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'RELATIONAL') (Obsoleted by RFC 5231) -- 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: 7 errors (**), 0 flaws (~~), 7 warnings (==), 13 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-05.txt University of Oslo 5 Expires Feb 10, 2006 10 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 ${10}. 211 f) changed name of document to align better with other extensions 212 (uses same format at 3431 and 3894) 214 0.3. Open Issues 216 This extension is in conflict with a MUST in [SIEVE] 2.4: "Tests MUST 217 NOT have side effects." This document therefore can't leave draft 218 status until a revised Sieve specification has been accepted by the 219 IESG. No significant changes to this draft are foreseen before 220 submission as a proposed standard. 222 1. Introduction 224 This is an extension to the Sieve language defined by [SIEVE]. It 225 adds support for storing and referencing named data. The mechanisms 226 detailed in this document will only apply to Sieve scripts that 227 include a require clause for the "variables" extension. The require 228 clauses themselves are not affected by this extension. 230 Conventions for notations are as in [SIEVE] section 1.1, including 231 use of [KEYWORDS] and [ABNF]. The grammar builds on the grammar of 232 [SIEVE]. In this document, "character" means a [UNICODE] character, 233 which may consist of multiple octets coded in [UTF-8], and "variable" 234 is a named reference to data stored or read back using the mechanisms 235 of this extension. 237 2. Capability Identifier 239 The capability string associated with the extension defined in this 240 document is "variables". 242 3. Interpretation of strings 244 This extension changes the semantics of quoted-string, multi-line- 245 literal and multi-line-dotstuff found in [SIEVE] to enable the 246 inclusion of the value of variables. 248 When a string is evaluated, substrings matching variable-ref SHALL be 249 replaced by the value of variable-name. Only one pass through the 250 string SHALL be done. Variable names are case insensitive, so "foo" 251 and "FOO" refer to the same variable. Unknown variables are replaced 252 by the empty string. 254 variable-ref = "${" [namespace] variable-name "}" 255 namespace = identifier "." *sub-namespace 256 sub-namespace = variable-name "." 257 variable-name = num-variable / identifier 258 num-variable = 1*DIGIT 260 Examples: 261 "&%${}!" => unchanged, as the empty string is an illegal 262 identifier 263 "${doh!}" => unchanged, as "!" is illegal in identifiers 265 The variable "company" holds the value "ACME". No other variables 266 are set. 268 "${full}" => the empty string 269 "${company}" => "ACME" 270 "${BAD${Company}" => "${BADACME" 271 "${President, ${Company} Inc.}" 272 => "${President, ACME Inc.}" 274 The expanded string MUST use the variable values which are current 275 when control reaches the statement the string is part of. 277 Strings where no variable substitutions take place are referred to as 278 constant strings. Future extensions may specify that passing non- 279 constant strings as arguments to its actions or tests is an error. 281 Namespaces are meant for future extensions which make internal state 282 available through variables. These variables SHOULD be put in a 283 namespace whose first component is the same as its capability string. 284 Such extensions SHOULD state which, if any, of the variables in its 285 namespace are modifiable with the "set" action. 287 References to namespaces without a prior require statement for the 288 relevant extension MUST cause an error. 290 Tests or actions in future extensions may need to access the 291 unexpanded version of the string argument and, e.g., do the expansion 292 after setting variables in its namespace. The design of the 293 implementation should allow this. 295 3.1. Quoting 297 The semantics of quoting using backslash are not changed: backslash 298 quoting is resolved before doing variable substitution. 300 Examples: 301 "${fo\o}" => ${foo} => the expansion of variable foo. 302 "${fo\\o}" => ${fo\o} => illegal identifier => left verbatim. 303 "\${foo}" => ${foo} => the expansion of variable foo. 304 "\\${foo}" => \${foo} => a backslash character followed by the 305 expansion of variable foo. 307 If it is required to include a character sequence such as "${beep}" 308 verbatim in a text literal, the user can define a variable to 309 circumvent expansion to the empty string. 311 Example: 312 set "dollar" "$"; 313 set "text" "regarding ${dollar}{beep}"; 315 3.2. Match variables 317 A "match variable" has a name consisting only of decimal digits and 318 has no namespace component. 320 The decimal value of the match variable name will index the list of 321 matching strings from the most recently evaluated successful match of 322 type ":matches". The list is empty if no match has been successful. 323 An extension describing a new match type (e.g., [REGEX]) MAY specify 324 that match variables are set as a side effect when the match type is 325 used in a script which has enabled the "variables" extension. 327 Note: Extra leading zeroes are allowed and ignored. 329 For ":matches", the list will contain one string for each wildcard 330 ("?" and "*") in the match pattern. Each string holds what the 331 corresponding wildcard expands to, possibly the empty string. The 332 wildcards match as little as possible (non-greedy matching). 334 The first string in the list has index 1. If the index is out of 335 range, the empty string will be substituted. Index 0 contains the 336 matched part of the source value. 338 The interpreter MUST short-circuit tests, ie. not perform more tests 339 than necessary to find the result. Evaluation order MUST be left to 340 right. If a test has two or more list arguments, the implementation 341 is free to choose which to iterate over first. 343 Example: 345 require ["fileinto", "variables"]; 347 if header :matches "List-ID" "*<*@*" { 348 fileinto "lists.${2}"; stop; 349 } 351 # Imagine the header 352 # Subject: [acme-users] [fwd] version 1.0 is out 353 if header :matches "Subject" "[*] *" { 354 # ${1} will hold "acme-users", 355 # ${2} will hold "[fwd] version 1.0 is out" 356 fileinfo "lists.${1}"; stop; 357 } 359 if address :matches ["To", "Cc"] ["coyote@**.com", 360 "wile@**.com"] { 361 # ${0} is the matching address. 362 # ${1} is always the empty string. 364 fileinto "business.${2}"; stop; 365 } else { 366 # Control wouldn't reach this block if any match was 367 # successful, so no match variables are set at this 368 # point. 369 } 371 if anyof (true, address :domain :matches "To" "*.com") { 372 # The second test is never evaluated, so there are 373 # still no match variables set. 374 stop; 375 } 377 4. Action set 379 Usage: set [MODIFIER] [COMPARATOR] 381 The "set" action stores the specified value in the variable 382 identified by name. The name MUST be a constant string and conform 383 to the syntax of variable-name. Match variables can not be set. A 384 namespace can not be used unless an extension explicitly allows its 385 use in "set". An invalid name MUST be detected as a syntax error. 387 Modifiers are applied on a value before it is stored in the variable. 388 See next section for details. 390 The default comparator is "i;ascii-casemap". The comparator only 391 affects the result when certain modifiers are used. 393 All variables have global scope: they are visible until processing 394 stops. Variable names are case insensitive. 396 Example: 397 set "honorific" "Mr"; 398 set "first_name" "Wile"; 399 set "last_name" "Coyote"; 400 set "vacation" text: 401 Dear ${HONORIFIC} ${last_name}, 402 I'm out, please leave a message after the meep. 403 . 404 ; 406 "set" does not affect the implicit keep. It is compatible with all 407 actions defined in [SIEVE]. 409 4.1. Modifiers 411 Usage: ":lower" / ":upper" / ":lowerfirst" / ":upperfirst" / 412 ":quotewildcard" / ":length" 414 Modifier names are case insensitive. Unknown modifiers MUST yield a 415 syntax error. More than one modifier can be specified, in which case 416 they are applied according to this precedence list, largest value 417 first: 419 +--------------------------------+ 420 | Precedence Modifier | 421 +--------------------------------+ 422 | 40 :lower | 423 | :upper | 424 +--------------------------------+ 425 | 30 :lowerfirst | 426 | :upperfirst | 427 +--------------------------------+ 428 | 20 :quotewildcard | 429 +--------------------------------+ 430 | 10 :length | 431 +--------------------------------+ 433 It is an error to use two or more modifiers of the same precedence in 434 a single SET command. 436 Examples: 437 # The value assigned to the variable is printed after the arrow 438 set "a" "juMBlEd lETteRS"; => "juMBlEd lETteRS" 439 set :length "b" "${a}"; => "15" 440 set :lower "b" "${a}"; => "jumbled letters" 441 set :lower :comparator "i;octet" 442 "b" "${a}"; => "juMBlEd lETteRS" 443 set :upperfirst "b" "${a}"; => "JuMBlEd lETteRS" 444 set :upperfirst :lower "b" "${a}"; => "Jumbled letters" 445 set :quotewildcard "b" "Rock*"; => "Rock\*" 447 4.1.1. Modifier ":length" 449 The value is the decimal number of characters in the expansion, 450 converted to a string. 452 4.1.2. Modifier ":quotewildcard" 454 This modifier adds the necessary quoting to ensure that the expanded 455 text will only match a literal occurence if used as a parameter to 456 :matches. Every character with special meaning ("*", "?" and "\") 457 is prefixed with "\" in the expansion. 459 4.1.3. Case modifiers 461 These modifiers change the letters of the text from upper to lower 462 case or vice versa. The implementation MUST support US-ASCII, but is 463 not required to handle the entire Unicode repertoire. The comparator 464 specified SHOULD be consulted to establish which locale to use. 466 4.1.3.1. Modifier ":upper" 468 All lower case letters are converted to their upper case counterpart. 470 4.1.3.2. Modifier ":lower" 472 All upper case letters are converted to their lower case counterpart. 474 4.1.3.3. Modifier ":upperfirst" 476 The first character of the string is converted to upper case if it is 477 a letter and set in lower case. The rest of the string is left 478 unchanged. 480 4.1.3.4. Modifier ":lowerfirst" 482 The first character of the string is converted to lower case if it is 483 a letter and set in upper case. The rest of the string is left 484 unchanged. 486 5. Test string 488 Usage: string [MATCH-TYPE] [COMPARATOR] 489 491 The "string" test evaluates to true if any of the source strings 492 matches any key. The type of match defaults to ":is". 494 Example: 496 set "state" "${state} pending"; 497 if string :matches " ${state} " "* pending *" { 498 # the above test always succeeds 499 } 501 The "relational" extension [RELATIONAL] adds a match type called 502 ":count". The count of a single string is 0 if it is the empty 503 string, or 1 otherwise. The count of a string list is the sum of the 504 counts of the member strings. 506 6. Implementation Limits 508 An implementation of this draft MUST support at least 128 distinct 509 variables. The supported length of variable names MUST be at least 510 32 characters. Each variable MUST be able to hold at least 4000 511 characters. Attempts to set the variable to a value larger than what 512 the implementation supports SHOULD be reported as an error at 513 compile-time if possible. If the attempt is discovered during run- 514 time, the value SHOULD be truncated and it MUST NOT be treated as an 515 error. 517 Match variables ${1} through ${9} MUST be supported. References to 518 higher indices than the implementation supports MUST be treated as a 519 syntax error which SHOULD be discovered at compile-time. 521 7. Security Considerations 523 When match variables are used, and the author of the script isn't 524 careful, strings can contain arbitrary values controlled by the 525 sender of the mail. 527 Since values stored by SET exceeding implementation limits are 528 silently truncated, it's not appropriate to store large structures 529 with security implications in variables. 531 The introduction of variables makes advanced decision making easier 532 to write, but since no looping construct is provided, all Sieve 533 scripts will terminate in an orderly manner. 535 Sieve filtering should not be relied on as a security measure against 536 hostile mail messages. Sieve is designed to do simple, mostly static 537 tests, and is not suitable for use as a spam or virus checker, where 538 the perpetrator has a motivation to vary the format of the mail in 539 order to avoid filtering rules. See also [SPAMTEST]. 541 8. IANA Considerations 543 The following template specifies the IANA registration of the 544 variables Sieve extension specified in this document: 546 To: iana@iana.org 547 Subject: Registration of new Sieve extension 549 Capability name: variables 550 Capability keyword: variables 551 Capability arguments: N/A 552 Standards Track/IESG-approved experimental RFC number: 553 this RFC 554 Person and email address to contact for further information: 555 Kjetil Torgrim Homme 556 kjetilho@ifi.uio.no 558 This information should be added to the list of sieve extensions 559 given on http://www.iana.org/assignments/sieve-extensions. 561 9. Acknowledgments 563 Thanks to Cyrus Daboo, Jutta Degener, Ned Freed, Lawrence Greenfield, 564 Jeffrey Hutzelman, Mark E. Mallett, Alexey Melnikov, Peder Stray and 565 Nigel Swinson for valuable feedback. 567 10. Author's Address 569 Kjetil T. Homme 570 University of Oslo 571 PO Box 1080 572 0316 Oslo, Norway 574 Phone: +47 9366 0091 575 E-mail: kjetilho@ifi.uio.no 577 11. References 579 11.1. Normative references 581 [ABNF] Crocker, D. and Overell, P., "Augmented BNF for Syntax 582 Specifications: ABNF", RFC 2234, November 1997. 584 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 585 Requirement Levels", RFC 2119, March 1997. 587 [RELATIONAL] Segmuller, W., "Sieve Extension: Relational Tests", 588 RFC 3431, December 2002. 590 [SIEVE] Guenther, P. and Showalter, T., "Sieve: An Email 591 Filtering Language", Work in Progress, draft-ietf- 592 sieve-3028bis-XX.txt 594 [UNICODE] The Unicode Consortium, "The Unicode Standard -- 595 Worldwide Character Encoding -- Version 1.0", Addison- 596 Wesley, Volume 1, 1991, Volume 2, 1992. 598 [UTF-8] Yergeau, F., "UTF-8, a transformation format of 599 Unicode and ISO 10646", RFC 3629, November 2003. 601 11.2. Informative References 603 [REGEX] Murchison, K., "Sieve Email Filtering -- Regular 604 Expression Extension", Work in Progress. 606 [SPAMTEST] Daboo, C., "SIEVE Email Filtering: Spamtest and 607 VirusTest Extensions", RFC 3685, February 2004 609 Appendix B. Intellectual Property Rights Statement 611 The IETF takes no position regarding the validity or scope of any 612 intellectual property or other rights that might be claimed to 613 pertain to the implementation or use of the technology described in 614 this document or the extent to which any license under such rights 615 might or might not be available; neither does it represent that it 616 has made any effort to identify any such rights. Information on the 617 IETF's procedures with respect to rights in standards-track and 618 standards-related documentation can be found in BCP-11. Copies of 619 claims of rights made available for publication and any assurances of 620 licenses to be made available, or the result of an attempt made to 621 obtain a general license or permission for the use of such 622 proprietary rights by implementors or users of this specification can 623 be obtained from the IETF Secretariat. 625 Appendix C. Full Copyright Statement 627 Copyright (C) The Internet Society (2005). 629 This document is subject to the rights, licenses and restrictions 630 contained in BCP 78, and except as set forth therein, the authors 631 retain all their rights. 633 This document and the information contained herein are provided on an 634 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 635 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 636 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 637 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 638 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 639 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 641 Intellectual Property 643 The IETF takes no position regarding the validity or scope of any 644 Intellectual Property Rights or other rights that might be claimed to 645 pertain to the implementation or use of the technology described in 646 this document or the extent to which any license under such rights 647 might or might not be available; nor does it represent that it has 648 made any independent effort to identify any such rights. Information 649 on the procedures with respect to rights in RFC documents can be 650 found in BCP 78 and BCP 79. 652 Copies of IPR disclosures made to the IETF Secretariat and any 653 assurances of licenses to be made available, or the result of an 654 attempt made to obtain a general license or permission for the use of 655 such proprietary rights by implementers or users of this 656 specification can be obtained from the IETF on-line IPR repository at 657 http://www.ietf.org/ipr. 659 The IETF invites any interested party to bring to its attention any 660 copyrights, patents or patent applications, or other proprietary 661 rights that may cover technology that may be required to implement 662 this standard. Please address the information to the IETF at ietf- 663 ipr@ietf.org. 665 Acknowledgement 667 Funding for the RFC Editor function is currently provided by the 668 Internet Society.