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'ABNF' -- No information found for draft-ietf-sieve-3431bis-XX - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'RELATIONAL' -- No information found for draft-ietf-sieve-3028bis-XX - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'SIEVE' -- Possible downref: Non-RFC (?) normative reference: ref. 'UNICODE' -- Obsolete informational reference (is this intentional?): RFC 3685 (ref. 'SPAMTEST') (Obsoleted by RFC 5235) Summary: 5 errors (**), 0 flaws (~~), 7 warnings (==), 17 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group K. T. Homme 3 Updates: 3028 4 Document: draft-ietf-sieve-variables-07.txt University of Oslo 5 Expires Apr 14, 2006 14 Oct 2005 7 Sieve Extension: Variables 9 Status of this Memo 11 This document is an Internet-Draft and is subject to all provisions 12 of section 3 of RFC 3978. By submitting this Internet-Draft, each 13 author represents that any applicable patent or other IPR claims of 14 which he or she is aware have been or will be disclosed, and any of 15 which he or she becomes aware will be disclosed, in accordance with 16 Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 Distribution of this memo is unlimited. 36 Abstract 38 In advanced mail filtering rule sets, it is useful to keep state or 39 configuration details across rules. This extension to the filtering 40 language Sieve changes the interpretation of strings, adds an action 41 to store data in variables, and supplies a new test so that the value 42 of a string can be examined. 44 0. Meta-information on this draft 46 This information is intended to facilitate discussion. It will be 47 removed when this document leaves the Internet-Draft stage. 49 0.1. Discussion 51 This draft is intended to be an extension to the Sieve mail filtering 52 language, available from the RFC repository as 53 . 55 This draft and the Sieve language itself are being discussed on the 56 MTA Filters mailing list at . Subscription 57 requests can be sent to (send an 58 mail message with the word "subscribe" in the body). More 59 information on the mailing list along with a WWW archive of back 60 messages is available at . 62 0.2. Noted Changes 64 0.2.1. Changes since -00 66 a) allow generic time zone names, without requiring implementations to 67 support it. added a "${timezone}" variable so that the user can 68 check if the implementation does support the time zone name he 69 wants. the default time zone was changed to localtime again. 71 b) allow back references from :matches as well as :regex. 73 c) added a section on implementation limits. 75 d) clarified global scope so that it spans include. 77 e) clarified that this draft only affects scripts which require 78 "variables". 80 f) changed modifiers into being tagged arguments for SET, added 81 precedence table. 83 g) added optional COMPARATOR to SET to solve the internationalisation 84 problem with :lower etc. 86 h) the name of the variable being SET is passed in a string to conform 87 with overall Sieve grammar. this string is explicitly disallowed 88 from containing variable references. 90 0.2.2. Changes since -01 92 a) clarify that a character is a Unicode character. 94 b) added paragraph warning against relying on Sieve for virus checking 95 to security section. 97 c) added a paragraph defining constant string. 99 d) added namespace to grammar. 101 e) removed SETDATE. 103 f) added wording and example requiring short-circuiting of test 104 evaluation. 106 0.2.3. Changes since -02 108 a) add references to Unicode and UTF-8, also more boilerplate 110 b) fixed a meaningless example. 112 c) changed term "numeric variables" to "numbered variables" to reduce 113 the chance of it being interpreted as variables holding integer 114 values. 116 d) allow future extensions to access the raw string value. 118 e) an unsuccessful match does NOT reset the numbered variables. 120 f) added definition of "string :count" 122 g) exceeding implementation limits on variable lengths should not make 123 scripts abort. 125 0.2.4. Changes since -03 127 a) clarify short-circuiting. 129 b) editorial changes. 131 0.2.5. Changes since -04 133 a) the wildcards in :matches was changed from greedy to non-greedy to 134 better support "principle of least surprise". added example to 135 illustrate the difference. 137 b) add definition of "variable"; clarify grammar is based on [SIEVE]; 138 clarify role of namespaces; add informative references for [REGEX] 139 and [SPAMTEST]; add normative reference for [RELATIONAL] 141 c) the use of unsupported numbered variables must be flagged as a 142 syntax error by implementations. 144 0.2.6. Changes since -00 (WG series) 146 a) added example for string test 148 b) moved introductory text for MODIFIER from 5.1 into 5.0 150 c) added Syntax line for MODIFIER. 152 d) added comment to an example showing that the non-greedy "*" still 153 matches everything due to implicit anchors. 155 e) added example of expansion of string with unbalanced braces. 157 f) updated reference to [SPAMTEST]. 159 0.2.7. Changes since -01 161 a) moved References from appendix into the document itself. 163 b) added example of SET with a comparator. 165 c) changed "highest value" to the less ambiguous "largest value". 167 d) updated reference to [UTF-8]. 169 e) allow numbered variables in namespaces. 171 f) change ${0} to mean the complete match. 173 0.2.8. Changes since -02 175 a) explicitly state compatibility with actions in base spec. 177 b) "numbered variables" are now called "match variables". 179 c) clarify definition of "match variable". 181 d) it's not the whole namespace which should match the extension 182 keyword, only the first component. 184 e) allow level 2 and above of the namespace specification to be all- 185 digit. 187 f) combining :upper and :lower etc. is now a syntax error. 189 g) allow SET to set variables in namespaces if the extension allows 190 it. 192 0.2.9. Changes since -03 194 a) added two new modifiers, ":quoteregex" and ":quotewildcard". 196 b) added wording about security implications of silent truncation. 198 0.2.10. Changes since -04 200 a) fix buggy markup and add missing modifier to syntax description 202 b) changed two "syntax error" (which really weren't) into just 203 "error". 205 c) changed "Syntax:" into "Usage:" to mirror [SIEVE] convention. 207 d) removed description of regex interaction and :quoteregex 209 e) added note to clarify that ${0010} is the same as ${10}. 211 f) changed name of document to align better with other extensions 212 (uses same format at 3431 and 3894) 214 0.2.11. Changes since -05 216 a) removed "open issues" section. 218 b) updated [RELATIONAL] reference 220 0.2.12. Changes since -06 222 a) updated abstract to mention what this document extends. 224 b) changed default scoping behaviour in anticipation of "include" 225 extension. 227 c) updated reference to RFC 2234. 229 d) clarified whitespace stripping behaviour for "string" test. 231 1. Introduction 233 This is an extension to the Sieve language defined by [SIEVE]. It 234 adds support for storing and referencing named data. The mechanisms 235 detailed in this document will only apply to Sieve scripts that 236 include a require clause for the "variables" extension. The require 237 clauses themselves are not affected by this extension. 239 Conventions for notations are as in [SIEVE] section 1.1, including 240 use of [KEYWORDS] and [ABNF]. The grammar builds on the grammar of 241 [SIEVE]. In this document, "character" means a [UNICODE] character, 242 which may consist of multiple octets coded in [UTF-8], and "variable" 243 is a named reference to data stored or read back using the mechanisms 244 of this extension. 246 2. Capability Identifier 248 The capability string associated with the extension defined in this 249 document is "variables". 251 3. Interpretation of strings 253 This extension changes the semantics of quoted-string, multi-line- 254 literal and multi-line-dotstuff found in [SIEVE] to enable the 255 inclusion of the value of variables. 257 When a string is evaluated, substrings matching variable-ref SHALL be 258 replaced by the value of variable-name. Only one pass through the 259 string SHALL be done. Variable names are case insensitive, so "foo" 260 and "FOO" refer to the same variable. Unknown variables are replaced 261 by the empty string. 263 variable-ref = "${" [namespace] variable-name "}" 264 namespace = identifier "." *sub-namespace 265 sub-namespace = variable-name "." 266 variable-name = num-variable / identifier 267 num-variable = 1*DIGIT 269 Examples: 271 "&%${}!" => unchanged, as the empty string is an illegal 272 identifier 273 "${doh!}" => unchanged, as "!" is illegal in identifiers 275 The variable "company" holds the value "ACME". No other variables 276 are set. 278 "${full}" => the empty string 279 "${company}" => "ACME" 280 "${BAD${Company}" => "${BADACME" 281 "${President, ${Company} Inc.}" 282 => "${President, ACME Inc.}" 284 The expanded string MUST use the variable values which are current 285 when control reaches the statement the string is part of. 287 Strings where no variable substitutions take place are referred to as 288 constant strings. Future extensions may specify that passing non- 289 constant strings as arguments to its actions or tests is an error. 291 Namespaces are meant for future extensions which make internal state 292 available through variables. These variables SHOULD be put in a 293 namespace whose first component is the same as its capability string. 294 Such extensions SHOULD state which, if any, of the variables in its 295 namespace are modifiable with the "set" action. 297 References to namespaces without a prior require statement for the 298 relevant extension MUST cause an error. 300 Tests or actions in future extensions may need to access the 301 unexpanded version of the string argument and, e.g., do the expansion 302 after setting variables in its namespace. The design of the 303 implementation should allow this. 305 3.1. Quoting 307 The semantics of quoting using backslash are not changed: backslash 308 quoting is resolved before doing variable substitution. 310 Examples: 311 "${fo\o}" => ${foo} => the expansion of variable foo. 312 "${fo\\o}" => ${fo\o} => illegal identifier => left verbatim. 313 "\${foo}" => ${foo} => the expansion of variable foo. 314 "\\${foo}" => \${foo} => a backslash character followed by the 315 expansion of variable foo. 317 If it is required to include a character sequence such as "${beep}" 318 verbatim in a text literal, the user can define a variable to 319 circumvent expansion to the empty string. 321 Example: 322 set "dollar" "$"; 323 set "text" "regarding ${dollar}{beep}"; 325 3.2. Match variables 327 A "match variable" has a name consisting only of decimal digits and 328 has no namespace component. 330 The decimal value of the match variable name will index the list of 331 matching strings from the most recently evaluated successful match of 332 type ":matches". The list is empty if no match has been successful. 334 Note: Extra leading zeroes are allowed and ignored. 336 The list will contain one string for each wildcard ("?" and "*") in 337 the match pattern. Each string holds what the corresponding wildcard 338 expands to, possibly the empty string. The wildcards match as little 339 as possible (non-greedy matching). 341 The first string in the list has index 1. If the index is out of 342 range, the empty string will be substituted. Index 0 contains the 343 matched part of the source value. 345 The interpreter MUST short-circuit tests, ie. not perform more tests 346 than necessary to find the result. Evaluation order MUST be left to 347 right. If a test has two or more list arguments, the implementation 348 is free to choose which to iterate over first. 350 An extension describing a new match type (e.g., [REGEX]) MAY specify 351 that match variables are set as a side effect when the match type is 352 used in a script which has enabled the "variables" extension. 354 Example: 356 require ["fileinto", "variables"]; 358 if header :matches "List-ID" "*<*@*" { 359 fileinto "lists.${2}"; stop; 360 } 362 # Imagine the header 363 # Subject: [acme-users] [fwd] version 1.0 is out 364 if header :matches "Subject" "[*] *" { 365 # ${1} will hold "acme-users", 366 # ${2} will hold "[fwd] version 1.0 is out" 367 fileinfo "lists.${1}"; stop; 368 } 370 if address :matches ["To", "Cc"] ["coyote@**.com", 371 "wile@**.com"] { 372 # ${0} is the matching address. 373 # ${1} is always the empty string. 374 fileinto "business.${2}"; stop; 375 } else { 376 # Control wouldn't reach this block if any match was 377 # successful, so no match variables are set at this 378 # point. 379 } 381 if anyof (true, address :domain :matches "To" "*.com") { 382 # The second test is never evaluated, so there are 383 # still no match variables set. 384 stop; 385 } 387 4. Action set 389 Usage: set [MODIFIER] [COMPARATOR] 391 The "set" action stores the specified value in the variable 392 identified by name. The name MUST be a constant string and conform 393 to the syntax of variable-name. Match variables can not be set. A 394 namespace can not be used unless an extension explicitly allows its 395 use in "set". An invalid name MUST be detected as a syntax error. 397 Modifiers are applied on a value before it is stored in the variable. 398 See next section for details. 400 The default comparator is "i;ascii-casemap". The comparator only 401 affects the result when certain modifiers are used. 403 Variables are only visible to the currently running script. Note: 404 Future extensions may provide different scoping rules for variables. 406 Variable names are case insensitive. 408 Example: 409 set "honorific" "Mr"; 410 set "first_name" "Wile"; 411 set "last_name" "Coyote"; 412 set "vacation" text: 413 Dear ${HONORIFIC} ${last_name}, 414 I'm out, please leave a message after the meep. 415 . 416 ; 418 "set" does not affect the implicit keep. It is compatible with all 419 actions defined in [SIEVE]. 421 4.1. Modifiers 423 Usage: ":lower" / ":upper" / ":lowerfirst" / ":upperfirst" / 424 ":quotewildcard" / ":length" 426 Modifier names are case insensitive. Unknown modifiers MUST yield a 427 syntax error. More than one modifier can be specified, in which case 428 they are applied according to this precedence list, largest value 429 first: 431 +--------------------------------+ 432 | Precedence Modifier | 433 +--------------------------------+ 434 | 40 :lower | 435 | :upper | 436 +--------------------------------+ 437 | 30 :lowerfirst | 438 | :upperfirst | 439 +--------------------------------+ 440 | 20 :quotewildcard | 441 +--------------------------------+ 442 | 10 :length | 443 +--------------------------------+ 445 It is an error to use two or more modifiers of the same precedence in 446 a single "set" action. 448 Examples: 449 # The value assigned to the variable is printed after the arrow 450 set "a" "juMBlEd lETteRS"; => "juMBlEd lETteRS" 451 set :length "b" "${a}"; => "15" 452 set :lower "b" "${a}"; => "jumbled letters" 453 set :lower :comparator "i;octet" 454 "b" "${a}"; => "juMBlEd lETteRS" 455 set :upperfirst "b" "${a}"; => "JuMBlEd lETteRS" 456 set :upperfirst :lower "b" "${a}"; => "Jumbled letters" 457 set :quotewildcard "b" "Rock*"; => "Rock\*" 459 4.1.1. Modifier ":length" 461 The value is the decimal number of characters in the expansion, 462 converted to a string. 464 4.1.2. Modifier ":quotewildcard" 466 This modifier adds the necessary quoting to ensure that the expanded 467 text will only match a literal occurence if used as a parameter to 468 :matches. Every character with special meaning ("*", "?" and "\") 469 is prefixed with "\" in the expansion. 471 4.1.3. Case modifiers 473 These modifiers change the letters of the text from upper to lower 474 case or vice versa. The implementation MUST support US-ASCII, but is 475 not required to handle the entire Unicode repertoire. The comparator 476 specified SHOULD be consulted to establish which locale to use. 478 4.1.3.1. Modifier ":upper" 480 All lower case letters are converted to their upper case counterpart. 482 4.1.3.2. Modifier ":lower" 484 All upper case letters are converted to their lower case counterpart. 486 4.1.3.3. Modifier ":upperfirst" 488 The first character of the string is converted to upper case if it is 489 a letter and set in lower case. The rest of the string is left 490 unchanged. 492 4.1.3.4. Modifier ":lowerfirst" 494 The first character of the string is converted to lower case if it is 495 a letter and set in upper case. The rest of the string is left 496 unchanged. 498 5. Test string 500 Usage: string [MATCH-TYPE] [COMPARATOR] 501 503 The "string" test evaluates to true if any of the source strings 504 matches any key. The type of match defaults to ":is". 506 In the "string" test, both source and key-list are taken from the 507 script, not the message, and whitespace stripping MUST NOT be done 508 unless the script explicitly requests this through some future 509 mechanism. 511 Example: 512 set "state" "${state} pending"; 513 if string :matches " ${state} " "* pending *" { 514 # the above test always succeeds 515 } 517 The "relational" extension [RELATIONAL] adds a match type called 518 ":count". The count of a single string is 0 if it is the empty 519 string, or 1 otherwise. The count of a string list is the sum of the 520 counts of the member strings. 522 6. Implementation Limits 524 An implementation of this draft MUST support at least 128 distinct 525 variables. The supported length of variable names MUST be at least 526 32 characters. Each variable MUST be able to hold at least 4000 527 characters. Attempts to set the variable to a value larger than what 528 the implementation supports SHOULD be reported as an error at 529 compile-time if possible. If the attempt is discovered during run- 530 time, the value SHOULD be truncated and it MUST NOT be treated as an 531 error. 533 Match variables ${1} through ${9} MUST be supported. References to 534 higher indices than the implementation supports MUST be treated as a 535 syntax error which SHOULD be discovered at compile-time. 537 7. Security Considerations 539 When match variables are used, and the author of the script isn't 540 careful, strings can contain arbitrary values controlled by the 541 sender of the mail. 543 Since values stored by "set" which exceed implementation limits are 544 silently truncated, it's not appropriate to store large structures 545 with security implications in variables. 547 The introduction of variables makes advanced decision making easier 548 to write, but since no looping construct is provided, all Sieve 549 scripts will terminate in an orderly manner. 551 Sieve filtering should not be relied on as a security measure against 552 hostile mail messages. Sieve is designed to do simple, mostly static 553 tests, and is not suitable for use as a spam or virus checker, where 554 the perpetrator has a motivation to vary the format of the mail in 555 order to avoid filtering rules. See also [SPAMTEST]. 557 8. IANA Considerations 559 The following template specifies the IANA registration of the 560 variables Sieve extension specified in this document: 562 To: iana@iana.org 563 Subject: Registration of new Sieve extension 565 Capability name: variables 566 Capability keyword: variables 567 Capability arguments: N/A 568 Standards Track/IESG-approved experimental RFC number: 569 this RFC 570 Person and email address to contact for further information: 571 Kjetil Torgrim Homme 572 kjetilho@ifi.uio.no 574 This information should be added to the list of sieve extensions 575 given on http://www.iana.org/assignments/sieve-extensions. 577 9. Acknowledgments 579 Thanks to Cyrus Daboo, Jutta Degener, Ned Freed, Lawrence Greenfield, 580 Jeffrey Hutzelman, Mark E. Mallett, Alexey Melnikov, Peder Stray and 581 Nigel Swinson for valuable feedback. 583 10. Author's Address 585 Kjetil T. Homme 586 University of Oslo 587 PO Box 1080 588 0316 Oslo, Norway 589 Phone: +47 9366 0091 590 E-mail: kjetilho@ifi.uio.no 592 11. References 594 11.1. Normative references 596 [ABNF] Crocker, D. and Overell, P., "Augmented BNF for Syntax 597 Specifications: ABNF", Work in Progress, draft- 598 crocker-abnf-rfc2234bis-XX.txt 600 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 601 Requirement Levels", RFC 2119, March 1997. 603 [RELATIONAL] Leiba, B. and Segmuller, W., "Sieve Extension: 604 Relational Tests", Work in Progress, draft-ietf- 605 sieve-3431bis-XX.txt 607 [SIEVE] Guenther, P. and Showalter, T., "Sieve: An Email 608 Filtering Language", Work in Progress, draft-ietf- 609 sieve-3028bis-XX.txt 611 [UNICODE] The Unicode Consortium, "The Unicode Standard -- 612 Worldwide Character Encoding -- Version 1.0", Addison- 613 Wesley, Volume 1, 1991, Volume 2, 1992. 615 [UTF-8] Yergeau, F., "UTF-8, a transformation format of 616 Unicode and ISO 10646", RFC 3629, November 2003. 618 11.2. Informative References 620 [REGEX] Murchison, K., "Sieve Email Filtering -- Regular 621 Expression Extension", Work in Progress. 623 [SPAMTEST] Daboo, C., "SIEVE Email Filtering: Spamtest and 624 VirusTest Extensions", RFC 3685, February 2004 626 Appendix B. Intellectual Property Rights Statement 628 The IETF takes no position regarding the validity or scope of any 629 intellectual property or other rights that might be claimed to 630 pertain to the implementation or use of the technology described in 631 this document or the extent to which any license under such rights 632 might or might not be available; neither does it represent that it 633 has made any effort to identify any such rights. Information on the 634 IETF's procedures with respect to rights in standards-track and 635 standards-related documentation can be found in BCP-11. Copies of 636 claims of rights made available for publication and any assurances of 637 licenses to be made available, or the result of an attempt made to 638 obtain a general license or permission for the use of such 639 proprietary rights by implementors or users of this specification can 640 be obtained from the IETF Secretariat. 642 Appendix C. Full Copyright Statement 644 Copyright (C) The Internet Society (2005). 646 This document is subject to the rights, licenses and restrictions 647 contained in BCP 78, and except as set forth therein, the authors 648 retain all their rights. 650 This document and the information contained herein are provided on an 651 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 652 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 653 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 654 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 655 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 656 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 658 Intellectual Property 660 The IETF takes no position regarding the validity or scope of any 661 Intellectual Property Rights or other rights that might be claimed to 662 pertain to the implementation or use of the technology described in 663 this document or the extent to which any license under such rights 664 might or might not be available; nor does it represent that it has 665 made any independent effort to identify any such rights. Information 666 on the procedures with respect to rights in RFC documents can be 667 found in BCP 78 and BCP 79. 669 Copies of IPR disclosures made to the IETF Secretariat and any 670 assurances of licenses to be made available, or the result of an 671 attempt made to obtain a general license or permission for the use of 672 such proprietary rights by implementers or users of this 673 specification can be obtained from the IETF on-line IPR repository at 674 http://www.ietf.org/ipr. 676 The IETF invites any interested party to bring to its attention any 677 copyrights, patents or patent applications, or other proprietary 678 rights that may cover technology that may be required to implement 679 this standard. Please address the information to the IETF at ietf- 680 ipr@ietf.org. 682 Acknowledgement 684 Funding for the RFC Editor function is currently provided by the 685 Internet Society.