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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Melnikov 3 Internet-Draft Isode Ltd. 4 Obsoletes: 4551 (if approved) September 11, 2013 5 Updates: 3501, 2683 (if approved) 6 Intended status: Standards Track 7 Expires: March 15, 2014 9 IMAP Extension for Conditional STORE Operation or Quick Flag Changes 10 Resynchronization 11 draft-ietf-qresync-rfc4551bis-04.txt 13 Abstract 15 Often, multiple IMAP (RFC 3501) clients need to coordinate changes to 16 a common IMAP mailbox. Examples include different clients working on 17 behalf of the same user, and multiple users accessing shared 18 mailboxes. These clients need a mechanism to synchronize state 19 changes for messages within the mailbox. They must be able to 20 guarantee that only one client can change message state (e.g., 21 message flags) at any time. An example of such an application is use 22 of an IMAP mailbox as a message queue with multiple dequeueing 23 clients. 25 The Conditional Store facility provides a protected update mechanism 26 for message state information that can detect and resolve conflicts 27 between multiple writing mail clients. 29 The Conditional Store facility also allows a client to quickly 30 resynchronize mailbox flag changes. 32 This document defines an extension to IMAP (RFC 3501). 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at http://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on March 15, 2014. 50 Copyright Notice 52 Copyright (c) 2013 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3 68 2. Conventions Used in This Document . . . . . . . . . . . . . . 5 69 3. IMAP Protocol Changes . . . . . . . . . . . . . . . . . . . . 6 70 3.1. New OK Untagged Responses for SELECT and EXAMINE . . . . 6 71 3.1.1. HIGHESTMODSEQ Response Code . . . . . . . . . . . . . 6 72 3.1.2. NOMODSEQ Response Code . . . . . . . . . . . . . . . 7 73 3.2. STORE and UID STORE Commands . . . . . . . . . . . . . . 8 74 3.3. FETCH and UID FETCH Commands . . . . . . . . . . . . . . 14 75 3.3.1. CHANGEDSINCE FETCH Modifier . . . . . . . . . . . . . 14 76 3.3.2. MODSEQ Message Data Item in FETCH Command . . . . . . 14 77 3.4. MODSEQ Search Criterion in SEARCH . . . . . . . . . . . . 17 78 3.5. Modified SEARCH Untagged Response . . . . . . . . . . . . 18 79 3.6. HIGHESTMODSEQ Status Data Items . . . . . . . . . . . . . 18 80 3.7. CONDSTORE Parameter to SELECT and EXAMINE . . . . . . . . 19 81 3.8. Interaction with IMAP SORT and THREAD extensions . . . . 19 82 3.9. Interaction with IMAP ESORT and ESEARCH extensions . . . 20 83 3.10. Additional Quality-of-Implementation Issues . . . . . . . 20 84 4. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 20 85 5. Server Implementation Considerations . . . . . . . . . . . . 23 86 6. Long Command Lines . . . . . . . . . . . . . . . . . . . . . 24 87 7. Security Considerations . . . . . . . . . . . . . . . . . . . 24 88 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 89 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25 90 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 91 10.1. Normative References . . . . . . . . . . . . . . . . . . 25 92 10.2. Informative References . . . . . . . . . . . . . . . . . 26 93 Appendix A. Changes since RFC 4551 . . . . . . . . . . . . . . . 26 94 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 27 96 1. Introduction and Overview 98 The Conditional STORE extension is present in any IMAP4 99 implementation that returns "CONDSTORE" as one of the supported 100 capabilities in the CAPABILITY command response. 102 An IMAP server that supports this extension MUST associate a positive 103 unsigned 64-bit value called a modification sequence (mod-sequence) 104 with every IMAP message. This is an opaque value updated by the 105 server whenever a metadata item is modified. The server MUST 106 guarantee that each STORE command performed on the same mailbox 107 (including simultaneous stores to different metadata items from 108 different connections) will get a different mod-sequence value. 109 Also, for any two successful STORE operations performed in the same 110 session on the same mailbox, the mod-sequence of the second completed 111 operation MUST be greater than the mod-sequence of the first 112 completed. Note that the latter rule disallows the use of the system 113 clock as a mod-sequence, because if system time changes (e.g., an NTP 114 [RFC1305] client adjusting the time), the next generated value might 115 be less than the previous one. 117 Mod-sequences allow a client that supports the CONDSTORE extension to 118 determine if a message metadata has changed since some known moment. 119 Whenever the state of a flag changes (i.e., the flag is added where 120 previously it wasn't set, or the flag is removed and before it was 121 set) the value of the modification sequence for the message MUST be 122 updated. Adding the flag when it is already present or removing when 123 it is not present SHOULD NOT change the mod-sequence. 125 When a message is appended to a mailbox (via the IMAP APPEND command, 126 COPY to the mailbox, or using an external mechanism) the server 127 generates a new modification sequence that is higher than the highest 128 modification sequence of all messages in the mailbox and assigns it 129 to the appended message. 131 The server MAY store separate (per-message) modification sequence 132 values for different metadata items. If the server does so, per- 133 message mod-sequence is the highest mod-sequence of all metadata 134 items for the specified message. 136 The server that supports this extension is not required to be able to 137 store mod-sequences for every available mailbox. Section 3.1.2 138 describes how the server may act if a particular mailbox doesn't 139 support the persistent storage of mod-sequences. 141 This extension makes the following changes to the IMAP4 protocol: 143 a. adds UNCHANGEDSINCE STORE modifier. 145 b. adds the MODIFIED response code which should be used with an OK 146 response to the STORE command. (It can also be used in a NO 147 response.) 149 c. adds a new MODSEQ message data item for use with the FETCH 150 command. 152 d. adds CHANGEDSINCE FETCH modifier. 154 e. adds a new MODSEQ search criterion. 156 f. extends the syntax of untagged SEARCH responses to include mod- 157 sequence. 159 g. adds new OK untagged responses for the SELECT and EXAMINE 160 commands. 162 h. defines an additional parameter to SELECT/EXAMINE commands. 164 i. adds the HIGHESTMODSEQ status data item to the STATUS command. 166 A client supporting CONDSTORE extension indicates its willingness to 167 receive mod-sequence updates in all untagged FETCH responses by 168 issuing: 170 o a SELECT or EXAMINE command with the CONDSTORE parameter, 172 o a STATUS (HIGHESTMODSEQ) command, 174 o a FETCH or SEARCH command that includes the MODSEQ message data 175 item, 177 o a FETCH command with the CHANGEDSINCE modifier, 179 o a STORE command with the UNCHANGEDSINCE modifier, or 181 o an ENABLE command containing "CONDSTORE" as one of the parameters. 182 (This requirement only applies to servers that also implement the 183 ENABLE extension [RFC5161].) 185 The server MUST include mod-sequence data in all subsequent untagged 186 FETCH responses (until the connection is closed), whether they were 187 caused by a regular STORE, a STORE with UNCHANGEDSINCE modifier, or 188 an external agent. 190 This document uses the term "CONDSTORE-aware client" to refer to a 191 client that announces its willingness to receive mod-sequence updates 192 as described above. The term "CONDSTORE enabling command" will refer 193 any of the commands listed above. A future extension to this 194 document may extend the list of CONDSTORE enabling commands. A first 195 CONDSTORE enabling command executed in the session with a mailbox 196 selected MUST cause the server to return HIGHESTMODSEQ 197 (Section 3.1.1) for the mailbox, unless the server has sent NOMODSEQ 198 (Section 3.1.2) response code when the currently selected mailbox was 199 selected. 201 The rest of this document describes the protocol changes more 202 rigorously. 204 2. Conventions Used in This Document 206 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 207 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 208 document are to be interpreted as described in RFC 2119 [RFC2119]. 210 In examples, lines beginning with "S:" are sent by the IMAP server, 211 and lines beginning with "C:" are sent by the client. Line breaks 212 may appear in example commands solely for editorial clarity; when 213 present in the actual message, they are represented by "CRLF". 215 Formal syntax is defined using ABNF [RFC5234]. 217 The term "metadata" or "metadata item" is used throughout this 218 document. It refers to any system or user-defined keyword. Future 219 documents may extend "metadata" to include other dynamic message 220 data. 222 Some IMAP mailboxes are private, accessible only to the owning user. 223 Other mailboxes are not, either because the owner has set an Access 224 Control List [RFC4314] that permits access by other users, or because 225 it is a shared mailbox. Let's call a metadata item "shared" for the 226 mailbox if any changes to the metadata items are persistent and 227 visible to all other users accessing the mailbox. Otherwise, the 228 metadata item is called "private". Note that private metadata items 229 are still visible to all sessions accessing the mailbox as the same 230 user. Also note that different mailboxes may have different metadata 231 items as shared. 233 See Section 1 for the definition of a "CONDSTORE-aware client" and a 234 "CONDSTORE enabling command". 236 3. IMAP Protocol Changes 238 3.1. New OK Untagged Responses for SELECT and EXAMINE 240 This document adds two new response codes, HIGHESTMODSEQ and 241 NOMODSEQ. One of these response codes MUST be returned in the OK 242 untagged response for a successful SELECT/EXAMINE command. 244 When opening a mailbox, the server must check if the mailbox supports 245 the persistent storage of mod-sequences. If the mailbox supports the 246 persistent storage of mod-sequences and the mailbox open operation 247 succeeds, the server MUST send the OK untagged response including 248 HIGHESTMODSEQ response code. If the persistent storage for the 249 mailbox is not supported, the server MUST send the OK untagged 250 response including NOMODSEQ response code instead. 252 3.1.1. HIGHESTMODSEQ Response Code 254 This document adds a new response code that is returned in the OK 255 untagged response for the SELECT and EXAMINE commands. A server 256 supporting the persistent storage of mod-sequences for the mailbox 257 MUST send the OK untagged response including HIGHESTMODSEQ response 258 code with every successful SELECT or EXAMINE command: 260 OK [HIGHESTMODSEQ ] 262 where is the highest mod-sequence value of 263 all messages in the mailbox. When the server changes UIDVALIDITY 264 for a mailbox, it doesn't have to keep the same HIGHESTMODSEQ for 265 the mailbox. 267 Note that this requirement applies whether or not a CONDSTORE 268 enabling command was issued in the session. 270 A disconnected client can use the value of HIGHESTMODSEQ to check if 271 it has to refetch metadata from the server. If the UIDVALIDITY value 272 has changed for the selected mailbox, the client MUST delete the 273 cached value of HIGHESTMODSEQ. If UIDVALIDITY for the mailbox is the 274 same, and if the HIGHESTMODSEQ value stored in the client's cache is 275 less than the value returned by the server, then some metadata items 276 on the server have changed since the last synchronization, and the 277 client needs to update its cache. The client MAY use SEARCH MODSEQ 278 (Section 3.4) to find out exactly which metadata items have changed. 279 Alternatively, the client MAY issue FETCH with the CHANGEDSINCE 280 modifier (Section 3.3.1) in order to fetch data for all messages that 281 have metadata items changed since some known modification sequence. 283 C: A142 SELECT INBOX 284 S: * 172 EXISTS 285 S: * 1 RECENT 286 S: * OK [UNSEEN 12] Message 12 is first unseen 287 S: * OK [UIDVALIDITY 3857529045] UIDs valid 288 S: * OK [UIDNEXT 4392] Predicted next UID 289 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) 290 S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited 291 S: * OK [HIGHESTMODSEQ 715194045007] 292 S: A142 OK [READ-WRITE] SELECT completed 294 Example 1 296 3.1.2. NOMODSEQ Response Code 298 A server that doesn't support the persistent storage of mod-sequences 299 for the mailbox MUST send the OK untagged response including NOMODSEQ 300 response code with every successful SELECT or EXAMINE command. Note 301 that this requirement applies whether or not a CONDSTORE enabling 302 command was issued in the session. 304 A server that returned NOMODSEQ response code for a mailbox, which 305 subsequently receives one of the following commands while the mailbox 306 is selected: 308 o a FETCH command with the CHANGEDSINCE modifier, 310 o a FETCH or SEARCH command that includes the MODSEQ message data 311 item, or 313 o a STORE command with the UNCHANGEDSINCE modifier 315 MUST reject any such command with a tagged BAD response. 317 C: A142 SELECT INBOX 318 S: * 172 EXISTS 319 S: * 1 RECENT 320 S: * OK [UNSEEN 12] Message 12 is first unseen 321 S: * OK [UIDVALIDITY 3857529045] UIDs valid 322 S: * OK [UIDNEXT 4392] Predicted next UID 323 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) 324 S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited 325 S: * OK [NOMODSEQ] Sorry, this mailbox format doesn't support 326 modsequences 327 S: A142 OK [READ-WRITE] SELECT completed 329 Example 2 331 3.2. STORE and UID STORE Commands 333 This document defines the following STORE modifier (see Section 2.5 334 of [RFC4466]): 336 UNCHANGEDSINCE For each message specified in the 337 message set, the server performs the following. If the mod- 338 sequence of any metadata item of the message is equal to or less 339 than the specified UNCHANGEDSINCE value, then the requested 340 operation (as described by the message data item) is performed. 341 If the operation is successful, the server MUST update the mod- 342 sequence attribute of the message. An untagged FETCH response 343 MUST be sent, even if the .SILENT suffix is specified, and the 344 response MUST include the MODSEQ message data item. This is 345 required to update the client's cache with the correct mod- 346 sequence values. See Section 3.3.2 for more details. 348 However, if the mod-sequence of any metadata item of the message is 349 greater than the specified UNCHANGEDSINCE value, then the requested 350 operation MUST NOT be performed. In this case, the mod-sequence 351 attribute of the message is not updated, and the message number (or 352 unique identifier in the case of the UID STORE command) is added to 353 the list of messages that failed the UNCHANGEDSINCE test. 355 When the server finishes performing the operation on all the messages 356 in the message set, it checks for a non-empty list of messages that 357 failed the UNCHANGEDSINCE test. If this list is non-empty, the 358 server MUST return in the tagged response a MODIFIED response code. 359 The MODIFIED response code includes the message set (for STORE) or 360 set of UIDs (for UID STORE) of all messages that failed the 361 UNCHANGEDSINCE test. 363 All messages pass the UNCHANGEDSINCE test. 365 C: a103 UID STORE 6,4,8 (UNCHANGEDSINCE 12121230045) 366 +FLAGS.SILENT (\Deleted) 367 S: * 1 FETCH (UID 4 MODSEQ (12121231000)) 368 S: * 2 FETCH (UID 6 MODSEQ (12121230852)) 369 S: * 4 FETCH (UID 8 MODSEQ (12121130956)) 370 S: a103 OK Conditional Store completed 372 Example 3 374 C: a104 STORE * (UNCHANGEDSINCE 12121230045) +FLAGS.SILENT 375 (\Deleted $Processed) 376 S: * 50 FETCH (MODSEQ (12111230047)) 377 S: a104 OK Store (conditional) completed 379 Example 4 381 C: c101 STORE 50 (UNCHANGEDSINCE 12121230045) -FLAGS.SILENT 382 (\Deleted) 383 S: * OK [HIGHESTMODSEQ 12111230047] 384 S: * 50 FETCH (MODSEQ (12111230048)) 385 S: c101 OK Store (conditional) completed 387 HIGHESTMODSEQ response code was sent by the server presumably because 388 this was the first CONDSTORE enabling command. 390 Example 5 392 The failure of the conditional STORE operation for any particular 393 message or messages (7 in this example) does not stop the server from 394 finding all messages that fail the UNCHANGEDSINCE test. All such 395 messages are returned in the MODIFIED response code. 397 C: d105 STORE 7,5,9 (UNCHANGEDSINCE 320162338) 398 +FLAGS.SILENT (\Deleted) 399 S: * 5 FETCH (MODSEQ (320162350)) 400 S: d105 OK [MODIFIED 7,9] Conditional STORE failed 402 Example 6 404 Same as above, but the server follows the SHOULD recommendation in 405 Section 6.4.6 of [RFC3501]. 407 C: d105 STORE 7,5,9 (UNCHANGEDSINCE 320162338) 408 +FLAGS.SILENT (\Deleted) 409 S: * 7 FETCH (MODSEQ (320162342) FLAGS (\Seen \Deleted)) 410 S: * 5 FETCH (MODSEQ (320162350)) 411 S: * 9 FETCH (MODSEQ (320162349) FLAGS (\Answered)) 412 S: d105 OK [MODIFIED 7,9] Conditional STORE failed 414 Use of UNCHANGEDSINCE with a modification sequence of 0 always fails 415 if the metadata item exists. A system flag MUST always be considered 416 existent, whether it was set or not. 418 Example 7 420 C: a102 STORE 12 (UNCHANGEDSINCE 0) 421 +FLAGS.SILENT ($MDNSent) 423 S: a102 OK [MODIFIED 12] Conditional STORE failed 425 The client has tested the presence of the $MDNSent user-defined 426 keyword. 428 Example 8 430 Note: A client trying to make an atomic change to the state of a 431 particular metadata item (or a set of metadata items) should be 432 prepared to deal with the case when the server returns the MODIFIED 433 response code if the state of the metadata item being watched hasn't 434 changed (but the state of some other metadata item has). This is 435 necessary, because some servers don't store separate mod-sequences 436 for different metadata items. However, a server implementation 437 SHOULD avoid generating spurious MODIFIED responses for +FLAGS/-FLAGS 438 STORE operations, even when the server stores a single mod-sequence 439 per message. Section 5 describes how this can be achieved. 441 Unless the server has included an unsolicited FETCH to update 442 client's knowledge about messages that have failed the UNCHANGEDSINCE 443 test, upon receipt of the MODIFIED response code, the client SHOULD 444 try to figure out if the required metadata items have indeed changed 445 by issuing FETCH or NOOP command. It is RECOMMENDED that the server 446 avoids the need for the client to do that by sending an unsolicited 447 FETCH response (Examples 9 and 10). 449 If the required metadata items haven't changed, the client SHOULD 450 retry the command with the new mod-sequence. The client SHOULD allow 451 for a configurable but reasonable number of retries (at least 2). 453 In the example below, the server returns the MODIFIED response code 454 without sending information describing why the STORE UNCHANGEDSINCE 455 operation has failed. 457 C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) 458 +FLAGS.SILENT ($Processed) 459 S: * 100 FETCH (MODSEQ (303181230852)) 460 S: * 102 FETCH (MODSEQ (303181230852)) 461 ... 462 S: * 150 FETCH (MODSEQ (303181230852)) 463 S: a106 OK [MODIFIED 101] Conditional STORE failed 465 The flag $Processed was set on the message 101... 467 C: a107 NOOP 468 S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed)) 469 S: a107 OK 471 Example 9 473 Or the flag hasn't changed, but another has (note that this server 474 behaviour is discouraged. Server implementers should also see 475 Section 5)... 477 C: b107 NOOP 478 S: * 101 FETCH (MODSEQ (303011130956) FLAGS (\Deleted \Answered)) 479 S: b107 OK 481 ...and the client retries the operation for the message 101 with 482 the updated UNCHANGEDSINCE value 484 C: b108 STORE 101 (UNCHANGEDSINCE 303011130956) 485 +FLAGS.SILENT ($Processed) 486 S: * 101 FETCH (MODSEQ (303181230852)) 487 S: b108 OK Conditional Store completed 489 Same as above, but the server avoids the need for the client to poll 490 for changes. 492 The flag $Processed was set on the message 101 by another 493 client... 495 C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) 496 +FLAGS.SILENT ($Processed) 497 S: * 100 FETCH (MODSEQ (303181230852)) 498 S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed)) 499 S: * 102 FETCH (MODSEQ (303181230852)) 500 ... 501 S: * 150 FETCH (MODSEQ (303181230852)) 502 S: a106 OK [MODIFIED 101] Conditional STORE failed 504 Example 10 506 Or the flag hasn't changed, but another has (note that this server 507 behaviour is discouraged. Server implementers should also see 508 Section 5)... 510 C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) 511 +FLAGS.SILENT ($Processed) 512 S: * 100 FETCH (MODSEQ (303181230852)) 513 S: * 101 FETCH (MODSEQ (303011130956) FLAGS (\Deleted \Answered)) 514 S: * 102 FETCH (MODSEQ (303181230852)) 515 ... 516 S: * 150 FETCH (MODSEQ (303181230852)) 517 S: a106 OK [MODIFIED 101] Conditional STORE failed 519 ...and the client retries the operation for the message 101 with 520 the updated UNCHANGEDSINCE value 522 C: b108 STORE 101 (UNCHANGEDSINCE 303011130956) 523 +FLAGS.SILENT ($Processed) 524 S: * 101 FETCH (MODSEQ (303181230852)) 525 S: b108 OK Conditional Store completed 527 Or the flag hasn't changed, but another has (nice server behaviour. 528 Server implementers should also see Section 5)... 530 C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) 531 +FLAGS.SILENT ($Processed) 532 S: * 100 FETCH (MODSEQ (303181230852)) 533 S: * 101 FETCH (MODSEQ (303011130956) FLAGS ($Processed \Deleted 534 \Answered)) 535 S: * 102 FETCH (MODSEQ (303181230852)) 536 ... 537 S: * 150 FETCH (MODSEQ (303181230852)) 538 S: a106 OK Conditional STORE completed 540 The following example is based on the example from the Section 4.2.3 541 of [RFC2180] and demonstrates that the MODIFIED response code may be 542 also returned in the tagged NO response. 544 Client tries to conditionally STORE flags on a mixture of expunged 545 and non-expunged messages; one message fails the UNCHANGEDSINCE 546 test. 548 C: B001 STORE 1:7 (UNCHANGEDSINCE 320172338) +FLAGS (\SEEN) 549 S: * 1 FETCH (MODSEQ (320172342) FLAGS (\SEEN)) 550 S: * 3 FETCH (MODSEQ (320172342) FLAGS (\SEEN)) 551 S: B001 NO [MODIFIED 2] Some of the messages no longer exist. 553 C: B002 NOOP 554 S: * 4 EXPUNGE 555 S: * 4 EXPUNGE 556 S: * 4 EXPUNGE 557 S: * 4 EXPUNGE 558 S: * 2 FETCH (MODSEQ (320172340) FLAGS (\Deleted \Answered)) 559 S: B002 OK NOOP Completed. 561 By receiving FETCH responses for messages 1 and 3, and EXPUNGE 562 responses that indicate that messages 4 through 7 have been 563 expunged, the client retries the operation only for the message 2. 564 The updated UNCHANGEDSINCE value is used. 566 C: b003 STORE 2 (UNCHANGEDSINCE 320172340) +FLAGS (\Seen) 567 S: * 2 FETCH (MODSEQ (320180050) FLAGS (\SEEN \Flagged)) 568 S: b003 OK Conditional Store completed 570 Example 11 572 Note: If a message is specified multiple times in the message set, 573 and the server doesn't internally eliminate duplicates from the 574 message set, it MUST NOT fail the conditional STORE operation for the 575 second (or subsequent) occurrence of the message if the operation 576 completed successfully for the first occurrence. For example, if the 577 client specifies: 579 e105 STORE 7,3:9 (UNCHANGEDSINCE 12121230045) +FLAGS.SILENT 580 (\Deleted) 582 the server must not fail the operation for message 7 as part of 583 processing "3:9" if it succeeded when message 7 was processed the 584 first time. 586 As specified in Section 1, once the client specified the 587 UNCHANGEDSINCE modifier in a STORE command, the server starts 588 including the MODSEQ fetch response data items in all subsequent 589 unsolicited FETCH responses. 591 This document also changes the behaviour of the server when it has 592 performed a STORE or UID STORE command and the UNCHANGEDSINCE 593 modifier is not specified. If the operation is successful for a 594 message, the server MUST update the mod-sequence attribute of the 595 message. The server is REQUIRED to include the mod-sequence value 596 whenever it decides to send the unsolicited FETCH response to all 597 CONDSTORE-aware clients that have opened the mailbox containing the 598 message. 600 Server implementers should also see Section 3.10 for additional 601 quality of implementation issues related to the STORE command. 603 3.3. FETCH and UID FETCH Commands 605 3.3.1. CHANGEDSINCE FETCH Modifier 607 This document defines the following FETCH modifier (see Section 2.4 608 of [RFC4466]): 610 CHANGEDSINCE CHANGEDSINCE FETCH modifier allows to 611 create a further subset of the list of messages described by 612 sequence set. The information described by message data items is 613 only returned for messages that have mod-sequence bigger than 614 . 616 When CHANGEDSINCE FETCH modifier is specified, it implicitly adds 617 MODSEQ FETCH message data item (Section 3.3.2). 619 C: s100 UID FETCH 1:* (FLAGS) (CHANGEDSINCE 12345) 620 S: * 1 FETCH (UID 4 MODSEQ (65402) FLAGS (\Seen)) 621 S: * 2 FETCH (UID 6 MODSEQ (75403) FLAGS (\Deleted)) 622 S: * 4 FETCH (UID 8 MODSEQ (29738) FLAGS ($NoJunk $AutoJunk 623 $MDNSent)) 624 S: s100 OK FETCH completed 626 Example 12 628 3.3.2. MODSEQ Message Data Item in FETCH Command 630 This extension adds a MODSEQ message data item to the FETCH command. 631 The MODSEQ message data item allows clients to retrieve mod-sequence 632 values for a range of messages in the currently selected mailbox. 634 As specified in Section 1, once the client has specified the MODSEQ 635 message data item in a FETCH request, the server starts including the 636 MODSEQ fetch response data items in all subsequent unsolicited FETCH 637 responses. 639 Syntax: MODSEQ The MODSEQ message data item causes the server to 640 return MODSEQ fetch response data items. 642 Syntax: MODSEQ ( ) MODSEQ response data items 643 contain per-message mod-sequences. 645 The MODSEQ response data item is returned if the client issued 646 FETCH with MODSEQ message data item. It also allows the server to 647 notify the client about mod-sequence changes caused by conditional 648 STOREs (Section 3.2) and/or changes caused by external sources. 650 C: a FETCH 1:3 (MODSEQ) 651 S: * 1 FETCH (MODSEQ (624140003)) 652 S: * 2 FETCH (MODSEQ (624140007)) 653 S: * 3 FETCH (MODSEQ (624140005)) 654 S: a OK Fetch complete 656 In this example, the client requests per-message mod-sequences for a 657 set of messages. 659 Example 13 661 When a flag for a message is modified in a different session, the 662 server sends an unsolicited FETCH response containing the mod- 663 sequence for the message. 665 (Session 1, authenticated as a user "alex"). The user adds a 666 shared flag \Deleted: 668 C: A142 SELECT INBOX 669 ... 670 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) 671 S: * OK [PERMANENTFLAGS (\Answered \Deleted \Seen \*)] Limited 672 ... 673 C: A160 STORE 7 +FLAGS.SILENT (\Deleted) 674 S: * 7 FETCH (MODSEQ (2121231000)) 675 S: A160 OK Store completed 677 (Session 2, also authenticated as the user "alex"). Any changes 678 to flags are always reported to all sessions authenticated as the 679 same user as in the session 1. 681 C: C180 NOOP 682 S: * 7 FETCH (FLAGS (\Deleted \Answered) MODSEQ (12121231000)) 683 S: C180 OK Noop completed 685 (Session 3, authenticated as a user "andrew"). As \Deleted is a 686 shared flag, changes in session 1 are also reported in session 3: 688 C: D210 NOOP 689 S: * 7 FETCH (FLAGS (\Deleted \Answered) MODSEQ (12121231000)) 690 S: D210 OK Noop completed 692 The user modifies a private flag \Seen in session 1... 694 C: A240 STORE 7 +FLAGS.SILENT (\Seen) 695 S: * 7 FETCH (MODSEQ (12121231777)) 696 S: A240 OK Store completed 698 ...which is only reported in session 2... 700 C: C270 NOOP 701 S: * 7 FETCH (FLAGS (\Deleted \Answered \Seen) MODSEQ 702 (12121231777)) 703 S: C270 OK Noop completed 705 ...but not in session 3. 707 C: D300 NOOP 708 S: D300 OK Noop completed 710 And finally, the user removes flags \Answered (shared) and \Seen 711 (private) in session 1. 713 C: A330 STORE 7 -FLAGS.SILENT (\Answered \Seen) 714 S: * 7 FETCH (MODSEQ (12121245160)) 715 S: A330 OK Store completed 717 Both changes are reported in the session 2... 719 C: C360 NOOP 720 S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (12121245160)) 721 S: C360 OK Noop completed 723 ...and only changes to shared flags are reported in session 3. 725 C: D390 NOOP 726 S: * 7 FETCH (FLAGS (\Deleted) MODSEQ (12121245160)) 727 S: D390 OK Noop completed 729 Example 14 731 Server implementers should also see Section 3.10 for additional 732 quality of implementation issues related to the FETCH command. 734 3.4. MODSEQ Search Criterion in SEARCH 736 The MODSEQ criterion for the SEARCH (or UID SEARCH) command allows a 737 client to search for the metadata items that were modified since a 738 specified moment. 740 Syntax: MODSEQ [ ] 742 Messages that have modification values that are equal to or 743 greater than . This allows a client, for 744 example, to find out which messages contain metadata items that 745 have changed since the last time it updated its disconnected 746 cache. The client may also specify (name of metadata 747 item) and (type of metadata item) before . can be one of "shared", "priv" 749 (private), or "all". The last means that the server should use 750 the biggest value among "priv" and "shared" mod- sequences for the 751 metadata item. If the server doesn't store internally separate 752 mod-sequences for different metadata items, it MUST ignore and . Otherwise, the server should use them 754 to narrow down the search. 756 For a flag , the corresponding has a form " 757 /flags/" as defined in [RFC4466]. Note that the leading 758 "\" character that denotes a system flag has to be escaped as per 759 Section 4.3 of [RFC3501], as the uses syntax for 760 quoted strings. 762 If client specifies a MODSEQ criterion in a SEARCH (or UID SEARCH) 763 command and the server returns a non-empty SEARCH result, the server 764 MUST also append (to the end of the untagged SEARCH response) the 765 highest mod-sequence for all messages being returned. See also 766 Section 3.5. Note that other IMAP extensions such as ESEARCH 767 [RFC4731] can override this requirement (see Section 3.9 for more 768 details.) 769 C: a SEARCH MODSEQ "/flags/\\draft" all 620162338 770 S: * SEARCH 2 5 6 7 11 12 18 19 20 23 (MODSEQ 917162500) 771 S: a OK Search complete 773 In the above example, the message numbers of any messages containing 774 the string "IMAP4" in the "value" attribute of the "/comment" entry 775 and having a mod-sequence equal to or greater than 620162338 for the 776 "\Draft" flag are returned in the search results. 778 Example 15 780 C: t SEARCH OR NOT MODSEQ 720162338 LARGER 50000 781 S: * SEARCH 782 S: t OK Search complete, nothing found 784 Example 16 786 3.5. Modified SEARCH Untagged Response 788 Data: zero or more numbers 789 mod-sequence value (omitted if no match) 791 This document extends syntax of the untagged SEARCH response to 792 include the highest mod-sequence for all messages being returned. 794 If a client specifies a MODSEQ criterion in a SEARCH (or UID SEARCH) 795 command and the server returns a non-empty SEARCH result, the server 796 MUST also append (to the end of the untagged SEARCH response) the 797 highest mod-sequence for all messages being returned. See 798 Section 3.4 for examples. 800 3.6. HIGHESTMODSEQ Status Data Items 802 This document defines a new status data item: 804 HIGHESTMODSEQ The highest mod-sequence value of all messages in the 805 mailbox. This is the same value that is returned by the server in 806 the HIGHESTMODSEQ response code in an OK untagged response (see 807 Section 3.1.1). If the server doesn't support the persistent 808 storage of mod-sequences for the mailbox (see Section 3.1.2), the 809 server MUST return 0 as the value of HIGHESTMODSEQ status data 810 item. 812 C: A042 STATUS blurdybloop (UIDNEXT MESSAGES HIGHESTMODSEQ) 813 S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292 814 HIGHESTMODSEQ 7011231777) 815 S: A042 OK STATUS completed 816 Example 17 818 3.7. CONDSTORE Parameter to SELECT and EXAMINE 820 The CONDSTORE extension defines a single optional select parameter, 821 "CONDSTORE", which tells the server that it MUST include the MODSEQ 822 fetch response data items in all subsequent unsolicited FETCH 823 responses. 825 The CONDSTORE parameter to SELECT/EXAMINE helps avoid a race 826 condition that might arise when one or more metadata items are 827 modified in another session after the server has sent the 828 HIGHESTMODSEQ response code and before the client was able to issue a 829 CONDSTORE enabling command. 831 C: A142 SELECT INBOX (CONDSTORE) 832 S: * 172 EXISTS 833 S: * 1 RECENT 834 S: * OK [UNSEEN 12] Message 12 is first unseen 835 S: * OK [UIDVALIDITY 3857529045] UIDs valid 836 S: * OK [UIDNEXT 4392] Predicted next UID 837 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) 838 S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited 839 S: * OK [HIGHESTMODSEQ 715194045007] 840 S: A142 OK [READ-WRITE] SELECT completed, CONDSTORE is now enabled 842 Example 18 844 3.8. Interaction with IMAP SORT and THREAD extensions 846 MODSEQ Search Criterion (see Section 3.4) causes modifications to 847 SORT [RFC5256] responses similar to modifications to SEARCH responses 848 defined in Section 3.5: 850 SORT response Data: zero or more numbers 851 mod-sequence value (omitted if no match) 853 This document extends syntax of the untagged SORT response to include 854 the highest mod-sequence for all messages being returned. 856 If a client specifies a MODSEQ criterion in a SORT (or UID SORT) 857 command and the server returns a non-empty SORT result, the server 858 MUST also append (to the end of the untagged SORT response) the 859 highest mod-sequence for all messages being returned. Note that 860 other IMAP extensions such as ESORT [RFC5267] can override this 861 requirement (see Section 3.9 for more details.) 862 THREAD commands which include a MODSEQ Search Criterion return THREAD 863 responses as specified in [RFC5256]. 865 3.9. Interaction with IMAP ESORT and ESEARCH extensions 867 If a client specifies a MODSEQ criterion in an extended SEARCH (or 868 extended UID SEARCH) [RFC4731] command and the server returns a non- 869 empty SEARCH result, the server MUST return the ESEARCH response 870 containing the MODSEQ result option as defined in Section 3.2 of 871 [RFC4731]. 873 C: a SEARCH RETURN (ALL) MODSEQ 1234 874 S: * ESEARCH (TAG "a") ALL 1:3,5 MODSEQ 1236 875 S: a OK Extended SEARCH completed 877 Example 19 879 If a client specifies a MODSEQ criterion in an extended SORT (or 880 extended UID SORT) [RFC5267] command and the server returns a non- 881 empty SORT result, the server MUST return the ESEARCH response 882 containing the MODSEQ result option defined in Section 3.2 of 883 [RFC4731]. 885 C: a SORT RETURN (ALL) (DATE) UTF-8 MODSEQ 1234 886 S: * ESEARCH (TAG "a") ALL 5,3,2,1 MODSEQ 1236 887 S: a OK Extended SORT completed 889 Example 20 891 3.10. Additional Quality-of-Implementation Issues 893 Server implementations should follow the following rule, which 894 applies to any successfully completed STORE/UID STORE (with and 895 without UNCHANGEDSINCE modifier), as well as to a FETCH command that 896 implicitly sets \Seen flag: 898 Adding the flag when it is already present or removing when it is 899 not present SHOULD NOT change the mod-sequence. 901 This will prevent spurious client synchronization requests. 903 However, note that client implementers MUST NOT rely on this server 904 behavior. A client can't distinguish between the case when a server 905 has violated the SHOULD mentioned above, and that when one or more 906 clients set and unset (or unset and set) the flag in another session. 908 4. Formal Syntax 909 The following syntax specification uses the Augmented Backus-Naur 910 Form (ABNF) [RFC5234] notation. Elements not defined here can be 911 found in the formal syntax of the ABNF [RFC5234], IMAP [RFC3501], and 912 IMAP ABNF extensions [RFC4466] specifications. 914 Except as noted otherwise, all alphabetic characters are case- 915 insensitive. The use of upper- or lowercase characters to define 916 token strings is for editorial clarity only. Implementations MUST 917 accept these strings in a case-insensitive fashion. 919 capability =/ "CONDSTORE" 921 status-att =/ "HIGHESTMODSEQ" 922 ;; extends non-terminal defined in RFC 3501. 924 status-att-val =/ "HIGHESTMODSEQ" SP mod-sequence-valzer 925 ;; extends non-terminal defined in [RFC4466]. 926 ;; Value 0 denotes that the mailbox doesn't 927 ;; support persistent mod-sequences 928 ;; as described in Section 3.1.2 [[Check the ref]] 930 store-modifier =/ "UNCHANGEDSINCE" SP mod-sequence-valzer 931 ;; Only a single "UNCHANGEDSINCE" may be 932 ;; specified in a STORE operation 934 fetch-modifier =/ chgsince-fetch-mod 935 ;; conforms to the generic "fetch-modifier" 936 ;; syntax defined in [RFC4466]. 938 chgsince-fetch-mod = "CHANGEDSINCE" SP mod-sequence-value 939 ;; CHANGEDSINCE FETCH modifier conforms to 940 ;; the fetch-modifier syntax 942 fetch-att =/ fetch-mod-sequence 943 ;; modifies original IMAP4 fetch-att 945 fetch-mod-sequence = "MODSEQ" 947 fetch-mod-resp = "MODSEQ" SP "(" permsg-modsequence ")" 949 msg-att-dynamic =/ fetch-mod-resp 951 search-key =/ search-modsequence 952 ;; modifies original IMAP4 search-key 953 ;; 954 ;; This change applies to all commands 955 ;; referencing this non-terminal, in 956 ;; particular SEARCH, SORT and THREAD. 958 search-modsequence = "MODSEQ" [search-modseq-ext] SP 959 mod-sequence-valzer 961 search-modseq-ext = SP entry-name SP entry-type-req 963 resp-text-code =/ "HIGHESTMODSEQ" SP mod-sequence-value / 964 "NOMODSEQ" / 965 "MODIFIED" SP sequence-set 967 entry-name = entry-flag-name 969 entry-flag-name = DQUOTE "/flags/" attr-flag DQUOTE 970 ;; each system or user defined flag 971 ;; is mapped to "/flags/". 972 ;; 973 ;; follows the escape rules 974 ;; used by "quoted" string as described in 975 ;; Section 4.3 of [RFC3501], e.g., for the flag 976 ;; \Seen the corresponding is 977 ;; "/flags/\\seen", and for the flag 978 ;; $MDNSent, the corresponding 979 ;; is "/flags/$mdnsent". 981 entry-type-resp = "priv" / "shared" 982 ;; metadata item type 984 entry-type-req = entry-type-resp / "all" 985 ;; perform SEARCH operation on private 986 ;; metadata item, shared metadata item or both 988 permsg-modsequence = mod-sequence-value 989 ;; per message mod-sequence 991 mod-sequence-value = 1*DIGIT 992 ;; Positive unsigned 64-bit integer 993 ;; (mod-sequence) 994 ;; (1 <= n < 18,446,744,073,709,551,615) 996 mod-sequence-valzer = "0" / mod-sequence-value 998 search-sort-mod-seq = "(" "MODSEQ" SP mod-sequence-value ")" 1000 select-param =/ condstore-param 1001 ;; conforms to the generic "select-param" 1002 ;; non-terminal syntax defined in [RFC4466]. 1004 condstore-param = "CONDSTORE" 1005 mailbox-data =/ "SEARCH" [1*(SP nz-number) SP 1006 search-sort-mod-seq] 1008 sort-data = "SORT" [1*(SP nz-number) SP 1009 search-sort-mod-seq] 1010 ; Updates SORT response from RFC 5256 1012 attr-flag = "\\Answered" / "\\Flagged" / "\\Deleted" / 1013 "\\Seen" / "\\Draft" / attr-flag-keyword / 1014 attr-flag-extension 1015 ;; Does not include "\\Recent" 1017 attr-flag-extension = "\\" atom 1018 ;; Future expansion. Client implementations 1019 ;; MUST accept flag-extension flags. Server 1020 ;; implementations MUST NOT generate 1021 ;; flag-extension flags except as defined by 1022 ;; future standard or standards-track 1023 ;; revisions of [RFC3501]. 1025 attr-flag-keyword = atom 1027 5. Server Implementation Considerations 1029 This section describes how a server implementation that doesn't store 1030 separate per-metadata mod-sequences for different metadata items can 1031 avoid sending the MODIFIED response to any of the following 1032 conditional STORE operations: 1034 +FLAGS 1036 -FLAGS 1038 +FLAGS.SILENT 1040 -FLAGS.SILENT 1042 Note that the optimization described in this section can't be 1043 performed in case of a conditional STORE FLAGS operation. 1045 Let's use the following example. The client has issued 1047 C: a106 STORE 100:150 (UNCHANGEDSINCE 212030000000) 1048 +FLAGS.SILENT ($Processed) 1050 When the server receives the command and parses it successfully, it 1051 iterates through the message set and tries to execute the conditional 1052 STORE command for each message. 1054 Each server internally works as a client, i.e., it has to cache the 1055 current state of all IMAP flags as it is known to the client. In 1056 order to report flag changes to the client, the server compares the 1057 cached values with the values in its database for IMAP flags. 1059 Imagine that another client has changed the state of a flag \Deleted 1060 on the message 101 and that the change updated the mod-sequence for 1061 the message. The server knows that the mod-sequence for the mailbox 1062 has changed; however, it also knows that: 1064 a. the client is not interested in \Deleted flag, as it hasn't 1065 included it in +FLAGS.SILENT operation; and 1067 b. the state of the flag $Processed hasn't changed (the server can 1068 determine this by comparing cached flag state with the state of 1069 the flag in the database). 1071 Therefore, the server doesn't have to report MODIFIED to the client. 1072 Instead, the server may set $Processed flag, update the mod-sequence 1073 for the message 101 once again and send an untagged FETCH response 1074 with new mod-sequence and flags: 1076 S: * 101 FETCH (MODSEQ (303011130956) 1077 FLAGS ($Processed \Deleted \Answered)) 1079 See also Section 3.10 for additional quality-of-implementation 1080 issues. 1082 6. Long Command Lines 1084 This document updates recommended line length limits specified in 1085 Section 3.2.1.5 of [RFC2683]. While the advice in the first 1086 paragraph of that section still applies ("use compact message/UID set 1087 representations"), the 1000 octet limit suggested in the second 1088 paragraph turned out to be quite problematic when the CONDSTORE 1089 extension is used. The updated recommendation is as follows: a 1090 client should limit the length of the command lines it generates to 1091 approximately 8192 octets (including all quoted strings but not 1092 including literals). 1094 7. Security Considerations 1095 It is believed that the Conditional STORE extension doesn't raise any 1096 new security concerns that are not already discussed in [RFC3501]. 1097 However, the availability of this extension may make it possible for 1098 IMAP4 to be used in critical applications it could not be used for 1099 previously, making correct IMAP server implementation and operation 1100 even more important. 1102 8. IANA Considerations 1104 IMAP4 capabilities are registered by publishing a standards track or 1105 IESG approved experimental RFC. The registry is currently located 1106 at: 1108 http://www.iana.org/assignments/imap4-capabilities 1110 This document defines the CONDSTORE IMAP capability. IANA has added 1111 it to the registry accordingly. 1113 9. Acknowledgements 1115 Thank you to Steve Hole for co-editing RFC 4551. 1117 Thank you to Dave Cridland for helping to convert the original text 1118 RFC to xml2rfc format. 1120 Some text was borrowed from "IMAP ANNOTATE Extension" [RFC5257] by 1121 Randall Gellens and Cyrus Daboo and from "ACAP -- Application 1122 Configuration Access Protocol" [RFC2244] by Chris Newman and John 1123 Myers. 1125 Many thanks to Randall Gellens for his thorough review of the 1126 document. 1128 The authors also acknowledge the feedback provided by Pete Maclean, 1129 Cyrus Daboo, Larry Greenfield, Chris Newman, Harrie Hazewinkel, Arnt 1130 Gulbrandsen, Timo Sirainen, Mark Crispin, Ned Freed, Ken Murchison, 1131 and Dave Cridland. 1133 10. References 1135 10.1. Normative References 1137 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1138 Requirement Levels", BCP 14, RFC 2119, March 1997. 1140 [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 1141 4rev1", RFC 3501, March 2003. 1143 [RFC4466] Melnikov, A. and C. Daboo, "Collected Extensions to IMAP4 1144 ABNF", RFC 4466, April 2006. 1146 [RFC5161] Gulbrandsen, A. and A. Melnikov, "The IMAP ENABLE 1147 Extension", RFC 5161, March 2008. 1149 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1150 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1152 [RFC5256] Crispin, M. and K. Murchison, "Internet Message Access 1153 Protocol - SORT and THREAD Extensions", RFC 5256, June 1154 2008. 1156 10.2. Informative References 1158 [RFC1305] Mills, D., "Network Time Protocol (Version 3) 1159 Specification, Implementation", RFC 1305, March 1992. 1161 [RFC2180] Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice", RFC 1162 2180, July 1997. 1164 [RFC2244] Newman, C. and J. Myers, "ACAP -- Application 1165 Configuration Access Protocol", RFC 2244, November 1997. 1167 [RFC2683] Leiba, B., "IMAP4 Implementation Recommendations", RFC 1168 2683, September 1999. 1170 [RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", 1171 RFC 4314, December 2005. 1173 [RFC4731] Melnikov, A. and D. Cridland, "IMAP4 Extension to SEARCH 1174 Command for Controlling What Kind of Information Is 1175 Returned", RFC 4731, November 2006. 1177 [RFC5257] Daboo, C. and R. Gellens, "Internet Message Access 1178 Protocol - ANNOTATE Extension", RFC 5257, June 2008. 1180 [RFC5267] Cridland, D. and C. King, "Contexts for IMAP4", RFC 5267, 1181 July 2008. 1183 Appendix A. Changes since RFC 4551 1185 Fixed errata 3401, 3506 and 3509. 1187 Updated references. 1189 Incorporated some text from RFC 5161 (no semantic change.) 1190 Editorial corrections. 1192 Author's Address 1194 Alexey Melnikov 1195 Isode Ltd. 1196 5 Castle Business Village 1197 36 Station Road 1198 Hampton, Middlesex TW12 2BX 1199 UK 1201 Email: Alexey.Melnikov@isode.com