Provided by: isc-dhcp-dev_4.4.3-P1-1ubuntu1_amd64 
NAME
dhcpctl_initialize — dhcpctl library initialization.
SYNOPSIS
#include <dhcpctl/dhcpctl.h>
dhcpctl_status
dhcpctl_initialize(void);
dhcpctl_status
dhcpctl_connect(dhcpctl_handle *cxn, const char *host, int port, dhcpctl_handle auth);
dhcpctl_status
dhcpctl_timed_connect(dhcpctl_handle *cxn, const char *host, int port, dhcpctl_handle auth,
dhcpctl_status *status);
dhcpctl_status
dhcpctl_disconnect(dhcpctl_handle *cxn, int force);
dhcpctl_status
dhcpctl_wait_for_completion(dhcpctl_handle object, dhcpctl_status *status);
dhcpctl_status
dhcpctl_timed_wait_for_completion(dhcpctl_handle object, dhcpctl_status *status,
struct timeval *timeout);
dhcpctl_status
dhcpctl_get_value(dhcpctl_data_string *value, dhcpctl_handle object, const char *name);
dhcpctl_status
dhcpctl_get_boolean(int *value, dhcpctl_handle object, const char *name);
dhcpctl_status
dhcpctl_set_value(dhcpctl_handle object, dhcpctl_data_string value, const char *name);
dhcpctl_status
dhcpctl_set_string_value(dhcpctl_handle object, const char *value, const char *name);
dhcpctl_status
dhcpctl_set_boolean_value(dhcpctl_handle object, int value, const char *name);
dhcpctl_status
dhcpctl_set_int_value(dhcpctl_handle object, int value, const char *name);
dhcpctl_status
dhcpctl_object_update(dhcpctl_handle connection, dhcpctl_handle object);
dhcpctl_status
dhcpctl_object_refresh(dhcpctl_handle connection, dhcpctl_handle object);
dhcpctl_status
dhcpctl_object_remove(dhcpctl_handle connection, dhcpctl_handle object);
dhcpctl_status
dhcpctl_set_callback(dhcpctl_handle object, void *data,
void (*function) (dhcpctl_handle, dhcpctl_status, void *));
dhcpctl_status
dhcpctl_new_authenticator(dhcpctl_handle *object, const char *name, const char *algorithm,
const char *secret, unsigned secret_len);
dhcpctl_status
dhcpctl_new_object(dhcpctl_handle *object, dhcpctl_handle connection,
const char *object_type);
dhcpctl_status
dhcpctl_open_object(dhcpctl_handle object, dhcpctl_handle connection, int flags);
isc_result_t
omapi_data_string_new(dhcpctl_data_string, *data, unsigned, int, length, const, char,
*filename,, int, lineno);
isc_result_t
dhcpctl_data_string_dereference(dhcpctl_data_string *, const char *, int);
DESCRIPTION
The dhcpctl set of functions provide an API that can be used to communicate with and
manipulate a running ISC DHCP server. All functions return a value of isc_result_t. The
return values reflects the result of operations to local data structures. If an operation
fails on the server for any reason, then the error result will be returned through the
second parameter of the dhcpctl_wait_for_completion() call.
dhcpctl_initialize() sets up the data structures the library needs to do its work. This
function must be called once before any other.
dhcpctl_connect() opens a connection to the DHCP server at the given host and port. If an
authenticator has been created for the connection, then it is given as the 4th argument. On
a successful return the address pointed at by the first argument will have a new connection
object assigned to it.
For example:
s = dhcpctl_connect(&cxn, "127.0.0.1", 7911, NULL);
connects to the DHCP server on the localhost via port 7911 (the standard OMAPI port). No
authentication is used for the connection.
dhcpctl_timed_connect() opens a connection to the DHCP server at the given host and port. If
an authenticator has been created for the connection, then it is given as the 4th argument.
On a successful return the address pointed at by the first argument will have a new
connection object assigned to it. How long the function waits for complete the connection
is dictated by the value of the parameter, timeout. If the value is null, it will wait
indefinitely Otherwise it will wait for the amount of time specified by timeout
(tv_sec:tv_usec). Values of zero for both fields are valid but not recommended. An example
is shown below:
For example:
struct timeval timeout;
timeout.tv_sec = 5; /* wait for 5 seconds */
timeout.tv_usec = 0;
s = dhcpctl_connect(&cxn, "127.0.0.1", 7911, NULL, &timeout);
connects to the DHCP server on the localhost via port 7911 (the standard OMAPI port). No
authentication is used for the connection. It allows 5 seconds for the connect to complete.
dhcpctl_disconnect() closes the open connection specified by the first parameter, cxn. Note
that this call will free the connection object and cxn will be set to
nul. If the second parameter,force, is nonzero, the connection will be closed immediately.
Otherwise the receiving end will be shut down but any unsent data will be sent before
actually closing the socket. Note that disconnecting only destroys the connection object,
any other objects previously created will still exist.
For example:
s = dhcpctl_disconnect(&cxn, 1);
will close the connection immediately. This funcion should be considered EXPERIMENTAL.
dhcpctl_wait_for_completion() flushes a pending message to the server and waits for the
response. The result of the request as processed on the server is returned via the second
parameter.
s = dhcpctl_wait_for_completion(cxn, &wv);
if (s != ISC_R_SUCCESS)
local_failure(s);
else if (wv != ISC_R_SUCCESS)
server_failure(wc);
The call to dhcpctl_wait_for_completion() won't return until the remote message processing
completes or the connection to the server is lost.
dhcpctl_timed_wait_for_completion() flushes a pending message to the server and waits for
the response. How long the function waits for a response is dictated by the value of the
third parameter, timeout. If the value is null, it will wait indefinitely or until the
connection is lost. Otherwise it will wait for the amount of time specified by timeout
(tv_sec:tv_usec). Values of zero for both fields are valid but not recommended. The result
of the request as processed on the server is returned via the second parameter. An example
is shown below:
struct timeval timeout;
timeout.tv_sec = 5; /* wait for 5 seconds */
timeout.tv_usec = 0;
s = dhcpctl_wait_for_completion(cxn, &wv, &timeout);
if (s != ISC_R_SUCCESS) {
local_failure(s);
} else if (wv != ISC_R_SUCCESS) {
server_failure(wc);
}
If the function times out, the status returned will be ISC_R_TIMEDOUT. Please note that even
though the function is no longer waiting for a response, the server does not abandon the
request and may still respond by writing the response to the socket. A subsequent call to
either this function or dhcpctl_wait_for_completion() will see that data and read it.
Depending on the application logic flow this may or may not be desired. Currently though
only mechanism for "flushing" this data is to close the connection by calling disconnet(),
and then reconnecting via connect(). Please note this function should be considered
EXPERIMENTAL.
dhcpctl_get_value() extracts a value of an attribute from the handle. The value can be of
any length and is treated as a sequence of bytes. The handle must have been created first
with dhcpctl_new_object() and opened with dhcpctl_open_object(). The value is returned via
the parameter named “value”. The last parameter is the name of attribute to retrieve.
dhcpctl_data_string value = NULL;
dhcpctl_handle lease;
time_t thetime;
s = dhcpctl_get_value (&value, lease, "ends");
assert(s == ISC_R_SUCCESS && value->len == sizeof(thetime));
memcpy(&thetime, value->value, value->len);
dhcpctl_get_boolean() extracts a boolean valued attribute from the object handle.
The dhcpctl_set_value(), dhcpctl_set_string_value(), dhcpctl_set_boolean_value(), and
dhcpctl_set_int_value() functions all set a value on the object handle.
dhcpctl_object_update() function queues a request for all the changes made to the object
handle be sent to the remote for processing. The changes made to the attributes on the
handle will be applied to remote object if permitted.
dhcpctl_object_refresh() queues up a request for a fresh copy of all the attribute values to
be sent from the remote to refresh the values in the local object handle.
dhcpctl_object_remove() queues a request for the removal on the server of the object
referenced by the handle.
The dhcpctl_set_callback() function sets up a user-defined function to be called when an
event completes on the given object handle. This is needed for asynchronous handling of
events, versus the synchronous handling given by dhcpctl_wait_for_completion(). When the
function is called the first parameter is the object the event arrived for, the second is
the status of the message that was processed, the third is the same value as the second
parameter given to dhcpctl_set_callback().
The dhcpctl_new_authenticator() creates a new authenticator object to be used for signing
the messages that cross over the network. The “name”, “algorithm”, and “secret” values must
all match what the server uses and are defined in its configuration file. The created object
is returned through the first parameter and must be used as the 4th parameter to
dhcpctl_connect(). Note that the 'secret' value must not be base64 encoded, which is
different from how the value appears in the dhcpd.conf file.
dhcpctl_new_object() creates a local handle for an object on the server. The “object_type”
parameter is the ascii name of the type of object being accessed. e.g. "lease". This
function only sets up local data structures, it does not queue any messages to be sent to
the remote side, dhcpctl_open_object() does that.
dhcpctl_open_object() builds and queues the request to the remote side. This function is
used with handle created via dhcpctl_new_object(). The flags argument is a bit mask with
the following values available for setting:
DHCPCTL_CREATE
if the object does not exist then the remote will create it
DHCPCTL_UPDATE
update the object on the remote side using the attributes already set in the
handle.
DHCPCTL_EXCL
return and error if the object exists and DHCPCTL_CREATE was also specified
The omapi_data_string_new() function allocates a new dhcpctl_data_string object. The data
string will be large enough to hold “length” bytes of data. The “file” and “lineno”
arguments are the source file location the call is made from, typically by using the
__FILE__ and __LINE__ macros or the MDL macro defined in
dhcpctl_data_string_dereference() deallocates a data string created by
omapi_data_string_new(). The memory for the object won't be freed until the last reference
is released.
EXAMPLES
The following program will connect to the DHCP server running on the local host and will get
the details of the existing lease for IP address 10.0.0.101. It will then print out the time
the lease is due to expire. Note that most error checking has been omitted for brevity.
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "omapip/result.h"
#include "dhcpctl.h"
int main (int argc, char **argv) {
dhcpctl_data_string ipaddrstring = NULL;
dhcpctl_data_string value = NULL;
dhcpctl_handle connection = NULL;
dhcpctl_handle lease = NULL;
isc_result_t waitstatus;
struct in_addr convaddr;
time_t thetime;
dhcpctl_initialize ();
dhcpctl_connect (&connection, "127.0.0.1",
7911, 0);
dhcpctl_new_object (&lease, connection,
"lease");
memset (&ipaddrstring, 0, sizeof
ipaddrstring);
inet_pton(AF_INET, "10.0.0.101",
&convaddr);
omapi_data_string_new (&ipaddrstring,
4, MDL);
memcpy(ipaddrstring->value, &convaddr.s_addr, 4);
dhcpctl_set_value (lease, ipaddrstring,
"ip-address");
dhcpctl_open_object (lease, connection, 0);
dhcpctl_wait_for_completion (lease,
&waitstatus);
if (waitstatus != ISC_R_SUCCESS) {
/* server not authoritative */
exit (0);
}
dhcpctl_data_string_dereference(&ipaddrstring,
MDL);
dhcpctl_get_value (&value, lease, "ends");
memcpy(&thetime, value->value, value->len);
dhcpctl_data_string_dereference(&value, MDL);
fprintf (stdout, "ending time is %s",
ctime(&thetime));
}
SEE ALSO
omapi(3), omshell(1), dhcpd(8), dhclient(8), dhcpd.conf(5), dhclient.conf(5).
AUTHOR
dhcpctl is maintained by ISC. To learn more about Internet Systems Consortium, see
https://www.isc.org