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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Service Location Working Group Erik Guttman 2 INTERNET DRAFT Charles Perkins 3 James Kempf 4 14 October 1998 Sun Microsystems 6 Service Templates and service: Schemes 7 draft-ietf-svrloc-service-scheme-11.txt 9 Status of This Memo 11 This document is a submission by the Service Location Working Group 12 of the Internet Engineering Task Force (IETF). Comments should be 13 submitted to the srvloc@corp.home.net mailing list. 15 Distribution of this memo is unlimited. 17 This document is an Internet-Draft. Internet-Drafts are working 18 documents of the Internet Engineering Task Force (IETF), its areas, 19 and its working groups. Note that other groups may also distribute 20 working documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at 24 any time. It is inappropriate to use Internet- Drafts as reference 25 material or to cite them other than as ``work in progress.'' 27 To view the entire list of current Internet-Drafts, please check 28 the ``1id-abstracts.txt'' listing contained in the Internet-Drafts 29 Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern 30 Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific 31 Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). 33 Abstract 35 The "service:" URL scheme name is used to define URLs (called 36 "service: URLs" in this document) that are primarily intended to 37 be used by the Service Location Protocol in order to distribute 38 service access information. These schemes provide an extensible 39 framework for client-based network software to obtain configuration 40 information required to make use of network services. When 41 registering a service: URL, the URL is accompanied by a set of 42 well-defined attributes which define the service. These attributes 43 convey configuration information to client software, or service 44 characteristics meaningful to end users. 46 This document describes a formal procedure for defining and 47 standardizing new service types and attributes for use with the 48 "service:" scheme. The formal descriptions of service types and 49 attributes are templates that are human and machine understandable. 50 They SHOULD be used by administrative tools to parse service 51 registration information and by client applications to provide 52 localized translations of service attribute strings. 54 Contents 56 Status of This Memo i 58 Abstract i 60 1. Introduction 2 61 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.2. Service Location Protocol . . . . . . . . . . . . . . . . 4 63 1.2.1. Compatibility with SLPv1 . . . . . . . . . . . . 4 65 2. Service URL Syntax and Semantics 5 66 2.1. Service URL Syntax . . . . . . . . . . . . . . . . . . . 5 67 2.2. Service URL Semantics . . . . . . . . . . . . . . . . . . 7 68 2.3. Use of service: URLs . . . . . . . . . . . . . . . . . . 8 69 2.4. Specifying the Service Type-Specific URL Syntax . . . . . 9 70 2.5. Accommodating Abstract Service Types . . . . . . . . . . 9 71 2.5.1. Advertising Abstract Service Types . . . . . . . 10 73 3. Syntax and Semantics of Service Type Specifications 11 74 3.1. Syntax of Service Type Templates . . . . . . . . . . . . 11 75 3.2. Semantics of Service Type Templates . . . . . . . . . . . 14 76 3.2.1. Definition of a Service Template . . . . . . . . 14 77 3.2.2. Service Type . . . . . . . . . . . . . . . . . . 15 78 3.2.3. Version Number . . . . . . . . . . . . . . . . . 15 79 3.2.4. Description . . . . . . . . . . . . . . . . . . . 15 80 3.2.5. Syntax of the Service Type-specific URL Part . . 15 81 3.2.6. Attribute Definition . . . . . . . . . . . . . . 16 83 4. A Process For Standardizing New Service Types 20 85 5. IANA Considerations 21 87 6. Internationalization Considerations 22 88 6.1. Language Identification and Translation . . . . . . . . . 23 90 7. Security Considerations 23 92 A. Service Template Examples 24 93 A.1. FOO . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 94 A.2. Abstract Service Type: Net-Transducer . . . . . . . . . 25 95 A.3. Concrete Service Type: Net-Transducer:Thermometer . . . 26 96 A.4. service: URLs and SLP . . . . . . . . . . . . . . . . . . 27 98 B. Full Copyright Statement 28 99 C. Acknowledgments 28 101 1. Introduction 103 This document describes a URL scheme, called service: URL, which 104 defines network access information for network services using a 105 formal notation. In addition it describes how to define a set of 106 attributes to associate with a service: URL. These attributes will 107 allow end users and programs to select between network services of 108 the same type that have different capabilities. The attributes 109 are defined in a template document that is readable by people and 110 machines. 112 A client uses attributes to select a particular service. Service 113 selection occurs by obtaining the service: URL that offers the right 114 configuration for the client. Service type templates define the 115 syntax of service: URLs for a particular service type, as well as the 116 attributes which accompany a service: URL in a service registration. 118 Templates are used for the following distinct purposes: 120 1. Standardization 122 The template is reviewed before it is standardized. Once it is 123 standardized, all versions of the template are archived by IANA. 125 2. Service Registration 127 Servers making use of the Service Location Protocol [11] register 128 themselves and their attributes. They use the templates to 129 generate the service registrations. In registering, the service 130 must use the specified values for its attributes. 132 3. Client presentation of Service Information 134 Client applications may display service information. The 135 template provides type information and explanatory text which may 136 be helpful in producing user interfaces. 138 4. Internationalization 140 Entities with access to the template for a given service type in 141 two different languages may translate between the two languages. 143 A service may register itself in more than one language using 144 templates, though it has been configured by an operator who 145 registered service attributes in a single language. 147 All grammar encoding follows the Augmented BNF (ABNF) [8] for syntax 148 specifications. 150 1.1. Terminology 152 This section introduces some terminology for describing service: 153 URLs. 155 service scheme 157 A URL scheme whose name starts with the string "service:" and 158 is followed by the service type name, constructed according to 159 the rules in this document. An example is "service:lpr:" for 160 the lpr print service [15]. 162 service: URL 164 A URL constructed according to the service scheme definition. 165 It typically provides at least the following: The name of an 166 access protocol, and an address locating this service. The 167 service: URL may include url path information specific to the 168 type of service, as well as attribute information encoded 169 according to the URL grammar. The service: URL is used by 170 the Service Location Protocol to register and discover the 171 location of services. It may be used by other protocols and in 172 documents as well. 174 service type 176 A name identifying the semantics by which the remainder of 177 the service: URL is to be understood. It may denote either a 178 particular network protocol, or an abstract service associated 179 with a variety of protocols. If the service type denotes a 180 particular protocol, then the service type name SHOULD either 181 be assigned the name of a particular well known port [2] by 182 convention or be the Assigned Numbers name for the service [1]. 184 abstract service type 186 A service type name which is associated with a variety of 187 different protocols. An example is given in Section A. 188 Section 2 discusses various ways that abstract types can be 189 accommodated. 191 service registration 193 A service: URL and optionally a set of attributes comprise 194 a service registration. This registration is made by or on 195 behalf of a given service. The URL syntax and attributes must 196 conform to the service template for the registered service. 198 service template 200 A formal description of the service attributes and service 201 scheme associated with a particular service type. 203 1.2. Service Location Protocol 205 The Service Location Protocol version 2 [11] allows service: URLs to 206 be registered and discovered, though service: URLs may be also used 207 in other contexts. 209 Client applications discover service registrations by issuing queries 210 for services of a particular type, specifying the attributes of 211 the service: URLs to return. Clients retrieve the attributes of a 212 particular service by supplying its service: URL. Attributes for all 213 service registrations of a particular type can also be retrieved. 215 Services may register themselves, or registrations may be made on 216 their behalf. These registrations contain a service: URL, and 217 possibly attributes and digital signatures. 219 1.2.1. Compatibility with SLPv1 221 This document adopts the encoding conventions of SLPv2. 223 Compatibility with SLPv1 [[16]] is possible, if the following 224 conventions must be observed: 226 1. Abstract service types must not be used. SLPv2 specifies the 227 use of Service URLs with abstract service types. SLPv1 does not 228 support them. Thus, a service template which is to serve both 229 SLPv1 and SLPv2 must not use abstract service types. 231 2. The syntax for representing opaque values in this document is 232 consistent with SLPv2. The syntax must be converted for use with 233 SLPv1. Instead of a sequence of `\' HEX HEX for each byte in the 234 opaque value, SLPv1 uses radix-64 notation. 236 3. Escape characters are signified differently in SLPv1 and SLPv2. 237 Instead of using excaped byte notation for escaped characters, 238 SLPv1 uses the HTML convention `&' `#' 1*DIGIT `;' is used. 240 2. Service URL Syntax and Semantics 242 This section describes the syntax and semantics of service: URLs. 244 2.1. Service URL Syntax 246 The syntax of the service: URL MUST conform to an 'absolute URI' as 247 defined by [5]. The syntax of a service: URL differs enough from a 248 'generic URI' that it is best to treat it as an opaque URI unless a 249 specific parser for the service: URL is available. 251 All service: URLs have the same syntax up to the 'url-part' The 252 syntax for a service URL depends on the service type following the 253 service scheme. All service: URLs have a 255 The syntax for the field depends upon the service type 256 definition. The field is the service access point, and 257 describes how to access the service. In addition, although 258 both upper case and lower case characters are recognized in the 259 field for convenience, the name is case-folded into 260 lower case. Service types are therefore not distinguished on the 261 basis of case, so, for example, "http" and "HTTP" designate the same 262 service type. This is consistent with general URL practice, as 263 outlined in [5]. 265 The ABNF for a service: URL is: 267 service: URL = "service:" service-type ":" sap 268 service-type = abstract-type ":" url-scheme / concrete-type 269 abstract-type = type-name [ "." naming-auth ] 270 concrete-type = protocol [ "." naming-auth ] 271 type-name = resname 272 naming-auth = resname 273 url-scheme = resname 274 ; A recognized URL scheme name, standardized 275 ; either through common practice or through 276 ; approval of a standards body. 277 resname = alpha [ 1*(alpha / digit / "+" / "-") ] 278 sap = site [url-part] 279 site = ipsite / atsite / ipxsite 280 ipsite = "//" [ [ user "@" ] hostport ] 281 hostport = host [ ":" port ] 282 host = hostname / hostnumber 283 hostname = *( domainlabel "." ) toplabel 284 alphanum = alpha / digit 285 domainlabel = alphanum / alphanum *[alphanum / "-"] alphanum 286 toplabel = alpha / alpha *[ alphanum / "-" ] alphanum 287 hostnumber = ipv4-number / ipv6-number 288 ipv4-number = 1*3digit 3("." 1*3digit) 289 ipv6-number = 32hex 290 3digit = digit digit digit 291 port = 1*digit 292 ; A port number must be included if the 293 ; protocol field does not have an IANA 294 ; assigned port number. 295 user = *[ uchar / ";" / "+" / "&" / "=" ] 296 ipxsite = "/ipx/" ipx-net ":" ipx-node ":" ipx-socket 297 ipx-net = 8 HEXDIGIT 298 ipx-node = 12 HEXDIGIT 299 ipx-socket = 4 HEXDIGIT 300 atsite = "/at/" at-object ":" at-type "" at-zone 301 at-object = 1*31apple-char 302 at-type = 1*31apple-char 303 at-zone = 1*31apple-char 304 apple-char = alpha / digit / safe / escaped 305 = ; AppleAscii [7] values that are not 306 = ; from the restricted range must be escaped. 307 = ; NOTE: The escaped values do NOT correspond 308 = ; to UTF8 values here: They are AppleAscii 309 = ; bytes. 310 url-part = [ url-path ] [ attr-list ] 311 url-path = 1 * ( "/" *xchar ) 312 ; Each service type must define its 313 ; own syntax consistent 314 ; with [5]. 315 attr-list = 1 * ( ";" attr-asgn ) 316 attr-asgn = attr-id / attr-id "=" attr-value 317 safe = "$" / "-" / "_" / "." / "~" 318 extra = "!" / "*" / "'" / "(" / ")" / "," / "+" 319 uchar = unreserved / escaped 320 xchar = unreserved / reserved / escaped 321 escaped = "%" hex hex 322 hex "a" / "b" / "c" / "d" / "e" / digit 323 reserved = ";" / "/" / "?" / ":" / "@" / "&" / "=" / "+" 324 unreserved = alpha / digit / safe / extra 326 IPX addresses [14] are composed of a network, node and socket number. 327 The IPX network number is a four-byte number, in network order and 328 expressed in hexadecimal, that signifies an IPX subnet. The node 329 element represents a network interface card. It is a six-byte 330 number, expressed in hexadecimal, that is usually the same as the 331 node ID of the interface card. The socket element represents a 332 specific service access point, given an IPX network and node. IPX 333 sockets are analogous to TCP/IP ports, and are not to be confused 334 with Berkely sockets. 336 AppleTalk addresses [10] are composed of an object, type and 337 zone. The object is a human readable string. The type is an 338 identifier, not intentended for human readability. The zone refers 339 to the AppleTalk Zone name, which is also human readable. The 340 characters composing these names are drawn from the AppleAscii 341 character set [7]. Thus, they do not equate to escaped ASCII or UTF8 342 characters. The characters "=" and "*" are reserved and may not be 343 included in the names even in binary form. 345 In cases besides the AppleTalk grammar, some characters must be 346 escaped before use. To escape any character, precede the two digits 347 indicating its ASCII value by '%'. 349 2.2. Service URL Semantics 351 The service scheme-specific information following the "service:" 352 URL scheme identifier provides information necessary to access the 353 service. As described in the previous subsection, the form of a 354 service: URL is as follows: 356 service: URL = "service:" service-type ":" site url-path 358 where has one of the following forms could refer to an 359 , or if the service URL locates to an 360 IP, IPX or AppleTalk service access point, respectively. 362 As discussed in Section 1, the can be either a 363 concrete protocol name, or an abstract type name. 365 The field is typically either a domain name (DNS) or an IP 366 network protocol address for the service, and possibly a port number. 367 Note that use of DNS hostnames is preferred for ease of renumbering. 368 The field can be null if other information in the service URL 369 or service attributes is sufficient to use the service. 371 The field allows more information to be provided (by way of 372 and ) that can uniquely locate the service 373 or resource if the is not sufficient for that purpose. or 374 resource if the is not sufficient for that purpose. For 375 IP addresses, the field begins with "//". Other address 376 families supported are IPX [14] and AppleTalk [10]. 378 An field appears at the end of the field, 379 but is never required to exist in any service location registration. 380 The field is composed of a list of semicolon (";") 381 separated attribute assignments of the form: 383 attr-id "=" attr-value 385 or for keyword attributes: 387 attr-id 389 Attributes are part of service: URLs when the attributes are required 390 to access a particular service. For instance, an ACAP [13] service 391 might require that the client authenticate with it through Kerberos. 392 Including an attribute in the service registration allows the ACAP 393 client to make use of the correct SASL [12] authentication mechanism. 394 The ACAP server's registration might look like: 396 service:acap://some.where.net;authentication=KERBEROSV4 398 Note that there can be other attributes of an ACAP server which 399 are not appropriate to include in the URL. For instance, the list 400 of users who have access to the server is useful for selecting an 401 ACAP server, but is not required for a client to use the registered 402 service. 404 Attributes associated with the service: URL are not typically 405 included in the service: URL. They are stored and retrieved using 406 other mechanisms. The service: URL is uniquely identified with a 407 particular service agent or resource, and is used when registering or 408 requesting the attribute information. The Service Location Protocol 409 specifies how such information is registered by network services and 410 obtained by client software. 412 2.3. Use of service: URLs 414 The service: URL is intended to allow arbitrary client/server and 415 peer to peer systems to make use of a standardized dynamic service 416 access point discovery mechanism. 418 It is intended that service: URLs be selected according to the 419 suitability of associated attributes. A client application can 420 obtain the URLs of several services of the same type and distinguish 421 the most preferable among them by means of their attributes. The 422 client uses the service: URL to communicate directly to a service. 424 Attributes are specified with a formal service template syntax 425 described in Section 3. If a service: URL registration includes 426 attributes, the registering agent SHOULD also keep track of the 427 attributes which characterize the service. 429 Registrations can be checked against the formal attribute 430 specification defined in the template by the client or agent 431 representing the client. Service registration are typically done 432 using the Service Location Protocol [11] (SLP). SLP provides a 433 mechanism for service: URLs to be obtained dynamically, according to 434 the service's attributes. 436 It is also possible to obtain service: URLs from documents and using 437 other protocols. In this case, the URL may not be accompanied by 438 the service attributes. The context in which the URL appears should 439 make it clear, if possible, when the service is appropriate to use. 440 For example, in a mail message, a service might be recommended for 441 use when the user is in a branch office. Or, an HTML document might 442 include a service: URL as a pointer to a service, describing in text 443 what the service does and who is authorized to use it. 445 2.4. Specifying the Service Type-Specific URL Syntax 447 When a service type is specified, the specification includes the 448 definition of the syntax for all URLs that are registered by services 449 of that particular type. For instance, the "lpr" service type may be 450 defined with service: URLs in the following form: 452 service:printer:lpr://
/ 454 The section of the URL after the address of the printer: 456 "/" 458 is specific to the lpr service type and corresponds to the 459 field of the general service: URL syntax. This part is 460 specified when the lpr service type is specified. 462 2.5. Accommodating Abstract Service Types 464 An abstract service type is a service type that can be implemented by 465 a variety of different service agents. 467 In order to register an service: URL for an abstract service type the 468 'abstract-type' grammar rule described in section 3.1 is used. This 469 will result in a URL which includes enough information to use the 470 service, namely, the protocol, address and path information. Unlike 471 'concrete' service: URLs, however, the service type is not enough 472 to determine the service access. Rather, an abstract service type 473 denotes a class of service types. The following subsection discusses 474 this point in more detail. 476 2.5.1. Advertising Abstract Service Types 478 Some services may make use of several protocols that are in common 479 use and are distinct services in their own right. In these cases an 480 abstract service type is appropriate. What is essential is that all 481 the required information for the service is clearly defined. 483 For example, suppose a network service is being developed for 484 dynamically loading device drivers. The client requires the 485 following three pieces of information before it can successfully load 486 and instantiate the driver: 488 1. The protocol used to load the driver code, for example, "ftp", 489 "http" or "tftp" 491 2. A pathname identifying where the driver code is located, for 492 example "/systemhost/drivers/diskdrivers.drv", 494 3. The name of the driver, for example, "scsi". 496 The temptation is to form the first two items into a URL and embed 497 that into a service: URL. As an example which should be avoided, 499 service:ftp:/x3.bean.org/drivers/diskdrivers.drv;driver=scsi 501 is a service: URL which seems to indicate where to obtain the driver. 503 Rather, an abstract service-type SHOULD be used. The service type is 504 not "ftp", as the example indicates. Rather, it is "device-drivers". 505 The service: URL that should be used, consistent with the rules in 506 section [5], is the following: 508 service:device-drivers:ftp://x3.bean.org/drivers/diskdrivers.drv; 509 driver=scsi;platform=sys3.2-rs3000 511 Other URLs for the same service using other protocols are also 512 supported, as in: 514 service:device-drivers:tftp://x2.bean.org/vol3/disk/drivers.drv; 515 driver=scsi;platform=sys3.2-rs3000 517 service:device-drivers:http://www.bean.org/drivers/drivpak.drv; 518 driver=scsi;platform=sys3.2-rs3000 520 Using SLP, a search for the service type "device-drivers" may return 521 all of the three URLs listed above. The client selects the most 522 appropriate access protocol for the desired resource. 524 The fundamental requirement is that the abstract service type MUST 525 be well specified. This requirement is imposed so that program code 526 or human users have enough information to access the service. In 527 every case, a well-specified abstract type will include either an 528 access protocol and a network address where the service is available, 529 or an embedded URL for a standardized URL scheme that describes 530 how to access the service. In the example above, there are three 531 further requirements: A URL path is included for access protocols 532 indicating the document to download, and two attributes are included 533 to characterize the driver. 535 3. Syntax and Semantics of Service Type Specifications 537 Service type specifications are documents in a formal syntax defining 538 properties important to service registration. These properties are: 540 1. General information on the service type specification itself, 542 2. The syntax of the service type-specific part of the service URL, 544 3. The definition of attributes associated with a service. 546 The service type specification document is the service type template. 548 The following subsections describe the syntax and semantics of 549 service type templates. 551 3.1. Syntax of Service Type Templates 553 Service template documents are encoded in a simple form. They may 554 be translated into any language or character set, but the template 555 used for standardization MUST be encoded in the 0x00-0x7F subrange of 556 UTF8 [17] (which corresponds to ASCII character encoding) and be in 557 English. 559 A template document begins with a block of text assigning values to 560 five document identification items. The five identification items 561 can appear in any order within the block, but conventionally the 562 "type" item, which assigns the service type name, occurs at the very 563 top of the document in order to provide context for the rest of 564 the the document. The attribute definition item occurs after the 565 document identification items. 567 All items end with a blank line. The reserved characters are ";", 568 "%", "=", ",", "#", LF, and CR. Reserved characters MUST be escaped. 569 The escape sequence is the same as described in [5]. 571 The service template is encoded in a UTF8 character set, but 572 submitted as a part of an internet-draft, which is encoded in ASCII 573 characters. All characters which are outside of the ASCII range MUST 574 be escaped using the % HEX HEX syntax. For example, the letter e 575 accent aigue would be represented as "%c3%a9". Unfortunately, this 576 will detract from the readability of the service template in the 577 service template submission. Hopefully some public domain tools will 578 emerge for translating escaped UTF8 characters into humanly readable 579 ones. 581 Values in value lists are separated by commas. A value list is 582 terminated by a newline not preceded by a comma. If the newline is 583 preceded by a comma, the value list is interpreted to continue onto 584 the next line. 586 Attribute identifiers, attribute type names, and flags are all 587 case insensitive. For ease of presentation, upper and lower case 588 characters can be used to represent these in the template document. 589 Newlines are significant in the grammar. They delimit one item from 590 another, as well as separating parts of items internally. 592 String values are considered to be a sequence of non-whitespace 593 tokens potentially with embedded whitespace, separated from each 594 other by whitespace. Commas delimit lists of strings. String values 595 are trimmed so as to reduce any sequence of white space interior to a 596 string to a single white space. Preceding or trailing white space is 597 removed. For example: 599 " some value , another example " 601 is trimmed to 603 "some value" and "another example". 605 Note that there can be no ambiguity in string tokenization because 606 values in value lists are separated by a comma. String tokens are 607 not delimited by double quotes (") as is usually the case with 608 programming languages. 610 Attribute tags and values are useful for directory look-up. In this 611 case, decoding of character escapes and trimming white space MUST 612 be performed before string matching. In addition, string matching 613 SHOULD be case insensitive. 615 Templates obey the following ABNF [9] grammar: 617 template = tem-attrs attr-defs 618 tem-attrs = schemetype schemevers schemetext schemeurl 619 schemetype = "type" "=" scheme termdef 620 schemevers = "version" "=" version-no termdef 621 schemetext = "description" "=" newline desc-text termdef 622 schemeurl = "url-syntax" "=" newline url-bnf termdef 623 url-bnf = *[ com-chars ] 624 ; An ABNF describing the production 625 ; in the service: URL grammar of Section 2.1. 626 scheme = service-type [ "." naming-auth ] 627 service-type = scheme-name 628 naming-auth = scheme-name 629 scheme-name = alpha [1*schemechar] [ "." 1*schemechar ] 630 schemechar = alpha / digit / "-" / "+" / 631 version-no = 1*digit "." 1*digit 632 langtag = 2*lower-alpha ;see [3] 633 desc-text = *[ com-chars ] 634 ; A block of free-form text for reading by 635 ; people describing the service in a short, 636 ; informative manner. 637 termdef = newline newline 638 attr-defs = *( attr-def / keydef ) 639 attr-def = id "=" attrtail 640 keydef = id "=" "keyword" newline [help-text] newline 641 attrtail = type flags newline [value-list] [help-text] 642 [value-list] newline 643 id = 1*attrchar 644 type = "string" / "integer" / "boolean" / "opaque" 645 flags = ["m"/"M"] ["l"/"L"] ["o"/"O"] ["x"/"X"] 646 value-list = value newline / value "," value-list / 647 value "," newline value-list 648 help-text = 1*( "#" help-line ) 649 ; A block of free-form text for reading by 650 ; people describing the attribute and 651 ; its values. 652 help-line = *[ com-chars ] newline 653 attrchar = schemechar / ":" / "_" / "$" / "~" / "@" / "." / 654 "|" / "<" / ">" / "*" / "&" 655 value = string / integer / boolean / opaque 656 string = safe-char *[safe-char / white-sp] safe-char 657 integer = [ "+" | "-" ] 1*DIGIT 658 boolean = "true" / "false" 659 opaque = 1*( `\' HEX HEX ) 660 ; Each byte of opaque value is hex encoded. 661 ; Newlines are ignored in decoding opaque 662 ; values. 663 com-chars = safe-char / white-sp / "," / ";"/ "%" 664 safe-char = attrchar / escaped / " " / "!" / '"' / "'" / 665 "|" / "(" / ")" / "+" / "-" / "." / ":" / 666 "=" / "?" / "[" / "]" / "{" / "/" / "{" / 667 "$" 668 ; All UTF8 printable characters are 669 ; included except ",", "%", ";", and "#". 670 escaped = "%" HEX HEX 671 white-sp = SPACE / HT 672 newline = CR / ( CR LF ) 674 3.2. Semantics of Service Type Templates 676 The service type template defines the service attributes and service: 677 URL syntax for a particular service type. The attribute definition 678 includes the attribute type, default values, allowed values and other 679 information. 681 3.2.1. Definition of a Service Template 683 There are six items included in the service template. The semantics 684 of each item is summarized below. 686 - type 688 The scheme name of the service scheme. The scheme name consists 689 of the service type name and an optional naming authority name, 690 separated from the service type name by a period. See 3.2.2 for 691 the conventions governing service type names. 693 - version 695 The version number of the service type specification. 697 - description 699 A description of the service suitable for inclusion in text read 700 by people. 702 - url-syntax 704 The syntax of the service type-specific URL part of the service: 705 URL. 707 - attribute definitions 709 A collection of zero or more definitions for attributes 710 associated with the service in service registrations. 712 Each of the following subsections deals with one of these items. 714 3.2.2. Service Type 716 The service scheme consists of the service type name and an optional 717 naming authority name separated from the service type name by a 718 period. The service scheme is a string that is appended to the 719 'service:' URL scheme identifier, and is the value of the "type" 720 item in the template document. If the naming authority name is 721 absent it is assumed to be IANA. 723 3.2.3. Version Number 725 The version number of the service type template is the value of the 726 "version" item. A draft proposal starts at 0.0, and the minor number 727 increments once per revision. A standardized template starts at 1.0. 728 Additions of optional attributes add one to the minor number, and 729 additions of required attributes, changes of definition, or removal 730 of attributes add one to the major number. The intent is that an 731 old service template still accurately, if incompletely, defines the 732 attributes of a service registration if the template only differs 733 from the registration in its minor version. See Section 4 for more 734 detail on how to use the version attribute. 736 3.2.4. Description 738 The description is a block of text readable by people in the language 739 of the template and is the value of the "description" item. It 740 should be sufficient to identify the service to human readers and 741 provide a short, informative description of what the service does. 743 If the service type corresponds to a particular protocol, the 744 protocol specification must be cited here. The protocol need not be 745 a standardized protocol. The template might refer to a proprietary 746 specification, and refer the reader of the template to a contact 747 person for further information. 749 3.2.5. Syntax of the Service Type-specific URL Part 751 The syntax of the service type-specific part of the service: 752 URL is provided in the template document as the value of the 753 "url-syntax" item. The field of the service: URL is 754 designed to provide additional information to locate a service when 755 the field is not sufficient. The field 756 distinguishes URLs of a particular service type from those of another 757 service type. For instance, in the case of the lpr service type, the 758 must include the queue name [15], but other service types 759 may not require this information. 761 The syntax for the field MUST accompany the definition 762 of a new service type, unless the URL scheme has already been 763 standardized and is not a service: URL. The syntax is included in the 764 template document as an ABNF [9] following the rules for URL syntax 765 described in [5]. There is no requirement for a service scheme to 766 support a . The field can be very simple, 767 or even omitted. If the URL scheme has already been standardized, 768 the "url-syntax" item SHOULD include a reference to the appropriate 769 standardization documents. Abstract service types may defer this 770 field to the template documents describing their concrete instances. 772 3.2.6. Attribute Definition 774 The bulk of the template is typically devoted to defining service 775 type-specific attributes. An attribute definition precisely 776 specifies the attribute's type, other restrictions on the attribute 777 (whether it is multi-valued, optional, etc), some text readable by 778 people describing the attribute, and lists of default and allowed 779 values. The only required information is the attribute's type, the 780 rest are optional. Registration, deregistration and the use of 781 attributes in queries can be accomplished using the Service Location 782 Protocol [11] or other means, and discussion of this is beyond the 783 scope of the document. 785 Attributes are used to convey information about a given service for 786 purposes of differentiating different services of the same type. 787 They convey information to be used in the selection of a particular 788 service to establish communicate with, either through a program 789 offering a human interface or programmatically. Attributes can be 790 encoded in different character sets and in different languages. The 791 procedure for doing this is described in Section 6. 793 An attribute definition begins with the specification of the 794 attribute's identifier and ends with a single empty line. Attributes 795 definitions have five components (in order of appearance in a 796 definition): 798 1. An attribute identifier which acts as the name of the attribute, 800 2. Attribute descriptors (type and flags), 802 3. An optional list of values which are assigned to the attribute by 803 default, 805 4. An optional block of text readable by people providing a short, 806 informative description of the attribute, 808 5. An optional list of allowed values which restrict the value or 809 values the attribute can take on. 811 3.2.6.1. The Attribute Identifier 813 An attribute definition starts with the specification of the 814 attribute's identifier. The attribute's identifier functions as the 815 name of the attribute. Note that the characters used to compose an 816 attribute identifier are restricted to those characters considered 817 unrestricted for inclusion in a URL according to [5]. The reason 818 is that services can display prominent attributes in their service: 819 URL registrations. Each attribute identifier must be unique in the 820 template. Since identifiers are case folded, upper case and lower 821 case characters are the same. 823 3.2.6.2. The Attribute Type 825 Attributes can have one of five different types: string, integer, 826 boolean, opaque, or keyword. The attribute's type specification is 827 separated from the attribute's identifier by an equal sign ("=") and 828 follows the equal sign on the same line. The string, signed integer, 829 and boolean types have the standard programming language or database 830 semantics. Integers are restricted to those signed values that can 831 be represented in 32 bits. The character set used to represent 832 strings is not specified at the time the template is defined, but 833 rather is determined by the service registration. Booleans have the 834 standard syntax. Opaques are byte escaped values that can be used 835 to represent any other kind of data. Keywords are attributes that 836 have no characteristics other than their existence (and possibly the 837 descriptive text in their definition). 839 Keyword and boolean attributes impose restrictions on the following 840 parts of the attribute definition. Keyword attribute definitions 841 MUST have no flag information following the type definition, nor any 842 default or allowed values list. Boolean attributes are single value 843 only, i.e., multi-valued boolean attributes are not allowed. 845 3.2.6.3. Attribute Flags 847 Flags determine other characteristics of an attribute. With the 848 exception of keyword attributes, which may not have any flags, 849 flags follow the attribute type on the same line as the attribute 850 identifier, and are separated from each other by whitespace. Flags 851 may appear in any order after the attribute type. Other information 852 must not follow the flags, and only one flag identifier of a 853 particular flag type is allowed per attribute definition. 855 The semantics of the flags are as follows: 857 - o or O 859 Indicates that the attribute is optional. If this flag is 860 missing, the attribute is required in every service registration. 862 - m or M 864 Indicates that the attribute can take on multiple values. If 865 this flag is present, every value in a multi-valued attribute 866 has the same type as the type specified in the type part of the 867 attribute definition. Boolean attributes must not include this 868 flag. 870 - l or L 872 Indicates that attribute is literal, i.e. is not meant to be 873 translated into other languages. If this flag is present, the 874 attribute is not considered to be readable by people and should 875 not be translated when the template is translated. See Section 6 876 for more information about translation. 878 - x or X 880 Indicates that clients SHOULD include the indicated attribute 881 in requests for services. Neglecting to include this attribute 882 will not sufficiently differentiate the service. If services are 883 obtained without selecting this attribute they will quite likely 884 be useless to the client. 886 The values for multivalued attributes are an unordered set. 887 Deletions of individual values from a multivalued attribute are not 888 supported, and deletion of the attribute causes the entire set of 889 values to be removed. 891 3.2.6.4. Default Value or List 893 If the attribute definition includes a default value or, in the 894 case of multivalued attributes, a default values list, it begins 895 on the second line of the attribute definition and continues 896 over the following lines until a line ends without a comma. As a 897 consequence, newlines cannot be embedded in values unless escaped. 898 See Section 2.1. 900 Particular attribute types and definitions restrict the default 901 values list. Keyword attributes must not have a list of defaults. 902 If an optional attribute's definition has an allowed values list, 903 then a default value or list is not optional but required. The 904 motivation for this is that defining an attribute with an allowed 905 values list is meant to restrict the values the attribute can take 906 on, and requiring a default value or list assures that the default 907 value is a member of the given set of allowed values. 909 The default value or list indicates what values the attribute is 910 given if no values are assigned to the attribute when a service 911 is registered. If an optional attribute's definition includes no 912 default value or list, the following defaults are assigned: 914 1. String values are assigned the empty string, 916 2. Integer values are assigned zero, 918 3. Boolean values are assigned false, 920 4. Opaque values are assigned a byte array containing no values, 922 5. Multi-valued attributes are initialized with a single value. 924 For purposes of translating nonliteral attributes, the default values 925 list is taken to be an ordered set, and translations MUST maintain 926 that order. 928 3.2.6.5. Descriptive Text 930 Immediately after the default values list, if any, a block of 931 descriptive text SHOULD be included in the attribute definition. 932 This text is meant to be readable by people, and should include 933 a short, informative description of the attribute. It may also 934 provide additional information, such as a description of the allowed 935 values. This text is primarily designed for display by interactive 936 browsing tools. The descriptive text is set off from the surrounding 937 definition by a crosshatch character ("#") at the beginning of 938 the line. The text should not, however, be treated as a comment 939 by parsing and other tools, since it is an integral part of the 940 attribute definition. Within the block of descriptive text, the text 941 is transferred verbatim, including indentation and line breaks, so 942 any formatting is preserved. 944 3.2.6.6. Allowed Values List 946 Finally, the attribute definition concludes with an optional 947 allowed values list. The allowed values list, if any, follows the 948 descriptive text, or, if the descriptive text is absent, the initial 949 values list. The syntax of the allowed values list is identical to 950 that of the initial values list. The allowed values list is also 951 terminated by a line that does not end in a comma. If the allowed 952 values list is present, assignment to attributes is restricted to 953 members of the list. 955 As with the default values list, the allowed values list is also 956 considered to be an ordered set for purposes of translation. 958 3.2.6.7. Conclusion of An Attribute Definition 960 An attribute definition concludes with a single empty line. 962 4. A Process For Standardizing New Service Types 964 New service types can be suggested simply by providing a service type 965 template and a short description about how to use the service. The 966 template MUST have its "version" template attribute set to 0.0. 968 MAJOR revision numbers come before the '.', MINOR revision numbers 969 come after the '.'. 971 The minor version number increments once with each change until it 972 achieves 1.0. There is no guarantee any version of the service 973 template is backward compatible before it reaches 1.0. 975 Once a service template has reached 1.0, the definition is "frozen" 976 for that version. New templates must be defined, of course, to 977 refine that definition, but the following rules must be followed: 979 A MINOR revision number signifies the introduction of a compatible 980 change. A MAJOR revision number signifies the introduction of an 981 incompatible change. This is formalized by the following rules: 983 - Any new optional attribute defined for the template increases 984 the minor version number by one. All other attributes for the 985 version must continue to be supported as before. A client which 986 supports 1.x can still use later versions of 1.y (where x "." "." 1056 Each of these fields are defined in Section 2. They correspond 1057 to the values of the template fields "type", "version" and 1058 "lang". The files for the example templates in this 1059 document are called "foo.0.0.en", "Net-Transducer.0.0.en" and 1060 "Net-Transducer:Thermomoter.0.0.en". See Section A. 1062 The reviewer will ensure that the template submission to IANA has the 1063 correct form and required fields. 1065 No service type template will be accepted for inclusion in the 1066 service template registry unless the submission includes a security 1067 considerations section and contact information for the template 1068 document author. 1070 The IANA will maintain a registry containing both the service type 1071 templates, and the template description document containing the 1072 service type template, including all previous versions. The IANA 1073 will receive notice to include a service template in the registry 1074 by email from the reviewer. This message will include the service 1075 template itself, which is to be registered. 1077 Neither the reviewer nor the IANA will take any position on claims of 1078 copyright or trademark issues with regard to templates. 1080 6. Internationalization Considerations 1082 The service: URL must be encoded using the rules set forth in [5]. 1083 The character set encoding is limited to specific ranges within the 1084 US-ASCII character set [4]. 1086 The template is encoded in UTF8 characters. 1088 6.1. Language Identification and Translation 1090 The language used in attribute strings should be identified 1091 supplying a Language Tag [3] in the Service Template submission (see 1092 Section 5). 1094 A program can translate a service registration from one language to 1095 another provided it has both the template of the language for the 1096 registration and the template of the desired target language. All 1097 standardized attributes are in the same order in both templates. 1098 All non-arbitrary strings, including the descriptive help text, is 1099 directly translatable from one language to another. Non-literal 1100 attribute definitions, attribute identifiers, attribute type names, 1101 attribute flags, and the boolean constants "true" and "false" are 1102 never translated. Translation of attribute identifiers is prohibited 1103 because, as with domain names, they can potentially be part of a 1104 service: URL and therefore their character set is restricted. In 1105 addition, as with variable identifiers in programming languages, they 1106 could become embedded into program code. 1108 All strings used in attribute values are assumed translatable unless 1109 explicitly defined as being literal, so that best effort translation 1110 (see below) does not modify strings which are meant to be interpreted 1111 by a program, not a person. 1113 There are two ways to go about translation: standardization and best 1114 effort. 1116 When the service type is standardized, more than one document can 1117 be submitted for review. One service type description is approved 1118 as a master, so that when a service type template is updated in one 1119 language, all the translations (at least eventually) reflect the same 1120 semantics. 1122 If no document exists describing the standard translation of the 1123 service type, a 'best effort' translation for strings should be done. 1125 7. Security Considerations 1127 Service type templates provide information that is used to interpret 1128 information obtained by the Service Location Protocol. If these 1129 templates are modified or false templates are distributed, services 1130 may not correctly register themselves, or clients might not be able 1131 to interpret service information. 1133 The service: URLs themselves specify the service access point and 1134 protocol for a particular service type. These service: URLs could 1135 be distributed and indicate the location of a service other than 1136 that normally want to used. The Service Location Protocol [11] 1137 distributes service: URLs and has an authentication mechanism that 1138 allows service: URLs of registered services to be signed and for the 1139 signatures to be verified by clients. 1141 Each Service Template will include a security considerations section 1142 which will describe security issues with using the service scheme for 1143 the specific Service Type. 1145 A. Service Template Examples 1147 The text in the template example sections is to be taken as being a 1148 single file. They are completely fictitious (ie. the examples do 1149 not represent real services). 1151 The FOO example shows how to use service templates for an application 1152 that has very few attributes. Clients request the FOO server where 1153 their user data is located by including their user name as the value 1154 of the user attribute. 1156 The Net-Transducer example shows how abstract service types are 1157 defined and how a corresponding concrete instance is defined. A 1158 system might support any of several NetTransducer services. Here we 1159 give only one concrete instance of the abstract type. 1161 It is not necessary to register concrete templates for an abstract 1162 service type if the abstract service type template is completely 1163 clear as to what possible values can be used as a concrete type, and 1164 what their interpretation is. 1166 A.1. FOO 1168 The FOO service template submission example follows: 1170 Name of submitter: "Erik Guttman" 1171 Language of service template: en 1172 Security Considerations: 1173 If the USER and GROUPS attributes are included a 1174 possibility exists that the list of identities for users or groups 1175 can be discovered. This information would otherwise be difficult 1176 to discover. 1177 Template Text: 1178 -------------------------template begins here----------------------- 1179 type=FOO 1181 version=0.0 1182 description= 1183 The FOO service URL provides the location of an FOO service. 1185 url-syntax= 1186 url-path= ; There is no URL path defined for a FOO URL. 1188 users= string M L O 1189 # The list of all users which the FOO server supports. 1191 groups= string M L O 1192 # The list of all groups which the FOO server supports. 1193 --------------------------template ends here------------------------ 1195 A.2. Abstract Service Type: Net-Transducer 1197 An example submission of an abstract service type template is: 1199 Name of submitter: "Erik Guttman" 1200 Language of service template: en 1201 Security Considerations: 1202 See the security considerations of the concrete service types. 1203 Template Text: 1204 -------------------------template begins here----------------------- 1205 type=Net-Transducer 1207 version=0.0 1209 description= 1210 This is an abstract service type. The purpose of the Net- 1211 Transducer service type is to organize into a single category 1212 all network enabled Transducers which have certain properties. 1214 url-syntax= 1215 url-path= ; Depends on the concrete service type. 1216 ; See these templates. 1218 sample-units= string L 1219 # The units of sample that the Transducer provides, for instance 1220 # C (degrees Celsius), V (Volts), kg (Kilograms), etc. 1222 sample-resolution= string L 1223 # The resolution of the Transducer. For instance, 10^-3 means 1224 # that the Transducer has resolution to 0.001 unit. 1226 sample-rate= integer L 1227 # The speed at which samples are obtained per second. For 1228 # instance 1000 means that one sample is obtained every millisecond. 1230 --------------------------template ends here------------------------ 1232 A.3. Concrete Service Type: Net-Transducer:Thermometer 1234 This is another service template submission example, supplying a 1235 concrete service type corresponding to the abstract template above. 1237 Name of submitter: "Erik Guttman" 1238 Language of service template: en 1239 Security Considerations: 1240 There is no authentication of the Transducer output. Thus, 1241 the Thermometer output could easily be spoofed. 1242 Template Text: 1243 -------------------------template begins here----------------------- 1244 type=service:Net-Transducer:Thermometer 1246 version=0.0 1248 description= 1249 The Thermometer is a Net-Transducer capable of reading temperature. 1250 The data is read by opening a TCP connection to one of the ports 1251 in the service URL and reading an ASCII string until an NULL 1252 character is encountered. The client may continue reading data at 1253 no faster than the sample-rate, or close the connection. 1255 url-syntax= 1256 url-path = ; ports 1257 port-list = ";ports=" port-list 1258 ports = port / port "," ports 1259 ; See the Service URL production rule. 1260 ; These are the ports connections can be made on. 1262 location-description=string 1263 # The location where the Thermometer is located. 1265 operator=string O 1266 # The operator to contact to have the Thermometer serviced. 1268 --------------------------template ends here------------------------ 1270 A.4. service: URLs and SLP 1272 A user with an FOO enabled calendar application should not be 1273 bothered with knowing the address of their FOO server. The 1274 calendar client program can use SLP to obtain the FOO service: URL 1275 automatically, say 'service:foo://server1.nosuch.org', by issuing 1276 a Service Request. In the event that this FOO server failed, the 1277 Calendar client can issue the same service request again to find the 1278 backup FOO server, say 'service:foo://server2.nosuch.org'. In both 1279 cases, the service: URL conforms to the FOO service template as do 1280 the associated attributes (user and group.) 1282 A network thermometer could be advertised as: 1284 URL = service:net-transducer:thermometer://v33.test/ports=3211 1285 Attributes = (location-description=Missile bay 32), 1286 (operator=Joe Agent), (sample-units=C), 1287 (sample-resolution=10^-1),(sample-rate=10) 1289 This might be very useful for a technician who wanted to find a 1290 Thermometers in Missile bay 32, for example. 1292 B. Full Copyright Statement 1294 Copyright (C) The Internet Society (1997). All Rights Reserved. 1296 This document and translations of it may be copied and furnished to 1297 others, and derivative works that comment on or otherwise explain it 1298 or assist in its implmentation may be prepared, copied, published 1299 and distributed, in whole or in part, without restriction of any 1300 kind, provided that the above copyright notice and this paragraph 1301 are included on all such copies and derivative works. However, 1302 this document itself may not be modified in any way, such as by 1303 removing the copyright notice or references to the Internet Society 1304 or other Internet organizations, except as needed for the purpose 1305 of developing Internet standards in which case the procedures 1306 for copyrights defined in the Internet Standards process must be 1307 followed, or as required to translate it into languages other than 1308 English. 1310 The limited permissions granted above are perpetual and will not be 1311 revoked by the Internet Society or its successors or assigns. 1313 This document and the information contained herein is provided on an 1314 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 1315 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 1316 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 1317 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 1318 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." 1320 C. Acknowledgments 1322 Thanks to Michael Day and Leland Wallace for assisting with the IPX 1323 and AppleTalk address syntax portions. Ryan Moats provided valuable 1324 feedback throughout the writing of this document. 1326 References 1328 [1] Protocol and service names, October 1994. 1329 ftp://ftp.isi.edu/in-notes/iana/assignments/service-names. 1331 [2] Port numbers, July 1997. 1332 ftp://ftp.isi.edu/in-notes/iana/assignments/port-numbers. 1334 [3] H. Alvestrand. Tags for the Identification of Languages. RFC 1335 1766, March 1995. 1337 [4] ANSI. Coded Character Set -- 7-bit American Standard code for 1338 Information Interchange. X3.4-1986, 1986. 1340 [5] T. Berners-Lee, R. Fielding, and L. Masinter. Uniform Resource 1341 Identifiers (URI): Generic Syntax. RFC 2396, August 1998. 1343 [7] Apple Computer. Inside Macintosh: Text. Addison-Wesley, 1993. 1345 [8] D. Crocker and P. Overell. Augmented BNF for Syntax 1346 Specifications: ABNF. RFC 2234, November 1997. 1348 [9] D. Crocker and P. Overell. Augmented BNF for Syntax 1349 Specifications: ABNF. draft-ietf-drums-abnf-04.txt, September 1350 1997. (work in progress). 1352 [10] S. Gursharan, R. Andrews, and A. Oppenheimer. Inside AppleTalk. 1353 Addison-Wesley, 1990. 1355 [11] E. Guttman, C. Perkins, J. Veizades, and M. Day. Service 1356 Location Protocol version 2. draft-ietf-svrloc-protocol-v2-04.txt, 1357 March 1998. (work in progress). 1359 [12] J. Myers. Simple Authentication and Security Layer (SASL). RFC 1360 2222, October 1997. 1362 [13] C. Newman and J. G. Myers. ACAP -- Application Configuration 1363 Access Prototol. RFC 2244, November 1997. 1365 [14] Novell, Inc. IPX RIP and SAP Router Specification. Part Number 1366 107-000029-001, Version 1.30, May 1996. 1368 [15] Pete St. Pierre. Definition of lpr: URLs for use with Service 1369 Location. draft-ietf-svrloc-lpr-scheme-01.txt, December 1997. 1370 (work in progress). 1372 [16] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service 1373 Location Protocol. RFC 2165, July 1997. 1375 [17] F. Yergeau. UTF-8, a transformation format of ISO 10646. RFC 1376 2279, January 1998. 1378 Authors' Addresses 1380 Questions about this memo can be directed to: 1382 Erik Guttman Charles E. Perkins James Kempf 1383 Sun Microsystems Sun Microsystems Sun Microsystems 1384 Bahnstr. 2 901 San Antonio Rd. 901 San Antonio Rd. 1385 74915 Waibstadt Palo Alto, CA, 94303 Palo Alto, CA, 94303 1386 Germany USA USA 1387 +49 7263 911484 +1 650 786 6464 +1 650 786 5890 1388 +1 650 786 5992 +1 650 786 6445 (fax) +1 650 786 6445 (fax) 1389 erik.guttman@sun.com charles.perkins@sun.com james.kempf@sun.com