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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 EXTRA S. Bosch 3 Internet-Draft Dovecot Oy 4 Intended status: Standards Track March 24, 2018 5 Expires: September 25, 2018 7 Internet Message Access Protocol (IMAP) - STATUS=SIZE Extension 8 draft-ietf-extra-imap-status-size-01 10 Abstract 12 This document adds a new capability called "STATUS=SIZE" to the 13 Internet Message Access Protocol (IMAP). It allows retrieving the 14 total storage size of a mailbox with a single STATUS command rather 15 than retrieving and summing the sizes of all individual messages in 16 that mailbox. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on September 25, 2018. 35 Copyright Notice 37 Copyright (c) 2018 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Conventions Used in This Document . . . . . . . . . . . . . . 2 54 3. STATUS Command and Response Extensions . . . . . . . . . . . 3 55 4. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 4 56 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 57 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 58 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 59 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 8.1. Normative References . . . . . . . . . . . . . . . . . . 4 61 8.2. Informative References . . . . . . . . . . . . . . . . . 5 62 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 64 1. Introduction 66 This document extends Internet Message Access Protocol (IMAP) 67 [IMAP4rev1] with a new capability called "STATUS=SIZE". To determine 68 the total storage size of a mailbox, an IMAP client currently needs 69 to retrieve all message sizes individually using the FETCH command 70 with the RFC822.SIZE data item. The "STATUS=SIZE" capability 71 provides a more efficient means to achieve this. It extends the 72 STATUS command with a new "SIZE" data item, which indicates the total 73 size of all messages in the target mailbox. This way, this 74 information can be queried with just one STATUS command. When the 75 "LIST-STATUS" IMAP capability [LIST-STATUS] is also available, the 76 SIZE data item can be queried for many mailboxes at once using just 77 one LIST command. 79 This capability is particularly useful for IMAP clients that do not 80 cache the state of the message store, such as most webmail clients. 81 Without the "STATUS=SIZE" capability, such clients need to fetch all 82 message sizes from the server when the size of a mailbox needs to be 83 determined, for example when the user requests detailed quota usage 84 information. The "QUOTA" capability [QUOTA] is no help in that 85 scenario, since the provided QUOTAROOT command can only yield the 86 "STORAGE" resource usage of a whole quota root, but not for a single 87 mailbox within that root. 89 2. Conventions Used in This Document 91 In examples, "C:" indicates lines sent by a client that is connected 92 to a server. "S:" indicates lines sent by the server to the client. 94 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 95 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 96 document are to be interpreted as described in [KEYWORDS]. 98 3. STATUS Command and Response Extensions 100 This extension defines one new status data item for the STATUS 101 command and response: 103 SIZE 104 The total size of the mailbox in octets. This is not strictly 105 required to be an exact value, but it MUST be equal to or greater 106 than the sum of the values of the RFC822.SIZE FETCH message data 107 item [IMAP4rev1] of all messages in the mailbox. When the "QUOTA" 108 capability [QUOTA] is also supported, this value SHOULD be equal 109 to the storage usage value used to enforce the "STORAGE" resource 110 limit for this mailbox. This way, the client can directly infer 111 the quota usage. 113 Example: 115 C: A01 STATUS frop (MESSAGES SIZE UIDNEXT) 116 S: * STATUS frop (MESSAGES 8 SIZE 44421 UIDNEXT 242344) 117 S: A01 OK STATUS completed 119 The same information can be obtained by using the following commands, 120 albeit less efficient: 122 C: A02 SELECT "frop" 123 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) 124 S: * 8 EXISTS 125 S: * 1 RECENT 126 S: * OK [UNSEEN 7] First unseen. 127 S: * OK [UIDVALIDITY 1364851417] UIDs valid 128 S: * OK [UIDNEXT 242344] Predicted next UID 129 S: * OK [HIGHESTMODSEQ 3914] Highest 130 S: A02 OK [READ-WRITE] Select completed. 131 C: A03 FETCH 1:* (RFC822.SIZE) 132 S: * 1 FETCH (RFC822.SIZE 3224) 133 S: * 2 FETCH (RFC822.SIZE 1222) 134 S: * 3 FETCH (RFC822.SIZE 444) 135 S: * 4 FETCH (RFC822.SIZE 4516) 136 S: * 5 FETCH (RFC822.SIZE 544) 137 S: * 6 FETCH (RFC822.SIZE 922) 138 S: * 7 FETCH (RFC822.SIZE 31126) 139 S: * 8 FETCH (RFC822.SIZE 2423) 140 S: A03 OK Fetch completed. 142 When the LIST-STATUS IMAP capability [LIST-STATUS] is also available, 143 the STATUS command can be combined with the LIST command to further 144 improve efficiency. This way, the sizes of many mailboxes can be 145 queried with just one LIST command. 147 Example: 149 C: A04 LIST "" % RETURN (STATUS (MESSAGES SIZE)) 150 S: * LIST () "." "INBOX" 151 S: * STATUS "INBOX" (MESSAGES 17 SIZE 16234) 152 S: * LIST () "." "frop" 153 S: * STATUS "frop" (MESSAGES 8 SIZE 44421) 154 S: A04 OK List completed. 156 4. Formal Syntax 158 The following syntax specification augments the grammar specified in 159 [IMAP4rev1]. It uses the Augmented Backus-Naur Form (ABNF) notation 160 as specified in [ABNF]. Elements not defined here are taken from 161 [IMAP4rev1]. 163 capability =/ "STATUS=SIZE" 165 status-att =/ "SIZE" 167 5. Security Considerations 169 There are no known additional security issues with this extension 170 beyond those described for the base protocol [IMAP4rev1] and for the 171 LIST-STATUS extension [LIST-STATUS]. 173 6. IANA Considerations 175 The IANA is requested to add "STATUS=SIZE" to the "IMAP Capabilities" 176 registry located at . 179 7. Acknowledgements 181 Thanks to Bron Gondwana, Alexey Melnikov, Stan Kalisch, and Michael 182 Slusarz for reviews and suggestions. 184 8. References 186 8.1. Normative References 188 [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax 189 Specifications: ABNF", STD 68, RFC 5234, January 2008. 191 [IMAP4rev1] 192 Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 193 4rev1", RFC 3501, March 2003. 195 [KEYWORDS] 196 Bradner, S., "Key words for use in RFCs to Indicate 197 Requirement Levels", BCP 14, RFC 2119, March 1997. 199 [LIST-STATUS] 200 Melnikov, A. and T. Sirainen, "IMAP4 Extension for 201 Returning STATUS Information in Extended LIST", RFC 5819, 202 March 2010. 204 8.2. Informative References 206 [QUOTA] Myers, J., "IMAP4 QUOTA extension", RFC 2087, January 207 1997. 209 Author's Address 211 Stephan Bosch 212 Dovecot Oy 213 Lars Sonckin Kaari 10 214 Espoo 02600 215 Finland 217 Email: stephan.bosch@dovecot.fi