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'ABNF') (Obsoleted by RFC 4234) -- 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: 6 errors (**), 0 flaws (~~), 7 warnings (==), 15 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-06.txt University of Oslo 5 Expires Feb 16, 2006 16 Aug 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 filtering rule sets, it is useful to keep state or 39 configuration details across rules. This extension changes the 40 interpretation of strings, adds an action to store data in variables, 41 and supplies a new test so that the value of a string can be 42 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 ${10}. 211 f) changed name of document to align better with other extensions 212 (uses same format at 3431 and 3894) 214 0.2.11. Changes since -05 216 a) removed "open issues" section. 218 b) updated [RELATIONAL] reference 220 1. Introduction 222 This is an extension to the Sieve language defined by [SIEVE]. It 223 adds support for storing and referencing named data. The mechanisms 224 detailed in this document will only apply to Sieve scripts that 225 include a require clause for the "variables" extension. The require 226 clauses themselves are not affected by this extension. 228 Conventions for notations are as in [SIEVE] section 1.1, including 229 use of [KEYWORDS] and [ABNF]. The grammar builds on the grammar of 230 [SIEVE]. In this document, "character" means a [UNICODE] character, 231 which may consist of multiple octets coded in [UTF-8], and "variable" 232 is a named reference to data stored or read back using the mechanisms 233 of this extension. 235 2. Capability Identifier 237 The capability string associated with the extension defined in this 238 document is "variables". 240 3. Interpretation of strings 242 This extension changes the semantics of quoted-string, multi-line- 243 literal and multi-line-dotstuff found in [SIEVE] to enable the 244 inclusion of the value of variables. 246 When a string is evaluated, substrings matching variable-ref SHALL be 247 replaced by the value of variable-name. Only one pass through the 248 string SHALL be done. Variable names are case insensitive, so "foo" 249 and "FOO" refer to the same variable. Unknown variables are replaced 250 by the empty string. 252 variable-ref = "${" [namespace] variable-name "}" 253 namespace = identifier "." *sub-namespace 254 sub-namespace = variable-name "." 255 variable-name = num-variable / identifier 256 num-variable = 1*DIGIT 258 Examples: 259 "&%${}!" => unchanged, as the empty string is an illegal 260 identifier 261 "${doh!}" => unchanged, as "!" is illegal in identifiers 263 The variable "company" holds the value "ACME". No other variables 264 are set. 266 "${full}" => the empty string 267 "${company}" => "ACME" 268 "${BAD${Company}" => "${BADACME" 269 "${President, ${Company} Inc.}" 270 => "${President, ACME Inc.}" 272 The expanded string MUST use the variable values which are current 273 when control reaches the statement the string is part of. 275 Strings where no variable substitutions take place are referred to as 276 constant strings. Future extensions may specify that passing non- 277 constant strings as arguments to its actions or tests is an error. 279 Namespaces are meant for future extensions which make internal state 280 available through variables. These variables SHOULD be put in a 281 namespace whose first component is the same as its capability string. 282 Such extensions SHOULD state which, if any, of the variables in its 283 namespace are modifiable with the "set" action. 285 References to namespaces without a prior require statement for the 286 relevant extension MUST cause an error. 288 Tests or actions in future extensions may need to access the 289 unexpanded version of the string argument and, e.g., do the expansion 290 after setting variables in its namespace. The design of the 291 implementation should allow this. 293 3.1. Quoting 295 The semantics of quoting using backslash are not changed: backslash 296 quoting is resolved before doing variable substitution. 298 Examples: 299 "${fo\o}" => ${foo} => the expansion of variable foo. 300 "${fo\\o}" => ${fo\o} => illegal identifier => left verbatim. 301 "\${foo}" => ${foo} => the expansion of variable foo. 302 "\\${foo}" => \${foo} => a backslash character followed by the 303 expansion of variable foo. 305 If it is required to include a character sequence such as "${beep}" 306 verbatim in a text literal, the user can define a variable to 307 circumvent expansion to the empty string. 309 Example: 310 set "dollar" "$"; 311 set "text" "regarding ${dollar}{beep}"; 313 3.2. Match variables 315 A "match variable" has a name consisting only of decimal digits and 316 has no namespace component. 318 The decimal value of the match variable name will index the list of 319 matching strings from the most recently evaluated successful match of 320 type ":matches". The list is empty if no match has been successful. 322 Note: Extra leading zeroes are allowed and ignored. 324 The list will contain one string for each wildcard ("?" and "*") in 325 the match pattern. Each string holds what the corresponding wildcard 326 expands to, possibly the empty string. The wildcards match as little 327 as possible (non-greedy matching). 329 The first string in the list has index 1. If the index is out of 330 range, the empty string will be substituted. Index 0 contains the 331 matched part of the source value. 333 The interpreter MUST short-circuit tests, ie. not perform more tests 334 than necessary to find the result. Evaluation order MUST be left to 335 right. If a test has two or more list arguments, the implementation 336 is free to choose which to iterate over first. 338 An extension describing a new match type (e.g., [REGEX]) MAY specify 339 that match variables are set as a side effect when the match type is 340 used in a script which has enabled the "variables" extension. 342 Example: 344 require ["fileinto", "variables"]; 346 if header :matches "List-ID" "*<*@*" { 347 fileinto "lists.${2}"; stop; 348 } 350 # Imagine the header 351 # Subject: [acme-users] [fwd] version 1.0 is out 352 if header :matches "Subject" "[*] *" { 353 # ${1} will hold "acme-users", 354 # ${2} will hold "[fwd] version 1.0 is out" 355 fileinfo "lists.${1}"; stop; 356 } 358 if address :matches ["To", "Cc"] ["coyote@**.com", 359 "wile@**.com"] { 360 # ${0} is the matching address. 361 # ${1} is always the empty string. 362 fileinto "business.${2}"; stop; 363 } else { 364 # Control wouldn't reach this block if any match was 365 # successful, so no match variables are set at this 366 # point. 367 } 369 if anyof (true, address :domain :matches "To" "*.com") { 370 # The second test is never evaluated, so there are 371 # still no match variables set. 372 stop; 373 } 375 4. Action set 377 Usage: set [MODIFIER] [COMPARATOR] 379 The "set" action stores the specified value in the variable 380 identified by name. The name MUST be a constant string and conform 381 to the syntax of variable-name. Match variables can not be set. A 382 namespace can not be used unless an extension explicitly allows its 383 use in "set". An invalid name MUST be detected as a syntax error. 385 Modifiers are applied on a value before it is stored in the variable. 386 See next section for details. 388 The default comparator is "i;ascii-casemap". The comparator only 389 affects the result when certain modifiers are used. 391 All variables have global scope: they are visible until processing 392 stops. Variable names are case insensitive. 394 Example: 395 set "honorific" "Mr"; 396 set "first_name" "Wile"; 397 set "last_name" "Coyote"; 398 set "vacation" text: 399 Dear ${HONORIFIC} ${last_name}, 400 I'm out, please leave a message after the meep. 401 . 402 ; 404 "set" does not affect the implicit keep. It is compatible with all 405 actions defined in [SIEVE]. 407 4.1. Modifiers 409 Usage: ":lower" / ":upper" / ":lowerfirst" / ":upperfirst" / 410 ":quotewildcard" / ":length" 412 Modifier names are case insensitive. Unknown modifiers MUST yield a 413 syntax error. More than one modifier can be specified, in which case 414 they are applied according to this precedence list, largest value 415 first: 417 +--------------------------------+ 418 | Precedence Modifier | 419 +--------------------------------+ 420 | 40 :lower | 421 | :upper | 422 +--------------------------------+ 423 | 30 :lowerfirst | 424 | :upperfirst | 425 +--------------------------------+ 426 | 20 :quotewildcard | 427 +--------------------------------+ 428 | 10 :length | 429 +--------------------------------+ 431 It is an error to use two or more modifiers of the same precedence in 432 a single "set" action. 434 Examples: 435 # The value assigned to the variable is printed after the arrow 436 set "a" "juMBlEd lETteRS"; => "juMBlEd lETteRS" 437 set :length "b" "${a}"; => "15" 438 set :lower "b" "${a}"; => "jumbled letters" 439 set :lower :comparator "i;octet" 440 "b" "${a}"; => "juMBlEd lETteRS" 441 set :upperfirst "b" "${a}"; => "JuMBlEd lETteRS" 442 set :upperfirst :lower "b" "${a}"; => "Jumbled letters" 443 set :quotewildcard "b" "Rock*"; => "Rock\*" 445 4.1.1. Modifier ":length" 447 The value is the decimal number of characters in the expansion, 448 converted to a string. 450 4.1.2. Modifier ":quotewildcard" 452 This modifier adds the necessary quoting to ensure that the expanded 453 text will only match a literal occurence if used as a parameter to 454 :matches. Every character with special meaning ("*", "?" and "\") 455 is prefixed with "\" in the expansion. 457 4.1.3. Case modifiers 459 These modifiers change the letters of the text from upper to lower 460 case or vice versa. The implementation MUST support US-ASCII, but is 461 not required to handle the entire Unicode repertoire. The comparator 462 specified SHOULD be consulted to establish which locale to use. 464 4.1.3.1. Modifier ":upper" 466 All lower case letters are converted to their upper case counterpart. 468 4.1.3.2. Modifier ":lower" 470 All upper case letters are converted to their lower case counterpart. 472 4.1.3.3. Modifier ":upperfirst" 474 The first character of the string is converted to upper case if it is 475 a letter and set in lower case. The rest of the string is left 476 unchanged. 478 4.1.3.4. Modifier ":lowerfirst" 480 The first character of the string is converted to lower case if it is 481 a letter and set in upper case. The rest of the string is left 482 unchanged. 484 5. Test string 486 Usage: string [MATCH-TYPE] [COMPARATOR] 487 489 The "string" test evaluates to true if any of the source strings 490 matches any key. The type of match defaults to ":is". 492 Example: 493 set "state" "${state} pending"; 494 if string :matches " ${state} " "* pending *" { 495 # the above test always succeeds 496 } 498 The "relational" extension [RELATIONAL] adds a match type called 499 ":count". The count of a single string is 0 if it is the empty 500 string, or 1 otherwise. The count of a string list is the sum of the 501 counts of the member strings. 503 6. Implementation Limits 505 An implementation of this draft MUST support at least 128 distinct 506 variables. The supported length of variable names MUST be at least 507 32 characters. Each variable MUST be able to hold at least 4000 508 characters. Attempts to set the variable to a value larger than what 509 the implementation supports SHOULD be reported as an error at 510 compile-time if possible. If the attempt is discovered during run- 511 time, the value SHOULD be truncated and it MUST NOT be treated as an 512 error. 514 Match variables ${1} through ${9} MUST be supported. References to 515 higher indices than the implementation supports MUST be treated as a 516 syntax error which SHOULD be discovered at compile-time. 518 7. Security Considerations 520 When match variables are used, and the author of the script isn't 521 careful, strings can contain arbitrary values controlled by the 522 sender of the mail. 524 Since values stored by "set" which exceed implementation limits are 525 silently truncated, it's not appropriate to store large structures 526 with security implications in variables. 528 The introduction of variables makes advanced decision making easier 529 to write, but since no looping construct is provided, all Sieve 530 scripts will terminate in an orderly manner. 532 Sieve filtering should not be relied on as a security measure against 533 hostile mail messages. Sieve is designed to do simple, mostly static 534 tests, and is not suitable for use as a spam or virus checker, where 535 the perpetrator has a motivation to vary the format of the mail in 536 order to avoid filtering rules. See also [SPAMTEST]. 538 8. IANA Considerations 540 The following template specifies the IANA registration of the 541 variables Sieve extension specified in this document: 543 To: iana@iana.org 544 Subject: Registration of new Sieve extension 545 Capability name: variables 546 Capability keyword: variables 547 Capability arguments: N/A 548 Standards Track/IESG-approved experimental RFC number: 549 this RFC 550 Person and email address to contact for further information: 551 Kjetil Torgrim Homme 552 kjetilho@ifi.uio.no 554 This information should be added to the list of sieve extensions 555 given on http://www.iana.org/assignments/sieve-extensions. 557 9. Acknowledgments 559 Thanks to Cyrus Daboo, Jutta Degener, Ned Freed, Lawrence Greenfield, 560 Jeffrey Hutzelman, Mark E. Mallett, Alexey Melnikov, Peder Stray and 561 Nigel Swinson for valuable feedback. 563 10. Author's Address 565 Kjetil T. Homme 566 University of Oslo 567 PO Box 1080 568 0316 Oslo, Norway 570 Phone: +47 9366 0091 571 E-mail: kjetilho@ifi.uio.no 573 11. References 575 11.1. Normative references 577 [ABNF] Crocker, D. and Overell, P., "Augmented BNF for Syntax 578 Specifications: ABNF", RFC 2234, November 1997. 580 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 581 Requirement Levels", RFC 2119, March 1997. 583 [RELATIONAL] Leiba, B. and Segmuller, W., "Sieve Extension: 584 Relational Tests", Work in Progress, draft-ietf- 585 sieve-3431bis-XX.txt 587 [SIEVE] Guenther, P. and Showalter, T., "Sieve: An Email 588 Filtering Language", Work in Progress, draft-ietf- 589 sieve-3028bis-XX.txt 591 [UNICODE] The Unicode Consortium, "The Unicode Standard -- 592 Worldwide Character Encoding -- Version 1.0", Addison- 593 Wesley, Volume 1, 1991, Volume 2, 1992. 595 [UTF-8] Yergeau, F., "UTF-8, a transformation format of 596 Unicode and ISO 10646", RFC 3629, November 2003. 598 11.2. Informative References 600 [REGEX] Murchison, K., "Sieve Email Filtering -- Regular 601 Expression Extension", Work in Progress. 603 [SPAMTEST] Daboo, C., "SIEVE Email Filtering: Spamtest and 604 VirusTest Extensions", RFC 3685, February 2004 606 Appendix B. Intellectual Property Rights Statement 608 The IETF takes no position regarding the validity or scope of any 609 intellectual property or other rights that might be claimed to 610 pertain to the implementation or use of the technology described in 611 this document or the extent to which any license under such rights 612 might or might not be available; neither does it represent that it 613 has made any effort to identify any such rights. Information on the 614 IETF's procedures with respect to rights in standards-track and 615 standards-related documentation can be found in BCP-11. Copies of 616 claims of rights made available for publication and any assurances of 617 licenses to be made available, or the result of an attempt made to 618 obtain a general license or permission for the use of such 619 proprietary rights by implementors or users of this specification can 620 be obtained from the IETF Secretariat. 622 Appendix C. Full Copyright Statement 624 Copyright (C) The Internet Society (2005). 626 This document is subject to the rights, licenses and restrictions 627 contained in BCP 78, and except as set forth therein, the authors 628 retain all their rights. 630 This document and the information contained herein are provided on an 631 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 632 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 633 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 634 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 635 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 636 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 638 Intellectual Property 640 The IETF takes no position regarding the validity or scope of any 641 Intellectual Property Rights or other rights that might be claimed to 642 pertain to the implementation or use of the technology described in 643 this document or the extent to which any license under such rights 644 might or might not be available; nor does it represent that it has 645 made any independent effort to identify any such rights. Information 646 on the procedures with respect to rights in RFC documents can be 647 found in BCP 78 and BCP 79. 649 Copies of IPR disclosures made to the IETF Secretariat and any 650 assurances of licenses to be made available, or the result of an 651 attempt made to obtain a general license or permission for the use of 652 such proprietary rights by implementers or users of this 653 specification can be obtained from the IETF on-line IPR repository at 654 http://www.ietf.org/ipr. 656 The IETF invites any interested party to bring to its attention any 657 copyrights, patents or patent applications, or other proprietary 658 rights that may cover technology that may be required to implement 659 this standard. Please address the information to the IETF at ietf- 660 ipr@ietf.org. 662 Acknowledgement 664 Funding for the RFC Editor function is currently provided by the 665 Internet Society.