Chapter 9
Comparing Values in Entries
This chapter explains how to use the API functions to compare data in entries in the directory. The LDAP API includes functions that you can call to compare the value of an attribute in an entry against a specified value.
The chapter includes the following sections:
Comparing the Value of an Attribute
To determine if an attribute contains a certain value, call one of the following functions:
For more information about the difference between synchronous and asynchronous functions, see "Calling Synchronous and Asynchronous Functions."
Note that both of these functions compare values that are in berval structures; this allows you to compare binary values. If you just want to compare string values, you can call the ldap_compare() or ldap_compare_s() function.
Performing a Synchronous Comparison Operation
If 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 berval structures or wait for the results of the compare operation to complete before continuing, call the synchronous ldap_compare_s() function to compare string values. These functions send an LDAP compare request to the server and block until the server sends the results of the operation back to your client.
Both the ldap_compare_ext_s() function and the ldap_compare_s() function return one of the following values after the LDAP 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.
See the documentation on the ldap_compare_ext_s() function for a list of the possible result codes.
The following section of code uses the synchronous ldap_compare_s() function to determine if an entry has the value "bjensen2airius.com" in the mail attribute.
Code Example 9-1 Applying the ldap_compare_s() function
#include <stdio.h>
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#include "ldap.h"
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...
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#define COMPARE_DN "uid=bjensen,ou=People,o=airius.com"
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#define COMPARE_ATTR "mail"
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#define COMPARE_VALUE "bjensen@airius.com"
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...
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LDAP *ld;
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char *matched_msg = NULL, *error_msg = NULL;
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int rc;
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...
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/* Perform the compare operation. */
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rc = ldap_compare_s( ld, COMPARE_DN, COMPARE_ATTR, COMPARE_VALUE );
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switch( rc ) {
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case LDAP_COMPARE_TRUE:
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printf( "%s has the value %s in the %s attribute.\n", COMPARE_DN,
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COMPARE_VALUE, COMPARE_ATTR );
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break;
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case LDAP_COMPARE_FALSE:
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printf( "%s does not have the value %s in the %s attribute.\n",
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COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR );
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break;
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default:
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fprintf( stderr, "ldap_compare_s: %s\n", ldap_err2string( rc ) );
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ldap_get_lderrno( ld, &matched_msg, &error_msg );
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if ( error_msg != NULL && *error_msg != '\0' ) {
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fprintf( stderr, "%s\n", error_msg );
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}
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if ( matched_msg != NULL && *matched_msg != '\0' ) {
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fprintf( stderr,
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"Part of the DN that matches an existing entry: %s\n",
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matched_msg );
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}
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break;
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}
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ldap_unbind_s( ld );
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...
|
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Performing an Asynchronous Comparison Operation
If 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 an LDAP 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 the ldap_compare_ext() function and the ldap_compare() function 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 this message ID. The ldap_result() function 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. (For a list of possible result codes for an LDAP compare operation, see the result code documentation for the ldap_compare_ext_s() function.)
The following section of code calls ldap_compare() to determine if an entry has the value "bjensen@airius.com" in the mail attribute.
Code Example 9-2 Applying the ldap_compare() function
#include <stdio.h>
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#include "ldap.h"
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...
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#define COMPARE_DN "uid=bjensen,ou=People,o=airius.com"
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#define COMPARE_ATTR "mail"
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#define COMPARE_VALUE "bjensen@airius.com"
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...
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LDAP *ld;
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LDAPMessage *res;
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LDAPControl **serverctrls;
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char *matched_msg = NULL, *error_msg = NULL;
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char **referrals;
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int rc, parse_rc, msgid, finished = 0;
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struct timeval zerotime;
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zerotime.tv_sec = zerotime.tv_usec = 0L;
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...
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/* Send the LDAP compare request. */
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msgid = ldap_compare( ld, COMPARE_DN, COMPARE_ATTR, COMPARE_VALUE );
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if ( msgid < 0 ) {
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fprintf( stderr, "ldap_compare: %s\n", ldap_err2string( rc ) );
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ldap_unbind( ld );
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return( 1 );
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}
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/* Poll the server for the results of the LDAP compare operation. */
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while ( !finished ) {
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rc = ldap_result( ld, msgid, 0, &zerotime, &res );
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switch ( rc ) {
|
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case -1:
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/* An error occurred. */
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rc = ldap_get_lderrno( ld, NULL, NULL );
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fprintf( stderr, "ldap_result: %s\n", ldap_err2string( rc ) );
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ldap_unbind( ld );
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return( 1 );
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case 0:
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/* The timeout period specified by zerotime was exceeded, so
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call ldap_result() again and continue to poll for the
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results. */
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break;
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default:
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/* The client has received the results of the
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LDAP compare operation from the server. */
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finished = 1;
|
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/* Parse the results received from the server.*/
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parse_rc = ldap_parse_result( ld, res, &rc, &matched_msg,
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&error_msg, &referrals, &serverctrls, 1 );
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if ( parse_rc != LDAP_SUCCESS ) {
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fprintf( stderr, "ldap_parse_result: %s\n",
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ldap_err2string( parse_rc ) );
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ldap_unbind( ld );
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return( 1 );
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}
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/* Check the results of the LDAP compare operation. */
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switch ( rc ) {
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case LDAP_COMPARE_TRUE:
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printf( "%s has the value %s in the %s attribute.\n",
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COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR );
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break;
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case LDAP_COMPARE_FALSE:
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printf( "%s does not have the value %s in the %s attribute.\n",
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COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR );
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break;
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default:
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fprintf( stderr, "ldap_compare: %s\n", ldap_err2string( rc ) );
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if ( error_msg != NULL & *error_msg != '\0' ) {
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fprintf( stderr, "%s\n", error_msg );
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}
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if ( matched_msg != NULL && *matched_msg != '\0' ) {
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fprintf( stderr,
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"Part of the DN that matches an existing entry: %s\n",
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matched_msg );
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}
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break;
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}
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}
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}
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...
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|
Example: Comparing a Value in an Entry (Synchronous)
The following sample program calls the synchronous ldap_compare_s() function to determine if a user's entry has the value "bjensen@airius.com" in the mail attribute.
Code Example 9-3 Comparing entry values using ldap_compare_s()
#include <stdio.h>
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#include "ldap.h"
|
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/* Change these as needed. */
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#define HOSTNAME "localhost"
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#define PORTNUMBER LDAP_PORT
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#define COMPARE_DN "uid=bjensen,ou=People,o=airius.com"
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#define COMPARE_ATTR "mail"
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#define COMPARE_VALUE "bjensen@airius.com"
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int
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main( int argc, char **argv )
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{
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LDAP *ld;
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char *matched_msg = NULL, *error_msg = NULL;
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int rc;
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/* Get a handle to an LDAP connection. */
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if ( (ld = ldap_init( HOSTNAME, PORTNUMBER )) == NULL ) {
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perror( "ldap_init" );
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return( 1 );
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}
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/* Bind anonymously to the server. */
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rc = ldap_simple_bind_s( ld, NULL, NULL );
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if ( rc != LDAP_SUCCESS ) {
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fprintf( stderr, "ldap_simple_bind_s: %s\n", ldap_err2string( rc ) );
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ldap_get_lderrno( ld, &matched_msg, &error_msg );
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if ( error_msg != NULL && *error_msg != '\0' ) {
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fprintf( stderr, "%s\n", error_msg );
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}
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if ( matched_msg != NULL && *matched_msg != '\0' ) {
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fprintf( stderr,
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"Part of the DN that matches an existing entry: %s\n",
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matched_msg );
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}
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ldap_unbind_s( ld );
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return( 1 );
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}
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/* Perform the compare operation. */
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rc = ldap_compare_s( ld, COMPARE_DN, COMPARE_ATTR, COMPARE_VALUE );
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switch( rc ) {
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case LDAP_COMPARE_TRUE:
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printf( "%s has the value %s in the %s attribute.\n", COMPARE_DN,
COMPARE_VALUE, COMPARE_ATTR );
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break;
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case LDAP_COMPARE_FALSE:
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printf( "%s does not have the value %s in the %s attribute.\n",
COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR );
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break;
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default:
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fprintf( stderr, "ldap_compare_s: %s\n", ldap_err2string( rc ) );
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ldap_get_lderrno( ld, &matched_msg, &error_msg );
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if ( error_msg != NULL && *error_msg != '\0' ) {
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fprintf( stderr, "%s\n", error_msg );
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}
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if ( matched_msg != NULL && *matched_msg != '\0' ) {
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fprintf( stderr,
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"Part of the DN that matches an existing entry: %s\n",
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matched_msg );
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}
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break;
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}
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ldap_unbind_s( ld );
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return 0;
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}
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|
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Example: Comparing a Value in an Entry (Asynchronous)
The following sample program calls the asynchronous ldap_compare() function to determine if a user's entry has the value "bjensen@airius.com" in the mail attribute.
Code Example 9-4 Comparing entry values using ldap_compare()
#include <stdio.h>
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#include "ldap.h"
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void do_other_work();
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int global_counter = 0;
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/* Change these as needed. */
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#define HOSTNAME "localhost"
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#define PORTNUMBER LDAP_PORT
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#define COMPARE_DN "uid=bjensen,ou=People,o=airius.com"
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#define COMPARE_ATTR "mail"
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#define COMPARE_VALUE "bjensen@airius.com"
|
int
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main( int argc, char **argv )
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{
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LDAP *ld;
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LDAPMessage *res;
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LDAPControl **serverctrls;
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char *matched_msg = NULL, *error_msg = NULL;
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char **referrals;
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int rc, parse_rc, msgid, finished = 0;
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struct timeval zerotime;
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zerotime.tv_sec = zerotime.tv_usec = 0L;
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/* Get a handle to an LDAP connection. */
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if ( (ld = ldap_init( HOSTNAME, PORTNUMBER )) == NULL ) {
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perror( "ldap_init" );
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return( 1 );
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}
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/* Bind anonymously to the server. */
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rc = ldap_simple_bind_s( ld, NULL, NULL );
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if ( rc != LDAP_SUCCESS ) {
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fprintf( stderr, "ldap_simple_bind_s: %s\n", ldap_err2string( rc ) );
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ldap_get_lderrno( ld, NULL, &error_msg );
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if ( error_msg != NULL && *error_msg != '\0' ) {
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fprintf( stderr, "%s\n", error_msg );
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}
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ldap_unbind_s( ld );
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return( 1 );
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}
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/* Send the LDAP compare request. */
|
msgid = ldap_compare( ld, COMPARE_DN, COMPARE_ATTR, COMPARE_VALUE );
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if ( msgid < 0 ) {
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fprintf( stderr, "ldap_compare: %s\n", ldap_err2string( rc ) );
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ldap_unbind( ld );
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return( 1 );
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}
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/* Poll the server for the results of the LDAP compare operation. */
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while ( !finished ) {
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rc = ldap_result( ld, msgid, 0, &zerotime, &res );
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switch ( rc ) {
|
case -1:
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/* An error occurred. */
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rc = ldap_get_lderrno( ld, NULL, NULL );
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fprintf( stderr, "ldap_result: %s\n", ldap_err2string( rc ) );
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ldap_unbind( ld );
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return( 1 );
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case 0:
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/* 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. */
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break;
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default:
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/* The client has received the results of the
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LDAP compare operation from the server. */
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finished = 1;
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/* Parse the results received from the server. Note the last
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argument is a non-zero value, which indicates that the
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LDAPMessage structure will be freed when done. (No need
|
to call ldap_msgfree().) */
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parse_rc = ldap_parse_result( ld, res, &rc, &matched_msg, &error_msg,
&referrals, &serverctrls, 1 );
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if ( parse_rc != LDAP_SUCCESS ) {
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fprintf( stderr, "ldap_parse_result: %s\n", ldap_err2string( parse_rc
) );
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ldap_unbind( ld );
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return( 1 );
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}
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/* Check the results of the LDAP compare operation. */
|
switch ( rc ) {
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case LDAP_COMPARE_TRUE:
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printf( "%s has the value %s in the %s attribute.\n"
|
"Counted to %d while waiting for the compare operation.\n",
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COMPARE_DN, COMPARE_VALUE, COMPARE_ATTR, global_counter );
|
break;
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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++;
|
}
|
|
|