| Sun Java System LDAP SDK for C Programming Guide |
Chapter 8
Comparing EntriesThis chapter explains how to use the Sun™ Java System LDAP SDK for C functions to compare data among entries in the directory. It includes the following sections:
OverviewThe LDAP SDK for C has functions to determine if an attribute contains a certain string or binary value. To determine if an attribute contains a certain string value, call:
- The synchronous ldap_compare_s() function.
- The asynchronous ldap_compare() function.
To determine if an attribute contains a certain binary value, call:
- The synchronous ldap_compare_ext_s() function.
- The asynchronous ldap_compare_ext() function.
Synchronous Comparison OperationsIf you want to wait for the results of the compare operation to complete before continuing, call the synchronous ldap_compare_ext_s() function to compare values in berval structures or the synchronous ldap_compare_s() function to compare string values. These functions send a compare request to the server and block work until the server sends the results of the operation back to your client. Both functions return one of the following values after the compare operation completes:
- LDAP_COMPARE_TRUE indicates that the attribute contains the specified value.
- LDAP_COMPARE_FALSE indicates that the attribute does not contain the specified value.
An error code indicates that a problem has occurred during the operation.
Note
See the documentation on the ldap_compare_ext_s() function or the ldap_compare_s() function for a list of the possible result codes.
Code Example 8-1 uses the synchronous ldap_compare_s() function to determine if an entry has the value bjensen@example.com in the mail attribute.
Code Example 8-2 is a sample program that calls the synchronous ldap_compare_s() function to determine if a user’s entry has the value bjensen@example.com in the mail attribute.
Code Example 8-2 Sample Synchronous Comparison Program
#include <stdio.h>
#include "ldap.h"
/* Change these as needed. */
#define HOSTNAME "localhost"
#define PORTNUMBER LDAP_PORT
#define COMPARE_DN "uid=bjensen,ou=People,dc=example,dc=com"
#define COMPARE_ATTR "mail"
#define COMPARE_VALUE "bjensen@example.com"
int
main( int argc, char **argv )
{
LDAP *ld;
char *matched_msg = NULL, *error_msg = NULL;
int rc;
/* Get a handle to an LDAP connection. */
if ( (ld = ldap_init( HOSTNAME, PORTNUMBER )) == NULL ) {
perror( "ldap_init" );
return( 1 );
}
/* Bind anonymously to the server. */
rc = ldap_simple_bind_s( ld, NULL, NULL );
if ( rc != LDAP_SUCCESS ) {
fprintf( stderr, "ldap_simple_bind_s: %s\n", ldap_err2string( rc ) );
ldap_get_lderrno( ld, &matched_msg, &error_msg );
if ( error_msg != NULL && *error_msg != '\0' ) {
fprintf( stderr, "%s\n", error_msg );
}
if ( matched_msg != NULL && *matched_msg != '\0' ) {
fprintf( stderr,
"Part of the DN that matches an existing entry: %s\n",
matched_msg );
}
ldap_unbind_s( ld );
return( 1 );
}
/* Perform the compare operation. */
rc = ldap_compare_s( ld, COMPARE_DN, COMPARE_ATTR, COMPARE_VALUE );
switch( rc ) {
case LDAP_COMPARE_TRUE:
printf( "%s has the value %s in the %s attribute.\n", COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR );
break;
case LDAP_COMPARE_FALSE:
printf( "%s does not have the value %s in the %s attribute.\n", COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR );
break;
default:
fprintf( stderr, "ldap_compare_s: %s\n", ldap_err2string( rc ) );
ldap_get_lderrno( ld, &matched_msg, &error_msg );
if ( error_msg != NULL && *error_msg != '\0' ) {
fprintf( stderr, "%s\n", error_msg );
}
if ( matched_msg != NULL && *matched_msg != '\0' ) {
fprintf( stderr,
"Part of the DN that matches an existing entry: %s\n",
matched_msg );
}
break;
}
ldap_unbind_s( ld );
return 0;
}
Asynchronous Comparison OperationsIf you want to perform other work (in parallel) while waiting for the comparison to complete, call the asynchronous ldap_compare_ext() function to compare values in berval structures or the asynchronous ldap_compare() function to compare string values. These functions send a compare request to the server and return an LDAP_SUCCESS result code if the request was successfully sent or an LDAP result code if an error occurred.
Both functions pass back a message ID identifying the compare operation. To determine whether the server sent a response for this operation to your client, call the ldap_result() function and pass in the message ID. ldap_result() uses the message ID to determine if the server sent the results of the compare operation. The function passes back the results in an LDAPMessage structure. You can call the ldap_parse_result() function to parse the LDAPMessage structure to determine if the operation was successful. The result code should be one of the following:
- LDAP_COMPARE_TRUE indicates that the attribute contains the specified value.
- LDAP_COMPARE_FALSE indicates that the attribute does not contain the specified value.
An error code indicates that a problem occurred during the operation.
Note
See the documentation on the ldap_compare_ext() function or the ldap_compare() function for a list of the possible result codes.
Code Example 8-3 calls ldap_compare() to determine if an entry has the value bjensen@example.com in the mail attribute.
Code Example 8-3 Asynchronous Compare Operation
#include <stdio.h>
#include "ldap.h"
...
#define COMPARE_DN "uid=bjensen,ou=People,dc=example,dc=com"
#define COMPARE_ATTR "mail"
#define COMPARE_VALUE "bjensen@example.com"
...
LDAP *ld;
LDAPMessage *res;
LDAPControl **serverctrls;
char *matched_msg = NULL, *error_msg = NULL;
char **referrals;
int rc, parse_rc, msgid, finished = 0;
struct timeval zerotime;
zerotime.tv_sec = zerotime.tv_usec = 0L;
...
/* Send the LDAP compare request. */
msgid = ldap_compare( ld, COMPARE_DN, COMPARE_ATTR, COMPARE_VALUE );
if ( msgid < 0 ) {
fprintf( stderr, "ldap_compare: %s\n", ldap_err2string( rc ) );
ldap_unbind( ld );
return( 1 );
}
/* Poll the server for the results of the LDAP compare operation. */
while ( !finished ) {
rc = ldap_result( ld, msgid, 0, &zerotime, &res );
switch ( rc ) {
case -1:
/* An error occurred. */
rc = ldap_get_lderrno( ld, NULL, NULL );
fprintf( stderr, "ldap_result: %s\n", ldap_err2string( rc ) );
ldap_unbind( ld );
return( 1 );
case 0:
/* The timeout period specified by zerotime was exceeded, so
call ldap_result() again and continue to poll for the
results. */
break;
default:
/* The client has received the results of the
LDAP compare operation from the server. */
finished = 1;
/* Parse the results received from the server.*/
parse_rc = ldap_parse_result( ld, res, &rc, &matched_msg,
&error_msg, &referrals, &serverctrls, 1 );
if ( parse_rc != LDAP_SUCCESS ) {
fprintf( stderr, "ldap_parse_result: %s\n",
ldap_err2string( parse_rc ) );
ldap_unbind( ld );
return( 1 );
}
/* Check the results of the LDAP compare operation. */
switch ( rc ) {
case LDAP_COMPARE_TRUE:
printf( "%s has the value %s in the %s attribute.\n",
COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR );
break;
case LDAP_COMPARE_FALSE:
printf( "%s does not have the value %s in the %s attribute.\n",
COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR );
break;
default:
fprintf( stderr, "ldap_compare: %s\n", ldap_err2string( rc ) );
if ( error_msg != NULL & *error_msg != '\0' ) {
fprintf( stderr, "%s\n", error_msg );
}
if ( matched_msg != NULL && *matched_msg != '\0' ) {
fprintf( stderr,
"Part of the DN that matches an existing entry: %s\n",
matched_msg );
}
break;
}
}
}
...
Code Example 8-4 is a sample program that calls the asynchronous ldap_compare() function to determine if a user’s entry has the value bjensen@example.com in the mail attribute.
Code Example 8-4 Sample Asynchronous Comparison Program
#include <stdio.h>
#include "ldap.h"
void do_other_work();
int global_counter = 0;
/* Change these as needed. */
#define HOSTNAME "localhost"
#define PORTNUMBER LDAP_PORT
#define COMPARE_DN "uid=bjensen,ou=People,dc=example,dc=com"
#define COMPARE_ATTR "mail"
#define COMPARE_VALUE "bjensen@example.com"
int
main( int argc, char **argv )
{
LDAP *ld;
LDAPMessage *res;
LDAPControl **serverctrls;
char *matched_msg = NULL, *error_msg = NULL;
char **referrals;
int rc, parse_rc, msgid, finished = 0;
struct timeval zerotime;
zerotime.tv_sec = zerotime.tv_usec = 0L;
/* Get a handle to an LDAP connection. */
if ( (ld = ldap_init( HOSTNAME, PORTNUMBER )) == NULL ) {
perror( "ldap_init" );
return( 1 );
}
/* Bind anonymously to the server. */
rc = ldap_simple_bind_s( ld, NULL, NULL );
if ( rc != LDAP_SUCCESS ) {
fprintf( stderr, "ldap_simple_bind_s: %s\n", ldap_err2string( rc ) );
ldap_get_lderrno( ld, NULL, &error_msg );
if ( error_msg != NULL && *error_msg != '\0' ) {
fprintf( stderr, "%s\n", error_msg );
}
ldap_unbind_s( ld );
return( 1 );
}
/* Send the LDAP compare request. */
msgid = ldap_compare( ld, COMPARE_DN, COMPARE_ATTR, COMPARE_VALUE );
if ( msgid < 0 ) {
fprintf( stderr, "ldap_compare: %s\n", ldap_err2string( rc ) );
ldap_unbind( ld );
return( 1 );
}
/* Poll the server for the results of the LDAP compare operation. */
while ( !finished ) {
rc = ldap_result( ld, msgid, 0, &zerotime, &res );
switch ( rc ) {
case -1:
/* An error occurred. */
rc = ldap_get_lderrno( ld, NULL, NULL );
fprintf( stderr, "ldap_result: %s\n", ldap_err2string( rc ) );
ldap_unbind( ld );
return( 1 );
case 0:
/* The timeout period specified by zerotime was exceeded.
This means that your client has not yet received the
results of the LDAP compare operation.
Break out of this switch statement, and continue calling
ldap_result() to poll for the results. */
break;
default:
/* The client has received the results of the
LDAP compare operation from the server. */
finished = 1;
/* Parse the results received from the server. Note the last
argument is a non-zero value, which indicates that the
LDAPMessage structure will be freed when done. (No need
to call ldap_msgfree().) */
parse_rc = ldap_parse_result( ld, res, &rc, &matched_msg, &error_msg, &referrals, &serverctrls, 1 );
if ( parse_rc != LDAP_SUCCESS ) {
fprintf( stderr, "ldap_parse_result: %s\n", ldap_err2string( parse_rc ) );
ldap_unbind( ld );
return( 1 );
}
/* Check the results of the LDAP compare operation. */
switch ( rc ) {
case LDAP_COMPARE_TRUE:
printf( "%s has the value %s in the %s attribute.\n"
"Counted to %d while waiting for the compare operation.\n",
COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR, global_counter );
break;
case LDAP_COMPARE_FALSE:
printf( "%s does not have the value %s in the %s attribute.\n"
"Counted to %d while waiting for the compare operation.\n",
COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR, global_counter );
break;
default:
fprintf( stderr, "ldap_compare: %s\n", ldap_err2string( rc ) );
if ( error_msg != NULL & *error_msg != '\0' ) {
fprintf( stderr, "%s\n", error_msg );
}
if ( matched_msg != NULL && *matched_msg != '\0' ) {
fprintf( stderr,
"Part of the DN that matches an existing entry: %s\n",
matched_msg );
}
break;
}
}
/* Do other work while waiting for the results of the compare operation. */
if ( !finished ) {
do_other_work();
}
}
ldap_unbind( ld );
return 0;
}
/*
* Perform other work while polling for results. This doesn't do anything
* useful, but it could.
*/
void
do_other_work()
{
global_counter++;
}
