SLP_API(3SLP)SLP_API(3SLP)NAMEslp_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 imple‐
mentation 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 func‐
tion per protocol request. Parameters are for the most part charac‐
ter buffers. Memory management is kept simple because the client allo‐
cates most memory and client callback functions are required to copy
incoming parameters into memory allocated by the client code. Any mem‐
ory 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 escap‐
ing and unescaping strings.
Unless otherwise noted, parameters to API functions and callbacks are
non-NULL. Some parameters may have other restrictions. If any parame‐
ter 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 "". Subsequent characters are the escaped values for the orig‐
inal bytes in the opaque. The escape convention is relatively simple.
An escape consists of a backslash followed by the two hexadecimal dig‐
its 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 with‐
out interruption by substituting the default for the erroneous parame‐
ter. In general, individual agents should rarely be required to over‐
ride 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 deal‐
location on the part of the client are SLPParseSrvURL(), SLPFind‐
Scope(), 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_HAN‐
DLE_IN_USE. Prohibiting recursive callbacks on the same handle simpli‐
fies 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 multi‐
cast for awhile and the API library multicast
code is giving up on that (as an optimiza‐
tion).
Maximum results
The user has set the net.slp.maxResults prop‐
erty and that number of replies has been col‐
lected 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 sec‐
onds, 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 rereg‐
istered 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 identifica‐
tion.
The host and port should be sufficient to open a
socket to the machine hosting the service; the remain‐
der 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 partic‐
ular API operation in the parameter list when the API function is
invoked. The callback function is called with the results of the opera‐
tion 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) opera‐
tion. The cookie parameter allows the client code that starts the oper‐
ation by invoking the API function to pass information down to the
callback without using global variables. The callback returns an SLP‐
Boolean 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 fol‐
lowing 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 parame‐
ter 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 follow‐
ing values.
SLP_LAST_CALL
The SLP_LAST_CALL code is passed to call‐
back functions when the API library has
no more data for them and therefore no
further calls will be made to the call‐
back on the currently outstanding opera‐
tion. 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 collec‐
tion loops. On the last call of a call‐
back during both a synchronous and asyn‐
chronous 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 mal‐
formed 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 sup‐
ported 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 ser‐
vice type or scope different than that in
the initial registration.
SLP_REFRESH_REJECTED
The SA attempted to refresh a registra‐
tion 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 maxi‐
mum 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 maxi‐
mum 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 prop‐
erly, 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 opera‐
tion 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 ROUTINESSLPOpen()
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 ALSOslpd(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.
Jan 16, 2003 SLP_API(3SLP)
