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| author | Eduardo Chappa <echappa@gmx.com> | 2013-02-03 00:59:38 -0700 |
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| committer | Eduardo Chappa <echappa@gmx.com> | 2013-02-03 00:59:38 -0700 |
| commit | 094ca96844842928810f14844413109fc6cdd890 (patch) | |
| tree | e60efbb980f38ba9308ccb4fb2b77b87bbc115f3 /imap/docs/draft/i18n.txt | |
| download | alpine-094ca96844842928810f14844413109fc6cdd890.tar.xz | |
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+
+Network Working Group Chris Newman
+Internet-Draft Sun Microsystems
+Intended Status: Proposed Standard Arnt Gulbrandsen
+ Oryx Mail Systems GmhH
+ Alexey Melnikov
+ Isode Limited
+ February 1, 2008
+
+ Internet Message Access Protocol Internationalization
+ draft-ietf-imapext-i18n-15.txt
+
+
+Status of this Memo
+ By submitting this Internet-Draft, each author represents that any
+ 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
+ aware will be disclosed, in accordance with Section 6 of BCP 79.
+
+ Internet-Drafts are working documents of the Internet Engineering
+ Task Force (IETF), its areas, and its working groups. Note that
+ other groups may also distribute working documents as Internet-
+ Drafts.
+
+ Internet-Drafts are draft documents valid for a maximum of six
+ months and may be updated, replaced, or obsoleted by other documents
+ at any time. It is inappropriate to use Internet-Drafts as
+ reference material or to cite them other than as "work in progress".
+
+ The list of current Internet-Drafts can be accessed at
+ http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-
+ Draft Shadow Directories can be accessed at
+ http://www.ietf.org/shadow.html.
+
+ This Internet-Draft expires in August 2008.
+
+
+Copyright Notice
+
+ Copyright (C) The IETF Trust (2008).
+
+
+Abstract
+
+ Internet Message Access Protocol (IMAP) version 4rev1 has basic
+ support for non-ASCII characters in mailbox names and search
+ substrings. It also supports non-ASCII message headers and content
+ encoded as specified by Multipurpose Internet Mail Extensions
+ (MIME). This specification defines a collection of IMAP extensions
+
+
+
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+ which improve international support including comparator negotiation
+ for search, sort and thread, language negotiation for international
+ error text, and translations for namespace prefixes.
+
+
+Table of Contents
+
+ 1. Conventions Used in this Document . . . . . . . . . . . . . . 2
+ 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
+ 3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . 3
+ 3.1 LANGUAGE Extension Requirements . . . . . . . . . . . . . . . 3
+ 3.2 LANGUAGE Command . . . . . . . . . . . . . . . . . . . . . . 4
+ 3.3 LANGUAGE Response . . . . . . . . . . . . . . . . . . . . . . 6
+ 3.4 TRANSLATION Extension to the NAMESPACE Response . . . . . . . 6
+ 3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6
+ 4. I18NLEVEL=1 and I18NLEVEL=2 Extensions . . . . . . . . . . . 7
+ 4.1 Introduction and Overview . . . . . . . . . . . . . . . . . . 8
+ 4.2 Requirements common to both I18NLEVEL=1 and I18NLEVEL=2 . . .
+ 4.3 I18NLEVEL=1 Extension Requirements . . . . . . . . . . . . . 8
+ 4.4 I18NLEVEL=2 Extension Requirements . . . . . . . . . . . . . 8
+ 4.5 Compatibility Notes
+ 4.6 Comparators and Charsets . . . . . . . . . . . . . . . . . . 9
+ 4.7 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . 9
+ 4.8 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10
+ 4.9 BADCOMPARATOR Response Code . . . . . . . . . . . . . . . . .
+ 4.10 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 10
+ 5. Other IMAP Internationalization Issues . . . . . . . . . . . 11
+ 5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11
+ 5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 11
+ 5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 11
+ 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
+ 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
+ 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
+ 9. Relevant Standards for i18n IMAP Implementations . . . . . . 13
+ Normative References . . . . . . . . . . . . . . . . . . . . 13
+ Informative References . . . . . . . . . . . . . . . . . . . 14
+ Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 15
+ Intellectual Property and Copyright Statements . . . . . . . 16
+
+
+Conventions Used in This Document
+
+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+ "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+ document are to be interpreted as described in [RFC2119].
+
+ The formal syntax use the Augmented Backus-Naur Form (ABNF)
+ [RFC4234] notation including the core rules defined in Appendix A.
+
+
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+ The UTF8-related productions are defined in [RFC3629].
+
+ In examples, "C:" and "S:" indicate lines sent by the client and
+ server respectively. If a single "C:" or "S:" label applies to
+ multiple lines, then the line breaks between those lines are for
+ editorial clarity only and are not part of the actual protocol
+ exchange.
+
+
+2. Introduction
+
+ This specification defines two IMAP4rev1 [RFC3501] extensions to
+ enhance international support. These extensions can be advertised
+ and implemented separately.
+
+ The LANGUAGE extension allows the client to request a suitable
+ language for protocol error messages and in combination with the
+ NAMESPACE extension [RFC2342] enables namespace translations.
+
+ The I18NLEVEL=2 extension allows the client to request a suitable
+ collation which will modify the behavior of the base specification's
+ SEARCH command as well as the SORT and THREAD extensions [SORT].
+ This leverages the collation registry [RFC4790].
+
+
+3. LANGUAGE Extension
+
+ IMAP allows server responses to include human-readable text that in
+ 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
+ preserve backwards compatibility with deployed IMAP implementations.
+ This section specifies a way for an IMAP client to negotiate which
+ language the server should use when sending human-readable text.
+
+ The LANGUAGE extension only provides a mechanism for altering fixed
+ server strings such as response text and NAMESPACE folder names.
+ Assigning localized language aliases to shared mailboxes would be
+ done with a separate mechanism such as the proposed METADATA
+ extension (see [METADATA]).
+
+
+3.1 LANGUAGE Extension Requirements
+
+ IMAP servers that support this extension MUST list the keyword
+ LANGUAGE in their CAPABILITY response as well as in the greeting
+ CAPABILITY data.
+
+ A server that advertises this extension MUST use the language "i-
+
+
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+ default" as described in [RFC2277] as its default language until
+ 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
+ the NAMESPACE extension [RFC2342].
+
+ The LANGUAGE command is valid in all states. Clients are urged to
+ issue LANGUAGE before authentication, since some servers send
+ valuable user information as part of authentication (e.g. "password
+ is correct, but expired"). If a security layer (such as SASL or
+ TLS) is subsequently negotiated by the client, it MUST re-issue the
+ LANGUAGE command in order to make sure that no previous active
+ attack (if any) on LANGUAGE negotiation has effect on subsequent
+ error messages. (See Section 7 for a more detailed explanation of
+ the attack.)
+
+
+
+3.2 LANGUAGE Command
+
+ Arguments: Optional language range arguments.
+
+ Response: A possible LANGUAGE response (see section 3.3).
+ A possible NAMESPACE response (see section 3.4).
+
+ Result: OK - Command completed
+ NO - Could not complete command
+ BAD - arguments invalid
+
+ The LANGUAGE command requests that human-readable text emitted by
+ the server be localized to a language matching one of the language
+ range argument as described by section 2 of [RFC4647].
+
+ If the command succeeds, the server will return human-readable
+ responses in the first supported language specified. These
+ responses will be in UTF-8 [RFC3629]. The server MUST send a
+ LANGUAGE response specifying the language used, and the change takes
+ effect immediately after the LANGUAGE response.
+
+ If the command fails, the server continues to return human-readable
+ responses in the language it was previously using.
+
+ The special "default" language range argument indicates a request to
+ use a language designated as preferred by the server administrator.
+ The preferred language MAY vary based on the currently active user.
+
+ If a language range does not match a known language tag exactly but
+
+
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+ does match a language by the rules of [RFC4647], the server MUST
+ send an untagged LANGUAGE response indicating the language selected.
+
+ If there aren't any arguments, the server SHOULD send an untagged
+ LANGUAGE response listing the languages it supports. If the server
+ is unable to enumerate the list of languages it supports it MAY
+ return a tagged NO response to the enumeration request.
+
+ < The server defaults to using English i-default responses until
+ the user explicitly changes the language. >
+
+ C: A001 LOGIN KAREN PASSWORD
+ S: A001 OK LOGIN completed
+
+ < Client requested MUL language, which no server supports. >
+
+ C: A002 LANGUAGE MUL
+ S: A002 NO Unsupported language MUL
+
+ < A LANGUAGE command with no arguments is a request to enumerate
+ the list of languages the server supports. >
+
+ C: A003 LANGUAGE
+ S: * LANGUAGE (EN DE IT i-default)
+ S: A003 OK Supported languages have been enumerated
+
+ C: B001 LANGUAGE
+ S: B001 NO Server is unable to enumerate supported languages
+
+ < Once the client changes the language, all responses will be in
+ that language starting after the LANGUAGE response. Note that
+ this includes the NAMESPACE response. Because RFCs are in US-
+ ASCII, this document uses an ASCII transcription rather than
+ UTF-8 text, e.g. ue in the word "ausgefuehrt" >
+
+ C: C001 LANGUAGE DE
+ S: * LANGUAGE (DE)
+ S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
+ ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
+ "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
+ S: C001 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
+
+ < If a server does not support the requested primary language,
+ responses will continue to be returned in the current language
+ the server is using. >
+
+ C: D001 LANGUAGE FR
+ S: D001 NO Diese Sprache ist nicht unterstuetzt
+
+
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+ C: D002 LANGUAGE DE-IT
+ S: * LANGUAGE (DE-IT)
+ S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION"
+ ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
+ "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
+ S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
+ C: D003 LANGUAGE "default"
+ S: * LANGUAGE (DE)
+ S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
+
+ < Server does not speak French, but does speak English. User
+ speaks Canadian French and Canadian English. >
+
+ C: E001 LANGUAGE FR-CA EN-CA
+ S: * LANGUAGE (EN)
+ S: E001 OK Now speaking English
+
+
+
+3.3 LANGUAGE Response
+
+ Contents: A list of one or more language tags.
+
+ The LANGUAGE response occurs as a result of a LANGUAGE command. A
+ LANGUAGE response with a list containing a single language tag
+ indicates that the server is now using that language. A LANGUAGE
+ response with a list containing multiple language tags indicates the
+ server is communicating a list of available languages to the client,
+ and no change in the active language has been made.
+
+
+3.4 TRANSLATION Extension to the NAMESPACE Response
+
+ If localized representations of the namespace prefixes are available
+ in the selected language, the server SHOULD include these in the
+ TRANSLATION extension to the NAMESPACE response.
+
+ The TRANSLATION extension to the NAMESPACE response returns a single
+ string, containing the modified UTF-7 [RFC3501] encoded translation
+ of the namespace prefix. It is the responsibility of the client to
+ convert between the namespace prefix and the translation of the
+ namespace prefix when presenting mailbox names to the user.
+
+ In this example a server supports the IMAP4 NAMESPACE command. It
+ uses no prefix to the user's Personal Namespace, a prefix of "Other
+ Users" to its Other Users' Namespace and a prefix of "Public
+ Folders" to its only Shared Namespace. Since a client will often
+ display these prefixes to the user, the server includes a
+
+
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+ translation of them that can be presented to the user.
+
+ C: A001 LANGUAGE DE-IT
+ S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
+ ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
+ "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
+ S: A001 OK LANGUAGE-Befehl ausgefuehrt
+
+
+3.5 Formal Syntax
+
+ The following syntax specification inherits ABNF [RFC4234] rules
+ from IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the
+ Identifying Languages [RFC4646], UTF-8 [RFC3629] and Collected
+ Extensions to IMAP4 ABNF [RFC4466].
+
+ command-any =/ language-cmd
+ ; LANGUAGE command is valid in all states
+
+ language-cmd = "LANGUAGE" *(SP lang-range-quoted)
+
+ response-payload =/ language-data
+
+ language-data = "LANGUAGE" SP "(" lang-tag-quoted *(SP
+ lang-tag-quoted) ")"
+
+ namespace-trans = SP DQUOTE "TRANSLATION" DQUOTE SP "(" string ")"
+ ; the string is encoded in Modified UTF-7.
+ ; this is a subset of the syntax permitted by
+ ; the Namespace-Response-Extension rule in [RFC4466]
+
+ lang-range-quoted = astring
+ ; Once any literal wrapper or quoting is removed, this
+ ; follows the language-range rule in [RFC4647]
+
+ lang-tag-quoted = astring
+ ; Once any literal wrapper or quoting is removed, this follows
+ ; the Language-Tag rule in [RFC4646]
+
+ resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR
+ *(UTF8-TEXT-CHAR / "[")
+ ; After the server is changed to a language other than
+ ; i-default, this resp-text rule replaces the resp-text
+ ; rule from [RFC3501].
+
+ UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4
+ ; UTF-8 excluding 7-bit control characters and "["
+
+
+
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+4. I18NLEVEL=1 and I18NLEVEL=2 Extensions
+
+
+4.1 Introduction and Overview
+
+ IMAP4rev1 [RFC3501] includes the SEARCH command which can be used to
+ locate messages matching criteria including human-readable text.
+ The SORT extension [SORT] to IMAP allows the client to ask the
+ server to determine the order of messages based on criteria
+ including human-readable text. These mechanisms require the ability
+ to support non-English search and sort functions.
+
+ Section 4 defines two IMAP extensions for internationalizing IMAP
+ SEARCH, SORT and THREAD [SORT] using the comparator framework
+ [RFC4790].
+
+ 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.
+
+ The I18NLEVEL=2 extension is a superset of the I18NLEVEL=1
+ extension. It adds to I18NLEVEL=1 extension the ability to determine
+ the active comparator (see definition below) and negotiate use of
+ 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
+ by SEARCH and SORT absent any negotiation using the COMPARATOR (see
+ Section 4.7) command. The term "active comparator" refers to the
+ comparator which will be used within a session e.g. by SEARCH and
+ SORT. The COMPARATOR command is used to change the active
+ comparator.
+
+ The active comparator applies to the following SEARCH keys: "BCC",
+ "BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER". If the
+ server also advertises the "SORT" extension, then the active
+ comparator applies to the following SORT keys: "CC", "FROM",
+ "SUBJECT" and "TO". If the server advertises THREAD=ORDEREDSUBJECT,
+ then the active comparator applies to the ORDEREDSUBJECT threading
+ algorithm. If the server advertises THREAD=REFERENCES, then the
+ active comparator applies to the subject field comparisons done by
+ REFERENCES threading algorithm. Future extensions may choose to
+ apply the active comparator to their SEARCH keys.
+
+
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+ For SORT and THREAD, the pre-processing necessary to extract the
+ base subject text from a Subject header occurs prior to the
+ application of a comparator.
+
+ A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
+ implement the i;unicode-casemap comparator, as defined in [UCM].
+
+ A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
+ support UTF-8 as a SEARCH charset.
+
+
+4.3 I18NLEVEL=1 Extension Requirements
+
+ An IMAP server 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 its
+ CAPABILITY data once IMAP enters the authenticated state, and MAY
+ list that keyword in other states.
+
+
+
+4.4 I18NLEVEL=2 Extension Requirements
+
+ IMAP server that satisfies all requirements specified in sections
+ 4.2, 4.4, 4.6-4.10 (and doesn't support/advertise any other
+ I18NLEVEL=<n> extension, where n > 2) MUST list the keyword
+ I18NLEVEL=2 in its CAPABILITY data once IMAP enters the
+ authenticated state, and MAY list that keyword in other states.
+
+ A server that advertises this extension MUST implement the
+ i;unicode-casemap comparator, as defined in [UCM]. It MAY implement
+ 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
+ as the default comparator. (Note that i;unicode-casemap is the
+ default comparator for I18NLEVEL=1, but not necessarily the default
+ for I18NLEVEL=2.) The selection of the default comparator MAY be
+ adjustable by the server administrator, and MAY be sensitive to the
+ current user. Once the IMAP connection enters authenticated state,
+ the default comparator MUST remain static for the remainder of that
+ connection.
+
+ Note that since SEARCH uses the substring operation, IMAP servers
+ can only implement collations that offer the substring operation
+ (see [RFC4790 section 4.2.2). Since SORT uses ordering operation
+ (and by implication equality), IMAP servers which advertise the SORT
+ extension can only implement collations that offer all three
+
+
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+ operations (see [RFC4790] sections 4.2.2-4).
+
+ If the active collation does not provide the operations needed by an
+ IMAP command, the server MUST respond with a tagged BAD.
+
+
+4.5 Compatibility Notes
+
+ 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:
+
+ In all search keys that use strings, a message matches
+ the key if the string is a substring of the field. The
+ matching is case-insensitive.
+
+ When performing the SEARCH operation, the active comparator is
+ applied instead of the case-insensitive matching specified above.
+
+ An IMAP server which performs collation operations (e.g., as part of
+ commands such as SEARCH, SORT, THREAD) does so according to the
+ following procedure:
+
+ (a) MIME encoding (for example see [RFC2047] for headers and
+ [RFC2045] for body parts) MUST be removed in the texts being
+ collated.
+
+ If MIME encoding removal fails for a message (e.g., a body part
+ of the message has an unsupported Content-Transfer-Encoding,
+ uses characters not allowed by the Content-Transfer-Encoding,
+ etc.), the collation of this message is undefined by this
+ specification, and is handled in an implementation-dependent
+
+
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+ manner.
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+ (b) The decoded text from (a) MUST be converted to the charset
+ expected by the active comparator.
+
+ (c) For the substring operation:
+ If step (b) failed (e.g., the text is in an unknown charset,
+ contains a sequence which is not valid according in that
+ charset, etc.), the original decoded text from (a) (i.e.,
+ before the charset conversion attempt) is collated using the
+ i;octet comparator (see [RFC4790]).
+
+ If step (b) was successful, the converted text from (b) is
+ collated according to the active comparator.
+
+
+ For the ordering operation:
+
+ All strings that were successfully converted by step (b) are
+ separated from all strings that failed step (b). Strings in
+ each group are collated independently. All strings successfully
+ converted by step (b) are then validated by the active
+ comparator. Strings that pass validation are collated using the
+ active comparator. All strings that either fail step (b) or fail
+ the active collation's validity operation are collated (after
+ applying step (a)) using the i;octet comparator (see [RFC4790]).
+ The resulting sorted list is produced by appending all collated
+ "failed" strings after all strings collated using the active
+ comparator.
+
+
+ Example: The following example demonstrates ordering of 4
+ different strings using i;unicode-casemap [UCM] comparator.
+ Strings are represented using hexadecimal notation used by
+ ABNF [RFC4234].
+
+ (1) %xD0 %xC0 %xD0 %xBD %xD0 %xB4 %xD1 %x80 %xD0 %xB5
+ %xD0 %xB9 (labeled with charset=UTF-8)
+ (2) %xD1 %x81 %xD0 %x95 %xD0 %xA0 %xD0 %x93 %xD0 %x95
+ %xD0 %x99 (labeled with charset=UTF-8)
+ (3) %xD0 %x92 %xD0 %xB0 %xD1 %x81 %xD0 %xB8 %xD0 %xBB
+ %xD0 %xB8 %xFF %xB9 (labeled with charset=UTF-8)
+ (4) %xE1 %xCC %xC5 %xCB %xD3 %xC5 %xCA (labeled with
+ charset=KOI8-R)
+
+ Step (b) will convert string # 4 to the following
+ sequence of octets (in UTF-8):
+
+
+
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+ %xD0 %x90 %xD0 %xBB %xD0 %xB5 %xD0 %xBA %xD1 %x81 %xD0
+ %xB5 %xD0 %xB9
+
+ and will reject strings (1) and (3), as they contain
+ octets not allowed in charset=UTF-8.
+ After that, using the i;unicode-casemap collation,
+ string (4) will collate before string (2). Using the
+ i;octet collation on the original strings, string (3)
+ will collate before string (1). So the final ordering
+ is as follows: (4) (2) (3) (1).
+
+ If the substring operation (e.g., IMAP SEARCH) of the active
+ comparator returns the "undefined" result (see section 4.2.3 of
+ [RFC4790]) for either the text specified in the SEARCH command or
+ the message text, then the operation is repeated on the result of
+ step (a) using the i;octet comparator.
+
+ The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate
+ the following together: strings encoded using unknown or invalid
+ character encodings, strings in unrecognized charsets, and invalid
+ input (as defined by the active collation).
+
+
+
+4.7 COMPARATOR Command
+
+ Arguments: Optional comparator order arguments.
+
+ Response: A possible COMPARATOR response (see Section 4.8).
+
+ Result: OK - Command completed
+ NO - No matching comparator found
+ BAD - arguments invalid
+
+ The COMPARATOR command is valid in authenticated and selected
+ states.
+
+ The COMPARATOR command is used to determine or change the active
+ comparator. When issued with no arguments, it results in a
+ COMPARATOR response indicating the currently active comparator.
+
+ When issued with one or more comparator argument, it changes the
+ active comparator as directed. (If more than one installed
+ comparator is matched by an argument, the first argument wins.) The
+ COMPARATOR response lists all matching comparators if more than one
+ matches the specified patterns.
+
+ The argument "default" refers to the server's default comparator.
+
+
+
+Newman & Co Expires August 2008 FF[Page 12]
+
+
+
+
+
+Internet-draft February 2008
+
+
+ Otherwise each argument is an collation specification as defined in
+ the Internet Application Protocol Comparator Registry [RFC4790].
+
+ < The client requests activating a Czech comparator if possible,
+ or else a generic international comparator which it considers
+ suitable for Czech. The server picks the first supported
+ comparator. >
+
+ C: A001 COMPARATOR "cz;*" i;basic
+ S: * COMPARATOR i;basic
+ S: A001 OK Will use i;basic for collation
+
+
+4.8 COMPARATOR Response
+
+ Contents: The active comparator.
+ An optional list of available matching comparators
+
+ The COMPARATOR response occurs as a result of a COMPARATOR command.
+ The first argument in the comparator response is the name of the
+ active comparator. The second argument is a list of comparators
+ which matched any of the arguments to the COMPARATOR command and is
+ present only if more than one match is found.
+
+
+4.9 BADCOMPARATOR response code
+
+ This response code SHOULD be returned as a result of server failing
+ an IMAP command (returning NO), when the server knows that none of
+ the specified comparators match the requested comparator(s).
+
+
+4.10 Formal Syntax
+
+ The following syntax specification inherits ABNF [RFC4234] rules
+ from IMAP4rev1 [RFC3501], and Internet Application Protocol
+ Comparator Registry [RFC4790].
+
+ command-auth =/ comparator-cmd
+
+ resp-text-code =/ "BADCOMPARATOR"
+
+ comparator-cmd = "COMPARATOR" *(SP comp-order-quoted)
+
+ response-payload =/ comparator-data
+
+ comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "("
+ comp-id-quoted *(SP comp-id-quoted) ")"]
+
+
+
+Newman & Co Expires August 2008 FF[Page 13]
+
+
+
+
+
+Internet-draft February 2008
+
+
+ comp-id-quoted = astring
+ ; Once any literal wrapper or quoting is removed, this
+ ; follows the collation-id rule from [RFC4790]
+
+ comp-order-quoted = astring
+ ; Once any literal wrapper or quoting is removed, this
+ ; follows the collation-order rule from [RFC4790]
+
+ comp-sel-quoted = astring
+ ; Once any literal wrapper or quoting is removed, this
+ ; follows the collation-selected rule from [RFC4790]
+
+
+5. Other IMAP Internationalization Issues
+
+ The following sections provide an overview of various other IMAP
+ internationalization issues. These issues are not resolved by this
+ specification, but could be resolved by other standards work, such
+ as that being done by the EAI group (see [IMAP-EAI]).
+
+
+5.1 Unicode Userids and Passwords
+
+ IMAP4rev1 currently restricts 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
+ standards track RFC states otherwise. Servers are encouraged to
+ 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.
+ Servers MAY reject the use of any 8-bit in the "userid" or
+ "password" field.
+
+ When AUTHENTICATE is used, some servers may support userids and
+ passwords in Unicode [RFC3490] since SASL (see [RFC4422]) allows
+ that. However, such userids cannot be used as part of email
+ addresses.
+
+
+5.2 UTF-8 Mailbox Names
+
+ 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
+ quo in 1996 when modified UTF-7 was first specified. At that time,
+ there was widespread unofficial use of local character sets such as
+ ISO-8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant
+ non-interoperability.
+
+ The requirements in section 5.1 of RFC 3501 are very important if
+
+
+
+Newman & Co Expires August 2008 FF[Page 14]
+
+
+
+
+
+Internet-draft February 2008
+
+
+ we're ever going to be able to deploy UTF-8 mailbox names. Servers
+ are encouraged to enforce them.
+
+
+5.3 UTF-8 Domains, Addresses and Mail Headers
+
+ There is now an IETF standard for Internationalizing Domain Names in
+ Applications [RFC3490]. While IMAP clients are free to support this
+ standard, an argument can be made that it would be helpful to simple
+ clients if the IMAP server could perform this conversion (the same
+ argument would apply to MIME header encoding [RFC2047]). However,
+ it would be unwise to move forward with such work until the work in
+ progress to define the format of international email addresses is
+ complete.
+
+
+6. IANA Considerations
+
+ The IANA is requested to add LANGUAGE, I18NLEVEL=1 and I18NLEVEL=2
+ to the IMAP4 Capabilities Registry. [Note to IANA:
+ http://www.iana.org/assignments/imap4-capabilities]
+
+
+7. Security Considerations
+
+ The LANGUAGE extension makes a new command available in "Not
+ Authenticated" state in IMAP. Some IMAP implementations run with
+ root privilege when the server is in "Not Authenticated" state and
+ do not revoke that privilege until after authentication is complete.
+ Such implementations are particularly vulnerable to buffer overflow
+ security errors at this stage and need to implement parsing of this
+ command with extra care.
+
+ A LANGUAGE command issued prior to activation of a security layer is
+ subject to an active attack which suppresses or modifies the
+ negotiation and thus makes STARTTLS or authentication error messages
+ more difficult to interpret. This is not a new attack as the error
+ messages themselves are subject to active attack. Clients MUST re-
+ issue the LANGUAGE command once a security layer is active, so this
+ does not impact subsequent protocol operations.
+
+ LANGUAGE, I18NLEVEL=1 and I18NLEVEL=2 extensions use the UTF-8
+ charset, thus the security considerations for UTF-8 [RFC3629] are
+ relevent. However, neither uses UTF-8 for identifiers so the most
+ serious concerns do not apply.
+
+
+8. Acknowledgements
+
+
+
+Newman & Co Expires August 2008 FF[Page 15]
+
+
+
+
+
+Internet-draft February 2008
+
+
+ The LANGUAGE extension is based on a previous Internet draft by Mike
+ Gahrns, a substantial portion of the text in that section was
+ written by him. Many people have participated in discussions about
+ an IMAP Language extension in the various fora of the IETF and
+ Internet working groups, so any list of contributors is bound to be
+ incomplete. However, the authors would like to thank Andrew McCown
+ for early work on the original proposal, John Myers for suggestions
+ regarding the namespace issue, along with Jutta Degener, Mark
+ Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo, Martin Duerst,
+ Timo Sirainen, Ben Campbell and Magnus Nystrom for their many
+ suggestions that have been incorporated into this document.
+
+ Initial discussion of the I18NLEVEL=2 extension involved input from
+ Mark Crispin and other participants of the IMAP Extensions WG.
+
+
+9. Relevant Standards for i18n IMAP Implementations
+
+ This is a non-normative list of standards to consider when
+ implementing i18n aware IMAP software.
+
+ o The LANGUAGE and I18NLEVEL=2 extensions to IMAP (this
+ specification).
+ 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
+ RFC 3501.
+ o MIME [RFC2045] for message bodies.
+ o MIME header encoding [RFC2047] for message headers.
+ o The IETF EAI working group.
+ o MIME Parameter Value and Encoded Word Extensions [RFC2231] for
+ filenames. Quality IMAP server implementations will
+ automatically combine multipart parameters when generating the
+ BODYSTRUCTURE. There is also some deployed non-standard use of
+ MIME header encoding inside double-quotes for filenames.
+ o IDNA [RFC3490] and punycode [RFC3492] for domain names
+ (currently only relevant to IMAP clients).
+ o The UTF-8 charset [RFC3629].
+ o The IETF policy on Character Sets and Languages [RFC2277].
+
+
+Normative References
+
+ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [RFC2277] Alvestrand, "IETF Policy on Character Sets and
+ Languages", BCP 18, RFC 2277, January 1998.
+
+
+
+
+Newman & Co Expires August 2008 FF[Page 16]
+
+
+
+
+
+Internet-draft February 2008
+
+
+ [RFC2342] Gahrns, Newman, "IMAP4 Namespace", RFC 2342, May 1998.
+
+ [RFC3501] Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
+ 4rev1", RFC 3501, March 2003.
+
+ [RFC3629] Yergeau, "UTF-8, a transformation format of ISO 10646",
+ STD 63, RFC 3629, November 2003.
+
+ [RFC4234] Crocker, Overell, "Augmented BNF for Syntax
+ Specifications: ABNF", RFC 4234, Brandenburg
+ Internetworking, Demon Internet Ltd, October 2005.
+
+ [RFC4422] Melnikov, Zeilenga, "Simple Authentication and Security
+ Layer (SASL)", RFC 4422, June 2006.
+
+ [RFC4466] Melnikov, Daboo, "Collected Extensions to IMAP4 ABNF",
+ RFC 4466, Isode Ltd., April 2006.
+
+ [RFC4646] Philips, Davis, "Tags for Identifying Languages", BCP 47,
+ RFC 4646, September 2006.
+
+ [RFC4647] Philips, Davis, "Matching of Language Tags", BCP 47, RFC
+ 4647, September 2006.
+
+ [RFC4790] Newman, Duerst, Gulbrandsen, "Internet Application
+ Protocol Comparator Registry", RFC 4790, February 2007.
+
+ [SORT] Crispin, M. and K. Murchison, "INTERNET MESSAGE ACCESS
+ PROTOCOL - SORT AND THREAD EXTENSION", draft-ietf-
+ imapext-sort-19 (work in progress), November 2006.
+
+ [UCM] Crispin, "i;unicode-casemap - Simple Unicode Collation
+ Algorithm", RFC 5051, October 2007.
+
+ [RFC2045] Freed, Borenstein, "Multipurpose Internet Mail Extensions
+ (MIME) Part One: Format of Internet Message Bodies", RFC
+ 2045, November 1996.
+
+ [RFC2047] Moore, "MIME (Multipurpose Internet Mail Extensions) Part
+ Three: Message Header Extensions for Non-ASCII Text", RFC
+ 2047, November 1996.
+
+
+Informative References
+
+
+ [RFC2231] Freed, Moore, "MIME Parameter Value and Encoded Word
+ Extensions: Character Sets, Languages, and
+
+
+
+Newman & Co Expires August 2008 FF[Page 17]
+
+
+
+
+
+Internet-draft February 2008
+
+
+ Continuations", RFC 2231, November 1997.
+
+ [RFC3490] Faltstrom, Hoffman, Costello, "Internationalizing Domain
+ Names in Applications (IDNA)", RFC 3490, March 2003.
+
+ [RFC3492] Costello, "Punycode: A Bootstring encoding of Unicode for
+ Internationalized Domain Names in Applications (IDNA)",
+ RFC 3492, March 2003.
+
+ [METADATA] Daboo, C., "IMAP METADATA Extension", draft-daboo-imap-
+ annotatemore-12 (work in progress), December 2007.
+
+ [IMAP-EAI] Resnick, Newman, "IMAP Support for UTF-8", draft-ietf-
+ eai-imap-utf8 (work in progress), May 2006.
+
+
+
+Authors' Addresses
+
+ Chris Newman
+ Sun Microsystems
+ 3401 Centrelake Dr., Suite 410
+ Ontario, CA 91761
+ US
+
+ Email: chris.newman@sun.com
+
+
+ Arnt Gulbrandsen
+ Oryx Mail Systems GmbH
+ Schweppermannstr. 8
+ D-81671 Muenchen
+ Germany
+
+ Email: arnt@oryx.com
+
+ Fax: +49 89 4502 9758
+
+
+ Alexey Melnikov
+ Isode Limited
+ 5 Castle Business Village, 36 Station Road,
+ Hampton, Middlesex, TW12 2BX, UK
+
+ Email: Alexey.Melnikov@isode.com
+
+
+
+
+
+
+Newman & Co Expires August 2008 FF[Page 18]
+
+
+
+
+
+Internet-draft February 2008
+
+
+Intellectual Property Statement
+
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+ Intellectual Property Rights or other rights that might be claimed to
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+
+ Copies of IPR disclosures made to the IETF Secretariat and any
+ assurances of licenses to be made available, or the result of an
+ attempt made to obtain a general license or permission for the use of
+ such proprietary rights by implementers or users of this specification
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+ http://www.ietf.org/ipr.
+
+ The IETF invites any interested party to bring to its attention any
+ copyrights, patents or patent applications, or other proprietary
+ rights that may cover technology that may be required to implement
+ this standard. Please address the information to the IETF at
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+
+
+Full Copyright Statement
+
+ Copyright (C) The IETF Trust (2008). This document is subject to
+ the rights, licenses and restrictions contained in BCP 78, and
+ except as set forth therein, the authors retain all their rights.
+
+ This document and the information contained herein are provided on
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+
+
+Acknowledgment
+
+ Funding for the RFC Editor function is currently provided by the
+ Internet Society.
+
+
+
+
+
+
+Newman & Co Expires August 2008 FF[Page 19]
+
+
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