Blocking 2 users from overriding the XML

1

HELP!!!

How can I ensure that no 2 users in different browsers booking the same plot dont override each other?

Much appreciated.

[COLOR=darkred]index.php[/COLOR]
[COLOR=darkred]<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd” >[/COLOR]
[COLOR=darkred]<html xmlns=“http://www.w3.org/1999/xhtml”>[/COLOR]
[COLOR=darkred]<head><title>Plot booking</title>[/COLOR]
[COLOR=darkred]<link href=“screen.css” rel=“stylesheet” type=“text/css” />[/COLOR]
[COLOR=darkred]</head>[/COLOR]

[COLOR=darkred]<?php[/COLOR]

[COLOR=darkred]echo ‘<body>[/COLOR]
[COLOR=darkred]<table>[/COLOR]
[COLOR=darkred]<tr>[/COLOR]
[COLOR=darkred]<td>[/COLOR]
[COLOR=darkred]<embed src=map.swf width=“600” height=“440”></embed>[/COLOR]
[COLOR=darkred]<form action=“processForm.php” method=“post”>[/COLOR]
[COLOR=darkred]<fieldset>’;[/COLOR]

[COLOR=darkred]function start_tag1($parser1, $name1, $attrs1){[/COLOR]
[COLOR=darkred]global $table_string1;[/COLOR]
[COLOR=darkred]$assign1=$attrs1[assigned];[/COLOR]
[COLOR=darkred]if ($assign1==“no”){[/COLOR]
[COLOR=darkred]$table_string1 .= “<option value=$attrs1[room]>$attrs1[room]</option>”;[/COLOR]
[COLOR=darkred]}[/COLOR]
[COLOR=darkred]}[/COLOR]
[COLOR=darkred]function end_tag1($parser1, $name1){}[/COLOR]
[COLOR=darkred]$parser1 = xml_parser_create();[/COLOR]
[COLOR=darkred]xml_parser_set_option($parser1, XML_OPTION_CASE_FOLDING, 0);[/COLOR]
[COLOR=darkred]xml_set_element_handler($parser1, “start_tag1”, “end_tag1”);[/COLOR]
[COLOR=darkred]$table_string1 = “<label>Plot number: <select type=text id=name name=name>”;[/COLOR]
[COLOR=darkred]xml_parse($parser1, file_get_contents(“bookings.xml”)) or die(“Error parsing XML file”);[/COLOR]
[COLOR=darkred]$table_string1 .= “</select> </label>”;[/COLOR]
[COLOR=darkred]echo $table_string1;[/COLOR]

[COLOR=darkred]echo ‘<label for=“student”>Student number:</label><input type=“text” id=“student” name=“student” />[/COLOR]
[COLOR=darkred]<input type=“submit” name=“action” value=“book”/>[/COLOR]
[COLOR=darkred]</fieldset>[/COLOR]
[COLOR=darkred]</form>[/COLOR]
[COLOR=darkred]</td>[/COLOR]
[COLOR=darkred]<td>[/COLOR]
[COLOR=darkred]<h1>Plots not available:</h1>’;[/COLOR]

[COLOR=darkred]function start_tag($parser, $name, $attrs){[/COLOR]
[COLOR=darkred]global $table_string;[/COLOR]
[COLOR=darkred]$assign=$attrs[assigned];[/COLOR]
[COLOR=darkred]if ($assign==“yes”){[/COLOR]
[COLOR=darkred]$table_string .= “<tr><td>$attrs[room]</td><td>$attrs[student]</td></tr>”;[/COLOR]
[COLOR=darkred]}[/COLOR]
[COLOR=darkred]}[/COLOR]
[COLOR=darkred]function end_tag($parser, $name){}[/COLOR]
[COLOR=darkred]$parser = xml_parser_create();[/COLOR]
[COLOR=darkred]xml_parser_set_option($parser, XML_OPTION_CASE_FOLDING, 0);[/COLOR]
[COLOR=darkred]xml_set_element_handler($parser, “start_tag”, “end_tag”);[/COLOR]
[COLOR=darkred]$table_string = “<table>[/COLOR]
[COLOR=darkred]<tr><th>Plot no.</th><th>Student</th></tr>”;[/COLOR]
[COLOR=darkred]xml_parse($parser, file_get_contents(“bookings.xml”)) or die(“Error parsing XML file”);[/COLOR]
[COLOR=darkred]$table_string .= “</table>”;[/COLOR]
[COLOR=darkred]echo $table_string;[/COLOR]

[COLOR=darkred]echo ‘</td>[/COLOR]
[COLOR=darkred]</tr>[/COLOR]
[COLOR=darkred]</table>[/COLOR]
[COLOR=darkred]</body>’;[/COLOR]
[COLOR=darkred]?>[/COLOR]

[COLOR=darkred]</html>[/COLOR]

[COLOR=darkslateblue]processForm.php[/COLOR]
[COLOR=darkslateblue]<!DOCTYPE HTML PUBLIC “-//W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”>[/COLOR]
[COLOR=darkslateblue]<html xmlns=“http://www.w3.org/1999/xhtml”>[/COLOR]
[COLOR=darkslateblue]<head>[/COLOR]
[COLOR=darkslateblue]<title>Plot booking processed</title>[/COLOR]
[COLOR=darkslateblue]<link href=“screen.css” rel=“stylesheet” type=“text/css” />[/COLOR]
[COLOR=darkslateblue]</style>[/COLOR]
[COLOR=darkslateblue]<SCRIPT LANGUAGE=“JavaScript”><!–[/COLOR]
[COLOR=darkslateblue]setTimeout(‘self.close()’,5000);[/COLOR]
[COLOR=darkslateblue]//–></SCRIPT>[/COLOR]
[COLOR=darkslateblue]</head>[/COLOR]
[COLOR=darkslateblue]<body>[/COLOR]
[COLOR=darkslateblue]<?[/COLOR]
[COLOR=darkslateblue]$bookings = Array();[/COLOR]
[COLOR=darkslateblue]function start_element($parser, $name, $attrs){[/COLOR]
[COLOR=darkslateblue]global $bookings;[/COLOR]
[COLOR=darkslateblue]if($name == “booking”){[/COLOR]
[COLOR=darkslateblue]array_push($bookings, $attrs);[/COLOR]
[COLOR=darkslateblue]}[/COLOR]
[COLOR=darkslateblue]}[/COLOR]
[COLOR=darkslateblue]function end_element ($parser, $name){}[/COLOR]
[COLOR=darkslateblue]$bookings_string = file_get_contents(“bookings.xml”);[/COLOR]
[COLOR=darkslateblue]$parser = xml_parser_create();[/COLOR]
[COLOR=darkslateblue]xml_set_element_handler($parser, “start_element”, “end_element”);[/COLOR]
[COLOR=darkslateblue]xml_parser_set_option($parser, XML_OPTION_CASE_FOLDING, 0);[/COLOR]
[COLOR=darkslateblue]xml_parse($parser, $bookings_string) or die(“Error parsing XML document.”);[/COLOR]
[COLOR=darkslateblue]print “<br />”;[/COLOR]
[COLOR=darkslateblue]if($_POST[‘action’] == “book”){[/COLOR]
[COLOR=darkslateblue]array_push($bookings, Array([/COLOR]
[COLOR=darkslateblue]“room” => $_POST[‘name’],[/COLOR]
[COLOR=darkslateblue]“student” => $_POST[‘student’],[/COLOR]
[COLOR=darkslateblue]“assigned” => “yes”));[/COLOR]
[COLOR=darkslateblue]$bookings_final = $bookings;[/COLOR]
[COLOR=darkslateblue]$plot = $_POST[‘name’];[/COLOR]
[COLOR=darkslateblue]$snumber = $_POST[‘student’];[/COLOR]
[COLOR=darkslateblue]}[/COLOR]
[COLOR=darkslateblue]$write_string = “<bookings>
“;[/COLOR]
[COLOR=darkslateblue]foreach($bookings_final as $booking){[/COLOR]
[COLOR=darkslateblue]if($booking[‘room’] != $_POST[‘name’]){[/COLOR]
[COLOR=darkslateblue]$bookings_blank = Array();[/COLOR]
[COLOR=darkslateblue]array_push($bookings_blank, $booking);[/COLOR]
[COLOR=darkslateblue]$write_string .= “<booking room=”$booking[room]” student=”$booking[student]" assigned="$booking[assigned]" />";[/COLOR]
[COLOR=darkslateblue]}[/COLOR]
[COLOR=darkslateblue]}[/COLOR]
[COLOR=darkslateblue]$write_string .= "
<booking room="$booking[room]" student="$booking[student]" assigned="$booking[assigned]" />
";[/COLOR]
[COLOR=darkslateblue]$write_string .= “</bookings>”;[/COLOR]
[COLOR=darkslateblue]$fp = fopen(“bookings.xml”, “w+”);[/COLOR]
[COLOR=darkslateblue]fwrite($fp, $write_string) or die(“Error writing to file”);[/COLOR]
[COLOR=darkslateblue]fclose($fp);[/COLOR]

[COLOR=darkslateblue]print “<em>Record added successfully.<em><br />”;[/COLOR]
[COLOR=darkslateblue]print “<h1>Confirmation page</h1><br />”;[/COLOR]
[COLOR=darkslateblue]print “<p>Plot no: </p>”;[/COLOR]
[COLOR=darkslateblue]print $plot;[/COLOR]
[COLOR=darkslateblue]print “<p>Booked by: </p>”;[/COLOR]
[COLOR=darkslateblue]print $snumber;[/COLOR]
[COLOR=darkslateblue]print “<br/><br/><br/>”;[/COLOR]
[COLOR=darkslateblue]echo date(‘l dS \of F Y h:i:s A’);[/COLOR]
[COLOR=darkslateblue]print “<br/><br/>”;[/COLOR]
[COLOR=darkslateblue]print “<a href=javascript:self.close();>Close this window</a>”;[/COLOR]
[COLOR=darkslateblue]?>[/COLOR]
[COLOR=darkslateblue]</body>[/COLOR]
[COLOR=darkslateblue]</html>[/COLOR]

[COLOR=darkorchid]bookings.xml[/COLOR]
[COLOR=darkorchid]<bookings>[/COLOR]
[COLOR=darkorchid]<booking room=“001” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“002” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“003” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“004” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“005” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“006” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“007” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“008” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“009” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]<booking room=“010” student="" assigned=“no” />[/COLOR]
[COLOR=darkorchid]</bookings>[/COLOR]