| Rfc | 2614 |
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| Title | An API for Service Location |
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| Author | J. Kempf, E. Guttman |
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| Date | June 1999 |
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| Format: | TXT, HTML |
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| Status: | INFORMATIONAL |
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|
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
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 RFC 2119 [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 RFC 1766 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 ]
;RFC 1766 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 between calls. It contains a comma separated list
with the results from the agent that immediately returned results.
If the handle was opened synchronously, the results must be 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.
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)" [7].
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.
4.3.4.4. Returns
The client code should return SLP_TRUE if more data is desired,
otherwise SLP_FALSE.
4.4. Opening and Closing an SLPHandle
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 asynchronous
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. However, 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.
An SLPHandle can only be used for one SLP API operation at a time.
If the original operation was started asynchronously, 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 a asynchronous( resp. synchronous) operation, due to
memory constraints or lack of threading support, the
SLP_NOT_IMPLEMENTED flag may be returned when the isAsync flag is
SLP_TRUE (resp. SLP_FALSE).
4.4.1.3. Parameters
pcLang
A pointer to an array of characters containing the RFC 1766
Language Tag [6] for the natural language locale of requests
and registrations issued on the handle.
isAsync
An SLPBoolean indicating whether the SLPHandle should be opened
for asynchronous operation or not.
phSLP
A pointer to an SLPHandle, in which the open SLPHandle is
returned. If an error occurs, the value upon return is 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 asynchronous 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().
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 *pcAttrs
SLPBoolean fresh,
SLPRegReport callback,
void *pvCookie);
4.5.1.2. Description
Registers the URL in pcSrvURL having the lifetime usLifetime with the
attribute list in pcAttrs. The pcAttrs list is a comma separated
list of attribute assignments in the wire format (including escaping
of reserved characters). The usLifetime parameter must be nonzero
and less than or equal to SLP_LIFETIME_MAXIMUM. 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.
The pcSrvType parameter is a service type name and can be included
for service URLs that are not in the service: scheme. If the URL is
in the service: scheme, the pcSrvType parameter is ignored. If the
fresh flag is SLP_FALSE, then an existing registration is updated.
Rules for new and updated registrations, and the format for pcAttrs
and pcScopeList can be found in [7]. Registrations and updates take
place in the language locale of the hSLP handle.
The API library is required to perform the operation in all scopes
obtained through configuration.
4.5.1.3. Parameters
hSLP
The language specific SLPHandle on which to register the
advertisement.
pcSrvURL
The URL to register. May not be 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.
pcAttrs
A comma separated list of attribute assignment expressions for
the attributes of the advertisement. Use empty string, "" for
no attributes.
fresh
An SLPBoolean that is SLP_TRUE if the registration is new or
SLP_FALSE if a reregistration.
callback
A callback to report the operation completion status.
pvCookie
Memory passed to the callback code from the client. May be
NULL.
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. Synopsis
SLPError SLPDereg(SLPHandle hSLP,
const char *pcURL,
SLPRegReport callback,
void *pvCookie);
4.5.2.2. Description
Deregisters the advertisement for URL pcURL in all scopes where the
service is registered and all language locales. The deregistration
is not just confined to the locale of the SLPHandle, it is in all
locales. The API library is required to perform the operation in all
scopes obtained through configuration.
4.5.2.3. Parameters
hSLP
The language specific SLPHandle to use for deregistering.
pcURL
The URL to deregister. May not be the empty string.
callback
A callback to report the operation completion status.
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. Synopsis
SLPError SLPDelAttrs(SLPHandle hSLP,
const char *pcURL,
const char *pcAttrs,
SLPRegReport callback,
void *pvCookie);
4.5.3.2. Description
Delete the selected attributes in the locale of the SLPHandle. The
API library is required to perform the operation in all scopes
obtained through configuration.
4.5.3.3. Parameters
hSLP
The language specific SLPHandle to use for deleting attributes.
pcURL
The URL of the advertisement from which the attributes should
be deleted. May not be the empty string.
pcAttrs
A comma separated list of attribute ids for the attributes to
deregister. See Section 9.8 in [7] for a description of the
list format. May not be the empty string.
callback
A callback to report the operation completion status.
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) then it
is omitted, as is the separating ".". Service type names from URLs
of the service: scheme are returned with the "service:" prefix
intact. [7] See [8] for more information on the syntax of service
type names.
4.5.4.2. Parameters
hSLP
The SLPHandle on which to search for types.
pcNamingAuthority
The naming authority to search. Use "*" for all naming
authorities and the empty string, "", for the default naming
authority.
pcScopeList
A pointer to a char containing comma separated list of scope
names to search for service types. May not be the empty
string, "".
callback
A callback function through which the results of the operation
are reported.
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,
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.
pcServiceType
The Service Type String, including authority string if any, for
the request, such as can be discovered using SLPSrvTypes().
This could be, for example "service:printer:lpr" or
"service:nfs". May not be the empty string.
pcScopeList
A pointer to a char containing comma separated list of scope
names. May not be the empty string, "".
pcSearchFilter
A query formulated of attribute pattern matching expressions in
the form of a LDAPv3 Search Filter, see [4]. If this filter
is empty, i.e. "", all services of the requested type in the
specified scopes are returned.
callback
A callback function through which the results of the operation
are reported.
pvCookie
Memory passed to the callback code from the client. May be
NULL.
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 *pcURLOrServiceType,
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 service URL or service type. If pcURLOrServiceType
is a service URL, the attribute information returned is for that
particular advertisement in the language locale of the SLPHandle.
If pcURLOrServiceType is a service type name (including naming
authority if any), then the attributes for all advertisements of that
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 [7]. 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.
pcURLOrServiceType
The service URL or service type. See [7] for URL and service
type syntax. May not be the empty string.
pcScopeList
A pointer to a char containing a comma separated list of scope
names. May not be 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 [7] for the exact format of the filter
string.
callback
A callback function through which the results of the operation
are reported.
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
4.6.1. SLPGetRefreshInterval
4.6.1.1. Synopsis
unsigned short SLPGetRefreshInterval();
4.6.1.2. Description
Returns the maximum across all DAs of the min-refresh-interval
attribute. This value satisfies the advertised refresh interval
bounds for all DAs, and, if used by the SA, assures that no refresh
registration will be rejected. If no DA advertises a min-refresh-
interval attribute, a value of 0 is returned.
4.6.1.3. Returns
If no error, the maximum refresh interval value allowed by all DAs (a
positive integer). If no DA advertises a min-refresh-interval
attribute, returns 0. If an error occurs, returns an SLP error code.
4.6.2. SLPFindScopes
4.6.2.1. Synopsis
SLPError SLPFindScopes(SLPHandle hSLP,
char** ppcScopeList);
4.6.2.2. 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, unicast to DAs on the net.slp.DAAddresses property, DHCP,
or through the 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".
4.6.2.3. Parameters
hSLP
The SLPHandle on which to search for scopes.
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().
4.6.2.4. Returns
If no error occurs, returns SLP_OK, otherwise, the appropriate error
code.
4.6.3. SLPParseSrvURL
4.6.3.1. Synopsis
SLPError SLPParseSrvURL(char *pcSrvURL
SLPSrvURL** ppSrvURL);
4.6.3.2. Description
Parses the URL passed in as the argument into a service URL structure
and returns 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
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.
4.6.3.3. 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.
ppSrvURL
A pointer to a pointer for the SLPSrvURL structure to receive
the parsed URL. The memory should be freed by a call to
SLPFree() when no longer needed.
4.6.3.4. Returns
If no error occurs, the return value is SLP_OK. Otherwise, the
appropriate error code is returned.
4.6.4. SLPEscape
4.6.4.1. Synopsis
SLPError SLPEscape(const char* pcInbuf,
char** ppcOutBuf,
SLPBoolean isTag);
4.6.4.2. 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 by returning 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.
4.6.4.3. 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.
4.6.4.4. Returns
Return SLP_PARSE_ERROR if any characters are bad tag characters and
the isTag flag is true, otherwise SLP_OK, or the appropriate error
code if another error occurs.
4.6.5. SLPUnescape
4.6.5.1. Synopsis
SLPError SLPUnescape(const char* pcInbuf,
char** ppcOutBuf,
SLPBoolean isTag);
4.6.5.2. 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.
4.6.5.3. 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.
4.6.5.4. Returns
Return SLP_PARSE_ERROR if any characters are bad tag characters and
the isTag flag is true, otherwise SLP_OK, or the appropriate error
code if another error occurs.
4.6.6. SLPFree
4.6.6.1. Synopsis
void SLPFree(void* pvMem);
4.6.6.2. Description
Frees memory returned from SLPParseSrvURL(), SLPFindScopes(),
SLPEscape(), and SLPUnescape().
4.6.6.3. Parameters
pvMem
A pointer to the storage allocated by the SLPParseSrvURL(),
SLPEscape(), SLPUnescape(), or SLPFindScopes() function.
Ignored if NULL.
4.6.7. SLPGetProperty
4.6.7.1. Synopsis
const char* SLPGetProperty(const char* pcName);
4.6.7.2. Description
Returns the value of the corresponding SLP property name. The
returned string is owned by the library and MUST NOT be freed.
4.6.7.3. Parameters
pcName
Null terminated string with the property name, from
Section 2.1.
4.6.7.4. Returns
If no error, returns a pointer to a character buffer containing the
property value. If the property was not set, returns the default
value. If an error occurs, returns NULL. The returned string MUST
NOT be freed.
4.6.8. SLPSetProperty
4.6.8.1. Synopsis
void SLPSetProperty(const char *pcName,
const char *pcValue);
4.6.8.2. Description
Sets the value of the SLP property to the new value. The pcValue
parameter should be the property value as a string.
4.6.8.3. Parameters
pcName
Null terminated string with the property name, from
Section 2.1.
pcValue
Null terminated string with the property value, in UTF-8
character encoding.
4.7. Implementation Notes
4.7.1. Refreshing Registrations
Clients indicate that they want URLs to be automatically refreshed by
setting the usLifetime parameter in the SLPReg() function call to
SLP_LIFETIME_MAXIMUM. This will cause the API implementation to
refresh the URL before it times out. Although using
SLP_LIFETIME_MAXIMUM to designate automatic reregistration means that
a transient URL can't be registered for the maximum lifetime, little
hardship is likely to occur, since service URL lifetimes are measured
in seconds and the client can simply use a lifetime of
SLP_LIFETIME_MAXIMUM - 1 if a transient URL near the maximum lifetime
is desired. API implementations MUST provide this facility.
4.7.2. Syntax for String Parameters
Query strings, attribute registration lists, attribute deregistration
lists, scope lists, and attribute selection lists follow the syntax
described in [7] 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 UTF-8-
encoded string, the first characters of which are the nonUTF-8
encoding '\ff'. Subsequent characters are the escaped values for the
original bytes in the opaque. The escape convention is relatively
simple. An escape consists of a backslash followed by the two
hexadecimal digits encoding the byte. An example is '\2c' for the
byte 0x2c. Clients handle opaque processing themselves, since the
algorithm is relatively simple and uniform.
4.7.3. Client Side Syntax Checking
Client side API implementations may do syntax checking of scope
names, naming authority names, and service type names, 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.
4.7.4. System Properties
The system properties established in the configuration file are
accessible through the SLPGetProperty() and SLPSetProperty()
functions. The SLPSetProperty() function only modifies properties in
the running process, not in the configuration file. Properties are
global to the process, affecting all threads and all handles created
with SLPOpen. 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. With the exception of net.slp.locale,
net.slp.typeHint, and net.slp.maxResults, clients of the API 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.
4.7.5. Memory Management
The only API functions returning memory specifically requiring
deallocation on the part of the client are SLPParseSrvURL(),
SLPFindScopes(), SLPEscape(), and SLPUnescape(). 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 parameter memory in callback parameters is allowed.
4.7.6. Asynchronous and Incremental Return Semantics
If a handle parameter to an API function was opened asynchronously,
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 occurred 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 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. On the other hand, it means
that handle creation should be fairly lightweight so a client program
can easily support multiple outstanding calls.
The total number of results received can be controlled by setting the
net.slp.maxResults parameter.
On the last call to a callback, whether asynchronous or synchronous,
the status code passed to the callback has value SLP_LAST_CALL. There
are four reasons why the call can terminate:
DA reply received
A reply from a DA has been received and therefore nothing more
is expected.
Multicast terminated
The multicast convergence time has elapsed and the API library
multicast code is giving up.
Multicast null results
Nothing new has been received during multicast for a while and
the API library multicast code is giving up on that (as an
optimization).
Maximum results
The user has set the net.slp.maxResults property and that
number of replies has been collected and returned
4.8. Example
This example illustrates how to discover a mailbox.
A POP3 server registers itself with the SLP framework. The
attributes it registers are "USER", a list of all users whose mail is
available through the POP3 server.
The POP3 server code is the following:
SLPHandle slph;
SLPRegReport errCallback = POPRegErrCallback;
/* Create an English SLPHandle, asynchronous processing. */
SLPError err = SLPOpen("en", SLP_TRUE, &slph);
if( err != SLP_OK ) {
/* Deal with error. */
}
/* Create the service: URL and attribute parameters. */
const char* surl = "service:pop3://mail.netsurf.de"; /* the URL */
const char *pcAttrs = "(user=zaphod,trillian,roger,marvin)"
/* Perform the registration. */
err = SLPReg(slph,
surl,
SLP_LIFETIME_DEFAULT,
ppcAttrs,
errCallback,
NULL);
if (err != SLP_OK ) {
/*Deal with error.*/
}
The errCallback reports any errors:
void
POPRegErrCallback(SLPHandle hSLP,
SLPError errCode,
unsigned short usLifetime,
void* pvCookie) {
if( errCode != SLP_OK ) {
/* Report error through a dialog, message, etc. */
}
/*Use lifetime interval to update periodically. */
}
The POP3 client locates the server for the user with the following
code:
/*
* 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=roger)"; /* the search filter */
SLPSrvURLCallback srvCallback = /* the callback */
POPSrvURLCallback;
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((void*)pSrvURL); /* Free the pSrvURL storage */
}
return SLP_FALSE; /* Done! */
}
A client that wanted to discover all the users receiving mail at the
server uses 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! */
}
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 modeled 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 non-null. 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 relevant
parameters could be erroneous.
Standard Java practice is to encode every exceptional condition as a
separate 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
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 = 1
public static final short PARSE_ERROR = 2
public static final short INVALID_REGISTRATION = 3
public static final short SCOPE_NOT_SUPPORTED = 4
public static final short AUTHENTICATION_ABSENT = 6
public static final short AUTHENTICATION_FAILED = 7
public static final short INVALID_UPDATE = 13
public static final short REFRESH_REJECTED = 15
public static final short NOT_IMPLEMENTED = 16
public static final short NETWORK_INIT_FAILED 17
public static final short NETWORK_TIMED_OUT = 18
public static final short NETWORK_ERROR = 19
public static final short INTERNAL_SYSTEM_ERROR = 20
public static final short TYPE_ERROR = 21
public static final short BUFFER_OVERFLOW = 22
5.2.1.4. Instance Methods
public short getErrorCode()
Return the error code. The error code takes on one of the static
field values.
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
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 IllegalArgumentException.
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 the
parameter should be null. String values can consist of any
Unicode character.
5.3.2.4. Class Methods
public static String escapeId(String id)
Returns an escaped version of the id parameter, suitable for
inclusion in a query. Any reserved characters as specified in [7]
are escaped using UTF-8 encoding. If any characters in the tag are
illegal, throws IllegalArgumentException.
Parameters:
id
The attribute id to escape. ServiceLocationException is thrown
if any characters are illegal for an attribute tag.
public static String escapeValue(Object value)
Returns a String containing the escaped value parameter as a string,
suitable for inclusion in a query. If the parameter is a string,
any reserved characters as specified in [7] are escaped using UTF-8
encoding. If the parameter is a byte array, then the escaped string
begins with the nonUTF-8 sequence `\ff` and the rest of the string
consists of the escaped bytes, which is the encoding for opaques.
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 type other than String, Integer, Boolean or byte[], 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 attribute vectors match. Note that the SLP string matching
algorithm [7] MUST NOT be used for comparing attribute identifiers or
string values.
public String toString()
Overrides Object.toString(). The string returned contains a
formatted representation of the attribute, giving the attribute's
id, values, and the Java type of the values. The returned string is
suitable for debugging purposes, but is not in SLP wire format.
public int hashCode()
Overrides Object.hashCode(). Hashes on the attribute's identifier.
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.
5.3.3.4. Methods
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, or the empty
string if the service type is not abstract. For example, if the type
name is "service:printing:ipp", the method returns "ipp". If the
type name is "service:ftp", the method returns "".
public String getPrincipleTypeName()
Returns the abstract type name for an abstract type, the protocol
name in a protocol type, or the URL scheme for a generic URL. For
example, in the abstract type name "service:printing:ipp", the method
returns "printing". In the protocol type name "service:ftp", the
method returns "ftp".
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. If not an abstract
type, returns the empty string. For example, in the abstract type
name "service:printing:ipp", the method returns "service:printing".
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
"service" prefix, naming authority, if any, abstract and concrete
type names for abstract types, protocol type name for protocol types,
and URL scheme for generic URLs.
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.
5.3.4.3. Class Variables
public static final int NO_PORT = 0
Indicates that no port information is required or was returned for
this URL.
public static final int LIFETIME_NONE = 0
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 = 10800
The default URL lifetime (3 hours) in seconds.
public static final int LIFETIME_MAXIMUM = 65535
The maximum URL lifetime (about 18 hours) in seconds.
public static final int LIFETIME_PERMANENT = -1
Indicates that the API implementation should continuously re-register
the URL until the application exits.
5.3.4.4. Constructors
public ServiceURL(String URL,int 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
generic URL according to RFC 2396 [2].
lifetime
The service advertisement lifetime in seconds. This value may
be between LIFETIME_NONE and LIFETIME_MAXIMUM.
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 non-IP transports, always
returns NO_PORT.
public String getURLPath()
Returns the URL path description, if any.
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 a 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 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 attributes)
throws ServiceLocationException
Register a new service with SLP having the given attributes.
The API library is required to perform the operation in all
scopes obtained through configuration.
Parameters:
URL
The URL for the service.
attributes
A vector of ServiceLocationAttribute objects describing the
service.
public abstract void deregister(ServiceURL URL)
throws ServiceLocationException
Deregister a service from the SLP framework. This has the effect
of deregistering the service from every language locale. The API
library is required to perform the operation in all scopes obtained
through configuration.
Parameters:
URL
The URL for the service.
public abstract void
addAttributes(ServiceURL URL,
Vector attributes)
throws ServiceLocationException
Update the registration by adding the given attributes. The API
library is required to perform the operation in all scopes obtained
through configuration.
Parameters:
URL
The URL for the service.
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 attributeIds)
throws ServiceLocationException
Delete the attributes from a URL for the locale with which the
Advertiser was created. The API library is required to perform the
operation in all scopes obtained through configuration.
Parameters:
URL
The URL for the service.
attributeIds
A vector of Strings indicating the ids of the attributes
to remove. The strings may be attribute ids or they
may be wildcard patterns to match ids. See [7] for the
syntax of wildcard patterns. The strings may include SLP
reserved characters, they will be escaped by the API before
transmission. May not be the empty vector or null.
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)
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. The vector 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. The vector should be selected from
the results of a findScopes() API invocation. Use "DEFAULT"
for the default scope.
searchFilter
An LDAPv3 [4] string encoded query. If the filter is empty,
i.e. "", all services of the requested type in the specified
scopes are returned. SLP reserved characters must be escaped
in the query. Use ServiceLocationAttribute.escapeId() and
ServiceLocationAttribute.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. The vector 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 [7], the patterns may include wildcards to match substrings.
The strings 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 regardless of the Locator's locale. The request is made
independent of language locale. If no attributes are found, an empty
vector is returned.
Parameters:
serviceType
The service type.
scopes
A Vector of scope names. The vector 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 [7], 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 int getRefreshInterval()
throws ServiceLocationException
Returns the maximum across all DAs of the min-refresh-interval
attribute. This value satisfies the advertised refresh interval
bounds for all DAs, and, if used by the SA, assures that no
refresh registration will be rejected. If no DA advertises a
min-refresh-interval attribute, a value of 0 is returned.
public static Vector findScopes()
throws ServiceLocationException
Returns an Vector of strings with all available scope names. The
list of scopes comes from a variety of sources, see Section 2.1 for
the scope discovery algorithm. There is always at least one string
in the Vector, the default scope, "DEFAULT".
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.
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 [8]. 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.
Parameters:
type
The service type.
documentURL
A string containing the URL of the template document. May not
be the empty string.
locale
A Locale object containing the language locale of the template.
version
The version number identifier 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
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. May not be the
empty string.
5.6.2. Interface ServiceLocationAttributeVerifier
5.6.2.1. Synopsis
public interface ServiceLocationAttributeVerifier
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 Locale getLocale()
Return the language locale of the template.
public abstract String getVersion()
Return the template version number identifier.
public abstract String getURLSyntax()
Return the URL syntax expression for the service: URL.
public abstract String getDescription()
Return the descriptive help text for the template.
public abstract ServiceLocationAttributeDescriptor
getAttributeDescriptor(String attrId)
Return the ServiceLocationAttributeDescriptor 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.
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 definition. 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.
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.
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
getRequiresExplicitMatch()
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 getIsMultivalued()
Returns true if the "M" flag is set.
public abstract boolean getIsOptional()
Returns true if the "O"" flag is set.
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.
5.7. Implementation Notes
5.7.1. Refreshing Registrations
A special lifetime constant, ServiceURL.LIFETIME_PERMANENT, is used
by clients to indicate that the URL should be automatically refreshed
until the application exits. The API implementation should interpret
this flag as indicating that the URL lifetime is
ServiceURL.LIFETIME_MAXIMUM, and MUST arrange for automatic refresh
to occur.
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 except to separate out the host identifier and the URL path.
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 non-IP transports, the
getPort() method returns NO_PORT.
5.7.3. String Attribute Values
In general, translation between Java types for attribute values and
the SLP on-the-wire string is straightforward. However, there are
two corner cases. If the Java attribute value type is String and the
value of the string has an on-the-wire representation that is
inferred by SLP as an integer, the registered attribute value may not
be what the API client intended. A similar problem could result if
the Java attribute value is the string "true" or "false", in which
case the on-the-wire representation is inferred to boolean. To
handle these corner cases, the Java API prepends a space onto the
string. So, for example, if the string attribute value is "123", the
Java API transforms the value to "123 ", which will have an on-the-
wire representation that is inferred by SLP to be string. Since
appended and prepended spaces have no effect on query handling, this
procedure should cause no problem with queries. API clients need to
be aware, however, that the transformation is occurring.
5.7.4. Client Side Syntax Checking
The syntax of scope names, service type names, naming authority
names, and URLs is described in [7] and [8]. 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 clients to obtain
escaped attribute id and value strings to facilitate query
construction.
5.7.5. 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 [7] is used,
namely "en". Note that the default SLP locale may not be the same as
the default Java locale.
5.7.6. 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. Program execution continues without
interruption by substituting the default for the erroneous parameter.
Errors are checked when the property is used and are logged.
The SLP configuration file cannot be read with the
java.util.Properties file reader because there are some syntactic
differences. The SLP configuration file syntax defines a different
escape convention for non-ASCII characters than the Java syntax.
However, after the file has been read, the properties are stored and
retrieved from java.util.Properties objects.
Properties are global for a process, affecting all threads and all
Locator and Advertiser objects obtained through the
ServiceLocationManager. With the exception of the net.slp.locale,
net.slp.typeHint, and net.slp.maxResults properties, clients 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.
5.7.7. Multithreading
Thread-safe operation is 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.
5.7.8. 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 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 concrete subclass can simply be omitted from an
implementation that only supports UA and/or SA clients, and the
TemplateRegistry.getRegistry() method can return null. In this way,
the API implementation can be tailored for the particular memory
requirements at hand.
In addition, if an implementation only supports the minimal subset of
SLP [7], the unsupported Locator and Advertiser interface operations
can throw an exception with ServiceLocationException.NOT_IMPLEMENTED
as the error code. This supports better source portability between
low and high memory platforms.
5.7.9. Asynchronous and Incremental Return Semantics
The Java API contains no specific support for asynchronous operation.
Incremental return is not needed for the Advertiser because service
registrations can be broken up into pieces when large. Asynchronous
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 synchronously or
asynchronously. 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
an attribute request by service type is made 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 asynchronous processing 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. Example
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 {
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 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.
adv.register(printerURL, attributes);
//If the template registry is available,
// register the printer's template.
if( tr != null ) {
tr.registerServiceTemplate(
new ServiceType("service:printer:lpr"),
"http://shop.arv/printer/printer-lpr.slp",
new Locale("en",""),
"1.0");
}
} catch( ServiceLocationException ex ) { } //Deal with error.
Suppose a client is looking for color printer. The following code is
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.
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 UTF-8 character set [3].
The attribute information associated with the service URL must be
expressed in UTF-8. See [8] for attribute internationalization
guidelines.
6.2. Character Set Encoding
Configuration and serialized registration files are encoded in the
UTF-8 character set [3]. This is fully compatible with US-ASCII
character values. C platforms that do not support UTF-8 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. This should require no additional implementation
effort, since the SLP wire protocol requires that strings are encoded
as UTF-8. C platforms without UTF-8 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 UTF-8 for C. Unicode is the default in Java. For C, the
standard US-ASCII 8 bits per character, null terminated C strings are
a subset of the UTF-8 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 UTF-8 strings. The strings 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
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 preferred
over those which don't. Dialects that do not match will not prevent
string matching or comparisons from occurring.
7. Security Considerations
Security is handled within the API library and is not exposed to API
clients except in the form of exceptions. The
net.slp.securityEnabled, property determines whether an SA client's
messages are signed, but a UA client should be prepared for an
authentication exception at any time, because it may contact a DA
with authenticated advertisements.
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 DAAdverts, SAAdverts, Service URLs and
Service Attributes to be verified using digital cryptography. For
this reason, all SLP agents should be configured to use SLP SPIs.
See [7] for a description of how this mechanism works.
8. Acknowledgements
The authors would like to thank Don Provan for his pioneering work
during the initial stages of API definition.
9. References
[1] Bradner, S., "Key Words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[2] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[3] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 2279, January 1998.
[4] Howes, T., "The String Representation of LDAP Search Filters",
RFC 2254 December 1997.
[5] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[6] Alvestrand, H., "Tags for the Identification of Languages",
RFC 1766, March 1995.
[7] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service
Location Protocol, Version 2", RFC 2608, June 1999.
[8] Guttman, E., Perkins, C. and J. Kempf, "Service Templates and
Service: Schemes", RFC 2609, June 1999.
10. Authors' Addresses
Questions about this memo can be directed to:
James Kempf
Sun Microsystems
901 San Antonio Rd.
Palo Alto, CA, 94303
USA
Phone: +1 650 786 5890
Fax: +1 650 786 6445
EMail: james.kempf@sun.com
Erik Guttman
Sun Microsystems
Bahnstr. 2
74915 Waibstadt
Germany
Phone: +49 7263 911 701
EMail: erik.guttman@sun.com
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