Table of Contents | Previous | Next | Index

Netscape Directory SDK 3.0 for C Programmer’s Guide

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:

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.

...
#include <stdio.h>
#include "ldap.h"
...
#define COMPARE_DN "uid=bjensen,ou=People,o=Airius.com"
#define COMPARE_ATTR "mail"
#define COMPARE_VALUE "bjensen@airius.com"
...
LDAP         *ld;
char         *matched_msg = NULL, *error_msg = NULL;
int         rc;
...
/* 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 );
...

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:

The following section of code calls ldap_compare() to determine if an entry has the value "bjensen@airius.com" in the mail attribute. 

...
#include <stdio.h>
#include "ldap.h"
...
#define COMPARE_DN "uid=bjensen,ou=People,o=Airius.com"
#define COMPARE_ATTR "mail"
#define COMPARE_VALUE "bjensen@airius.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;
      }
   }
}
...

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. 

#include <stdio.h>
#include "ldap.h"
/* Change these as needed. */
#define HOSTNAME "localhost"
#define PORTNUMBER LDAP_PORT
#define COMPARE_DN "uid=bjensen,ou=People,o=Airius.com"
#define COMPARE_ATTR "mail"
#define COMPARE_VALUE "bjensen@airius.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;
}   

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. 

#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,o=Airius.com"
#define COMPARE_ATTR "mail"
#define COMPARE_VALUE "bjensen@airius.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++;
}
Table of Contents | Previous | Next | Index

Last Updated: 10/01/98 17:04:27