Movatterモバイル変換

Internet Engineering Task Force (IETF)                          S. BoschRequest for Comments: 8438                                    Dovecot OyCategory: Standards Track                                    August 2018ISSN: 2070-1721IMAP Extension for STATUS=SIZEAbstract   This document adds a new capability called "STATUS=SIZE" to the   Internet Message Access Protocol (IMAP).  It allows retrieving the   total storage size of a mailbox with a single STATUS command rather   than retrieving and summing the sizes of all individual messages in   that mailbox.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8438.Copyright Notice   Copyright (c) 2018 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (https://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Bosch                        Standards Track                    [Page 1]

RFC 8438               IMAP STATUS=SIZE Extension            August 2018Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions Used in This Document . . . . . . . . . . . . . .33.  STATUS Command and Response Extensions  . . . . . . . . . . .34.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .55.  Security Considerations . . . . . . . . . . . . . . . . . . .56.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .57.  Normative References  . . . . . . . . . . . . . . . . . . . .5   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .6   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .61.  Introduction   This document extends the Internet Message Access Protocol (IMAP)   [IMAP4rev1] with a new capability called "STATUS=SIZE".  To determine   the total storage size of a mailbox, an IMAP client currently needs   to retrieve all message sizes individually using the FETCH command   with theRFC822.SIZE data item.  The STATUS=SIZE capability provides   a more efficient means of achieving this.  It extends the STATUS   command with a new "SIZE" data item, which indicates the total size   of all messages in the target mailbox.  This way, this information   can be queried with just one STATUS command.  When the LIST-STATUS   IMAP capability [LIST-STATUS] is also available, the SIZE data item   can be queried for many mailboxes at once using just one LIST   command.   This capability is particularly useful for IMAP clients that do not   cache the state of the message store, such as most webmail clients.   Without the "STATUS=SIZE" capability, such clients need to fetch all   message sizes from the server when the size of an individual mailbox   needs to be determined.  For example, a user may request detailed   quota usage information for each mailbox to find out which specific   mailboxes consume most of the available storage resources.  Using   this information, the user can get an overview of which mailboxes   need to be cleaned up to reduce quota usage.  The QUOTA capability   [QUOTA] is no help in that scenario, since the provided QUOTAROOT   command can only yield the STORAGE resource usage of a whole quota   root, not each individual mailbox within that root.Bosch                        Standards Track                    [Page 2]

RFC 8438               IMAP STATUS=SIZE Extension            August 20182.  Conventions Used in This Document   In examples, "C:" indicates lines sent by a client that is connected   to a server.  "S:" indicates lines sent by the server to the client.   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described inBCP 14 [KEYWORDS] [KEYWORDS2] when, and only when, they appear in all   capitals, as shown here.3.  STATUS Command and Response Extensions   This extension defines one new status data item for the STATUS   command and response:   SIZE      The total size of the mailbox in octets.  This is not strictly      required to be an exact value, but it MUST be equal to or greater      than the sum of the values of theRFC822.SIZE FETCH message data      item [IMAP4rev1] of all messages in the mailbox.  When the QUOTA      capability [QUOTA] is also supported, this value SHOULD be equal      to the storage usage value used to enforce the STORAGE resource      limit for this mailbox.  This way, the client can directly infer      the quota usage.   Since the total storage size of a mailbox can easily exceed 4 GB,   clients MUST be capable of receiving 63-bit SIZE data item values.   The message size is chosen to be at most 63 bits wide rather than 64   bits to make implementations on various platforms (such as Java)   easier.   Example:   C: A01 STATUS frop (MESSAGES SIZE UIDNEXT)   S: * STATUS frop (MESSAGES 8 SIZE 44421 UIDNEXT 242344)   S: A01 OK STATUS completedBosch                        Standards Track                    [Page 3]

RFC 8438               IMAP STATUS=SIZE Extension            August 2018   The same information can be obtained by using the following commands,   albeit less efficiently:   C: A02 SELECT "frop"   S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)   S: * 8 EXISTS   S: * 1 RECENT   S: * OK [UNSEEN 7] First unseen.   S: * OK [UIDVALIDITY 1364851417] UIDs valid   S: * OK [UIDNEXT 242344] Predicted next UID   S: * OK [HIGHESTMODSEQ 3914] Highest   S: A02 OK [READ-WRITE] Select completed.   C: A03 FETCH 1:* (RFC822.SIZE)   S: * 1 FETCH (RFC822.SIZE 3224)   S: * 2 FETCH (RFC822.SIZE 1222)   S: * 3 FETCH (RFC822.SIZE 444)   S: * 4 FETCH (RFC822.SIZE 4516)   S: * 5 FETCH (RFC822.SIZE 544)   S: * 6 FETCH (RFC822.SIZE 922)   S: * 7 FETCH (RFC822.SIZE 31126)   S: * 8 FETCH (RFC822.SIZE 2423)   S: A03 OK Fetch completed.   When the LIST-STATUS IMAP capability [LIST-STATUS] is also available,   the STATUS command can be combined with the LIST command to further   improve efficiency.  This way, the sizes of many mailboxes can be   queried with just one LIST command.   Example:   C: A04 LIST "" % RETURN (STATUS (MESSAGES SIZE))   S: * LIST () "." "INBOX"   S: * STATUS "INBOX" (MESSAGES 17 SIZE 16234)   S: * LIST () "." "frop"   S: * STATUS "frop" (MESSAGES 8 SIZE 44421)   S: A04 OK List completed.Bosch                        Standards Track                    [Page 4]

RFC 8438               IMAP STATUS=SIZE Extension            August 20184.  Formal Syntax   The following syntax specification augments the grammar specified in   [IMAP4rev1] and [IMAP4-ABNF].  It uses the Augmented Backus-Naur Form   (ABNF) notation as specified in [ABNF].  Elements not defined here   are taken from [IMAP4rev1] and [IMAP4-ABNF].   capability     =/ "STATUS=SIZE"   status-att     =/ "SIZE"   status-att-val =/ "SIZE" SP number64   number64       = 1*DIGIT                    ; Unsigned 63-bit integer                    ; (0 <= n <= 9,223,372,036,854,775,807)5.  Security Considerations   There are no known additional security issues with this extension   beyond those described for the base protocol [IMAP4rev1] and the   LIST-STATUS extension [LIST-STATUS].6.  IANA Considerations   IANA has added "STATUS=SIZE" to the "IMAP Capabilities" registry   located at <http://www.iana.org/assignments/imap-capabilities>.7.  Normative References   [ABNF]     Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF", STD 68,RFC 5234,              DOI 10.17487/RFC5234, January 2008,              <https://www.rfc-editor.org/info/rfc5234>.   [IMAP4-ABNF]              Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4              ABNF",RFC 4466, DOI 10.17487/RFC4466, April 2006,              <https://www.rfc-editor.org/info/rfc4466>.   [IMAP4rev1]              Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION              4rev1",RFC 3501, DOI 10.17487/RFC3501, March 2003,              <https://www.rfc-editor.org/info/rfc3501>.Bosch                        Standards Track                    [Page 5]

RFC 8438               IMAP STATUS=SIZE Extension            August 2018   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [KEYWORDS2]              Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC2119 Key Words",BCP 14,RFC 8174, DOI 10.17487/RFC8174,              May 2017, <https://www.rfc-editor.org/info/rfc8174>.   [LIST-STATUS]              Melnikov, A. and T. Sirainen, "IMAP4 Extension for              Returning STATUS Information in Extended LIST",RFC 5819,              DOI 10.17487/RFC5819, March 2010,              <https://www.rfc-editor.org/info/rfc5819>.   [QUOTA]    Myers, J., "IMAP4 QUOTA extension",RFC 2087,              DOI 10.17487/RFC2087, January 1997,              <https://www.rfc-editor.org/info/rfc2087>.Acknowledgements   Thanks to Bron Gondwana, Alexey Melnikov, Stan Kalisch, and Michael   Slusarz for reviews and suggestions.Author's Address   Stephan Bosch   Dovecot Oy   Lars Sonckin Kaari 12   Espoo  02600   Finland   Email: stephan.bosch@dovecot.fiBosch                        Standards Track                    [Page 6]