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.
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."<p>";
if ($ds) {
echo "Binding ...";
$r=ldap_bind($ds); // this is an "anonymous" bind, typically
// read-only access
echo "Bind result is ".$r."<p>";
echo "Searching for (sn=S*) ...";
// Search surname entry
$sr=ldap_search($ds,"o=My Company, c=US", "sn=S*");
echo "Search result is ".$sr."<p>";
echo "Number of entires returned is ".ldap_count_entries($ds,$sr)."<p>";
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] ."<p>";
}
echo "Closing connection";
ldap_close($ds);
} else {
echo "<h4>Unable to connect to LDAP server</h4>";
}
?>
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You will need to get and compile LDAP client libraries from
either the University of Michigan ldap-3.3 package or the
Netscape Directory SDK 3.0. You will also need to recompile PHP
with LDAP support enabled before PHP's LDAP calls will work.
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
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ldap_bind() // anonymous or authenticated "login"
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do something like search or update the directory
and display the results
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ldap_close() // "logout"
Lots of information about LDAP can be found at
The Netscape SDK contains a helpful Programmer's Guide in .html
format.
