Comparing dates

Before testing the script I naturally tried to think my way through it as carefully as I could. I spotted and corrected several typos (which are shown corrected on the previous page), but I realised that there is one bug which I think would cause failures to occur only on certain days. In the PHP I'm comparing dates like this...

if ( $date_of_file < $today ) {

...but that will do an alphabetical comparison rather than a proper comparison. It might give the right result when comparing, say, 28/08/02 and 27/08/02 but would give the wrong result when comparing 01/09/02 with 27/08/02! I think I can fix this fairly easily by converting dates to days elapsed relative to the "UNIX epoch", but I intend to leave that for later because I think it shouldn't stop the script from working for the remainder of this month.

Creating a test version

Given the complexity of the script I can't believe it's going to work first time, so I'm going to build in some echo statements so that I can see how far things are progressing:

<?php // "Expiry Checker" // A script to automatically remind FaCES web page owners... // ...when their web pages are older than their expiry dates. // author = Martin Bush, South Bank University // date = 13 August 2002 // filename = expirychecker.php3 // version = 1st prototype, 2nd version // history = as v1.1, plus some diagnostic echo statements // Comments in quotations are inherited from the pseudocode // "read Expiry Checker information (url&expiry&owner&message)" // "parse the information using the parse_str function" parse_str($QUERY_STRING); // defines $url, $expiry, $owner, $message echo "This should be the url... " . $url; echo "\nThis should be the expiry date... " . $expiry; echo "\nThis should be the owner... " . $owner; echo "\nThis should be the message... " . $message; // "if (expiry_date <= today's date) then" $today = date ("d/m/y") echo "\nThis should be today's date... " . $today; if ( $today <= $expiry ) { // "lock file reminders_sent_today.txt" -- abbreviate to "reminders" $reminders_file = "reminders_sent_today.txt"; //file is assumed to exist // need to open reminders file first -- "r+" means for reading and writing $reminders_file_pointer = fopen($reminders_file, "r+"); // now lock reminders file to ensure mutually exclusive access $lock = flock($reminders_file_pointer, 2); // "2" for exclusive writing lock // continue when lock is obtained if ($lock) { // "read date_of_file from file" -- assumed to be present and valid $date_of_file = fgets($reminders_file_pointer, 8); // reads up to 8 chars echo "\nThis should be the date_of_file... " . $date_of_file; // "if (date_of_file < today's date) then" if ( $date_of_file < $today ) { // "rewind file" rewind($reminders_file_pointer); // "write today's date to file" fwrite($reminders_file_pointer, "$today\n"); } // "endif" // "search file for url of web page" -- stored in alphabetical order $found = 0; // get next entry if there is one if (!feof($reminders_file_pointer)) { $next_entry = fgets($reminders_file_pointer, 256); echo "\nThis should be the first Expiry Checker entry... " . $next_entry; // "url" in web page corresponds to "filed_url" in reminders file... // ...and likewise for "expiry", "owner" and "message" parse_str($next_entry); // defines $filed_url, filed_expiry, etc. echo "\nThese should be its constituants... "; echo "\n..." . $filed_url; echo "\n..." . $filed_expiry; echo "\n..." . $filed_owner; echo "\n..." . $filed_message; // while loop stops if it goes past the point where $url should be while (!feof($reminders_file_pointer) & (($filed_url <= $url) & ($found == 0))) { if ($filed_url == $url) { $found = 1; } else { // accumulate entries read so far, and get next entry $file_contents_so_far = $file_contents_so_far.$next_entry; $next_entry = fgets($reminders_file_pointer, 256); } } } // "if (URL not found in file) then" if ($found == 0) { // "write URL to file" // must carry on reading contents first $file_contents_remainder = fread($reminders_file_pointer, filesize($reminders_file)); // now rewind the file rewind($reminders_file_pointer); // write accumulate entries up to point of insertion fwrite($reminders_file_pointer, "$file_contents_so_far\n"); // prepare new reminder entry $new_reminder = "filed-url=".$url."&filed-expiry=".$expiry. "&filed-owner=".$owner."&filed-message=".$message; // insert new reminder entry fwrite($reminders_file_pointer, "$new_reminder\n"); // write remainder fwrite($reminders_file_pointer, "$file_contents_remainder"); // "email URL and message to owner" $mail_message = "This message has been sent automatically, \nto remind you that the contents of this FaCES web page... \n @url \nnow needs your attention. \n\nHere is the message that accompanied your email address... \n @message"; mail($owner, "Expiry Checker: FaCES web page needs your attention.", $mail_message) } // "endif" } // endif ($lock) // "unlock file reminders_sent_today.txt" $lock = flock($respondees_file_pointer, 3); // "3" means unlock // need to close respondees file fclose($respondees_file_pointer); } // "endif" ( $today <= $expiry ) ?>