ldap_set_rebind_proc

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

ldap_set_rebind_proc — Set a callback function to do re-binds on referral chasing

Description

ldap_set_rebind_proc(LDAP\Connection $ldap, ?callable $callback): bool

Warning

This function is currently not documented; only its argument list is available.

Changelog

Version	Description
8.1.0	The `ldap` parameter expects an LDAP\Connection instance now; previously, a valid `ldap link` resource was expected.
8.0.0	`callback` is nullable now.

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User Contributed Notes 7 notes

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mvanbeek at forgetaboutit dot net ¶

11 years ago

The $referral that is used in the callback function isn't the bind dn, but the dn of the record that was being accessed (or rather it's location on the master server, I guess, if there is a difference in the two), so you need to rebind with your existing credentials. The connection ($ldap) appears to have already been made to the new server, so it is just a rebind process, nothing else more complicated than that. There must be a loop in the underlying library that re-submits the request that prompted the referral until either a success or fail is returned.



I guess if the bind dn you were using in the first place won't let you edit the record on the master, then that is an ldap rather than php issue. However, at least with the rebind procedure you have a way to modify the bind dn first.



So, the rebind process is really quite simple, now that I understand how it works! I was assuming it to be way more complicated. In it's simplest form, this is all you need, assuming your bind $dn and $pass are globals



<?php

function rebind($ldap, $referral) {

    // Set ldap options

    ldap_set_option($ldap, LDAP_OPT_PROTOCOL_VERSION, 3);

    ldap_set_option($ldap, LDAP_OPT_REFERRALS, True);

    ldap_set_rebind_proc($ldap, 'rebind');

    // Rebind

    if (!ldap_bind($ldap, $dn, $pass)) {

            echo 'Could not bind to referral server';

            return 1; // Yes, a 1 means a failure.

        }

    return 0; // Yes, return a 0 on success.

    }

?>

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leon at leonux dot co dot za ¶

13 years ago

I finally have referrals working using the ldap_set_rebind_proc function. Don't connect to the referral server in your callback function. This is done for you. You only have to bind. The callback must return 0 if the bind succeeds or 1 if it fails. 

Consider a master - slave LDAP setup where the slave is read-only and refers writes to the master. For the PHP on the slave, you need something like this:

<?php

// Callback function
function rebind($ldap, $referral) {
    // ldap options
    ldap_set_option($ldap, LDAP_OPT_PROTOCOL_VERSION, 3);
    ldap_set_option($ldap, LDAP_OPT_REFERRALS, True);
    ldap_set_rebind_proc($ldap, 'rebind');
    // The referral is of the form:
    //  ldaps://newhost/cn=user,ou=people,dc=example,dc=com
    $refparts = explode('/', $referral);
    if (count($refparts) > 2) {
        // Get the bind dn from referral
        $dn = $refparts[3];
        // Bind to new host
        if (!ldap_bind($ldap, $dn, $pass)) {
            echo 'Could not bind to referral server';
            return 1;
        }
    } else {
        // Try anonymous bind
        if (!ldap_bind($ldap)) {
            echo 'Could not bind to referral server anonymously';
            return 1;
        }
    }
    return 0;
}
    
// Initial ldap connection to slave server
$ldap_host = 'localhost'
$ds = ldap_connect($ldap_host);
// ldap options
ldap_set_option($ds, LDAP_OPT_PROTOCOL_VERSION, 3)
ldap_set_option($ds, LDAP_OPT_REFERRALS, True)
// Set callback function
ldap_set_rebind_proc($ds, 'rebind'))
// bind
ldap_bind($ds, $dn, $pass)
// ldap write
ldap_modify($ds, $dn, $attr);

?>

Accessing passwords and other data from your callback is easier if you use a class method as the callback function. The callback would be initialized like this:

<?php

ldap_set_rebind_proc($ldap, 'MyClass::rebind');

?>

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mvanbeek at forgetaboutit dot net ¶

14 years ago

I have had quite a hard time finding good information about chasing referrals so I am adding my tuppence worth here. I still haven't got my test code working fully so please look further down the page for updates.



The way this appears to have to work is that you use this function to set a callback function of your own to connect and bind to the referral server. you need to set this along with forcing v3 ldap and setting the referral chasing to on as part of setting up the initial connection, so just after the connect but before the bind, you need something like:



<?php

        $ds = ldap_connect($server);

        ldap_set_option($ds, LDAP_OPT_PROTOCOL_VERSION, 3);

        ldap_set_option($ds, LDAP_OPT_REFERRALS, 1);

        ldap_set_rebind_proc($ds, "rebind");

        ldap_bind($ds,$dn,$pass);

?>



This callback function (called rebind in the above example needs two arguments. These arguments are preset and are supplied when the callback function is called. The first is the ldap link identifier. I assume this is supplied as the function could be used successively by a number of consecutive referrals. The second is the ldap referral URL supplied by the initial server. I have seen notes that say this function must be defined prior to being set by ldap_set_rebind_proc, but as yet I cannot confirm this.



My setup is based on a master - slave ldap server configuration, with the PHP application residing on the slave where it does localhost lookups. When your try to write to the slave ldap server, the server returns a referral URL, and the internal PHP function then calls the callback function.



Despite the code already on this page, which appears to also be used to test the PHP code, I believe it is wrong. I think it simply reconnects to the initial server. I believe that what the callback function should do is to connect to the new server, and bind to it. My test code currently looks like this:



<?php

function rebind($ldap, $referral) {

        global $dn;

        global $pass;

        $server= preg_replace('!^(ldap://[^/]+)/.*$!', '\\1', $referral);

        if (!($ldap = ldap_connect($server))){

                echo "reconnect failed - <br>";

                return 1;

        }

        ldap_set_option($ldap, LDAP_OPT_PROTOCOL_VERSION, 3);

        ldap_set_option($ldap, LDAP_OPT_REFERRALS, 1);

        ldap_set_rebind_proc($ldap, "rebind");

        if (!ldap_bind($ldap,$dn,$pass)){

                echo "rebind failed - <br>";

                return 1;

        }

        return 0;

}

?>



As far as I can tell, a return value of 0 means success and any other value means it has failed. The complete lack of documentation doesn't help.



The above code works all the way to authenticating against the new server, but at the moment I appear to be getting an unbind request before it tries to write the record to the new server, so it fails.



I would also recommend adding a ldap_start_tls before the bind as well.

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pearcec at commnav dot com ¶

21 years ago

PHP expects the ldap function ldap_set_rebind_proc to be the one that has tree parameters.  As far as I can tell this isn't in the 2.0 release of OpenLDAP.  But made it into 2.1.  Configure will tell you

checking for 3 arg ldap_set_rebind_proc... no

down

night0wl at frost dot ath dot cx ¶

21 years ago

Couse there was no example code for this function, i had alot of troubles to make it work properly. 

So, here is working example:

function rebind_on_ref ($ds, $ldap_url) {
  global $binddn;    // DN used to bind
  global $bindpw;    // password used to bind

  // required by most modern LDAP servers, use LDAPv3
  ldap_set_option($a, LDAP_OPT_PROTOCOL_VERSION, 3);

  if (!ldap_bind($a,$binddn,$bindpw)) {
        print "Cannot bind";
  }
}

down

randy at kotmail dot com ¶

22 years ago

If rebind_proc isn't compiled in slapd, your will never get that funtction working. Check out the new alpha release of slapd and rtfm.

down

-1

Anonymous ¶

13 years ago

I have now spent enough time looking at this issue to say that ldap referrals, at least when trying to add, modify or delete a record on a slave server that correctly gives a referral to a master server, does not work in php. My suggestion is turn turn off ldap referrals and write your own add, modify and delete functions with built in referral handling. Something like this:



<?php

function ldap_referral_add($connection,$add_dn,$Add_entry,$bind_dn,$bind_pw)

    {

    $rconnection = $connection;

    $loop = 10; # max number of referral hops.

    # Turn off normal referrals

    ldap_get_option($connection,LDAP_OPT_REFERRALS,$old_referral_setting)

    do

        {

        $response = ldap_add($rconnection,$dn,$entry);

        # We get a success message:

        if ( $response ) 

            {

            ldap_unbind($rconnection);

            $loop = 0;    # Probably not needed

            ldap_set_option($connection,LDAP_OPT_REFERRALS,$old_referral_setting);

            return true;

            }

        # We get a referral message:

        elseif ( !$response && ldap_errno($rconnection) == 0x0a )

            {

            $new_server_url = $server= preg_replace('!^(ldap://[^/]+)/.*$!', '\\1', $ldap_error($rconnection)); # May need some sanity checking here

            $rconnection = ldap_connect($new_server_url);

            ldap_set_option($rconnection,LDAP_OPT_REFERRALS,0)

            ldap_set_option($rconnection,LDAP_OPT_PROTOCOL_VERSION, 3)

            ldap_bind($rconnection,$bind_dn,$bind_pw);

            $loop = $loop - 1;

            }

        else 

            {

            ldap_unbind($rconnection);

            $loop = 0;    # Probably not needed

            ldap_set_option($connection,LDAP_OPT_REFERRALS,$old_referral_setting);

            return false;

            }

        } while ( $loop > 0);

    }

?>

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