LXXV. LDAP Functions

Introduction

LDAP is the Lightweight Directory Access Protocol, and is a protocol used to access "Directory Servers". The Directory is a special kind of database that holds information in a tree structure.

The concept is similar to your hard disk directory structure, except that in this context, the root directory is "The world" and the first level subdirectories are "countries". Lower levels of the directory structure contain entries for companies, organisations or places, while yet lower still we find directory entries for people, and perhaps equipment or documents.

To refer to a file in a subdirectory on your hard disk, you might use something like:


     /usr/local/myapp/docs
    

The forwards slash marks each division in the reference, and the sequence is read from left to right.

The equivalent to the fully qualified file reference in LDAP is the "distinguished name", referred to simply as "dn". An example dn might be:


     cn=John Smith,ou=Accounts,o=My Company,c=US
    

The comma marks each division in the reference, and the sequence is read from right to left. You would read this dn as:


     country = US
     organization = My Company
     organizationalUnit = Accounts
     commonName = John Smith
    

In the same way as there are no hard rules about how you organise the directory structure of a hard disk, a directory server manager can set up any structure that is meaningful for the purpose. However, there are some conventions that are used. The message is that you can not write code to access a directory server unless you know something about its structure, any more than you can use a database without some knowledge of what is available.

Lots of information about LDAP can be found at

The Netscape SDK contains a helpful Programmer's Guide in HTML format.

Requirements

You will need to get and compile LDAP client libraries from either OpenLDAP or Bind9.net in order to compile PHP with LDAP support.

Installation

LDAP support in PHP is not enabled by default. You will need to use the --with-ldap[=DIR] configuration option when compiling PHP to enable LDAP support. DIR is the LDAP base install directory. To enable SASL support, be sure --with-ldap-sasl[=DIR] is used, and that sasl.h exists on the system.

Note to Win32 Users: In order for this extension to work, there are DLL files that must be available to the Windows system PATH. See the FAQ titled "How do I add my PHP directory to the PATH on Windows" for information on how to do this. Although copying DLL files from the PHP folder into the Windows system directory also works (because the system directory is by default in the systems PATH), it is not recommended. This extension requires the following files to be in the PATH: libeay32.dll and ssleay32.dll

Note to Win32 Users: Versions before PHP 4.3.0 additionally require libsasl.dll.

In order to use Oracle LDAP libraries, proper Oracle environment has to be set.

Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

Table 1. LDAP configuration options

NameDefaultChangeableChangelog
ldap.max_links"-1"PHP_INI_SYSTEM 
For further details and definitions of the PHP_INI_* constants, see the Appendix H.

Resource Types

Most LDAP functions operate on or return resources (e.g. ldap_connect() returns a positive LDAP link identifier required by most LDAP functions).

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

LDAP_DEREF_NEVER (integer)

LDAP_DEREF_SEARCHING (integer)

LDAP_DEREF_FINDING (integer)

LDAP_DEREF_ALWAYS (integer)

LDAP_OPT_DEREF (integer)

LDAP_OPT_SIZELIMIT (integer)

LDAP_OPT_TIMELIMIT (integer)

LDAP_OPT_PROTOCOL_VERSION (integer)

LDAP_OPT_ERROR_NUMBER (integer)

LDAP_OPT_REFERRALS (integer)

LDAP_OPT_RESTART (integer)

LDAP_OPT_HOST_NAME (integer)

LDAP_OPT_ERROR_STRING (integer)

LDAP_OPT_MATCHED_DN (integer)

LDAP_OPT_SERVER_CONTROLS (integer)

LDAP_OPT_CLIENT_CONTROLS (integer)

LDAP_OPT_DEBUG_LEVEL (integer)

GSLC_SSL_NO_AUTH (integer)

GSLC_SSL_ONEWAY_AUTH (integer)

GSLC_SSL_TWOWAY_AUTH (integer)

Examples

Retrieve information for all entries where the surname starts with "S" from a directory server, displaying an extract with name and email address.

Example 1. LDAP search example

<?php
// basic sequence with LDAP is connect, bind, search, interpret search
// result, close connection

echo "<h3>LDAP query test</h3>";
echo
"Connecting ...";
$ds=ldap_connect("localhost");  // must be a valid LDAP server!
echo "connect result is " . $ds . "<br />";

if (
$ds) {
    echo
"Binding ...";
    
$r=ldap_bind($ds);     // this is an "anonymous" bind, typically
                           // read-only access
    
echo "Bind result is " . $r . "<br />";

    echo
"Searching for (sn=S*) ...";
    
// Search surname entry
    
$sr=ldap_search($ds, "o=My Company, c=US", "sn=S*");  
    echo
"Search result is " . $sr . "<br />";

    echo
"Number of entires returned is " . ldap_count_entries($ds, $sr) . "<br />";

    echo
"Getting entries ...<p>";
    
$info = ldap_get_entries($ds, $sr);
    echo
"Data for " . $info["count"] . " items returned:<p>";

    for (
$i=0; $i<$info["count"]; $i++) {
        echo
"dn is: " . $info[$i]["dn"] . "<br />";
        echo
"first cn entry is: " . $info[$i]["cn"][0] . "<br />";
        echo
"first email entry is: " . $info[$i]["mail"][0] . "<br /><hr />";
    }

    echo
"Closing connection";
    
ldap_close($ds);

} else {
    echo
"<h4>Unable to connect to LDAP server</h4>";
}
?>

Using the PHP LDAP calls

Before you can use the LDAP calls you will need to know ..

  • The name or address of the directory server you will use

  • The "base dn" of the server (the part of the world directory that is held on this server, which could be "o=My Company,c=US")

  • Whether you need a password to access the server (many servers will provide read access for an "anonymous bind" but require a password for anything else)

The typical sequence of LDAP calls you will make in an application will follow this pattern:


  ldap_connect()    // establish connection to server
     |
  ldap_bind()       // anonymous or authenticated "login"
     |
  do something like search or update the directory
  and display the results
     |
  ldap_close()      // "logout"

Table of Contents
ldap_8859_to_t61 -- Translate 8859 characters to t61 characters
ldap_add -- Add entries to LDAP directory
ldap_bind -- Bind to LDAP directory
ldap_close -- Alias of ldap_unbind()
ldap_compare -- Compare value of attribute found in entry specified with DN
ldap_connect -- Connect to an LDAP server
ldap_count_entries -- Count the number of entries in a search
ldap_delete -- Delete an entry from a directory
ldap_dn2ufn -- Convert DN to User Friendly Naming format
ldap_err2str -- Convert LDAP error number into string error message
ldap_errno -- Return the LDAP error number of the last LDAP command
ldap_error -- Return the LDAP error message of the last LDAP command
ldap_explode_dn -- Splits DN into its component parts
ldap_first_attribute -- Return first attribute
ldap_first_entry -- Return first result id
ldap_first_reference -- Return first reference
ldap_free_result -- Free result memory
ldap_get_attributes -- Get attributes from a search result entry
ldap_get_dn -- Get the DN of a result entry
ldap_get_entries -- Get all result entries
ldap_get_option -- Get the current value for given option
ldap_get_values_len -- Get all binary values from a result entry
ldap_get_values -- Get all values from a result entry
ldap_list -- Single-level search
ldap_mod_add -- Add attribute values to current attributes
ldap_mod_del -- Delete attribute values from current attributes
ldap_mod_replace -- Replace attribute values with new ones
ldap_modify -- Modify an LDAP entry
ldap_next_attribute -- Get the next attribute in result
ldap_next_entry -- Get next result entry
ldap_next_reference -- Get next reference
ldap_parse_reference -- Extract information from reference entry
ldap_parse_result -- Extract information from result
ldap_read -- Read an entry
ldap_rename -- Modify the name of an entry
ldap_sasl_bind -- Bind to LDAP directory using SASL
ldap_search -- Search LDAP tree
ldap_set_option -- Set the value of the given option
ldap_set_rebind_proc -- Set a callback function to do re-binds on referral chasing
ldap_sort -- Sort LDAP result entries
ldap_start_tls -- Start TLS
ldap_t61_to_8859 -- Translate t61 characters to 8859 characters
ldap_unbind -- Unbind from LDAP directory