SLP_API(3SLP) Service Location Protocol Library Functions SLP_API(3SLP)


NAME


slp_api - Service Location Protocol Application Programming Interface

SYNOPSIS


cc [ flag ... ] file ... -lslp [ library ... ]
#include <slp.h>


DESCRIPTION


The slp_api is a C language binding that maps directly into the
Service Location Protocol ("SLP") defined by RFC 2614. This
implementation requires minimal overhead. With the exception of the
SLPDereg() and SLPDelAttrs() functions, which map into different uses
of the SLP deregister request, there is one C language function per
protocol request. Parameters are for the most part character buffers.
Memory management is kept simple because the client allocates most memory
and client callback functions are required to 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.

Syntax for String Parameters


Query strings, attribute registration lists, attribute deregistration
lists, scope lists, and attribute selection lists follow the syntax
described in RFC 2608. The API reflects the strings passed from clients
directly into protocol requests, and reflects out strings returned from
protocol replies directly 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 SLPEscape() and SLPUnescape()
functions can be used for escaping SLP reserved characters, but they
perform no opaque processing.


Opaque values consist of a character buffer that contains a UTF-8-encoded
string, the first characters of which are the non UTF-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.

System Properties


The system properties established in slp.conf(4), the configuration file,
are accessible through the SLPGetProperty() and SLPSetProperty()
functions. The SLPSetProperty() function modifies properties only in the
running process, not in the configuration file. Errors are checked when
the property is used and, as with parsing the configuration file, are
logged at the LOG_INFO priority. Program execution continues without
interruption by substituting the default for the erroneous parameter. In
general, individual agents should rarely be required to override these
properties, since they reflect properties of the SLP network that are not
of concern to individual agents. If changes are required, system
administrators should modify the configuration file.


Properties are global to the process, affecting all threads and all
handles created with SLPOpen().

Memory Management


The only API functions that return memory specifically requiring
deallocation on the part of the client are SLPParseSrvURL(),
SLPFindScope(), SLPEscape(), and SLPUnescape(). Free this memory with
SLPFree() when it is no longer needed. Do not free character strings
returned by means of the SLPGetProperty() function.


Any memory passed to callbacks belongs to the library, and it must not be
retained by the client code. Otherwise, crashes are possible. Clients
must copy data out of the callback parameters. No other use of the memory
in callback parameters is allowed.

Asynchronous and Incremental Return Semantics


If a handle parameter to an API function is opened asynchronously, the
API function calls on the handle to check the other parameters, opens the
appropriate operation, and returns immediately. If an error occurs in the
process of starting the operation, the error code is returned. If the
handle parameter is opened synchronously, the function call is blocked
until all results are available, and it returns only after the results
are reported through the callback function. The return code indicates
whether any errors occurred during the operation.


The callback function is called whenever the API library has results to
report. The callback code is required to check the error code parameter
before looking at the other parameters. If the error code is not SLP_OK,
the other parameters may be NULL or otherwise invalid. The API library
can terminate 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 to indicate that it is not
interested in receiving more results. Callback functions are not
permitted to recursively call into the API on the same SLPHandle. If an
attempt is made to call into the API, the API function returns
SLP_HANDLE_IN_USE. Prohibiting recursive callbacks on the same handle
simplifies implementation of thread safe code, since locks held on the
handle will not be in place during a second outcall on the handle.


The total number of results received can be controlled by setting the
net.slp.maxResults parameter.


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 awhile 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.


Configuration Files


The API library reads slp.conf(4), the default configuration file, to
obtain the operating parameters. You can specify the location of this
file with the SLP_CONF_FILE environment variable. If you do not set this
variable, or the file it refers to is invalid, the API will use the
default configuration file at /etc/inet/slp.conf instead.

Data Structures


The data structures used by the SLP API are as follows:

The URL Lifetime Type


typedef enum {
SLP_LIFETIME_DEFAULT = 10800,
SLP_LIFETIME_MAXIMUM = 65535
} SLPURLLifetime;


The enumeration SLPURLLifetime contains URL lifetime values, in
seconds, that are frequently used. SLP_LIFETIME_DEFAULT is 3 hours, while
SLP_LIFETIME_MAXIMUM is 18 hours, which corresponds to the maximum size
of the lifetime field in SLP messages. Note that on registration
SLP_LIFETIME_MAXIMUM causes the advertisement to be continually
reregistered until the process exits.

The SLPBoolean Type


typedef enum {
SLP_FALSE = 0,
SLP_TRUE = 1
} SLPBoolean;


The enumeration SLPBoolean is used as a Boolean flag.

The Service URL Structure


typedef struct srvurl {
char *s_pcSrvType;
char *s_pcHost;
int s_iPort;
char *s_pcNetFamily;
char *s_pcSrvPart;
} SLPSrvURL;


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, as follows:

s_pcSrvType
A pointer to a character string containing the service
type name, including naming authority.


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 "",
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; the remainder of the
URL should allow further differentiation of the service.


The SLPHandle


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.

Callbacks


Include a function pointer to a callback function specific to a
particular API operation 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. When the
callback function is invoked, 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.


Each callback parameter list contains parameters for reporting the
results of the operation, as well as 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.

SLPRegReport()
typedef void SLPRegReport(SLPHandle hSLP,
SLPError errCode,
void *pvCookie);


SLPRegReport() is the callback function to the SLPReg(), SLPDereg(), and
SLPDelAttrs() functions. The SLPRegReport() callback has the following
parameters:

hSLP
TheSLPHandle() 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. It may be
NULL.


SLPSrvTypeCallback()
typedef SLPBoolean SLPSrvTypeCallback(SLPHandle hSLP,
const char* pcSrvTypes,
SLPError errCode,
void *pvCookie);


The SLPSrvTypeCallback() type is the type of the callback function
parameter to the SLPFindSrvTypes() function. The results are collated
when the hSLP handle is opened either synchronously or asynchronously.
The SLPSrvTypeCallback() callback has the following 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
emory passed down from the client code that called the
original API function, starting the operation. It can be
NULL.


SLPSrvURLCallback


typedef SLPBoolean SLPSrvURLCallback(SLPHandle hSLP,
const char* pcSrvURL,
unsigned short usLifetime,
SLPError errCode,
void *pvCookie);


The SLPSrvURLCallback() type is the type of the callback function
parameter to the SLPFindSrvs() function. The results are collated,
regardless of whether the hSLP was opened collated or uncollated. The
SLPSrvURLCallback() callback has the following parameters:

hSLP
The SLPHandle used to initiate the operation.


pcSrvURL
A character buffer containing the returned service URL.


usLifetime
An unsigned short giving the life time of the service
advertisement. 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. It can be
NULL.


SLPAttrCallback


typedef SLPBoolean SLPAttrCallback(SLPHandle hSLP,
const char* pcAttrList,
SLPError errCode,
void *pvCookie);


The SLPAttrCallback() type is the type of the callback function parameter
to the SLPFindAttrs() function.


The behavior of the callback differs depending upon 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, in
addition to the last call, regardless of whether the handle was opened
asynchronously or synchronously. The pcAttrList parameter contains the
requested attributes as a comma-separated list. It is empty if no
attributes match the original tag list.


If the SLPFindAttrs() operation was originally called with a service
type, the value of pcAttrList and the calling behavior depend upon
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 is
collated between calls, and contains a comma-separated list of the
results from the agent that immediately returned. If the handle was
opened synchronously, the results are collated from all returning agents,
the callback is called once, and the pcAttrList parameter is set to the
collated result.


SLPAttrCallback() callback has the following parameters:

hSLP
The SLPHandle used to initiate the operation.


pcAttrList
A character buffer containing a comma-separated and null-
terminated list of attribute id/value assignments, in SLP
wire format.


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. It can be
NULL.


ERRORS


An interface that is part of the SLP API may return one of the following
values.

SLP_LAST_CALL
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 uses 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.


SLP_OK
The SLP_OK code indicates that the no error
occurred during the operation.


SLP_LANGUAGE_NOT_SUPPORTED
No DA or SA has service advertisement
information in the language requested, but
at least one DA or SA might have
information for that service in another
language.


SLP_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 damaged in transit.


SLP_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 accepts the registration.


SLP_SCOPE_NOT_SUPPORTED
The API returns this error if the UA or SA
has been configured with the
net.slp.useScopes list of scopes and the SA
request did not specify one or more of
these allowable scopes, and no others. It
may also be returned by a DA if the scope
included in a request is not supported by a
DA.


SLP_AUTHENTICATION_ABSENT
This error arises when the UA or SA failed
to send an authenticator for requests or
registrations when security is enabled and
thus required.


SLP_AUTHENTICATION_FAILED
This error arises when a authentication on
an SLP message received from a remote SLP
agent failed.


SLP_INVALID_UPDATE
An update for a nonexisting registration
was issued, or the update includes a
service type or scope different than that
in the initial registration.


SLP_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.


SLP_NOT_IMPLEMENTED
An outgoing request overflowed the maximum
network MTU size. The request should be
reduced in size or broken into pieces and
tried again.


SLP_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.


SLP_NETWORK_TIMED_OUT
When no reply can be obtained in the time
specified by the configured timeout
interval, this error is returned.


SLP_NETWORK_INIT_FAILED
If the network cannot initialize properly,
this error is returned.


SLP_MEMORY_ALLOC_FAILED
If the API fails to allocate memory, the
operationis aborted and returns this.


SLP_PARAMETER_BAD
If a parameter passed into an interface is
bad, this error is returned.


SLP_NETWORK_ERROR
The failure of networking during normal
operations causes this error to be
returned.


SLP_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.


SLP_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


LIST OF ROUTINES


SLPOpen()
open an SLP handle


SLPClose()
close an open SLP handle


SLPReg()
register a service advertisement


SLPDereg()
deregister a service advertisement


SLPDelAttrs()
delete attributes


SLPFindSrvTypes()
return service types


SLPFindSrvs()
return service URLs


SLPFindAttrs()
return service attributes


SLPGetRefreshInterval()
return the maximum allowed refresh interval
for SAs


SLPFindScopes()
return list of configured and discovered
scopes


SLPParseSrvURL()
parse service URL


SLPEscape()
escape special characters


SLPUnescape()
translate escaped characters into UTF-8


SLPGetProperty()
return SLP configuration property


SLPSetProperty()
set an SLP configuration property


slp_strerror()
map SLP error code to message


SLPFree()
free memory


ENVIRONMENT VARIABLES


When SLP_CONF_FILE is set, use this file for configuration.

ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|CSI | CSI-enabled |
+---------------+-----------------+
|MT-Level | Safe |
+---------------+-----------------+

SEE ALSO


slpd(1M), slp.conf(4), slpd.reg(4), attributes(5)


System Administration Guide: Network Services


Guttman, E., Perkins, C., Veizades, J., and Day, M. RFC 2608, Service
Location Protocol, Version 2. The Internet Society. June 1999.


Kempf, J. and Guttman, E. RFC 2614, An API for Service Location. The
Internet Society. June 1999.


January 16, 2003 SLP_API(3SLP)