RFC2614 - An API for Service Location

Network Working Group J. Kempf
Request for Comments: 2614 E. Guttman
Category: Informational Sun Microsystems
June 1999
An API for Service Location
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. 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 APIs for SLP in C and Java. The APIs are
modular and are designed to allow implementations 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
program code is difficult or impossible, and to portably exchange a
registration database.
Table of Contents
1. IntrodUCtion 4
1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . 4
2. File Formats 7
2.1. Configuration File Format . . . . . . . . . . . . . . 8
2.1.1. DA configuration . . . . . . . . . . . . . . 9
2.1.2. Static Scope Configuration . . . . . . . . . . 9
2.1.3. Tracing and Logging . . . . . . . . . . . . . 11
2.1.4. Serialized Proxy Registrations . . . . . . . . 11
2.1.5. Network Configuration Properties . . . . . . . 12
2.1.6. SA Configuration . . . . . . . . . . . . . . . 14
2.1.7. UA Configuration . . . . . . . . . . . . . . . 14
2.1.8. Security . . . . . . . . . . . . . . . . . . 15
2.2. Multihomed Machines. . . . . . . . . . . . . . . . . . 16
2.3. Serialized Registration File . . . . . . . . . . . . . 16
2.4. Processing Serialized Registration and Configuration
Files . . . . . . . . . . . . . . . . . . . . . . . . 18
3. Binding Independent Implementation Considerations 18
3.1. Multithreading . . . . . . . . . . . . . . . . . . . . 18
3.2. Asynchronous and Incremental . . . . . . . . . . . . . 19
3.3. Type Checking for Service Types. . . . . . . . . . . . 19
3.4. Refreshing Registrations . . . . . . . . . . . . . . . 19
3.5. Configuration File Processing . . . . . . . . . . . . 19
3.6. Attribute Types . . . . . . . . . . . . . . . . . . . 20
3.7. Removal of Duplicates . . . . . . . . . . . . . . . . 20
3.8. Character Set Encoding . . . . . . . . . . . . . . . . 20
3.9. Error Semantics . . . . . . . . . . . . . . . . . . . 20
3.10. Modular Implementations . . . . . . . . . . . . . . . 24
3.11. Handling Special Service Types . . . . . . . . . . . . 24
3.12. Scope Discovery and Handling . . . . . . . . . . . . . 24
4. C Language Binding 25
4.1. Constant Types . . . . . . . . . . . . . . . . . . . . 26
4.1.1. URL Lifetimes. . . . . . . . . . . . . . . . . 26
4.1.2. Error Codes. . . . . . . . . . . . . . . . . . 26
4.1.3. SLPBoolean . . . . . . . . . . . . . . . . . . 27
4.2. Struct Types . . . . . . . . . . . . . . . . . . . . 28
4.2.1. SLPSrvURL . . . . . . . . . . . . . . . . . . 28
4.2.2. SLPHandle . . . . . . . . . . . . . . . . . . 29
4.3. Callbacks . . . . . . . . . . . . . . . . . . . . . . 29
4.3.1. SLPRegReport . . . . . . . . . . . . . . . . 30
4.3.2. SLPSrvTypeCallback . . . . . . . . . . . . . . 30
4.3.3. SLPSrvURLCallback . . . . . . . . . . . . . . 31
4.3.4. SLPAttrCallback . . . . . . . . . . . . . . . 33
4.4. Opening and Closing an SLPHandle . . . . . . . . . . . 34
4.4.1. SLPOpen. . . . . . . . . . . . . . . . . . . . 34
4.4.2. SLPClose . . . . . . . . . . . . . . . . . . . 35
4.5. Protocol API . . . . . . . . . . . . . . . . . . . . 36
4.5.1. SLPReg . . . . . . . . . . . . . . . . . . . . 36
4.5.2. SLPDereg . . . . . . . . . . . . . . . . . . . 37
4.5.3. SLPDelAttrs . . . . . . . . . . . . . . . . . 38
4.5.4. SLPFindSrvTypes. . . . . . . . . . . . . . . . 39
4.5.5. SLPFindSrvs . . . . . . . . . . . . . . . . . 41
4.5.6. SLPFindAttrs . . . . . . . . . . . . . . . . . 42
4.6. Miscellaneous Functions . . . . . . . . . . . . . . . 43
4.6.1. SLPGetRefreshInterval . . . . . . . . . . . . 44
4.6.2. SLPFindScopes . . . . . . . . . . . . . . . . 44
4.6.3. SLPParseSrvURL . . . . . . . . . . . . . . . . 45
4.6.4. SLPEscape . . . . . . . . . . . . . . . . . . 46
4.6.5. SLPUnescape . . . . . . . . . . . . . . . . . 47
4.6.6. SLPFree . . . . . . . . . . . . . . . . . . . 48
4.6.7. SLPGetProperty . . . . . . . . . . . . . . . . 48
4.6.8. SLPSetProperty . . . . . . . . . . . . . . . . 49
4.7. Implementation Notes . . . . . . . . . . . . . . . . 49
4.7.1. Refreshing Registrations . . . . . . . . . . . 49
4.7.2. Syntax for String Parameters . . . . . . . . . 49
4.7.3. Client Side Syntax Checking . . . . . . . . . 50
4.7.4. System Properties . . . . . . . . . . . . . . 50
4.7.5. Memory Management . . . . . . . . . . . . . . 51
4.7.6. Asynchronous and Incremental Return Semantics. 51
4.8. Example. . . . . . . . . . . . . . . . . . . . . . . . 52
5. Java Language Binding 56
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . 56
5.2. Exceptions and Errors . . . . . . . . . . . . . . . . 56
5.2.1. Class ServiceLocationException . . . . . . . . 57
5.3. Basic Data Structures . . . . . . . . . . . . . . . . 58
5.3.1. Interface ServiceLocationEnumeration . . . . . 58
5.3.2. Class ServiceLocationAttribute . . . . . . . 58
5.3.3. Class ServiceType . . . . . . . . . . . . . . 61
5.3.4. Class ServiceURL . . . . . . . . . . . . . . 63
5.4. SLP Access Interfaces . . . . . . . . . . . . . . . . 67
5.4.1. Interface Advertiser . . . . . . . . . . . . . 67
5.4.2. Interface Locator . . . . . . . . . . . . . . 69
5.5. The Service Location Manager . . . . . . . . . . . . . 72
5.5.1. Class ServiceLocationManager . . . . . . . . . 72
5.6. Service Template Introspection . . . . . . . . . . . . 74
5.6.1. Abstract Class TemplateRegistry . . . . . . . 74
5.6.2. Interface ServiceLocationAttributeVerifier . . 77
5.6.3. Interface ServiceLocationAttributeDescriptor . 79
5.7. Implementation Notes . . . . . . . . . . . . . . . . . 81
5.7.1. Refreshing Registrations . . . . . . . . . . . 81
5.7.2. Parsing Alternate Transports in ServiceURL . . 81
5.7.3. String Attribute Values . . . . . . . . . . . 82
5.7.4. Client Side Syntax Checking. . . . . . . . . . 82
5.7.5. Language Locale Handling . . . . . . . . . . . 82
5.7.6. Setting SLP System Properties. . . . . . . . . 83
5.7.7. Multithreading . . . . . . . . . . . . . . . . 83
5.7.8. Modular Implementations . . . . . . . . . . . 83
5.7.9. Asynchronous and Incremental Return Semantics. 84
5.8. Example. . . . . . . . . . . . . . . . . . . . . . . . 85
6. Internationalization Considerations 87
6.1. service URL. . . . . . . . . . . . . . . . . . . . . . 87
6.2. Character Set Encoding . . . . . . . . . . . . . . . . 87
6.3. Language Tagging . . . . . . . . . . . . . . . . . . 88
7. Security Considerations 88
8. Acknowledgements 88
9. References 89
10. Authors" Addresses 90
11. Full Copyright Statement 91
1. Introduction
The Service Location API is designed for standardized access to 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.
The standardized configuration file and serialized file formats
provide a simple syntax with complete functional coverage of the
protocol, but without system dependent properties and secure
information.
1.2. Terminology
The key Words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [1].
Service Location Protocol (SLP)
The underlying protocol allowing dynamic and scalable service
discovery. This protocol is specified in the Service Location
Protocol Version 2 [7].
SLP framework
When a "Service Location framework" is mentioned, it refers to
both the SLP implementation and interface implementation; i.e.
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 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,
implementations 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
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 [6]. 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 [8] 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.
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 explicitly included. Service types
with the IANA naming authority are registered with the Internet
Assigned Numbers Authority (see [8] 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 UTF-8 character set [3].
Attribute tags and values in the serialized registration file require
SLP reserved characters to be escaped. The SLP reserved characters
are `(", `)", `,", `", `!", `<", `=", `>", `~" and control
characters (characters with UTF codes less than 0x0020 and the
character 0x007f, which is US-ASCII DEL). 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". In addition, the characters `n", `r", `t", and `_"
are prohibited from attribute tags by the SLP wire syntax grammar.
[7]
In serialized registration files, escaped strings beginning with
`ff`, an encoding for a nonUTF-8 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 signaled.
Escaped characters in URLs in serialized registration files use the
URL escape convention. [2].
Property names and values in the configuration file have a few
reserved characters that are involved in file"s lexical definition.
The characters "." and "=" are reserved in property names and must
be escape. The characters ",", "(", and ")" are reserved in property
values and must be escaped. In addition, scope names in the
net.slp.useScopes property use the SLP wire format escape convention
for SLP reserved characters. This simplifies implementation, since
the same code can be used to unescape scope names as is used in
processing the serialized registration file or for formatting wire
messages.
On platforms that only support US-ASCII and not UTF-8, the upper bit
of bytes incoming from the configuration and registration files
determines whether the character is US-ASCII or not US-ASCII.
According to the standard UTF-8 encoding, the upper bit is zero if
the character is US-ASCII and one if the character is multibyte and
thus not US-ASCII. Platforms without intrinsic UTF-8 support are
required to parse the multibyte character and store it in an
appropriate internal format. Support for UTF-8 is required to
implement the SLP protocol (see [7]), and can therefore be used in
file processing as well.
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.
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
grammar in ABNF [5] 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 "." tag
prop = 1*tagchar
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*stringchar
tagchar = DIGIT / ALPHA / tother / escape
tother = %x21-%x2d / %x2f /
%x3a / %x3c-%x40 /
%x5b-%x60 / %7b-%7e
; i.e., all characters except `.",
; and `=".
stringchar = DIGIT / ALPHA / sother / escape
sother = %x21-%x29 / %x2a-%x2b /
%x2d-%x2f / %x3a-%x40 /
%x5b-%x60 / %7b-%7e
; i.e., all characters except `,"
allchar = DIGIT / ALPHA / HTAB / SP
escape = "" HEXDIG HEXDIG
; Used for reserved characters
With the exception of net.slp.useScopes, net.slp.DAAddresses, and
net.slp.isBroadcastOnly, 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 net.slp.isBroadcastOnly property is read-only because
the API library needs to configure networking upon start up and
changing this property might invalidate the configuration. Whether
the local network uses broadcast or multicast is not likely to change
during the course of the program"s execution.
The properties break down into the following subsections describes an
area and its properties.
2.1.1. DA configuration
Important configuration properties 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 [7]. Ignored if isDA is false.
net.slp.DAAttributes
A comma-separated list of parenthesized attribute/value list
pairs that the DA must advertise in DAAdverts. The property
must be in the SLP attribute list wire format, including
escapes for reserved characters. [7]
2.1.2. Static Scope Configuration
These properties 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 registering, or the
scopes a DA must support. If not present for the DA and SA,
then in the absence of scope information from DHCP, the default
scope "DEFAULT" is used. If not present for the UA, and there
is no scope information available from DHCP, then the user
scoping model is in force. Active and passive DA discovery
or SA discovery are used for scope discovery, and the scope
"DEFAULT" is used if no other information is available. If a
DA or SA gets another scope in a request, a SCOPE_NOT_SUPPORTED
error should be returned, unless the request was multicast, in
which case it should be dropped. If a DA gets another scope in
a registration, a SCOPE_NOT_SUPPORTED error must be returned.
Unlike other properties, this property is "read-only", so
attempts to change it after the configuration file has been
read are ignored. See Section 3.12 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 host names
giving the SLPv2 DAs to use for statically configured UAs and
SAs. Ignored by DAs (unless the DA is also an SA server).
Default is none. Unlike other properties, this property is
"read-only", so attempts to change it after the configuration
file has been read are ignored.
The following grammar describes the property:
addr-list = addr / addr "," addr-list
addr = fqdn / hostnumber
fqdn = ALPHA / ALPHA *[ anum / "-" ] anum
anum = ALPHA / DIGIT
hostnumber = 1*3DIGIT 3("." 1*3DIGIT)
An example is:
sawah,mandi,sambal
IP addresses can be used instead of host names in networks
where DNS is not deployed, but network administrators are
reminded that using IP addresses will complicate machine
renumbering, since the SLP configuration property files
in statically configured networks will have to be changed.
Similarly, if host names are used, implementors must be careful
that a name service is available before SLP starts, in other
words, SLP cannot be used to find the name service.
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 messages 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.
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. Network Configuration Properties
The properties in this section allow various network configuration
properties to be set.
net.slp.isBroadcastOnly
A boolean indicating if broadcast should be used instead of
multicast. Like the net.slp.useScopes and net.slp.DAAddresses
properties, this property is "read-only", so attempts to change
it after the configuration file has been read are ignored.
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 255, giving the
multicast TTL. Default is 255.
net.slp.DAActiveDiscoveryInterval
A 16 bit positive integer giving the number of seconds
between DA active discovery queries. Default is 900 seconds
(15 minutes). This property corresponds to the protocol
specification parameter CONFIG_DA_FIND [7]. If the property is
set to zero, active discovery is turned off. This is useful
when the DAs available are explicitly restricted to those
oBTained from DHCP or the net.slp.DAAddresses property.
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 [7].
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. Default
is: 3000,3000,3000,3000,3000. In a fast network the
aggressive values of 1000,1250,1500,2000,4000 allow better
performance. This property corresponds to the CONFIG_MC_RETRY
parameter in the protocol specification [7]. 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_RETRY [7]. 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_RETRY_MAX [7].
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
parameters CONFIG_START_WAIT, CONFIG_REG_PASSIVE, and
CONFIG_REG_ACTIVE [7].
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. The maximum
size includes IP, and UDP or TCP headers. Default is 1400.
net.slp.interfaces
Value-list of strings giving the IP addresses of network
interfaces on which the DA or SA should listen on port 427 for
multicast, unicast UDP, and TCP messages. Default is empty,
i.e. use the default network interface. The grammar for this
property is:
addr-list = hostnumber / hostnumber "," addr-list
hostnumber = 1*3DIGIT 3("." 1*3DIGIT)
An example is:
195.42.42.42,195.42.142.1,195.42.120.1
The example machine has three interfaces on which the DA should
listen.
Note that since this property only takes IP addresses, it will
need to be changed if the network is renumbered.
2.1.6. SA Configuration
This section contains configuration properties for the SA. These
properties are typically set programmatically by the SA, since they
are specific to each SA.
net.slp.SAAttributes
A comma-separated list of parenthesized attribute/value list
pairs that the SA must advertise in SAAdverts. The property
must be in the SLP attribute list wire format, including
escapes for reserved characters. [7]
2.1.7. UA Configuration
This section contains configuration properties for the UA. These
properties can be set either programmatically by the UA or in the
configuration file.
net.slp.locale
A RFC1766 Language Tag [6] for the language locale. Setting
this property causes the property value to become the default
locale for SLP messages. Default is "en". This property is
also used for SA and DA configuration.
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 asynchronously.
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.
net.slp.typeHint
A value-list of service type names. In the absence of any
DAs, UAs perform SA discovery for finding scopes. These SA
discovery requests may contain a request for service types as
an attribute.
The API implementation will use the service type names supplied
by this property to discover only those SAs (and their scopes)
which support the desired service type or types. For example,
if net.slp.typeHint is set to "service:imap,service:pop3" then
SA discovery requests will include the search filter:
((service-type=service:imap)(service-type=service:pop3))
The API library can also use unicast to contact the discovered
SAs for subsequent requests for these service types, to
optimize network access.
2.1.8. Security
The property in this section allows security for all agents to be set
on or off. When the property is true, then the agent must include
security information on all SLP messages transacted by that agent.
Since security policy must be set network wide to be effective, a
single property controls security for all agents. Key management and
management of SLP SPI strings [7] are implementation and policy
dependent.
net.slp.securityEnabled
A boolean indicating whether the agent should enable
security for URLs, attribute lists, DAAdverts, and SAAdverts.
Each agent is responsible for interpreting the property
appropriately. Default is false.
2.2. Multihomed Machines
On multihomed machines, the bandwidth and latency characteristics on
different network interfaces may differ considerably, to the point
where different configuration properties are necessary to achieve
optimal performance. The net.slp.interfaces property indicates which
network interfaces are SLP enabled. An API library implementation
may support configuration customization on a per network interface
basis by allowing the interface IP address to be appended to the
property name. In that case, the values of the property are only
used for that particular interface, the generic property (or defaults
if no generic property is set) applies to all others.
For example, if a configuration has the following properties:
net.slp.interfaces=125.196.42.41,125.196.42.42,125.196.42.43
net.slp.multicastTTL.125.196.42.42=1
then the network interface on subnet 42 is restricted to a TTL of 1,
while the interfaces on the other subnets have the default multicast
radius, 255.
The net.slp.interfaces property must only be set if there is no
routing between the interfaces. If the property is set, the DA (if
any) and SAs should advertise with the IP address or host name
appropriate to the interface on the interfaces in the list. If
packets are routed between the interfaces, then the DA and SAs should
only advertise on the default interface. The property should also be
set if broadcast is used rather than multicast on the subnets
connected to the interfaces. Note that even if unicast packets are
not routed between the interfaces, multicast may be routed through
another router. The danger in listening for multicast on multiple
interfaces when multicast packets are routed is that the DA or SA may
receive the same multicast request via more than one interface.
Since the IP address is different on each interface, the DA or SA
cannot identify the request as having already being answered via the
previous responder"s list. The requesting agent will end up getting
URLs that refer to the same DA or service but have different
addresses or host names.
2.3. 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
encoding of the registrations is required to be UTF-8.
The syntax of the serialized registration file, in ABNF format [5],
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 "," lang "," ltime [ "," type ] newline
surl = ;The registration"s URL. See
; [8] for syntax.
lang = 1*8ALPHA [ "-" 1*8ALPHA ]
;RFC1766 Language Tag see [6].
ltime = 1*5DIGIT
; A positive 16-bit integer
; giving the lifetime
; of the registration.
type = ; The service type name, see [7]
; and [8] for syntax.
slist = "scopes" "=" scope-list newline
scope-list = scope-name / scope-name "," scope-list
scope = ; See grammar of [7] for
; scope-name syntax.
attr-list = attr-def / attr-def attr-list
attr-def = ( attr / keyword ) newline
keyword = attr-id
attr = attr-id "=" attr-val-list
attr-id = ;Attribute id, see [7] for syntax.
attr-val-list = attr-val / attr-val "," attr-val-list
attr-val = ;Attribute value, see [7] for syntax.
allchar = char / WSP
char = DIGIT / ALPHA / other
other = %x21-%x2f / %x3a-%x40 /
%x5b-%x60 / %7b-%7e
; All printable, nonwhitespace US-ASCII
; characters.
newline = CR / ( CRLF )
The syntax for scope names, attribute tags, and attribute values
requires escapes for special characters as specified in [7]. DAs and
SA servers that process serialized registrations must handle them
exactly as if they were registered by an SA. In the url-props
production, the type token is optional. If the type token is present
for a service: URL, a warning is signaled and the type name is
ignored. If the maximum lifetime is specified (65535 sec.), the
registration is taken to be permanent, and is continually refreshed
by the DA or SA server until it exits. 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-props production. If the optional scope list is present, the
registrations 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 should reject the registration and
issue a warning message.
2.4. Processing 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 relevant
configuration item is used. At the earliest, errors may be caught
when the relevant 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.
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
asynchronous 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 [8] 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. In
some cases, an application may want to have the URL continue being
registered for the entire time during which the application is
executing. The API includes provision for clients to indicate
whether they want URLs to be automatically refreshed.
Implementations of the SA API must provide this automatic refreshing
capability. Note that a client which uses this facility should
explicitly deregister the service URL before exiting, since the API
implementation may not be able to assure that the URL is deregistered
when the application exits, although it will time out in the DA
eventually.
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 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 property 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 [8] 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
asynchronous 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 UTF-8 to
maintain maximum compatibility on platforms that only support US-
ASCII and not UTF-8. API functions are still required to handle the
full range of UTF-8 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
UTF-8. 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 can be escaped by clients through convenience
functions provided by the API. The character encoding used in escapes
is UTF-8.
Due to constraints in SLP, no string parameter passed to the C or
Java API may exceed 64K bytes in length.
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 occurred among one of several successful replies, then the
error should be logged and the successful replies returned. For
asynchronous calls, an error occurring 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 or attribute 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.
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 non-existing registration was issued, or the
update includes a service type or scope different than that in
the initial registration, etc.
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 failed.
SCOPE_NOT_SUPPORTED
The API returns this error if the SA has been configured with
net.slp.useScopes value-list of scopes and the SA request did
not specify one or more of these allowable scopes, and no
others. It may be returned by a DA or SA if the scope included
in a request is not supported by the DA or SA.
REFRESH_REJECTED
The SA attempted to refresh a registration more frequently
than the minimum refresh interval. The SA should call the
appropriate API function to obtain the minimum refresh interval
to use.
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.
NETWORK_TIMED_OUT
When no reply can be obtained in the time specified by the
configured timeout interval for a unicast request, 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.
The SLP protocol errors OPTION_NOT_UNDERSTOOD, VERSION_NOT_SUPPORTED,
INTERNAL_ERROR, MSG_NOT_SUPPORTED, AUTHENTICATON_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 compatibility 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. Handling Special Service Types
The service types service:directory-agent and service:service-agent
are used internally in the SLP framework to discover DAs and SAs.
The mechanism of DA and SA discovery is not normally exposed to the
API client; however, the client may have interest in discovering DAs
and SAs independently of their role in discovering other services.
For example, a network management application may want to determine
which machines are running SLP DAs. To facilitate that, API
implementations must handle requests to find services and attributes
for these two service types so that API clients obtain the
information they expect.
In particular, if the UA is using a DA, SrvRqst and AttrRqst for
these service types must be multicast and not unicast to the DA, as
is the case for other service types. If the requests are not
multicast, the DA will respond with an empty reply to a request for
services of type service:service-agent and with its URL only to a
request for services of type service:directory-agent. The UA would
therefore not obtain a complete picture of the available DAs and SAs.
3.12. 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 property, unicast to DAs configured via
DHCP or the net.slp.DAAddresses property, and active and passive
discovery.
The API is required to be implemented in a way that re-enforces the
administrative and user scoping models described in [7]. SA clients
only support the administrative scoping model. SAs must know a
priori what DAs they need to register with since there is typically
no human intervention in scope selection for SAs. UAs must support
both administrative and user scoping because an application may
require human intervention in scope selection.
API implementations are required to support administrative scoping in
the following way. Scopes configured by DHCP and scopes of DAs
configured by DHCP have first priority (in that order) 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 scopes are not available from either
of these sources and the net.slp.DAAddresses property is set, then
the scopes available from the configured DAs must be returned. Note
that if both DAs and scopes are configured, the scopes of the
configured DAs must match the configured scope list; otherwise and
error is signaled and agent execution is terminated. If no
configured scope information is available, then an SA client has
default scope, "DEFAULT", and a UA client employs user scoping.
User scoping is supported in the following way. Scopes discovered
from active DA discovery, and from passive DA discovery all must be
returned. If no information is available from active and passive DA
discovery, then the API library may perform SA discovery, using the
service types in the net.slp.typeHint property to limit the search to
SAs supporting particular service types. If no net.slp.typeHint
property is set, the UA may perform SA discovery without any service
type query. 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. [7]. The API enforces this constraint by
not requiring the API client to supply any scopes as parameters to
API operations. The API library must obtain all currently known
scopes and use them in SA operations. UA API clients 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. The UA API library can optionally check the scope and
return the error without contacting a remote agent.
4. C Language Binding
The C language binding presents a minimal overhead implementation
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 client
allocate most memory and requiring that client callback functions
copy incoming parameters into memory allocated by the client code.
Any memory returned directly from the API functions is deallocated
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 UTF-8 but they may still be passed as a C string (a
null terminated sequence of bytes.) Escaped characters must be
encoded by the API client as UTF-8. In the common case of US-ASCII,
the usual one byte per character C strings work. API functions
assist in escaping and unescaping strings.
Unless otherwise noted, parameters to API functions and callbacks are
non-NULL. Some parameters may have other restrictions. If any
parameter fails to satisfy the restrictions on its value, the
operation returns a PARAMETER_BAD error.
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.
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 = -13,
SLP_REFRESH_REJECTED = -15,
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 occurred during the
operation.
The SLP_LAST_CALL code is passed to callback functions when the API
library has no more data for them and therefore 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 one call is made, with the error
parameter set to SLP_LAST_CALL.
4.1.3. SLPBoolean
4.1.3.1. Synopsis
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 a service
URL. The fields correspond to different parts of the URL. Note that
the structure is in conformance 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. The service type
name includes the "service:" if the URL is of the service:
scheme. [7]
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
is invoked. The callback function is called with the results of the
operation in both the synchronous and asynchronous cases. The memory
included in the callback parameters is owned by the API library, and
the client code in the callback must copy out 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 asynchronous) 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. If the value returned from the callback is
SLP_TRUE, asynchronous 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 occurred during the
operation.
pvCookie
Memory passed down from the client code that called the
original API function, starting the operation. May be NULL.
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. If the hSLP handle
parameter was opened asynchronously, the results returned through the
callback MAY be uncollated. If the hSLP handle parameter was opened
synchronously, then the returned results must be collated and
duplicates eliminated.
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 occurred 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.
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. If the hSLP handle parameter
was opened asynchronously, the results returned through the callback
MAY be uncollated. If the hSLP handle parameter was opened
synchronously, then the returned results must be collated and
duplicates eliminated.
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 occurred 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.
4.3.3.4. 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 behavior of the callback differs depending on whether the
attribute request was by URL or by service type. If the
SLPFindAttrs() operation was originally called with a URL, the
callback is called once regardless of whether the handle was opened
asynchronously 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).
If the SLPFindAttrs() operation was originally called with a service
type, the value of pcAttrList and calling behavior depend on whether
the handle was opened asynchronously or synchronously. If the handle
was opened asynchronously, the callback is called every time the API
library has results from a remote agent. The pcAttrList parameter
MAY be uncollated