/assignments/imap4-capabilities] http://www.iana.org/assignments/imap4-capabilities]
7. Security Considerations 7. Security Considerations
The LANGUAGE extension makes a new command available in "Not The LANGUAGE extension makes a new command available in "Not
Authenticated" state in IMAP. Some IMAP implementations run with Authenticated" state in IMAP. Some IMAP implementations run with
root privilege when the server is in "Not Authenticated" state and root privilege when the server is in "Not Authenticated" state and
do not revoke that privilege until after authentication is complete. do not revoke that privilege until after authentication is complete.
Such implementations are particularly vulnerable to buffer overflow Such implementations are particularly vulnerable to buffer overflow
security errors at this stage and need to implement parsing of this security errors at this stage and need to implement parsing of this
command with extra care. command with extra care.
A LANGUAGE command issued prior to activation of a security layer is A LANGUAGE command issued prior to activation of a security layer is
subject to an active attack which suppresses or modifies the subject to an active attack which suppresses or modifies the
negotiation and thus makes STARTTLS or authentication error messages negotiation and thus makes STARTTLS or authentication error messages
more difficult to interpret. This is not a new attack as the error more difficult to interpret. This is not a new attack as the error
messages themselves are subject to active attack. Clients MUST re- messages themselves are subject to active attack. Clients MUST re-
issue the LANGUAGE command once a security layer is active, so this issue the LANGUAGE command once a security layer is active, so this
does not impact subsequent protocol operations. does not impact subsequent protocol operations.
Both the LANGUAGE and COMPARATOR extensions use the UTF-8 charset, LANGUAGE, I18NLEVEL=1 and I18NLEVEL=2 extensions use the UTF-8
thus the security considerations for UTF-8 [RFC3629] are relevent. charset, thus the security considerations for UTF-8 [RFC3629] are
relevent. However, neither uses UTF-8 for identifiers so the most
Internet-draft November 2007 serious concerns do not apply.
However, neither uses UTF-8 for identifiers so the most serious Internet-draft December 2007
concerns do not apply.
8. Acknowledgements 8. Acknowledgements
The LANGUAGE extension is based on a previous Internet draft by Mike The LANGUAGE extension is based on a previous Internet draft by Mike
Gahrns and Alexey Melnikov, a substantial portion of the text in Gahrns, a substantial portion of the text in that section was
that section was written by them. Many people have participated in written by him. Many people have participated in discussions about
discussions about an IMAP Language extension in the various fora of an IMAP Language extension in the various fora of the IETF and
the IETF and Internet working groups, so any list of contributors is Internet working groups, so any list of contributors is bound to be
bound to be incomplete. However, the authors would like to thank incomplete. However, the authors would like to thank Andrew McCown
Andrew McCown for early work on the original proposal, John Myers for early work on the original proposal, John Myers for suggestions
for suggestions regarding the namespace issue, along with Jutta regarding the namespace issue, along with Jutta Degener, Mark
Degener, Mark Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo and Martin
and Martin Duerst for their many suggestions that have been Duerst for their many suggestions that have been incorporated into
incorporated into this document. this document.
Initial discussion of the COMPARATOR extension involved input from Initial discussion of the I18NLEVEL=2 extension involved input from
Mark Crispin and other participants of the IMAP Extensions WG. Mark Crispin and other participants of the IMAP Extensions WG.
9. Relevant Standards for i18n IMAP Implementations 9. Relevant Standards for i18n IMAP Implementations
This is a non-normative list of standards to consider when This is a non-normative list of standards to consider when
implementing i18n aware IMAP software. implementing i18n aware IMAP software.
o The LANGUAGE and COMPARATOR extensions to IMAP (this o The LANGUAGE and I18NLEVEL=2 extensions to IMAP (this
specification). specification).
o The 8-bit rules for mailbox naming in section 5.1 of RFC 3501. o The 8-bit rules for mailbox naming in section 5.1 of RFC 3501.
o The Mailbox International Naming Convention in section 5.1.3 of o The Mailbox International Naming Convention in section 5.1.3 of
RFC 3501. RFC 3501.
o MIME [RFC2045] for message bodies. o MIME [RFC2045] for message bodies.
o MIME header encoding [RFC2047] for message headers. o MIME header encoding [RFC2047] for message headers.
o The IETF EAI working group. o The IETF EAI working group.
o MIME Parameter Value and Encoded Word Extensions [RFC2231] for o MIME Parameter Value and Encoded Word Extensions [RFC2231] for
filenames. Quality IMAP server implementations will filenames. Quality IMAP server implementations will
automatically combine multipart parameters when generating the automatically combine multipart parameters when generating the
BODYSTRUCTURE. There is also some deployed non-standard use of BODYSTRUCTURE. There is also some deployed non-standard use of
MIME header encoding inside double-quotes for filenames. MIME header encoding inside double-quotes for filenames.
o IDNA [RFC3490] and punycode [RFC3492] for domain names o IDNA [RFC3490] and punycode [RFC3492] for domain names
(presently only relevant to IMAP clients). (currently only relevant to IMAP clients).
o The UTF-8 charset [RFC3629]. o The UTF-8 charset [RFC3629].
o The IETF policy on Character Sets and Languages [RFC2277]. o The IETF policy on Character Sets and Languages [RFC2277].
Normative References Normative References
Internet-draft November 2007
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2277] Alvestrand, "IETF Policy on Character Sets and [RFC2277] Alvestrand, "IETF Policy on Character Sets and
Internet-draft December 2007
Languages", BCP 18, RFC 2277, January 1998. Languages", BCP 18, RFC 2277, January 1998.
[RFC2342] Gahrns, Newman, "IMAP4 Namespace", RFC 2342, May 1998. [RFC2342] Gahrns, Newman, "IMAP4 Namespace", RFC 2342, May 1998.
[RFC3501] Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION [RFC3501] Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003. 4rev1", RFC 3501, March 2003.
[RFC3629] Yergeau, "UTF-8, a transformation format of ISO 10646", [RFC3629] Yergeau, "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003. STD 63, RFC 3629, November 2003.
skipping to change at page 16, line 5 skipping to change at page 16, line 51
Algorithm", RFC 5051, October 2007. Algorithm", RFC 5051, October 2007.
[RFC2045] Freed, Borenstein, "Multipurpose Internet Mail Extensions [RFC2045] Freed, Borenstein, "Multipurpose Internet Mail Extensions
(MIME) Part One: Format of Internet Message Bodies", RFC (MIME) Part One: Format of Internet Message Bodies", RFC
2045, November 1996. 2045, November 1996.
[RFC2047] Moore, "MIME (Multipurpose Internet Mail Extensions) Part [RFC2047] Moore, "MIME (Multipurpose Internet Mail Extensions) Part
Three: Message Header Extensions for Non-ASCII Text", RFC Three: Message Header Extensions for Non-ASCII Text", RFC
2047, November 1996. 2047, November 1996.
Internet-draft November 2007
Informative References Informative References
Internet-draft December 2007
[RFC2231] Freed, Moore, "MIME Parameter Value and Encoded Word [RFC2231] Freed, Moore, "MIME Parameter Value and Encoded Word
Extensions: Character Sets, Languages, and Extensions: Character Sets, Languages, and
Continuations", RFC 2231, November 1997. Continuations", RFC 2231, November 1997.
[RFC3490] Faltstrom, Hoffman, Costello, "Internationalizing Domain [RFC3490] Faltstrom, Hoffman, Costello, "Internationalizing Domain
Names in Applications (IDNA)", RFC 3490, March 2003. Names in Applications (IDNA)", RFC 3490, March 2003.
[RFC3492] Costello, "Punycode: A Bootstring encoding of Unicode for [RFC3492] Costello, "Punycode: A Bootstring encoding of Unicode for
Internationalized Domain Names in Applications (IDNA)", Internationalized Domain Names in Applications (IDNA)",
RFC 3492, March 2003. RFC 3492, March 2003.
skipping to change at page 17, line 5 skipping to change at page 17, line 49
Email: arnt@oryx.com Email: arnt@oryx.com
Fax: +49 89 4502 9758 Fax: +49 89 4502 9758
Alexey Melnikov Alexey Melnikov
Isode Limited Isode Limited
5 Castle Business Village, 36 Station Road, 5 Castle Business Village, 36 Station Road,
Hampton, Middlesex, TW12 2BX, UK Hampton, Middlesex, TW12 2BX, UK
Internet-draft November 2007
Email: Alexey.Melnikov@isode.com Email: Alexey.Melnikov@isode.com
Internet-draft November 2007 Internet-draft December 2007
Intellectual Property Statement Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed Intellectual Property Rights or other rights that might be claimed to
to pertain to the implementation or use of the technology described pertain to the implementation or use of the technology described in
in this document or the extent to which any license under such this document or the extent to which any license under such rights
rights might or might not be available; nor does it represent that might or might not be available; nor does it represent that it has
it has made any independent effort to identify any such rights. made any independent effort to identify any such rights. Information
Information on the procedures with respect to rights in RFC on the procedures with respect to rights in RFC documents can be found
documents can be found in BCP 78 and BCP 79. in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use attempt made to obtain a general license or permission for the use of
of such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this specification
specification can be obtained from the IETF on-line IPR repository can be obtained from the IETF on-line IPR repository at
at http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf- this standard. Please address the information to the IETF at
ipr@ietf.org. ietf-ipr@ietf.org.
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). This document is subject to Copyright (C) The IETF Trust (2007). This document is subject to
the rights, licenses and restrictions contained in BCP 78, and the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
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