RFC 2614
An API for Service Location
Pages: 91
Informational
Informational
Part 2 of 3 – Pages 25 to 55
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 results4.5.5.3. 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! */
}
(next page on part 3)