Service Location Working Group James Kempf INTERNET DRAFT Erik Guttman 30 May 1998 Sun Microsystems An API for Service Location draft-ietf-svrloc-api-05.txt Status of This Memo This document is a submission by the Service Location Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the srvloc@srvloc.org mailing list. Distribution of this memo is unlimited. This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``work in progress.'' To view the entire list of current Internet-Drafts, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this memo is unlimited. Abstract The Service Location Protocol (SLP) provides a new way for clients to dynamically discovery network services. With SLP, it is simple to offer highly available services that require no user configuration or assistance from network administrators prior to use. This document describes standardized API's for SLP in C and Java. The API's are modular and are designed to allow implementions to offer just the feature set needed. In addition, standardized file formats for configuration and serialized registrations are defined, allowing SLP agents to set network and other parameters in a portable way. The serialized file format allows legacy services to be registered with SLP directory agents in cases where modifying the legacy service Kempf, Guttman Expires 30 October 1998 [Page i]
Internet Draft Service Location API 30 May 1998 program code is difficult or impossible, and to portably exchange a registration database. Kempf, Guttman Expires 30 October 1998 [Page ii]
Internet Draft Service Location API 30 May 1998 Contents Status of This Memo i Abstract i 1. Introduction 1 1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 2. File Formats 4 2.1. Configuration File Format . . . . . . . . . . . . . . . . 5 2.1.1. DA configuration . . . . . . . . . . . . . . . . 6 2.1.2. Static Scope Configuration . . . . . . . . . . . 6 2.1.3. Tracing and Logging . . . . . . . . . . . . . . . 7 2.1.4. Serialized Proxy Registrations . . . . . . . . . 8 2.1.5. Networking Configuration Parameters . . . . . . . 8 2.1.6. UA Configuration . . . . . . . . . . . . . . . . 10 2.1.7. Security . . . . . . . . . . . . . . . . . . . . 10 2.2. Serialized Registration File . . . . . . . . . . . . . . 11 2.3. Proccessing Serialized Registration and Configuration Files . . . . . . . . . . . . . . . . . . . . . . . . 12 3. Binding Independent Implementation Considerations 13 3.1. Multithreading . . . . . . . . . . . . . . . . . . . . . 13 3.2. Asynchronous and Incremental . . . . . . . . . . . . . . 13 3.3. Type Checking for Service Types . . . . . . . . . . . . . 13 3.4. Refreshing Registrations . . . . . . . . . . . . . . . . 13 3.5. Configuration File Processing . . . . . . . . . . . . . . 14 3.6. Attribute Types . . . . . . . . . . . . . . . . . . . . . 14 3.7. Removal of Duplicates . . . . . . . . . . . . . . . . . . 14 3.8. Character Set Encoding . . . . . . . . . . . . . . . . . 14 3.9. Error Semantics . . . . . . . . . . . . . . . . . . . . . 15 3.10. Modular Implementations . . . . . . . . . . . . . . . . . 18 3.11. Scope Discovery and Handling . . . . . . . . . . . . . . 18 4. C Language Binding 19 4.1. Constant Types . . . . . . . . . . . . . . . . . . . . . 19 4.1.1. URL Lifetimes . . . . . . . . . . . . . . . . . . 19 4.1.2. Error Codes . . . . . . . . . . . . . . . . . . . 20 4.1.3. SLPBoolean . . . . . . . . . . . . . . . . . . . 21 4.2. Struct Types . . . . . . . . . . . . . . . . . . . . . . 21 4.2.1. SLPSrvURL . . . . . . . . . . . . . . . . . . . . 21 4.2.2. SLPHandle . . . . . . . . . . . . . . . . . . . . 22 4.3. Callbacks . . . . . . . . . . . . . . . . . . . . . . . . 22 4.3.1. SLPRegReport . . . . . . . . . . . . . . . . . . 23 Kempf, Guttman Expires 30 October 1998 [Page iii]
Internet Draft Service Location API 30 May 1998 4.3.2. SLPSrvTypeCallback . . . . . . . . . . . . . . . 24 4.3.3. SLPSrvURLCallback . . . . . . . . . . . . . . . . 25 4.3.4. SLPAttrCallback . . . . . . . . . . . . . . . . . 26 4.4. Opening and Closing the SLP Library . . . . . . . . . . . 27 4.4.1. SLPOpen . . . . . . . . . . . . . . . . . . . . . 27 4.4.2. SLPClose . . . . . . . . . . . . . . . . . . . . 28 4.5. Protocol API . . . . . . . . . . . . . . . . . . . . . . 29 4.5.1. SLPReg . . . . . . . . . . . . . . . . . . . . . 29 4.5.2. SLPDereg . . . . . . . . . . . . . . . . . . . . 31 4.5.3. SLPDelAttrs . . . . . . . . . . . . . . . . . . . 32 4.5.4. SLPFindSrvTypes . . . . . . . . . . . . . . . . . 33 4.5.5. SLPFindSrvs . . . . . . . . . . . . . . . . . . . 34 4.5.6. SLPFindAttrs . . . . . . . . . . . . . . . . . . 36 4.6. Miscellaneous Functions . . . . . . . . . . . . . . . . . 37 4.7. SLPFindScopes . . . . . . . . . . . . . . . . . . . . . . 37 4.8. SLPParseSrvURL . . . . . . . . . . . . . . . . . . . . . 38 4.9. SLPFree . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.10. SLPEscape . . . . . . . . . . . . . . . . . . . . . . . . 40 4.11. SLPUnescape . . . . . . . . . . . . . . . . . . . . . . . 41 4.12. SLPGetProperty . . . . . . . . . . . . . . . . . . . . . 42 4.13. SLPSetProperty . . . . . . . . . . . . . . . . . . . . . 42 4.14. Implementation Notes . . . . . . . . . . . . . . . . . . 43 4.14.1. Refreshing Registrations . . . . . . . . . . . . 43 4.14.2. Syntax for String Parameters . . . . . . . . . . 43 4.14.3. Client Side Syntax Checking . . . . . . . . . . . 44 4.14.4. System Properties . . . . . . . . . . . . . . . . 44 4.14.5. Memory Management . . . . . . . . . . . . . . . . 44 4.14.6. Asychronous and Incremental Return Semantics . . 45 4.15. Examples . . . . . . . . . . . . . . . . . . . . . . . . 45 4.15.1. Discovering one's mailbox . . . . . . . . . . . . 45 5. Java Language Binding 49 5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 49 5.2. Exceptions and Errors . . . . . . . . . . . . . . . . . . 49 5.2.1. Class ServiceLocationException . . . . . . . . . 50 5.3. Basic Data Structures . . . . . . . . . . . . . . . . . . 51 5.3.1. Interface ServiceLocationEnumeration . . . . . . 51 5.3.2. Class ServiceLocationAttribute . . . . . . . . . 51 5.3.3. Class ServiceType . . . . . . . . . . . . . . . . 54 5.3.4. Class ServiceURL . . . . . . . . . . . . . . . . 56 5.4. SLP Access Interfaces . . . . . . . . . . . . . . . . . . 59 5.4.1. Interface Advertiser . . . . . . . . . . . . . . 59 5.4.2. Interface Locator . . . . . . . . . . . . . . . . 62 5.5. The Service Location Manager . . . . . . . . . . . . . . 65 5.5.1. Class ServiceLocationManager . . . . . . . . . . 65 5.6. Service Template Introspection . . . . . . . . . . . . . 67 5.6.1. Abstract Class TemplateRegistry . . . . . . . . . 67 5.6.2. Interface ServiceLocationAttributeVerifier . . . 69 5.6.3. Interface ServiceLocationAttributeDescriptor . . 72 Kempf, Guttman Expires 30 October 1998 [Page iv]
Internet Draft Service Location API 30 May 1998 5.7. Implementation Notes . . . . . . . . . . . . . . . . . . 75 5.7.1. Refreshing Registrations . . . . . . . . . . . . 75 5.7.2. Parsing Alternate Transports in ServiceURL . . . 75 5.7.3. Client Side Syntax Checking . . . . . . . . . . . 75 5.7.4. Language Locale Handling . . . . . . . . . . . . 75 5.7.5. Setting SLP System Properties . . . . . . . . . . 76 5.7.6. Multithreading . . . . . . . . . . . . . . . . . 76 5.7.7. Modular Implementations . . . . . . . . . . . . . 76 5.7.8. Asynchronous and Incremental Return Semantics . . 77 5.8. Examples . . . . . . . . . . . . . . . . . . . . . . . . 77 6. Internationalization Considerations 80 6.1. service URL . . . . . . . . . . . . . . . . . . . . . . . 80 6.2. Character Set Encoding . . . . . . . . . . . . . . . . . 80 6.3. Language Tagging . . . . . . . . . . . . . . . . . . . . 80 7. Security Considerations 81 8. Acknowledgements 81 1. Introduction The Service Location API is designed for standardized access the Service Location Protocol (SLP). The APIs allow client and service programs to be be written or modified in a very simple manner to provide dynamic service discovery and selection. Bindings in the C and Java languages are defined in this document. In addition, standardized formats for configuration files and for serialized registration files are presented. These files allow SLP agents to configure network parameters, to register legacy services that have not been SLP enabled, and to portably exchange registration databases. 1.1. Goals The overall goal of the API is to enable source portability of applications that use the API between different implementations of SLP. The result should facilitate the adoption of SLP, and conversion of clients and service programs to SLP. The goals of the C binding are to create a minimal but complete access to the functionality of the SLP protocol, allowing for simple memory management and limited code size. The Java API provides for modular implementations (where unneeded features can be omitted) and an object oriented interface to the complete set of SLP data and functionality. Kempf, Guttman Expires 30 October 1998 [Page 1]
Internet Draft Service Location API 30 May 1998 The standardized configuration file and serialized file formats provide a simple syntax with complete functional coverage of the protocol, but without including secure information such as private keys. 1.2. Terminology Service Location Protocol (SLP) The underlying protocol allowing dynamic and scalable service discovery. This protocol is specified in the Service Location Protocol Version 2 [11]. SLP framework When a 'Service Location framework' is mentioned, it refers to both the SLP implementation and interface implementation; ie. whatever provides the SLP functionality to user level programs. This includes remote agents. Directory Agent (DA) A service that automatically gathers service advertisements from SAs in order to provide them to UAs. User Agent (UA) This is the Service Location process or library that allows SLP requests to be made on behalf of a client process. UAs automatically direct requests to DAs when they exist. In their absence, UAs make requests to SAs. Service Agent (SA) This is the Service Location process or library that allows service software to register and deregister itself with the SLP framework. SAs MUST respond to UA service requests, detect DAs and register service advertisements with them. SA Server Many operating system platforms only allow a single process to listen on a particular port number. Since SAs are required to listen on a multicast address for SLP service requests, implementaions of the SLP framework on such platforms that want to support multiple SAs on one machine need to arrange for a single process to do the listening while the advertising SAs communicate with that process through another mechanism. The Kempf, Guttman Expires 30 October 1998 [Page 2]
Internet Draft Service Location API 30 May 1998 single listening process is called an SA server. SA servers share many characteristics with DAs, but they are not the same. Service Advertisement A URL possibly combined with service attributes. These are made available to UAs by SAs, either directly or via a DA. Locale The language localization that applies to strings passed into or returned from the SLP API. The Locale is expressed using a Language Tag [10]. All attribute strings are associated with a particular locale. The locale is completely orthogonal to the ANSI C locale. The SLP locale is mapped into the Java locale in the Java API. Service Template A document that describes the syntax of the URL for a given service type and a definition of all service attributes including the meaning, defaults, and constraints on values the attributes may take. See [12] for more information on service templates. The service: URL A service of a particular type announces its availability with a service: URL that includes its service access point (domain name or ip address, and possibly its port number) and optionally basic configuration parameters. The syntax of the service: URL is defined in the service template. Other URL's can be used in service advertisements if desired. Service Attributes The attributes associated with a given service. The values that can be assigned to service attributes are defined by the service template. Scope A string used to control the availability of service advertisements. Every SLP Agent is configured with one or more scope strings. Scopes are assigned by site administrators to group services for many purposes, but chiefly as a means of scalability. DAs store only services advertised having a scope string matching the scopes with which they are configured. Kempf, Guttman Expires 30 October 1998 [Page 3]
Internet Draft Service Location API 30 May 1998 Naming Authority (NA) This is a 'suffix' to the service type string. It completely changes the meaning of the service type. NAs are used for private definitions of well known Service Types and experimental Service Type extensions. The default NA is "IANA", which MUST NOT be explicitely included. Service types with the IANA naming authority are registered with the Internet Assigned Numbers Authority (see [12] for more information on the registration procedure). 2. File Formats This section describes the configuration and serialized registration file formats. Both files are defined in the UTF8 character set [7]. String values in the configuration file require SLP reserved characters to be escaped. The SLP reserved characters are `(', `)', `,', `\', `!', `<', `=', `>', `~' and control characters such as newline. The escapes are formed exactly as for the wire protocol, i.e. a backslash followed by two hex digits representing the character. For example, the escape for ',' is '\2c'. Escaped strings beginning with `\ff`, an encoding for a nonUTF8 character, are treated as opaques. Exactly as in the wire protocol, syntactically correct opaque encodings consist of a string beginning with `\ff` and containing *only* escaped characters that are transformed to bytes. Such strings are only syntactically correct in the serialized registration file as attribute values. In other cases, whenever an escape is encountered and the character is not an SLP reserved character, an error is signalled. On platforms that only support the ASCII subset of UTF8, the upper bit of bytes incoming from the configuration and registration files determines whether the character is ASCII or nonASCII. According to the standard UTF8 encoding, the upper bit is zero if the character is ASCII and one if the character is multibyte and thus nonASCII. Platforms without intrinsic UTF8 support are required to parse the multibyte character and store it in an appropriate internal format. Support for UTF8 is required to implement the SLP protocol (see [11]) and can be reused during configuration file parsing. The location and name of the configuration file is system-dependent, but implementations of the API are encouraged to locate it together with other configuration files and name it consistently. Kempf, Guttman Expires 30 October 1998 [Page 4]
Internet Draft Service Location API 30 May 1998 2.1. Configuration File Format The configuration file format consists of a newline delimited list of zero or more property definitions. Each property definition corresponds to a particular configurable SLP, network, or other parameter in one or more of the three SLP agents. The file format grammer in ABNF [9] syntax is: config-file = line-list line-list = line / line line-list line = property-line / comment-line comment-line = ( "#" / ";" ) 1*allchar newline property-line = property newline property = tag "=" value-list tag = prop / prop "." property prop = 1*char value-list = value / value "," value-list value = int / bool / value-list / string int = 1*DIGIT bool = "true" / "false" / "TRUE" / "FALSE" newline = CR / ( CRLF ) string = 1*allchar char = DIGIT / ALPHA / other other = %x21-%x2f / %x3a-%x40 / %x5b-%x60 / %7b-%7e allchar = char / HT / SP / escape escape = "\" HEXDIG HEXDIG ; Used for SLP reserved characters With the exception of the net.slp.useScopes and the net.slp.DAAddresses properties, all other properties can be changed through property accessors in the C and Java APIs. The property accessors only change the property values in the running agent program and do not affect the values in the configuration file. The net.slp.useScopes and net.slp.DAAddresses properties are read-only because they control the agent's view of the scopes and DAs and are therefore critical to the function of the API scope discovery algorithm. Attempts to modify them are unlikely to yield productive results, and could harm the ability of the agent to find scopes and use DAs. The properties break down into seven general areas. Each of the following subsections describes an area and its properties. Kempf, Guttman Expires 30 October 1998 [Page 5]
Internet Draft Service Location API 30 May 1998 2.1.1. DA configuration Important configuration parameters for DAs are included in this section. These are: net.slp.isDA A boolean indicating if the SLP server is to act as a DA. If false, not run as a DA. Default is false. net.slp.DAHeartBeat A 32 bit integer giving the number of seconds for the DA heartbeat. Default is 3 hours (10800 seconds). This property corresponds to the protocol specification parameter CONFIG_DA_BEAT [11]. Ignored if isDA is false. 2.1.2. Static Scope Configuration These parameters allow various aspects of scope handling to be configured. net.slp.useScopes A value-list of strings indicating the only scopes a UA or SA is allowed to use when making requests or registring, or the scopes a DA must support. If not present, then in the absence of scope information from other sources (DHCP, active and passive discovery), the default is "DEFAULT". If another scope is used by a UA, a SCOPE_NOT_SUPPORTED error SHOULD be returned. If another scope is used by a SA, a SCOPE_NOT_SUPPORTED error MUST be returned, since SAs are required to register in all scopes with which they are configured. Unlike other parameters, this parameter is ``read-only'', so attempts to change it after the configuration file has been read are ignored. See Section 3.11 for the algorithm the API uses in determining what scope information to present. net.slp.DAAddresses A value-list of IP addresses or DNS-resolvable names giving the DAs to use for statically configured UAs and SAs, along with their scopes. If isDA is true, registrations and deregistrations in the appropriate scopes are forwarded these DAs. Default is none. Scopes from the net.slp.useScopes parameter and addresses and scopes obtained via DHCP take precedence over these. Unlike other parameters, this Kempf, Guttman Expires 30 October 1998 [Page 6]
Internet Draft Service Location API 30 May 1998 parameter is ``read-only'', so attempts to change it after the configuration file has been read are ignored. If scope and DA information is available from other sources, the information from this list is used as a supplement. The following grammer describes the property: addr-list = addr / addr "," addr-list addr = addrrep "(" scope-list ")" addrrep = ipv4-addr / ipv6-addr / fqdn ipv4-addr = 1*3DIGIT 3( "." 1*3DIGIT ) ipv6-addr = 64HEXDIGIT fqdn = ALPHA / ALPHA *[ anum / "-" ] anum anum = ALPHA / DIGIT scope-list = scope / scope "," scope-list scope = string ; See grammar of Section 2.1 ; and [11]. Scoped DAs are listed with a comma delimited list inside brackets following the DA address. For example: (da1.fr.org(default),da2.fr.org(scope1,scope2),da3.fr.org(default,scope3)) Here da1 has scope default, da2 has scope1 and scope2, da3 has default and scope3. 2.1.3. Tracing and Logging This section allows tracing and logging information to be printed by the various agents. net.slp.traceDATraffic A boolean controlling printing of messges about traffic with DAs. Default is false. net.slp.traceMsg A boolean controlling printing of details on SLP messages. The fields in all incoming messages and outgoing replies are printed. Default is false. Kempf, Guttman Expires 30 October 1998 [Page 7]
Internet Draft Service Location API 30 May 1998 net.slp.traceDrop A boolean controlling printing details when a SLP message is dropped for any reason. Default is false. net.slp.traceReg A boolean controlling dumps of all registered services upon registration and deregistration. If true, the contents of the DA or SA server are dumped after a registration or deregistration occurs. Default is false. 2.1.4. Serialized Proxy Registrations These properties control the reading and writing of serialized registrations. net.slp.serializedRegURL A string containing a URL pointing to a document containing serialized registrations that should be processed when the DA or SA server starts up. Default is none. 2.1.5. Networking Configuration Parameters The properties in this section allow various network configuration parameters to be set. net.slp.isBroadcastOnly A boolean indicating if broadcast should be used instead of multicast. Default is false. net.slp.passiveDADetection A boolean indicating whether passive DA detection should be used. Default is true. net.slp.multicastTTL A positive integer less than or equal to 32, giving the multicast TTL. Default is 32. net.slp.DAActiveDiscoveryInterval A 32 bit integer giving the number of seconds between DA active discovery queries. Default is 900 seconds (15 minutes). This Kempf, Guttman Expires 30 October 1998 [Page 8]
Internet Draft Service Location API 30 May 1998 property corresponds to the protocol specification parameter CONFIG_DA_FIND [11]. net.slp.multicastMaximumWait A 32 bit integer giving the maximum amount of time to perform multicast, in milliseconds. Default is 15000 ms (15 sec.). This property corresponds to the CONFIG_MC_MAX parameter in the protocol specification [11]. net.slp.multicastTimeouts A value-list of 32 bit integers used as timeouts, in milliseconds, to implement the multicast convergence algorithm. Each value specifies the time to wait before sending the next request, or until nothing new has been learned from two successive requests. Ignored if isDA is true. Default is: 3000,3000,3000,3000,3000. In a fast network the agressive values of 1000,1250,1500,2000,4000 allow better performance. This property corresponds to the CONFIG_MC_RETRY parameter in the protocol specification [11]. Note that the net.slp.DADiscoveryTimeouts property MUST be used for active DA discovery. net.slp.DADiscoveryTimeouts A value-list of 32 bit integers used as timeouts, in milliseconds, to implement the multicast convergence algorithm during active DA discovery. Each value specifies the time to wait before sending the next request, or until nothing new has been learned from two successive requests. This property corresponds to the protocol specification parameter CONFIG_DA_RETRY [11]. Default is: 2000,2000,2000,2000,3000,4000. net.slp.datagramTimeouts A value-list of 32 bit integers used as timeouts, in milliseconds, to implement unicast datagram transmission to DAs. The nth value gives the time to block waiting for a reply on the nth try to contact the DA. The sum of these values is the protocol specification property CONFIG_DA_MAX [11]. net.slp.randomWaitBound A 32 bit integer giving the maximum value for all random wait parameters, in milliseconds. Default is 1000 (1 sec.). This value corresponds to the protocol specification Kempf, Guttman Expires 30 October 1998 [Page 9]
Internet Draft Service Location API 30 May 1998 parameters CONFIG_START_WAIT, CONFIG_REG_PASSIVE, and CONFIG_REG_ACTIVE [11]. net.slp.MTU A 16 bit integer giving the network packet MTU, in bytes. This is the maximum size of any datagram to send, but the implementation might receive a larger datagram. Default is 1400. net.slp.multicastInterfaces Value-list of strings giving the names of network interfaces on which a DA or SA should listen for multicast. Default is empty, i.e. just listen on the default network interface. 2.1.6. UA Configuration This section contains configuration parameters for the UA. net.slp.locale A RFC 1766 Language Tag [10] for the language locale. Setting this property causes the property value to become the default locale for SLP messages. Default is "en". net.slp.maxResults A 32 bit integer giving the maximum number of results to accumulate and return for a synchronous request before the timeout, or the maximum number of results to return through a callback if the request results are reported asychronously. Positive integers and -1 are legal values. If -1, indicates that all results should be returned. Default value is -1. DAs and SAs always return all results that match the request. This configuration value applies only to UAs, that filter incoming results and only return as many values as net.slp.maxResults indicates. 2.1.7. Security The properties in this section allow security parameters to be configured. Key management is implementation dependent. Kempf, Guttman Expires 30 October 1998 [Page 10]
Internet Draft Service Location API 30 May 1998 net.slp.URLSignature A boolean indicating whether the SA should sign URLs. URLs are signed if true. Default is false. Applies to SAAdverts as well. net.slp.attributeSignature A boolean indicating whether the SA should sign attributes. Attributes are signed if true. Default is false. net.slp.DAAdvertSignature A boolean indicating whether the DA should sign DAAdverts. DAAdverts are signed if true. Default is false. 2.2. Serialized Registration File The serialized registration file contains a group of registrations that a DA or SA server (if one exists) registers when it starts up. These registrations are primarily for older service programs that do not internally support SLP and cannot be converted, and for portably exchanging registrations between SLP implementations. The character format of the registrations is required to be UTF8. The syntax of the serialized registration file, in ABNF format [9], is as follows: ser-file = reg-list reg-list = reg / reg reg-list reg = creg / ser-reg creg = comment-line ser-reg comment-line = ( "#" / ";" ) 1*allchar newline ser-reg = url-props [slist] attr-list newline url-props = surl sep lang sep ltime sep [ type ] sep = *WSP "," *WSP surl = ;The registration's URL. See ; [12] for syntax. lang = 2*3ALPHA [ "-" 1*ALPHA ] ;RFC 1766 Language Tag see [10]. ltime = 1*DIGIT ; A positive 16-bit integer ; giving the lifetime ; of the registration. type = string ; The service type name, see [11] ; and [12] for syntax. Kempf, Guttman Expires 30 October 1998 [Page 11]
Internet Draft Service Location API 30 May 1998 slist = attr ; Attribute definition with id "scopes" ; and value list containing scope names. ; See grammar of Section 2.1 ; and [11]. attr-list = attr-def / attr-def attr-list attr-def = attr / keyword keyword = attr-id attr = attr-id assgn-op attr-val-list newline assgn-op = *WSP "=" *WSP attr-id = ;Attribute id, see [11] for syntax. attr-val-list = attr-val / attr-val sep attr-val-list attr-val = ;Attribute value, see [11] for syntax. char = DIGIT / ALPHA / other ;'other' defined in section 2.1. allchar = char / WSP The syntax for attributes and attribute values requires escapes for special characters as specified in [11], in addition to nonASCII characters. DAs and SA servers that process serialized registrations MUST handle them exactly as if they were registered by an SA. In the urlprops production, the type token is optional. If the type token is present for a service: URL, a warning is signalled and type name is ignored. Scopes can be included in a registration by including an attribute definition with tag "scopes" followed by a comma separated list of scope names immediately after the URL registration. If the optional scope list is present, the registations are made in the indicated scopes; otherwise, they are registered in the scopes with which the DA or SA server was configured through the net.slp.useScopes property. If the scope list contains scopes that are not in the net.slp.useScopes property (provided that property is set) or are not specified by DHCP, the API library is required to abort the program. 2.3. Proccessing Serialized Registration and Configuration Files Implementations are encouraged to make processing of configuration and serialized files as transparent as possible to clients of the API. At the latest, errors MUST be caught when the relevent configuration item is used. At the earliest, errors MAY be caught when the relevent file is loaded into the executing agent. Errors SHOULD be reported by logging to the appropriate platform logging file, error output, or log device, and the default value substituted. Serialized registration file entries SHOULD be caught and reported when the file is loaded. Kempf, Guttman Expires 30 October 1998 [Page 12]
Internet Draft Service Location API 30 May 1998 Configuration file loading MUST be complete prior to the initiation of the first networking connection. Serialized registration MUST be complete before the DA accepts the first network request. 3. Binding Independent Implementation Considerations This section discusses a number of implementation considerations independent of language binding, with language specific notes where applicable. 3.1. Multithreading Implementations of both the C and Java APIs are required to make API calls thread-safe. Access to data structures shared between threads must be co-ordinated to avoid corruption or invalid access. One way to achieve this goal is to allow only one thread at a time in the implementing library. Performance in such an implementation suffers, however. Therefore, where possible, implementations are encouraged to allow multiple threads within the SLP API library. 3.2. Asynchronous and Incremental The APIs are designed to encourage implementations supporting asychronous and incremental client interaction. The goal is to allow large numbers of returned service URLs, service types, and attributes without requiring the allocation of huge chunks of memory. The particular design features to support this goal differ in the two language bindings. 3.3. Type Checking for Service Types Service templates [12] allow SLP registrations to be type checked for correctness. Implementations of the API are free to make use of service type information for type checking, but are not required to do so. If a type error occurs, the registration should terminate with TYPE_ERROR. 3.4. Refreshing Registrations SLP advertisements carry an explicit lifetime with them. After the lifetime expires, the DA flushes the registration from its cache. Implementations of the SA API are encouraged to provide an automatic refreshing capability, so that service advertiser applications can simply register their services for as long as they continue running. Kempf, Guttman Expires 30 October 1998 [Page 13]
Internet Draft Service Location API 30 May 1998 The SA API is required to deregister any such advertisements as soon as the calling application exits. 3.5. Configuration File Processing DAs, SAs and UAs processing the configuration file, and DAs and SA servers processing the serialized registration file are required to log any errors using whatever underlying error mechanism is appropriate for the platform. Examples include include writing error messages to the standard output, writing to a system logging device, or displaying the errors to a logging window. After the error is reported, the offending parameter must be set to the default and program execution continued. An agent MUST NOT fail if a file format error occurs. 3.6. Attribute Types String encoded attribute values do not include explicit type information. All UA implementations and those SA and DA implementations that choose to support type checking should use the type rules described in [12] in order to convert from the string representation on the wire to an object typed appropriately. 3.7. Removal of Duplicates The UA implementation SHOULD always collate results to remove duplicates during synchronous operations and for the Java API. During asychronous operation in C, the UA implementation SHOULD forgo duplicate elimination to reduce memory requirements in the library. This allows the API library to simply take the returned attribute value list strings, URL strings, or service type list strings and call the callback function with it, without any additional processing. Naturally, the burden of duplicate elimination is thrown onto the client in this case. 3.8. Character Set Encoding Character string parameters in the Java API are all represented in Unicode internally because that is the Java-supported character set. Characters buffer parameters in the C API are represented in UTF8 to maintain maximum compatibility on platforms that only support the ASCII subset of UTF8. API functions are still required to handle the full range of UTF8 characters because the SLP protocol requires it, but the API implementation can represent the characters internally in any convenient way. On the wire, all characters are converted to Kempf, Guttman Expires 30 October 1998 [Page 14]
Internet Draft Service Location API 30 May 1998 UTF8. Inside URLs, characters that are not allowed by URL syntax [2] must be escaped according to the URL escape character convention. Strings that are included in SLP messages may include SLP reserved characters and are escaped by convenience functions by the API. The character code used to encode the escaped characters is UTF8. The maximum length of any string parameter in C or Java is 64K bytes. 3.9. Error Semantics All errors encountered processing SLP messages SHOULD be logged. For synchronous calls, an error is only reported on a call if no successful replies were received from any SLP framework entity. If an error occured among one or several successful replies, then the error should be logged and the successful replies returned. For asychronous calls, an error occuring during correspondence with a particular remote SLP agent is reported through the first callback (in the C API) or enumeration method invocation (in the Java API) after the error occurs, which would normally report the results of the correspondence. This allows the callback or client code to determine whether the operation should be terminated or continue. In some cases, the error returned from the SLP framework may be fatal (SLP_PARSE_ERROR, etc.). In these cases, the API library terminates the operation. Both the Java and C APIs contain language specific error code mechanisms for returning error information. The names of the error codes are consistent between the two implementations, however. The following error codes are returned from a remote agent (DA or SA server): LANGUAGE_NOT_SUPPORTED No DA or SA has service advertisement information in the language requested, but at least one DA or SA indicated, via the LANGUAGE_NOT_SUPPORTED error code, that it might have information for that service in another language. PARSE_ERROR The SLP message was rejected by a remote SLP agent. The API returns this error only when no information was retrieved, and at least one SA or DA indicated a protocol error. The data supplied through the API may be malformed or a may have been damaged in transit. Kempf, Guttman Expires 30 October 1998 [Page 15]
Internet Draft Service Location API 30 May 1998 INVALID_REGISTRATION The API may return this error if an attempt to register a service was rejected by all DAs because of a malformed URL or attributes. SLP does not return the error if at least one DA accepted the registration. AUTHENTICATION_ABSENT If the SLP framework supports authentication, this error arises when the UA or SA failed to send an authenticator for requests or registrations in a protected scope. INVALID_UPDATE An update for a nonexisting registration was issued. The following errors result from interactions with remote agents or can occur locally: AUTHENTICATION_FAILED If the SLP framework supports authentication, this error arises when a authentication on an SLP message received from a remote SLP agent failed. SCOPE_NOT_SUPPORTED The API returns this error if the UA or SA has been configured with net.slp.useScopes value-list of scopes and the UA or SA request did not specify one or more of these allowable scopes, and no others. It may also be returned by a DA if the scope included in a request is not supported by a DA. The following errors are generated through a program interacting with the API implementation. They do not involve a remote SLP agent. NOT_IMPLEMENTED If an unimplemented feature is used, this error is returned. NETWORK_INIT_FAILED If the network cannot initialize properly, this error is returned. Kempf, Guttman Expires 30 October 1998 [Page 16]
Internet Draft Service Location API 30 May 1998 NETWORK_TIMED_OUT When no reply can be obtained in the time specified by the configured timeout interval, this error is returned. NETWORK_ERROR The failure of networking during normal operations causes this error to be returned. BUFFER_OVERFLOW An outgoing request overflowed the maximum network MTU size. The request should be reduced in size or broken into pieces and tried again. MEMORY_ALLOC_FAILED If the API fails to allocate memory, the operation is aborted and returns this. PARAMETER_BAD If a parameter passed into an interface is bad, this error is returned. INTERNAL_SYSTEM_ERROR A basic failure of the API causes this error to be returned. This occurs when a system call or library fails. The operation could not recover. HANDLE_IN_USE In the C API, callback functions are not permitted to recursively call into the API on the same SLPHandle, either directly or indirectly. If an attempt is made to do so, this error is returned from the called API function. TYPE_ERROR If the API supports type checking of registrations against service type templates, this error can arise if the attributes in a registration do not match the service type template for the service. Some error codes are handled differently in the Java API. These differences are discussed in Section 5. Kempf, Guttman Expires 30 October 1998 [Page 17]
Internet Draft Service Location API 30 May 1998 The errors OPTION_NOT_UNDERSTOOD, VER_NOT_SUPPORTED, INTERNAL_ERROR, RQST_NOT_SUPPORTED, AUTHENTICATON_ALGO_UNKNOWN, and DA_BUSY_NOW should be handled internally and not surfaced to clients through the API. 3.10. Modular Implementations Subset implementations that do not support the full range of functionality are required to nevertheless support every interface in order to maintain link compatiblity between compliant API implementations and applications. If a particular operation is not supported, a NOT_IMPLEMENTED error should be returned. The Java API has some additional conventions for handling subsets. Applications that are expected to run on a wide variety of platforms should be prepared for subset API implementations by checking returned error codes. 3.11. Scope Discovery and Handling Both APIs contain an operation to obtain a list of currently known scope names. This scope information comes from a variety of places: DHCP, the net.slp.useScopes and net.slp.DAAddresses properties, and active and passive discovery. API implementations are required to process presented scope information in the following way. Scopes returned by DHCP have first priority and MUST be returned if they are available. The net.slp.useScopes property has second priority, and scopes discovered through the net.slp.useScopes property MUST be returned if this property is set and there are no scopes available from DHCP. If neither of these sources provide information on scopes, then scopes obtained from the net.slp.DAAddresses property, from active DA discovery, and from passive DA discovery all MUST be returned. If no information is available from any of these sources, then the API library MAY perform SA discovery, using the service type hint passed in through the API to limit the search to SAs supporting a particular service type. In the absence of any of the above sources of information, the API MUST return the default scope, ``DEFAULT''. Note that the API MUST always return some scope information. SLP requires that SAs MUST perform their operations in all scopes currently known to them. [11]. The API enforces this constraint by checking the list of scopes presented in the call to SA operations, and signals a SCOPE_NOT_SUPPORTED error if any scopes are missing. UAs SHOULD use a scope obtained through one of the API operations for finding scopes. Any other scope name MAY result in a SCOPE_NOT_SUPPORTED error from a remote agent. Kempf, Guttman Expires 30 October 1998 [Page 18]
Internet Draft Service Location API 30 May 1998 Scopes are used in larger networks for administrators to control service access. Care must be taken by programmers using the API not to expose the ability to create or view arbitrary scopes in cases where the host has been preconfigured with a scope list. 4. C Language Binding The C language binding presents a minimal overhead implemention that maps directly into the protocol. There is one C language function per protocol request, with the exception of the SLPDereg() and SLPDelAttrs() functions, which map into different uses of the SLP deregister request. Parameters are for the most part character buffers. Memory management is kept simple by having the API library allocate memory and requiring that client callback functions copy incoming parameters into memory allocated by the client code. Memory returned directly from the API functions is deallocted using the SLPFree() function. To conform with standard C practice, all character strings passed to and returned through the API are null terminated, even though the SLP protocol does not use null terminated strings. Strings passed as parameters are UTF8 but they may still be passed as a C string (a null terminated sequence of bytes.) Escaped characters must be encoded as UTF8. In the common case of the ASCII subset of UTF8, the usual one byte per character C strings work. API functions assist in escaping and unescaping strings. 4.1. Constant Types 4.1.1. URL Lifetimes 4.1.1.1. Synopsis typedef enum { SLP_LIFETIME_DEFAULT = 10800, SLP_LIFETIME_MAXIMUM = 65535 } SLPURLLifetime; 4.1.1.2. Description The SLPURLLifetime enum type contains URL lifetime values, in seconds, that are frequently used. SLP_LIFETIME_DEFAULT is 3 hours, while SLP_LIFETIME_MAXIMUM is about 18 hours and corresponds to the maximum size of the lifetime field in SLP messages. Kempf, Guttman Expires 30 October 1998 [Page 19]
Internet Draft Service Location API 30 May 1998 4.1.2. Error Codes 4.1.2.1. Synopsis typedef enum { SLP_LAST_CALL = 1, SLP_OK = 0, SLP_LANGUAGE_NOT_SUPPORTED = -1, SLP_PARSE_ERROR = -2, SLP_INVALID_REGISTRATION = -3, SLP_SCOPE_NOT_SUPPORTED = -4, SLP_AUTHENTICATION_ABSENT = -6, SLP_AUTHENTICATION_FAILED = -7, SLP_INVALID_UPDATE = -9; SLP_NOT_IMPLEMENTED = -17, SLP_BUFFER_OVERFLOW = -18, SLP_NETWORK_TIMED_OUT = -19, SLP_NETWORK_INIT_FAILED = -20, SLP_MEMORY_ALLOC_FAILED = -21, SLP_PARAMETER_BAD = -22, SLP_NETWORK_ERROR = -23, SLP_INTERNAL_SYSTEM_ERROR = -24, SLP_HANDLE_IN_USE = -25, SLP_TYPE_ERROR = -26 } SLPError ; 4.1.2.2. Description The SLPError enum contains error codes that are returned from API functions. The SLP_OK code indicates that the no error occured during the operation. The SLP_LAST_CALL code is passed to callback functions when the API library has no more data for them and threfore no further calls will be made to the callback on the currently outstanding operation. The callback can use this to signal the main body of the client code that no more data will be forthcoming on the operation, so that the main body of the client code can break out of data collection loops. On the last call of a callback during both a synchronous and asynchronous call, the error code parameter has value SLP_LAST_CALL, and the other parameters are all null. If no results are returned by an API operation, then only call with the error parameter set to SLP_LAST_CALL is made. Kempf, Guttman Expires 30 October 1998 [Page 20]
Internet Draft Service Location API 30 May 1998 4.1.3. SLPBoolean 4.1.3.1. Synopsys typedef enum { SLP_FALSE = 0, SLP_TRUE = 1 } SLPBoolean; 4.1.3.2. Description The SLPBoolean enum is used as a boolean flag. 4.2. Struct Types 4.2.1. SLPSrvURL 4.2.1.1. Synopsis typedef struct srvurl { char *s_pcSrvType; char *s_pcHost; int s_iPort; char *s_pcNetFamily; char *s_pcSrvPart; } SLPSrvURL; 4.2.1.2. Description The SLPSrvURL structure is filled in by the SLPParseSrvURL() function with information parsed from a character buffer containing URL. The fields correspond to different parts of the URL. Note that the structure is conformant with the standard Berkeley sockets struct servent, with the exception that the pointer to an array of characters for aliases (s_aliases field) is replaced by the pointer to host name (s_pcHost field). s_pcSrvType A pointer to a character string containing the service type name, including naming authority. Kempf, Guttman Expires 30 October 1998 [Page 21]
Internet Draft Service Location API 30 May 1998 s_pcHost A pointer to a character string containing the host identification information. s_iPort The port number, or zero if none. The port is only available if the transport is IP. s_pcNetFamily A pointer to a character string containing the network address family identifier. Possible values are ``ipx'' for the IPX family, ``at'' for the Appletalk family, and ``'' (i.e. the empty string) for the IP address family. s_pcSrvPart The remainder of the URL, after the host identification. The host and port should be sufficient to open a socket to the machine hosting the service, and the remainder of the URL should allow further differentiation of the service. 4.2.2. SLPHandle 4.2.2.1. Synopsis typedef void* SLPHandle; The SLPHandle type is returned by SLPOpen() and is a parameter to all SLP functions. It serves as a handle for all resources allocated on behalf of the process by the SLP library. The type is opaque, since the exact nature differs depending on the implementation. 4.3. Callbacks A function pointer to a callback function specific to a particular API operation is included in the parameter list when the API function function is invoked. The callback function is called with the results of the operation in both the synchronous and asychronous cases. The memory included in the callback parameters is owned by the API library, and the client code in the callback MUST copy out Kempf, Guttman Expires 30 October 1998 [Page 22]
Internet Draft Service Location API 30 May 1998 the contents if it wants to maintain the information longer than the duration of the current callback call. In addition to parameters for reporting the results of the operation, each callback parameter list contains an error code parameter and a cookie parameter. The error code parameter reports the error status of the ongoing (for asychronous) or completed (for synchronous) operation. The cookie parameter allows the client code that starts the operation by invoking the API function to pass information down to the callback without using global variables. The callback returns an SLPBoolean to indicate whether the API library should continue processing the operation. Asychronous operations are terminated, synchronous operations ignore the return (since the operation is already complete). 4.3.1. SLPRegReport 4.3.1.1. Synopsis typedef void SLPRegReport(SLPHandle hSLP, SLPError errCode, void *pvCookie); 4.3.1.2. Description The SLPRegReport callback type is the type of the callback function to the SLPReg(), SLPDereg(), and SLPDelAttrs() functions. 4.3.1.3. Parameters hSLP The SLPHandle used to initiate the operation. errCode An error code indicating if an error occured during the operation. pvCookie Memory passed down from the client code that called the original API function, starting the operation. May be NULL. Kempf, Guttman Expires 30 October 1998 [Page 23]
Internet Draft Service Location API 30 May 1998 4.3.2. SLPSrvTypeCallback 4.3.2.1. Synopsis typedef SLPBoolean SLPSrvTypeCallback(SLPHandle hSLP, const char* pcSrvTypes, SLPError errCode, void *pvCookie); 4.3.2.2. Description The SLPSrvTypeCallback type is the type of the callback function parameter to SLPFindSrvTypes() function. The client should return a SLPBoolean value indicating whether it is interested in seeing more data on this operation. 4.3.2.3. Parameters hSLP The SLPHandle used to initiate the operation. pcSrvTypes A character buffer containing a comma separated, null terminated list of service types. errCode An error code indicating if an error occured during the operation. The callback should check this error code before processing the parameters. If the error code is other than SLP_OK, then the API library may choose to terminate the outstanding operation. pvCookie Memory passed down from the client code that called the original API function, starting the operation. May be NULL. 4.3.2.4. Returns The client code should return SLP_TRUE if more data is desired, otherwise SLP_FALSE. Kempf, Guttman Expires 30 October 1998 [Page 24]
Internet Draft Service Location API 30 May 1998 4.3.3. SLPSrvURLCallback 4.3.3.1. Synopsis typedef SLPBoolean SLPSrvURLCallback(SLPHandle hSLP, const char* pcSrvURL, unsigned short sLifetime, SLPError errCode, void *pvCookie); 4.3.3.2. Description The SLPSrvURLCallback type is the type of the callback function parameter to SLPFindSrvs() function. The client should return a SLPBoolean value indicating whether it is interested in seeing more data on this operation. 4.3.3.3. Parameters hSLP The SLPHandle used to initiate the operation. pcSrvURL A character buffer containing the returned service URL. sLifetime An unsigned short giving the life time of the service advertisement, in seconds. The value must be an unsigned integer less than or equal to SLP_LIFETIME_MAXIMUM. errCode An error code indicating if an error occured during the operation. The callback should check this error code before processing the parameters. If the error code is other than SLP_OK, then the API library may choose to terminate the outstanding operation. pvCookie Memory passed down from the client code that called the original API function, starting the operation. May be NULL. Kempf, Guttman Expires 30 October 1998 [Page 25]
Internet Draft Service Location API 30 May 1998 4.3.3.4. Returns The client code should return SLP_TRUE if more data is desired, otherwise SLP_FALSE. 4.3.4. SLPAttrCallback 4.3.4.1. Synopsis typedef SLPBoolean SLPAttrCallback(SLPHandle hSLP, const char* pcAttrList, SLPError errCode, void *pvCookie); 4.3.4.2. Description The SLPAttrCallback type is the type of the callback function parameter to SLPFindAttrs() function. The client should return a SLPBoolean value indicating whether it is interested in seeing more data on this operation. When the SLPFindAttrs() operation was originally called with a URL, the callback is called once regardless of whether the handle was opened asychronously or synchronously. The pcAttrList parameter contains the requested attributes as a comma separated list (or is empty if no attributes matched the original tag list). When the SLPFindAttrs() operation was originally called with a service type, the value of pcAttrList and calling behavior depend on whether the handle was opened asychronously or synchronously. If the handle was opened asychronously, the callback is called every time the API library has results from a remote agent. The pcAttrList parameter is uncollated between calls, and contains a comma separated list containing the results from the agent that immediately returned results. If the handle was opened synchronously, the results are collated from all returning agents and the callback is called once, with the pcAttrList parameter set to the collated result. 4.3.4.3. Parameters hSLP The SLPHandle used to initiate the operation. Kempf, Guttman Expires 30 October 1998 [Page 26]
Internet Draft Service Location API 30 May 1998 pcAttrList A character buffer containing a comma separated, null terminated list of attribute id/value assignments, in SLP wire format; i.e. "(attr-id=attr-value-list)" [11]. errCode An error code indicating if an error occured during the operation. The callback should check this error code before processing the parameters. If the error code is other than SLP_OK, then the API library may choose to terminate the outstanding operation. pvCookie Memory passed down from the client code that called the original API function, starting the operation. May be NULL. 4.3.4.4. Returns The client code should return SLP_TRUE if more data is desired, otherwise SLP_FALSE. 4.4. Opening and Closing the SLP Library 4.4.1. SLPOpen 4.4.1.1. Synopsis SLPError SLPOpen(const char *pcLang, SLPBoolean isAsync, SLPHandle *phSLP); 4.4.1.2. Description Returns a SLPHandle handle in the phSLP parameter for the language locale passed in as the pcLang parameter. The client indicates if operations on the handle are to be synchronous or asychronous through the isAsync parameter. The handle encapsulates the language locale for SLP requests issued through the handle, and any other resources required by the implementation. SLP properties are not encapsulated by the handle, they are global. The return value of the function is an SLPError code indicating the status of the operation. Upon failure, the phSLP parameter is NULL. Kempf, Guttman Expires 30 October 1998 [Page 27]
Internet Draft Service Location API 30 May 1998 An SLPHandle can only be used for one SLP API operation at a time. If the original operation was started asychronously, any attempt to start an additional operation on the handle while the original operation is pending results in the return of an SLP_HANDLE_IN_USE error from the API function. The SLPClose() API function terminates any outstanding calls on the handle. If an implementation is unable to support either asychronous or synchronous operation, due to memory constraints or lack of threading support, the SLP_NOT_IMPLEMENTED flag may be returned when the isAsync flag has the appropriate value. 4.4.1.3. Parameters pcLang A pointer to an array of characters containing the RFC 1766 Language Tag [10] for the natural language locale of requests and registrations issued on the handle. May not be NULL. 4.4.2. SLPClose 4.4.2.1. Synopsis void SLPClose(SLPHandle hSLP); 4.4.2.2. Description Frees all resources associated with the handle. If the handle was invalid, the function returns silently. Any outstanding synchronous or asychronous operations are cancelled so their callback functions will not be called any further. 4.4.2.3. Parameters SLPHandle A SLPHandle handle returned from a call to SLPOpen(). Kempf, Guttman Expires 30 October 1998 [Page 28]
Internet Draft Service Location API 30 May 1998 4.5. Protocol API 4.5.1. SLPReg 4.5.1.1. Synopsis SLPError SLPReg(SLPHandle hSLP, const char *pcSrvURL, const unsigned short usLifetime, const char *pcSrvType, const char *pcScopeList, const char *pcAttrs SLPBoolean fresh, SLPRegReport callback, void *pvCookie); 4.5.1.2. Description Registers the URL in pcSrvURL having the lifetime sLifetime with the attribute list in pcAttrs. The pcAttrs list is a comma separated list of attribute assignments in on the wire format (including escaping of reserved characters). The sLifetime parameter must be nonzero and less than or equal to SLP_LIFETIME_MAXIMUM. The registration is done in scopes that are part of pcScopeList. If the fresh flag is SLP_TRUE, then the registration is new (the SLP protocol FRESH flag is set) and the registration replaces any existing registrations. If the fresh flag is SLP_FALSE, then an existing registration is updated. Rules for new and updated registrations, and the format for pcAttrs can be found in [11]. Registrations and updates take place in the language locale of the hSLP handle. The pcScopeList parameter supplies a comma delimited list of scopes for the registration. This parameter MUST NOT be NULL or the empty string, "". The scopes in the scope list SHOULD be one or more of the scopes obtainable from SLPFindScopes(). If an unsupported scope is specified, a SLP_SCOPE_NOT_SUPPORTED error MAY be returned. If the net.slp.useScopes parameter has been configured, then the pcScopeList parameter MUST be a supported scope. Kempf, Guttman Expires 30 October 1998 [Page 29]
Internet Draft Service Location API 30 May 1998 4.5.1.3. Parameters hSLP The language specific SLPHandle on which to register the advertisement. May not be NULL. pcSrvURL The URL to register. May not be NULL or the empty string. usLifetime An unsigned short giving the life time of the service advertisement, in seconds. The value must be an unsigned integer less than or equal to SLP_LIFETIME_MAXIMUM and greater than zero. pcSrvType The service type. If pURL is a service: URL, then this parameter is ignored. May not be null. pcScopeList The comma separated list of scopes applying to the registration. MUST contain all the scopes returned from the results of a SLPFindScopes() API invocation. May not be NULL. pcAttrs A comma separated list of attribute assignment expressions for the attributes of the advertisement. May not be NULL. Use empty string, "" for no attributes. callback A callback to report the operation completion status. May not be NULL. pvCookie Memory passed to the callback code from the client. May be NULL. Kempf, Guttman Expires 30 October 1998 [Page 30]
Internet Draft Service Location API 30 May 1998 4.5.1.4. Returns If an error occurs in starting the operation, one of the SLPError codes is returned. 4.5.2. SLPDereg 4.5.2.1. Synopsys SLPError SLPDereg(SLPHandle hSLP, const char *pcURL, const char *pcScopeList, SLPRegReport callback, void *pvCookie); 4.5.2.2. Description Deregisters the advertisment for URL pURL in all scopes where the service is registered and all language locales, not just the locale of the SLPHandle. 4.5.2.3. Parameters hSLP The language specific SLPHandle to use for deregistering. May not be NULL. pcURL The URL to deregister. May not be NULL. pcScopeList The comma separated list of scopes applying to the registration. MUST contain all the scopes returned from the results of a SLPFindScopes() API invocation. May not be NULL. callback A callback to report the operation completion status. May not be NULL. Kempf, Guttman Expires 30 October 1998 [Page 31]
Internet Draft Service Location API 30 May 1998 pvCookie Memory passed to the callback code from the client. May be NULL. 4.5.2.4. Returns If an error occurs in starting the operation, one of the SLPError codes is returned. 4.5.3. SLPDelAttrs 4.5.3.1. Synopsys SLPError SLPDelAttrs(SLPHandle hSLP, const char *pcURL, const char *pcScopeList, const char *pcAttrs, SLPRegReport callback, void *pvCookie); 4.5.3.2. Description Delete the selected attributes in the locale of the SLPHandle. 4.5.3.3. Parameters hSLP The language specific SLPHandle to use for deleting attributes. May not be NULL. pURL The URL of the advertisement from which the attributes should be deleted. May not be NULL. pcScopeList The comma separated list of scopes applying to the registration. MUST contain all the scopes returned from the results of a SLPFindScopes() API invocation. May not be NULL. Kempf, Guttman Expires 30 October 1998 [Page 32]
Internet Draft Service Location API 30 May 1998 pcAttrs A comma separated list of attribute ids for the attributes to deregister. See Section 9.8 in [11] for a description of the list format. May not be NULL. callback A callback to report the operation completion status. May not be NULL. pvCookie Memory passed to the callback code from the client. May be NULL. 4.5.3.4. Returns If an error occurs in starting the operation, one of the SLPError codes is returned. 4.5.4. SLPFindSrvTypes 4.5.4.1. Synopsis SLPError SLPFindSrvTypes(SLPHandle hSLP, const char *pcNamingAuthority, const char *pcScopeList, SLPSrvTypeCallback callback, void *pvCookie); The SLPFindSrvType() function issues an SLP service type request for service types in the scopes indicated by the pcScopeList. The results are returned through the callback parameter. The service types are independent of language locale, but only for services registered in one of scopes and for the indicated naming authority. If the naming authority is "*", then results are returned for all naming authorities. If the naming authority is the empty string, i.e. "", then the default naming authority, "IANA", is used. "IANA" is not a valid naming authority name, and it is a PARAMETER_BAD error to include it explicitly. The service type names are returned with the naming authority intact. If the naming authority is the default (i.e. empty string) Kempf, Guttman Expires 30 October 1998 [Page 33]
Internet Draft Service Location API 30 May 1998 then it is omitted, as is the separating ``.''. See [12] for more information on the syntax of service type names. 4.5.4.2. Parameters hSLP The SLPHandle on which to search for types. May not be NULL. pcNamingAuthority The naming authority to search. Use "*" for all naming authorities and the empty string, "", for the default naming authority. May not be NULL. pcScopeList A pointer to a char containing comma separated list of scope names to search for service types. May not be NULL or the empty string, "". callback A callback function through which the results of the operation are reported. May not be NULL. pvCookie Memory passed to the callback code from the client. May be NULL. 4.5.4.3. Returns If an error occurs in starting the operation, one of the SLPError codes is returned. 4.5.5. SLPFindSrvs 4.5.5.1. Synopsis SLPError SLPFindSrvs(SLPHandle hSLP, const char *pcServiceType, const char *pcScopeList, const char *pcSearchFilter, SLPSrvURLCallback callback, Kempf, Guttman Expires 30 October 1998 [Page 34]
Internet Draft Service Location API 30 May 1998 void *pvCookie); 4.5.5.2. Description Issue the query for services on the language specific SLPHandle and return the results through the callback. The parameters determine the results 4.5.5.3. Parameters hSLP The language specific SLPHandle on which to search for services. May not be NULL. pcServiceType The Service Type String for the request, such as can be discovered using SLPSrvTypes(). This could be, for example "service:printer:lpr" or "service:nfs". May not be NULL. pcScopeList A pointer to a char containing comma separated list of scope names. May not be NULL or the empty string, "". pcSearchFilter A query formulated of attribute pattern matching expressions in the form of a LDAPv3 Search Filter, see [8]. If this filter is empty, ie. "", all services of the requested type in the specified scopes are returned. May not be NULL. callback A callback function through which the results of the operation are reported. May not be NULL. pvCookie Memory passed to the callback code from the client. May be NULL. Kempf, Guttman Expires 30 October 1998 [Page 35]
Internet Draft Service Location API 30 May 1998 4.5.5.4. Returns If an error occurs in starting the operation, one of the SLPError codes is returned. 4.5.6. SLPFindAttrs 4.5.6.1. Synopsis SLPError SLPFindAttrs(SLPHandle hSLP, const char *pcURL, const char *pcScopeList, const char *pcAttrIds, SLPAttrCallback callback, void *pvCookie); 4.5.6.2. Description This function returns service attributes matching the attribute ids for the indicated full or partial URL. If pcURL is a complete URL, the attribute information returned is for that particular service in the language locale of the SLPHandle. If pcURL is a partial URL, then all attributes for the service type are returned regardless of the language of registration. Results are returned through the callback. The result is filtered with an SLP attribute request filter string parameter, the syntax of which is described in [11]. If the filter string is the empty string, i.e. "", all attributes are returned. 4.5.6.3. Parameters hSLP The language specific SLPHandle on which to search for attributes. May not be NULL. pcURL The full or partial URL. See [11] for partial URL syntax. May not be NULL. Kempf, Guttman Expires 30 October 1998 [Page 36]
Internet Draft Service Location API 30 May 1998 pcScopeList A pointer to a char containing comma separated list of scope names. May not be NULL or the empty string, "". pcAttrIds The filter string indicating which attribute values to return. Use empty string, "", to indicate all values. Wildcards matching all attribute ids having a particular prefix or suffix are also possible. See [11] for the exact format of the filter string. May not be NULL. callback A callback function through which the results of the operation are reported. May not be NULL. pvCookie Memory passed to the callback code from the client. May be NULL. 4.5.6.4. Returns If an error occurs in starting the operation, one of the SLPError codes is returned. 4.6. Miscellaneous Functions 4.7. SLPFindScopes 4.7.0.5. Synopsis SLPError SLPFindScopes(SLPHandle hSLP, const char* pcTypeHint, char** ppcScopeList); 4.7.0.6. Description Sets ppcScopeList parameter to a pointer to a comma separated list including all available scope values. The list of scopes comes from a variety of sources: the configuration file's net.slp.useScopes property and the net.slp.DAAddresses property, DHCP, or through the Kempf, Guttman Expires 30 October 1998 [Page 37]
Internet Draft Service Location API 30 May 1998 DA discovery process. If there is any order to the scopes, preferred scopes are listed before less desirable scopes. There is always at least one name in the list, the default scope, "DEFAULT". 4.7.0.7. Parameters hSLP The SLPHandle on which to search for scopes. May not be NULL. pcTypeHint A service type name to use as a hint if no scope information is available from DAs and SA discovery is used. Must not be NULL. Note that the API is free to ignore the hint if SA discovery is not implemented or the API client passes in an empty string or syntactically invalid service type name. ppcScopeList A pointer to char pointer into which the buffer pointer is placed upon return. The buffer is null terminated. The memory should be freed by calling SLPFree(). 4.7.0.8. Returns If no error occurs, returns SLP_OK, otherwise, the appropriate error code. 4.8. SLPParseSrvURL 4.8.0.9. Synopsis SLPError SLPParseSrvURL(char *pcSrvURL SLPSrvURL** ppSrvURL); 4.8.0.10. Description Parses the URL passed in as the argument into a service URL structure and return it in the ppSrvURL pointer. If a parse error occurs, returns SLP_PARSE_ERROR. The input buffer pcSrvURL is destructively modified during the parse and used to fill in the fields of the return structure. The structure returned in ppSrvURL should be freed Kempf, Guttman Expires 30 October 1998 [Page 38]
Internet Draft Service Location API 30 May 1998 with SLPFreeURL(). If the URL has no service part, the s_pcSrvPart string is the empty string, "", i.e. not NULL. If pcSrvURL is not a service: URL, then the s_pcSrvType field in the returned data structure is the URL's scheme, which might not be the same as the service type under which the URL was registered. If the transport is IP, the s_pcTransport field is the empty string. If the transport is not IP or there is no port number, the s_iPort field is zero. 4.8.0.11. Parameters pcSrvURL A pointer to a character buffer containing the null terminated URL string to parse. It is destructively modified to produce the output structure. May not be NULL. ppSrvURL A pointer to a pointer for the SLPSrvURL structure to receive the parsed URL. May not be NULL. The memory should be freed by a call to SLPFree() when no longer needed. 4.8.0.12. Returns If no error occurs, the return value is the SLP_OK. Otherwise, if an error occurs, one of the SLPError codes is returned. If no memory is available to allocate the character strings, returns SLP_COULD_NOT_ALLOCATE_MEMORY. If a parse error occurs, returns SLP_PROTOCOL_PARSE_ERROR. 4.9. SLPFree 4.9.0.13. Synopsis void SLPFree(void* pvMem); 4.9.0.14. Description Frees memory returned from SLPParseSrvURL(), SLPEscape(), SLPUnescape(), and SLPFindScopes(). Kempf, Guttman Expires 30 October 1998 [Page 39]
Internet Draft Service Location API 30 May 1998 4.9.0.15. Parameters pvMem A pointer to the storage allocated by the SLPParseSrvURL(), SLPEscape(), SLPUnescape(), or SLPFindScopes() function. Ignored if NULL. 4.10. SLPEscape 4.10.0.16. Synopsis SLPError SLPEscape(const char* pcInbuf, char** ppcOutBuf, SLPBoolean isTag); 4.10.0.17. Description Process the input string in pcInbuf and escape any SLP reserved characters. If the isTag parameter is SLPTrue, then look for bad tag characters and signal an error if any are found with the SLP_PARSE_ERROR code. The results are put into a buffer allocated by the API library and returned in the ppcOutBuf parameter. This buffer should be deallocated using SLPFree() when the memory is no longer needed. 4.10.0.18. Parameters pcInbuf Pointer to he input buffer to process for escape characters. ppcOutBuf Pointer to a pointer for the output buffer with the SLP reserved characters escaped. Must be freed using SLPFree() when the memory is no longer needed. isTag When true, the input buffer is checked for bad tag characters. Kempf, Guttman Expires 30 October 1998 [Page 40]
Internet Draft Service Location API 30 May 1998 4.10.0.19. Returns Return SLP_PARSE_ERROR if any characters are bad tag characters and the isTag flag is true, otherwise SLP_OK. 4.11. SLPUnescape 4.11.0.20. Synopsis SLPError SLPUnescape(const char* pcInbuf, char** ppcOutBuf, SLPBoolean isTag); 4.11.0.21. Description Process the input string in pcInbuf and unescape any SLP reserved characters. If the isTag parameter is SLPTrue, then look for bad tag characters and signal an error if any are found with the SLP_PARSE_ERROR code. No transformation is performed if the input string is an opaque. The results are put into a buffer allocated by the API library and returned in the ppcOutBuf parameter. This buffer should be deallocated using SLPFree() when the memory is no longer needed. 4.11.0.22. Parameters pcInbuf Pointer to he input buffer to process for escape characters. ppcOutBuf Pointer to a pointer for the output buffer with the SLP reserved characters escaped. Must be freed using SLPFree() when the memory is no longer needed. isTag When true, the input buffer is checked for bad tag characters. Kempf, Guttman Expires 30 October 1998 [Page 41]
Internet Draft Service Location API 30 May 1998 4.11.0.23. Returns Return SLP_PARSE_ERROR if any characters are bad tag characters and the isTag flag is true, otherwise SLP_OK. 4.12. SLPGetProperty 4.12.0.24. Synopsis const char* SLPGetProperty(const char* pcName); 4.12.0.25. Description Returns the value of the corresponding SLP property name. The returned string is owned by the library and MUST NOT be freed. 4.12.0.26. Parameters pcName Null terminated string with the property name, from Section 2.1. May not be NULL. 4.12.0.27. Returns If no error, returns a pointer to the property value. If the property was not set, returns the empty string, "". If an error occurs, returns NULL. The returned string MUST NOT be freed. 4.13. SLPSetProperty 4.13.0.28. Synopsis void SLPSetProperty(const char *pcName, const char *pcValue); Kempf, Guttman Expires 30 October 1998 [Page 42]
Internet Draft Service Location API 30 May 1998 4.13.0.29. Description Sets the value of the SLP property to the new value. The pcValue parameter should be the property value as a string. 4.13.0.30. Parameters pcName Null terminated string with the property name, from Section 2.1. May not be NULL. pcValue Null terminated string with the property value, in character format. May not be NULL. 4.14. Implementation Notes 4.14.1. Refreshing Registrations Because not all C platforms support multithreading, implementing automatic refreshing of registrations in the SA may be difficult. Therefore, automatic registration refreshing is not required of C implementations, however, implementations with multithreading are encouraged to support this important feature. 4.14.2. Syntax for String Parameters Query strings, attribute registration lists, attribute deregistration lists, scope lists, and attribute selection lists follow the syntax described in [11] for the appropriate requests. The API directly reflects the strings passed in from clients into protocol requests, and directly reflects out strings returned from protocol replies to clients. As a consequence, clients are responsible for formatting request strings, including escaping and converting opaque values to escaped byte encoded strings. Similarly, on output, clients are required to unescape strings and convert escaped string encoded opaques to binary. The functions SLPEscape() and SLPUnescape() can be used for escaping SLP reserved characters, but perform no opaque processing. Opaque values consist of a character buffer containing a UTF8-encoded string, the first characters of which are the nonUTF8 encoding '\ff'. Subsequent characters are the escaped values for the original bytes in the opaque. The escape convention is relatively simple. An Kempf, Guttman Expires 30 October 1998 [Page 43]
Internet Draft Service Location API 30 May 1998 escape consists of a backslash followed by the two hexadecimal digits encoding the byte. in the ASCII subset of UTF8. An example is '\2c' for the byte 0x2c. Clients handle opaque processing themselves, since the algorithm is relatively simple and uniform. 4.14.3. Client Side Syntax Checking API implementations may do syntax checking of scope names, naming authority names, and service type names on the client side, but are not required to do so. Since the C API is designed to be a thin layer over the protocol, some low memory SA implementations may find extensive syntax checking on the client side to be burdensome. If syntax checking uncovers an error in a parameter, the SLP_PARAMETER_BAD error must be returned. If any parameter is NULL and is required to be nonNULL, SLP_PARAMETER_BAD is returned. 4.14.4. System Properties The system properties established in the configuration file are accessable through the SLPGetProperty() and SLPSetProperty() functions. The SLPSetProperty() function only modifies properties in the running process, not in the configuration file. Errors are checked when the property is used and, as with parsing the configuration file, are logged. Program execution continues without interruption by substituting the default for the erroneous parameter. In general, individual agents should rarely be required to override these properties, since they reflect properties of the SLP network that are not of concern to individual agents. If changes are required, system administrators should modify the configuration file. 4.14.5. Memory Management The only API functions returning memory specifically requiring deallocation on the part of the client are SLPParseSrvURL(), SLPEscape(), SLPUnescape(), and SLPFindScopes(). This memory should be freed using SLPFree() when no longer needed. Character strings returned via the SLPGetProperty() function should NOT be freed, they are owned by the SLP library. Memory passed to callbacks belongs to the library and MUST NOT be retained by the client code. Otherwise, crashes are possible. Clients are required to copy data out of the callback parameters. No other use of the memory in callback parameters is allowed. Kempf, Guttman Expires 30 October 1998 [Page 44]
Internet Draft Service Location API 30 May 1998 4.14.6. Asychronous and Incremental Return Semantics If a handle parameter to an API function was opened asychronously, API function calls on the handle check the other parameters, open the appropriate operation and return immediately. In an error occurs in the process of starting the operation, an error code is returned. If the handle parameter was opened synchronously, the API function call blocks until all results are available, and returns only after the results are reported through the callback function. The return code indicates whether any errors occured both starting and during the operation. The callback function is called whenever the API library has results to report. The callback code is required to check the error code parameter before looking at the other parameters. If the error code is not SLP_OK, the other parameters may be NULL or otherwise invalid. The API library has the option of terminating any outstanding operation on which an error occurs. The callback code can similarly indicate that the operation should be terminated by passing back SLP_FALSE. Callback functions are not permitted to recursively call into the API on the same SLPHandle. If an attempt is made to recursively call into the API, the API function returns SLP_HANDLE_IN_USE. Prohibiting recursive callbacks on the same handle simplifies implementation of thread safe code, since locks held on the handle will not be in place during a second outcall on the handle. The total number of results received can be controlled by setting the net.slp.maxResults parameter. 4.15. Examples 4.15.1. Discovering one's mailbox A POP3 server might register itself with the SLP framework. The attributes it registers are "USER", a comma delimited list of all users whose mail is available through the POP3 server. The POP3 server code could be the following: SLPHandle slph; SLPRegReport errCallback = POPRegErrCallback; /* Create an English SLPHandle, asynchronous processing. */ SLPError err = SLPOpen("en", SLP_TRUE, &slph); if( err != SLP_OK ) { Kempf, Guttman Expires 30 October 1998 [Page 45]
Internet Draft Service Location API 30 May 1998 /* Deal with error. */ } /* Create the service: URL and attribute parameters. */ const char* surl = "service:pop3://mail.netsurf.de"; /* the URL */ const char *pcScopeList = "default,engineering"; const char *pcAttrs = "(user=sally,sue,sandra,zsuzsa)" err = SLPReg(slph, surl, SLP_LIFETIME_DEFAULT, pcScopeList, pcAttrs, errCallback, NULL); if (err != SLP_OK ) { /*Deal with error.*/ } The errCallback reports any errors: void POPRegErrCallback(SLPHandle hSLP, SLPError errCode, void* pvCookie) { if( errCode != SLP_OK ) { /* Report error through a dialog, message, etc. */ } } The POP3 client may locate the server for the user: /* * The client calls SLPOpen(), exactly as above. */ const char *pcSrvType = "service:pop3"; /* the service type */ const char *pcScopeList = "default"; /* the scope */ const char *pcFilter = "(user=sue)"; /* the search filter */ SLPSrvURLCallback srvCallback = /* the callback */ POPSrvURLCallback; Kempf, Guttman Expires 30 October 1998 [Page 46]
Internet Draft Service Location API 30 May 1998 err = SLPFindSrvs(slph, pcSrvType, pcScopeList, pcFilter, srvCallback, NULL); if( err != SLP_OK ) { /* Deal with error. */ } Within the callback, the client code can use the returned POP service: SLPBoolean POPSrvURLCallback(SLPHandle hSLP, const char* pcSrvURL, unsigned short sLifetime, SLPError errCode, void* pvCookie) { if( errCode != SLP_OK ) { /* Deal with error. */ } SLPSrvURL* pSrvURL; errCode = SLPParseSrvURL(pcSrvURL, &pSrvURL); if (err != SLP_OK ) { /* Deal with error. */ } else { /* get the server's address */ struct hostent *phe = gethostbyname(pSrvURL.s_pcHost); /* use hostname in pSrvURL to connect to the POP3 server * . . . */ SLPFreeSrvURL(pSrvURL); /* Free the pSrvURL storage */ } return SLP_FALSE; /* Done! */ Kempf, Guttman Expires 30 October 1998 [Page 47]
Internet Draft Service Location API 30 May 1998 } A client that wanted to discover all the users receiving mail at the server could do so with the following query: /* * The client calls SLPOpen(), exactly as above. We assume the * service: URL was retrieved into surl. */ const char *pcScopeList = "default"; /* the scope */ const char *pcAttrFilter = "use"; /* the attribute filter */ SLPAttrCallback attrCallBack = /* the callback */ POPUsersCallback err = SLPFindAttrs(slph, surl, pcScopeList, pcAttrFilter, attrCallBack, NULL); if( err != SLP_OK ) { /* Deal with error. */ } The callback processes the attributes: SLPBoolean POPUsersCallback(const char* pcAttrList, SLPError errCode, void* pvCookie) { if( errCode != SLP_OK ) { /* Deal with error. */ } else { /* Parse attributes. */ } return SLP_FALSE; /* Done! */ } Kempf, Guttman Expires 30 October 1998 [Page 48]
Internet Draft Service Location API 30 May 1998 5. Java Language Binding 5.1. Introduction The Java API is designed to model the various SLP entities in classes and objects. APIs are provided for SA, UA, and service type template access capabilities. The ServiceLocationManager class contains methods that return instances of objects implementing SA and UA capability. Each of these is modelled in an interface. The Locator interface provides UA capability and the Advertiser interface provides SA capability. The TemplateRegistry abstract class contains methods that return objects for template introspection and attribute type checking. The ServiceURL, ServiceType, and ServiceLocationAttribute classes model the basic SLP concepts. A concrete subclass instance of TemplateRegistry is returned by a class method. All SLP classes and interfaces are located within a single package. The package name should begin with the name of the implementation and conclude with the suffix "slp". Thus, the name for a hypothetical implementation from the University of Michigan would look like: edu.umich.slp This follows the Java convention of prepending the top level DNS domain name for the organization implementing the package onto the organization's name and using that as the package prefix. 5.2. Exceptions and Errors Most parameters to API methods are required to be nonnull. The API description indicates if a null parameter is acceptable, or if other restrictions constrain a parameter. When parameters are checked for validity (such as not being null) or their syntax is checked, an error results in the RuntimeException subclass IllegalArgumentException being thrown. Clients of the API are reminded that IllegalArgumentException, derived from RuntimeException, is unchecked by the compiler. Clients should thus be careful to include try/catch blocks for it if the relevent parameters could be erroneous. Standard Java practice is to encode every exceptional condition as a seperate subclass of Exception. Because of the relatively high cost in code size of Exception subclasses, the API contains only a single Exception subclass with different conditions being determined by an integer error code property. A subset, appropriate to Java, of the error codes described in Section 3 are available as constants on the Kempf, Guttman Expires 30 October 1998 [Page 49]
Internet Draft Service Location API 30 May 1998 ServiceLocationException class. The subset excludes error codes such as MEMORY_ALLOC_FAILED. 5.2.1. Class ServiceLocationException 5.2.1.1. Synopsis public class ServiceLocationException extends Exception 5.2.1.2. Description The ServiceLocationException class is thrown by all methods when exceptional conditions occur in the SLP framework. The error code property determines the exact nature of the condition, and an optional message may provide more information. 5.2.1.3. Fields public static final short LANGUAGE_NOT_SUPPORTED; public static final short PARSE_ERROR; public static final short INVALID_REGISTRATION; public static final short SCOPE_NOT_SUPPORTED; public static final short AUTHENTICATION_FAILED; public static final short AUTHENTICATION_ABSENT; public static final short INVALID_UPDATE; public static final short NOT_IMPLEMENTED; public static final short NETWORK_INIT_FAILED; public static final short NETWORK_TIMED_OUT; public static final short NETWORK_ERROR; public static final short INTERNAL_SYSTEM_ERROR; public static final short TYPE_ERROR; 5.2.1.4. Instance Methods public short getErrorCode() Return the error code. The error code takes on one of the static field values. Kempf, Guttman Expires 30 October 1998 [Page 50]
Internet Draft Service Location API 30 May 1998 5.3. Basic Data Structures 5.3.1. Interface ServiceLocationEnumeration public interface ServiceLocationEnumeration extends Enumeration 5.3.1.1. Description The ServiceLocationEnumeration class is the return type for all Locator SLP operations. The Java API library may implement this class to block until results are available from the SLP operation, so that the client can achieve asynchronous operation by retrieving results from the enumeration in a separate thread. Clients use the superclass nextElement() method if they are unconcerned with SLP exceptions. 5.3.1.2. Instance Methods public abstract Object next() throws ServiceLocationException Return the next value or block until it becomes available. Throws: ServiceLocationException Thrown if the SLP operation encounters an error. NoSuchElementException If there are no more elements to return. 5.3.2. Class ServiceLocationAttribute 5.3.2.1. Synopsis public class ServiceLocationAttribute extends Object implements Serializable Kempf, Guttman Expires 30 October 1998 [Page 51]
Internet Draft Service Location API 30 May 1998 5.3.2.2. Description The ServiceLocationAttribute class models SLP attributes. Instances of this class are returned by Locator.findAttributes() and are communicated along with register/deregister requests. 5.3.2.3. Constructors public ServiceLocationAttribute(String id,Vector values) Construct a service location attribute. Errors in the id or values vector result in an IllegalParameterException. Parameters: id The attribute name. The String can consist of any Unicode character. values A Vector of one or more attribute values. Vector contents must be uniform in type and one of Integer, String, Boolean, or byte[]. If the attribute is a keyword attribute, then parameter should be null. String values can consist of any Unicode character. 5.3.2.4. Class Methods public static String escapeId(String id) throws ServiceLocationException Returns an escaped version of the id parameter, suitable for inclusion in a query. Any reserved characters as specified in [11] are escaped using UTF8 encoding. Parameters: id The attribute id to escape. ServiceLocationException is thrown if any characters are illegal in an id. Kempf, Guttman Expires 30 October 1998 [Page 52]
Internet Draft Service Location API 30 May 1998 public static String escapeValue(Object value) throws ServiceLocationException Returns a String containing the escaped value parameter as a String, suitable for inclusion in a query. If the value parameter is a string, any reserved characters as specified in [11] are escaped using UTF8 encoding. If the value parameter is a byte array, then the escaped string begins with the nonUTF8 sequence `\ff` and the rest of the string consists of the escaped bytes. If the value parameter is a Boolean or Integer, then the returned string contains the object converted into a string. If the value is any other type, an IllegalArgumentException is thrown. Parameters: value The attribute value to be converted into a string and escaped. 5.3.2.5. Instance Methods public Vector getValues() Returns a cloned vector of attribute values, or null if the attribute is a keyword attribute. If the attribute is single-valued, then the vector contains only one object. public String getId() Returns the attribute's name. public boolean equals(Object o) Overrides Object.equals(). Two attributes are equal if their identifiers are equal and their value vectors contain the same number of equal values as determined by the Object equals() method. Values having byte[] type are equal if the contents of all byte arrays in both vectors match. Kempf, Guttman Expires 30 October 1998 [Page 53]
Internet Draft Service Location API 30 May 1998 public String toString() Overrides Object.toString(). public int hashCode() Overrides Object.hashCode(). Hashes on the attribute's id. 5.3.3. Class ServiceType 5.3.3.1. Synopsis public class ServiceType extends Object implements Serializable 5.3.3.2. Description The ServiceType object models the SLP service type. It parses a string based service type specifier into its various components, and contains property accessors to return the components. URL schemes, protocol service types, and abstract service types are all handled. 5.3.3.3. Constructors public ServiceType(String type) Construct a service type object from the service type specifier. Throws IllegalArgumentException if the type name is syntactically incorrect. Parameters: type The service type name as a String. If the service type is from a service: URL, the "service:" prefix must be intact. Kempf, Guttman Expires 30 October 1998 [Page 54]
Internet Draft Service Location API 30 May 1998 5.3.3.4. Methods public boolean isServiceURL() Returns true if the type name contains the "service:" prefix. public boolean isServiceURL() Returns true if the type name contains the "service:" prefix. public boolean isAbstractType() Returns true if the type name is for an abstract type. public boolean isNADefault() Returns true if the naming authority is the default, i.e. is the empty string. public String getConcreteTypeName() Returns the concrete type name in an abstract type, the protocol name in a protocol type, or the URL scheme if the type name is not for a service: URL. public String getPrincipleTypeName() Returns the abstract type name for an abstract type or an empty string for a protocol type or URL scheme. public String getAbstractTypeName() If the type is an abstract type, returns the fully formatted abstract type name including the "service:" and naming authority but without the concrete type name or intervening colon. Kempf, Guttman Expires 30 October 1998 [Page 55]
Internet Draft Service Location API 30 May 1998 public String getNamingAuthority() Return the naming authority name, or the empty string if the naming authority is the default. public boolean equals(Object obj) Overrides Object.equals(). The two objects are equal if they are both ServiceType objects and the components of both are equal. public String toString() Returns the fully formatted type name, including the "service:" if the type was originally from a service: URL. public int hashCode() Overrides Object.hashCode(). Hashes on the string value of the individual components of the service type name. 5.3.4. Class ServiceURL 5.3.4.1. Synopsis public class ServiceURL extends Object implements Serializable 5.3.4.2. Description The ServiceURL object models the advertised SLP service URL. It can be either a service: URL or a regular URL. These objects are returned from service lookup requests, and describe the registered services. This class should be a subclass of java.net.URL but can't since that class is final. Kempf, Guttman Expires 30 October 1998 [Page 56]
Internet Draft Service Location API 30 May 1998 5.3.4.3. Class Variables public static final int NO_PORT Indicates that no port information is required or was returned for this URL. public static final int LIFETIME_NONE Indicates that the URL has a zero lifetime. This value is never returned from the API, but can be used to create a ServiceURL object to deregister, delete attributes, or find attributes. public static final int LIFETIME_DEFAULT The default URL lifetime (3 hours) in seconds. public static final short LIFETIME_MAXIMUM The maximum URL lifetime (about 18 hours) in seconds. 5.3.4.4. Constructors public ServiceURL(String URL,short lifetime) Construct a service URL object having the specified lifetime. Parameters: URL The URL as a string. Must be either a service: URL or a valid regular URL. lifetime The service advertisement lifetime in seconds. This value may be between LIFETIME_NONE and LIFETIME_MAXIMUM. Kempf, Guttman Expires 30 October 1998 [Page 57]
Internet Draft Service Location API 30 May 1998 5.3.4.5. Methods public ServiceType getServiceType() Returns the service type object representing the service type name of the URL. public final void setServiceType(ServiceType type) throws ServiceLocationException Set the service type name to the object. Ignored if the URL is a service: URL. Parameters: type The service type object. public String getTransport() Get the network layer transport identifier. If the transport is IP, an empty string, "", is returned. public String getHost() Returns the host identifier. For IP, this will be the machine name or IP address. public int getPort() Returns the port number, if any. For nonIP transports, always returns NO_PORT. public String getURLPath() Returns the URL path description, if any. Kempf, Guttman Expires 30 October 1998 [Page 58]
Internet Draft Service Location API 30 May 1998 public int getLifetime() Returns the service advertisement lifetime. This will be a positive int between LIFETIME_NONE and LIFETIME_MAXIMUM. public boolean equals(Object obj) Compares the object to the ServiceURL and returns true if the two are the same. Two ServiceURL objects are equal if their current service types match and they have the same host, port, transport, and URL path. public String toString() Returns formatted string with the URL. Overrides Object.toString(). The returned URL has the original service type or URL scheme, not the current service type. public int hashCode() Overrides Object.hashCode(). Hashes on the current service type, transport, host, port, and URL part. 5.4. SLP Access Interfaces 5.4.1. Interface Advertiser 5.4.1.1. Synopsis public interface Advertiser 5.4.1.2. Description The Advertiser is the SA interface, allowing clients to register new service instances with SLP, to change the attributes of existing services, and to deregister service instances. New registrations and modifications of attributes are made in the language locale Kempf, Guttman Expires 30 October 1998 [Page 59]
Internet Draft Service Location API 30 May 1998 with which the Advertiser was created, deregistrations of service instances are made for all locales. 5.4.1.3. Instance Methods public abstract Locale getLocale() Return the language locale with which this object was created. public abstract void register(ServiceURL URL, Vector scopes, Vector attributes) throws ServiceLocationException Register a new service with SLP having the given attributes and in the given scope. Parameters: URL The URL for the service. scopes A Vector of scope names. Scope Strings MUST contain all the scopes returned from the results of a findScopes() API invocation. attributes A vector of ServiceLocationAttribute objects describing the service. public abstract void deregister(ServiceURL URL,Vector scopes) throws ServiceLocationException Deregister a service from the SLP framework. This has the effect of deregistering the service from every language locale in the given scopes. Parameters: Kempf, Guttman Expires 30 October 1998 [Page 60]
Internet Draft Service Location API 30 May 1998 URL The URL for the service. scopes A Vector of scope names. Scope Strings MUST contain all the scopes returned from the results of a findScopes() API invocation. public abstract void addAttributes(ServiceURL URL, Vector scopes, Vector attributes) throws ServiceLocationException Update the registration by adding the given attributes in the given scopes. Parameters: URL The URL for the service. scopes A Vector of scope names. Scope Strings MUST contain all the scopes returned from the results of a findScopes() API invocation. attributes A Vector of ServiceLocationAttribute objects to add to the existing registration. Use an empty vector to update the URL alone. May not be null. public abstract void deleteAttributes(ServiceURL URL, Vector scopes, Vector attributeIds) throws ServiceLocationException Delete the attributes from a URL in all scopes for the locale with which the Advertiser was created. Kempf, Guttman Expires 30 October 1998 [Page 61]
Internet Draft Service Location API 30 May 1998 Parameters: URL The URL for the service. scopes A Vector of scope names. Scope Strings MUST contain all the scopes returned from the results of a findScopes() API invocation. attributeIds A vector of Strings indicating the ids of the attributes to remove. Use an empty vector to indicate all attributes. 5.4.2. Interface Locator 5.4.2.1. Synopsis public interface Locator 5.4.2.2. Description The Locator is the UA interface, allowing clients to query the SLP framework about existing service types, services instances, and about the attributes of an existing service instance or service type. Queries for services and attributes are made in the locale with which the Locator was created, queries for service types are independent of locale. 5.4.2.3. Instance Methods public abstract Locale getLocale() Return the language locale with which this object was created. public abstract ServiceLocationEnumeration findServiceTypes(String namingAuthority, Vector scopes) Kempf, Guttman Expires 30 October 1998 [Page 62]
Internet Draft Service Location API 30 May 1998 throws ServiceLocationException Returns an enumeration of ServiceType objects giving known service types for the given scopes and given naming authority. If no service types are found, an empty enumeration is returned. Parameters: namingAuthority The naming authority. Use "" for the default naming authority and "*" for all naming authorities. scopes A Vector of scope names. Scope Strings SHOULD be selected from the results of a findScopes() API invocation. Use "DEFAULT" for the default scope. public abstract ServiceLocationEnumeration findServices(ServiceType type, Vector scopes, String searchFilter) throws ServiceLocationException Returns a vector of ServiceURL objects for services matching the query, and having a matching type in the given scopes. If no services are found, an empty enumeration is returned. Parameters: type The SLP service type of the service. scopes A Vector of scope names. Scope Strings SHOULD be selected from the results of a findScopes() API invocation. Use "DEFAULT" for the default scope. searchFilter An LDAPv3 [8] string encoded query. If the filter is empty, ie. "", all services of the requested type in the specified scopes are returned. SLP reserved characters must be escaped Kempf, Guttman Expires 30 October 1998 [Page 63]
Internet Draft Service Location API 30 May 1998 in the query. Use ServiceLocationAttribute.escapeId() and ServiceLocatinAttribute.escapeValue() to construct the query. public abstract ServiceLocationEnumeration findAttributes(ServiceURL URL, Vector scopes, Vector attributeIds) throws ServiceLocationException For the URL and scope, return a Vector of ServiceLocationAttribute objects whose ids match the String patterns in the attributeIds Vector. The request is made in the language locale of the Locator. If no attributes match, an empty enumeration is returned. Parameters: URL The URL for which the attributes are desired. scopes A Vector of scope names. Scope Strings SHOULD be selected from the results of a findScopes() API invocation. Use "DEFAULT" for the default scope. attributeIds A Vector of String patterns identifying the desired attributes. An empty vector means return all attributes. As described in [11], the patterns may include wildcards to match all prefixes or suffixes. The patterns may include SLP reserved characters, they will be escaped by the API before transmission. public abstract ServiceLocationEnumeration findAttributes(ServiceType type, Vector scopes, Vector attributeIds) throws ServiceLocationException For the type and scope, return a Vector of all ServiceLocationAttribute objects whose ids match the String patterns in the attributeIds Vector. The request is made independent of language locale. If no attributes are found, an empty vector is returned. Kempf, Guttman Expires 30 October 1998 [Page 64]
Internet Draft Service Location API 30 May 1998 Parameters: serviceType The service type. scopes A Vector of scope names. Scope Strings SHOULD be selected from the results of a findScopes() API invocation. Use "DEFAULT" for the default scope. attributeIds A Vector of String patterns identifying the desired attributes. An empty vector means return all attributes. As described in [11], the patterns may include wildcards to match all prefixes or suffixes. The patterns may include SLP reserved characters, they will be escaped by the API before transmission. 5.5. The Service Location Manager 5.5.1. Class ServiceLocationManager 5.5.1.1. Synopsis public class ServiceLocationManager extends Object 5.5.1.2. Description The ServiceLocationManager manages access to the service location framework. Clients obtain the Locator and Advertiser objects for UA and SA, and a Vector of known scope names from the ServiceLocationManager. 5.5.1.3. Class Methods public static Vector findScopes(ServiceType typeHint) throws ServiceLocationException Kempf, Guttman Expires 30 October 1998 [Page 65]
Internet Draft Service Location API 30 May 1998 Returns an Vector of strings with all available scope names. The list of scopes comes from a variety of sources. Scope names obtained through DHCP have first priority, followed by scope names in the net.slp.useScopes property. These names are used to filter names obtained from the net.slp.DAAddresses property and through active and passive discovery. There is always at least one string in the Vector, the default scope, "DEFAULT". Parameters: typeHint A service type name to use as a hint if no scope information is available from DAs and SA discovery is used. May be null if SA discovery is not desired. Note that the API is free to ignore the hint if SA discovery is not implemented. public static Locator getLocator(Locale locale) throws ServiceLocationException Return a Locator object for the given language Locale. If the implementation does not support UA functionality, returns null. Parameters: locale The language locale of the Locator. The default SLP locale is used if null. public static Advertiser getAdvertiser(Locale locale) throws ServiceLocationException Return an Advertiser object for the given language locale. If the implementation does not support SA functionality, returns null. Parameters: locale The language locale of the Advertiser. The default SLP locale is used if null. Kempf, Guttman Expires 30 October 1998 [Page 66]
Internet Draft Service Location API 30 May 1998 5.6. Service Template Introspection 5.6.1. Abstract Class TemplateRegistry 5.6.1.1. Synopsis public abstract class TemplateRegistry 5.6.1.2. Description Subclasses of the TemplateRegistry abstract class provide access to service location templates [12]. Classes implementing TemplateRegistry perform a variety of functions. They manage the registration and access of service type template documents. They create attribute verifiers from service templates, for verification of attributes and introspection on template documents. Note that clients of the Advertiser are not required to verify attributes before registering (though they may get a TYPE_ERROR if the implementation supports type checking and there is a mismatch with the template). 5.6.1.3. Class Methods public static TemplateRegistry getTemplateRegistry(); Returns the distinguished TemplateRegistry object for performing operations on and with service templates. Returns null if the implementation doesn't support TemplateRegistry functionality. 5.6.1.4. Instance Methods public abstract void registerServiceTemplate(ServiceType type, String documentURL, Locale locale, String version) throws ServiceLocationException Register the service template with the template registry. Kempf, Guttman Expires 30 October 1998 [Page 67]
Internet Draft Service Location API 30 May 1998 Parameters: type The service type. documentURL The URL of the template document. locale A Locale object containing the language locale of the template. version The version number of template document. public abstract void deregisterServiceTemplate(ServiceType type, Locale locale, String version) throws ServiceLocationException Deregister the template for the service type. Parameters: type The service type. locale A Locale object containing the language locale of the template. version A String containing the version number. Use null to indicate the latest version. public abstract String findTemplateURL(ServiceType type, Locale locale, String version) throws ServiceLocationException Kempf, Guttman Expires 30 October 1998 [Page 68]
Internet Draft Service Location API 30 May 1998 Returns the URL for the template document. Parameters: type The service type. locale A Locale object containing the language locale of the template. version A String containing the version number. Use null to indicate the latest version. public abstract ServiceLocationAttributeVerifier attributeVerifier(String documentURL) throws ServiceLocationException Reads the template document URL and returns an attribute verifier for the service type. The attribute verifier can be used for verifying that registration attributes match the template, and for introspection on the template definition. Parameters: documentURL A String containing the template document's URL. 5.6.2. Interface ServiceLocationAttributeVerifier 5.6.2.1. Synopsis public interface ServiceLocationAttributeVerifier Kempf, Guttman Expires 30 October 1998 [Page 69]
Internet Draft Service Location API 30 May 1998 5.6.2.2. Description The ServiceLocationAttributeVerifier provides access to service templates. Classes implementing this interface parse SLP template definitions, provide information on attribute definitions for service types, and verify whether a ServiceLocationAttribute object matches a template for a particular service type. Clients obtain ServiceLocationAttributeVerifier objects for specific SLP service types through the TemplateRegistry. 5.6.2.3. Instance Methods public abstract ServiceType getServiceType() Returns the SLP service type for which this is the verifier. public abstract Vector getTemplateAttributeDescriptors() Returns a Vector of ServiceLocationAttributeDescriptor objects describing the template service type attributes. The template service type attributes are: service-type The SLP service type name (a String). version The version number of the template (a String). language The RFC 1766 [10] Language Tag locale of the template (a String). description A natural language description of the service in the language of the language locale (a String). Kempf, Guttman Expires 30 October 1998 [Page 70]
Internet Draft Service Location API 30 May 1998 url-syntax An ABNF [9] description for the of the service type's URL (a String). public abstract Vector getTemplateAttributes() Returns a Vector of ServiceLocationAttribute objects for the template attributes of this service type. The template attributes are listed above. The ServiceLocationAttribute objects in this vector have the actual values of the template attributes. public abstract ServiceLocationAttributeDescripton getAttributeDescriptor(String attrId) Return the ServiceLocationAttributeDescription for the attribute having the named id. If no such attribute exists in this template, return null. This method is primarily for GUI tools to display attribute information. Programmatic verification of attributes should use the verifyAttribute() method. public abstract Enumeration getAttributeDescriptors() Returns an Enumeration allowing introspection on the attribute definition in the service template. The Enumeration returns ServiceLocationAttributeDescriptor objects for the attributes. This method is primarily for GUI tools to display attribute information. Programmatic verification of attributes should use the verifyAttribute() method. public abstract void verifyAttribute( ServiceLocationAttribute attribute) throws ServiceLocationException Verify that the attribute matches the template definition. If the attribute doesn't match, ServiceLocationException is thrown with the error code as ServiceLocationException.PARSE_ERROR. Kempf, Guttman Expires 30 October 1998 [Page 71]
Internet Draft Service Location API 30 May 1998 Parameters: attribute The ServiceLocationAttribute object to be verified. public abstract void verifyRegistration( Vector attributeVector) throws ServiceLocationException Verify that the Vector of ServiceLocationAttribute objects matches the template for this service type. The vector must contain all the required attributes, and all attributes must match their template definitions. If the attributes don't match, ServiceLocationException is thrown with the error code as ServiceLocationException.PARSE_ERROR Parameters: attributeVector A Vector of ServiceLocationAttribute objects for the registration. 5.6.3. Interface ServiceLocationAttributeDescriptor 5.6.3.1. Synopsis public interface ServiceLocationAttributeDescriptor 5.6.3.2. Description The ServiceLocationAttributeDescriptor interface provides introspection on a template attribute defintion. Classes implementing the ServiceLocationAttributeDescriptor interface return information on a particular service location attribute definition from the service template. This information is primarily for GUI tools. Programmatic attribute verification should be done through the ServiceLocationAttributeVerifier. Kempf, Guttman Expires 30 October 1998 [Page 72]
Internet Draft Service Location API 30 May 1998 5.6.3.3. Instance Methods public abstract String getId() Return a String containing the attribute's id. public abstract String getValueType() Return a String containing the fully package-qualified Java type of the attribute. SLP types are translated into Java types as follows: STRING "java.lang.String" INTEGER "java.lang.Integer" BOOLEAN "java.lang.Boolean" OPAQUE "[B" (i.e. array of byte, byte[]) KEYWORD empty string, "" public abstract String getDescription() Return a String containing the attribute's help text. public abstract Enumeration getAllowedValues() Return an Enumeration of allowed values for the attribute type. For keyword attributes returns null. For no allowed values (i.e. unrestricted) returns an empty Enumeration. Kempf, Guttman Expires 30 October 1998 [Page 73]
Internet Draft Service Location API 30 May 1998 public abstract Enumeration getDefaultValues() Return an Enumeration of default values for the attribute type. For keyword attributes returns null. For no allowed values (i.e. unrestricted) returns an empty Enumeration. public abstract boolean getIsMultivalued() Returns true if the "M" flag is set. public abstract boolean getIsOptional() Returns true if the "O"" flag is set. public abstract boolean getRequiredAttribute() Returns true if the "X"" flag is set, indicating that the attribute SHOULD be included in an any Locator.findServices() request search filter. public abstract boolean getIsLiteral() Returns true if the "L" flag is set. public abstract boolean getIsKeyword() Returns true if the attribute is a keyword attribute. Kempf, Guttman Expires 30 October 1998 [Page 74]
Internet Draft Service Location API 30 May 1998 5.7. Implementation Notes 5.7.1. Refreshing Registrations Because Java supports threads at the language level, automatic refreshing of service advertisements in the Advertiser API is required. 5.7.2. Parsing Alternate Transports in ServiceURL The ServiceURL class is designed to handle multiple transports. The standard API performs no additional processing on transports other than IP. However, implementations are free to subclass ServiceURL and support additional methods that provide more detailed parsing of alternate transport information. For IP transport, the port number, if any, is returned from the getPort() method. For nonIP transports, the getPort() method returns NO_PORT. 5.7.3. Client Side Syntax Checking The syntax of scope names, service type names, naming authority names, and URLs is described in [11] and [12]. The various methods and classes taking String parameters for these entities should type check the parameters for syntax errors on the client side, and throw an IllegalArgumentException if an error occurs. In addition, character escaping should be implemented before network transmission for escapable characters in attribute ids and String values. This reduces the number of error messages transmitted. The ServiceLocationAttribute class provides methods for obtaining escaped attribute id and value strings to facilitate query construction. 5.7.4. Language Locale Handling The Locator and Advertiser interfaces are created with a Locale parameter. The language locale with which these objects are created is used in all SLP requests issued through the object. If the Locale parameter is null, the default SLP locale is used. The default SLP locale is determined by, first, checking the net.slp.locale System property. If that is unset, then the default SLP locale [11] is used, namely "en". The net.slp.locale property is the only SLP system property that a client of the API would routinely override. Kempf, Guttman Expires 30 October 1998 [Page 75]
Internet Draft Service Location API 30 May 1998 5.7.5. Setting SLP System Properties SLP system properties that are originally set in the configuration file can be overridden programmatically in API clients by simply invoking the System.getProperties() operation to get a copy of the system properties, modifying or adding the SLP property in question, then using System.setProperties() to set the properties to the modified Property object. Errors are checked when the property is used and, as with parsing the configuration file, are logged. Program execution continues without interruption by substituting the default for the erroneous parameter. In general, individual agents should rarely be required to override these properties, since they reflect properties of the SLP network that are not of concern to individual agents. If changes are required, system administrators should modify the configuration file. 5.7.6. Multithreading Thread-safe operation are relatively easy to achieve in Java. By simply making each method in the classes implementing the Locator and Advertiser interfaces synchronized, and by synchronizing access to any shared data structures within the class the Locator and Advertiser interfaces are made safe. Alternatively, finer grained synchronization is also possible within the classes implementing Advertiser and Locator. 5.7.7. Modular Implementations While, at first glance, the API may look rather heavyweight, the design has been carefully arranged so that modular implementations that provide only SA, only UA, or only service template access capability, or any combination of the three, are possible. Because the objects returned from the ServiceLocationManager.getLocator() and ServiceLocationManager.getAdvertiser() operations are interfaces, and because the objects returned through those interfaces are in the set of base data structures, an implementation is free to omit either UA or SA capability by simply returning null from the instance creation operation if the classes implementing the missing function is cannot be dynamically linked. API clients are encouraged to check for such a contingency, and to signal an exception if it occurs. Similarly, the TemplateRegistry subclass can simply be omitted from an implementation that only supports UA and/or SA clients, and the getRegistry() method can return null. In this way, the API implementation can be taylored for the particular memory requirements at hand. Kempf, Guttman Expires 30 October 1998 [Page 76]
Internet Draft Service Location API 30 May 1998 In addition, if an implementation only supports the minimal subset of SLP [11], the unsupported Locator and Advertiser interface operations can throw an exception with ServiceLocationException.NOT_IMPLEMENTED as the error code. This supports better source portablity between low and high memory platforms. 5.7.8. Asynchronous and Incremental Return Semantics The Java API contains no specific support for asychronous operation. Incremental return is not needed for the Advertiser because service registrations can be broken up into pieces when large. Asychronous return is also not needed because clients can always issue the Advertiser operation in a separate thread if the calling thread can't block. The Locator can be implemented either sychronously or asychronously. Since the return type for Locator calls is ServiceLocationEnumeration, a Java API implementation that supports asynchronous semantics can implement ServiceLocationEnumeration to dole results out as they come in, blocking when no results are available. If the client code needs to support other processing while the results are trickling in, the call into the enumeration to retrieve the results can be done in a separate thread. Unlike the C case, collation semantics for return of attributes when the request is made with a service type require that the API collate returned values so that only one attribute having a collation of all returned values appear to the API client. In practice, this may limit the amount of asychronony possible with the findAttributes() method. This requirement is imposed because memory management is much easier in Java and so implementing collation as part of the API should not be as difficult as in C, and it saves the client from having to do the collation. 5.8. Examples In this example, a printer server advertises its availability to clients. Additionally, the server advertises a service template for use by client software in validating service requests: //Get the Advertiser and TemplateRegistry. Advertiser adv = null; TemplateRegistry tr = null try { Kempf, Guttman Expires 30 October 1998 [Page 77]
Internet Draft Service Location API 30 May 1998 adv = ServiceLocationManager.getAdvertiser("en"); tr = TemplateRegistry.getTemplateRegistry(); } catch( ServiceLocationException ex ) { } //Deal with error. if( adv == null ) { //Serious error as printer can't be registered // if the implementation doesn't support SA // functionality. } //Get the scopes in which we are supposed to // register. Vector scopes = ServiceLocationManager.findScopes(); //Get the printer's attributes, from a file or // otherwise. We assume that the attributes // conform to the template, otherwise, we // could register the template here and verify // them. Vector attributes = getPrinterAttributes(); //Create the service: URL for the printer. ServiceURL printerURL = new ServiceURL( "service:printer:lpr://printshop/color2", ServiceURL.LIFETIME_MAXIMUM); try { //Register the printer in all scopes. adv.register(printerURL, scopes, attributes); //If the template registry is available, // register the printer's template. if( tr != null ) { tr.registerServiceTemplate( new ServiceType("service:printer"), "http://shop.arv/printer/printer-lpr.slp", new Locale("en",""), Kempf, Guttman Expires 30 October 1998 [Page 78]
Internet Draft Service Location API 30 May 1998 "1.0"); } } catch( ServiceLocationException ex ) { } //Deal with error. Suppose a client is looking for color printer. The following code might be used to issue a request for printer advertisements: Locator loc = null; TemplateRegistry tr = null; try { loc = ServiceLocationManager.getLocator("en"); } catch( ServiceLocationException ex ) { } //Deal with error. if( loc == null ) { //Serious error as client can't be located // if the implementation doesn't support // UA functionality. } //We want a color printer that does CMYK // and prints at least 600 dpi. String query = "(&(marker-type=CMYK)(resolution=600))"; //Get scopes. Vector scopes = ServiceLocationManager.findScopes(); Enumeration services; try { services = loc.findServices(new ServiceType("service:printer"),scopes,query); } catch { } //Deal with error. if (services.hasMoreElements() ) { //Printers can now be used. Kempf, Guttman Expires 30 October 1998 [Page 79]
Internet Draft Service Location API 30 May 1998 ServiceURL surl = (ServiceURL) services.next(); Socket sock = new Socket(surl.getHost, surl.getPort()); // Use the Socket... } 6. Internationalization Considerations 6.1. service URL The service URL itself must be encoded using the rules set forth in [2]. The character set encoding is limited to specific ranges within the UTF8 character set [7]. The attribute information associated with the service URL may be expressed in any character set, and in any language. See [12] for attribute internationalization guidelines. 6.2. Character Set Encoding Configuration and serialized registration files are encoded in the UTF8 character set [7]. This is fully compatible with ASCII character values. C platforms that do not support UTF8 are required to check the top bit of input bytes to determine whether the incoming character is multibyte. If it is, the character should be dealt with accordingly. Since the SLP wire protocol requires that strings are encoded as UTF8, C platforms without UTF8 support need to supply their own support, if only in the form of multibyte string handling. At the API level, the character encoding is specified to be Unicode for Java and UTF8 for C. Unicode is the default in Java. For C, the standard ASCII 8 bits per character, null terminated C strings are a subset of the UTF8 character set, and so work in the API. Because the C API is very simple, the API library needs to do a minimum of processing on UTF8 strings. They primarily just need to be reflected into the outgoing SLP messages, and reflected out of the API from incoming SLP messages. 6.3. Language Tagging All SLP requests and registrations are tagged to indicate in which language the strings included are encoded. This allows multiple languages to be supported. It also presents the possibility that Kempf, Guttman Expires 30 October 1998 [Page 80]
Internet Draft Service Location API 30 May 1998 error conditions result when a request is made in a language that is not supported. In this case, an error is only returned when there is data available, but not obtainable in the language requested. The dialect portion of the Language Tag is used on 'best effort' basis for matching strings by SLP. Dialects that match are prefered over those which don't. Dialects that do not match will not prevent string matching or comparisons to occur. 7. Security Considerations SLP makes use of an existing host based authentication framework once it becomes available as an Internet Standard. [5] An adversary could delete valid service advertisements, provide false service information and deny UAs knowledge of existing services unless the mechanisms in SLP for authenticating SLP messages are used. These mechanisms allow DA Adverts, SA Adverts, Service URLs and Service Attributes to be verified using digital cryptography. For this reason, all SLP agents SHOULD be configured to use protected scopes and DA Advertisement verifying cryptographic keys. See [11] for a description of how these mechanisms work. 8. Acknowledgements The authors would like to thank Don Provan for his pioneering work during the initial stages of API definition. Kempf, Guttman Expires 30 October 1998 [Page 81]
Internet Draft Service Location API 30 May 1998 References [1] ANSI. Coded Character Set -- 7-bit American Standard code for Information Interchange. X3.4-1986, 1986. [2] T. Berners-Lee, R. Fielding, and L. Masinter. Uniform Resource Locators (URL): Generic Syntax and Semantics. RFC1738 as amended by RFC1808 and updated by draft-fielding-url-syntax-05.txt, May 1997. (work in progress). [3] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service Location Protocol. RFC 2165, July 1997. [4] IANA IANA Character Set Registry <URL:http://www.isi.edu/in-notes/iana/assignments/character-sets> [5] R. Atkinson Security Architecture for the Internet RFC 1825 July 1995 [6] Geneva ISO Code for the representation of names of languages ISO 639:1998 (E/F) 1998 [7] F. Yerfeau UTF-8, a transformation format of ISO 10646. RFC 2279 January 1998. [8] T. Howes The String Representation of LDAP Search Filters RFC 2254 December 1997. [9] D. Crocker and P Overell. Augmented BNF for Syntax Specifications: ABNF. RFC 2234 November 1997. [10] H. Alvestrand. Tags for the Identification of Languages. RFC 1766 March 1995. [11] E. Guttman, C. Perkins, J. Veizades, and M. Day. Service Location Protocol. draft-ietf-svrloc-protocol-v2-04.txt A work in progress March 1998. [12] E. Guttman, C. Perkins, J. Kempf Service Templates and service: Schemes draft-ietf-svrloc-service-scheme-09.txt A work in progress March 1998. Kempf, Guttman Expires 30 October 1998 [Page 82]
Internet Draft Service Location API 30 May 1998 Authors' Addresses Questions about this memo can be directed to: James Kempf Erik Guttman Sun Microsystems Sun Microsystems 901 San Antonio Rd. Bahnstr. 2 Palo Alto, CA, 94303 74915 Waibstadt USA Germany +1 650 786 5890 +49 7263 911 701 +1 650 786 6445 (fax) james.kempf@sun.com erik.guttman@sun.com Kempf, Guttman Expires 30 October 1998 [Page 83]
