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.

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().

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.

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.

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.

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

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.

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

The enumeration SLPBoolean is used as a Boolean flag.

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.

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.

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.

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.

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

Memory passed down from the client code that called the original API function, starting the operation. It can be NULL.

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.

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.