[RESOLVED] Weird Problem

[minifairy]

I have a program that has been working fine for a couple of years. It is a program that allows clients to update a flat file database file (not mysql) It reads in the file matches up what has been changed and writes out the file again. As I said it has been working perfectly for a couple of years no problems. Today somehow one of my clients managed to write out a 0byte data file using the program (presumeably I wasn't there don't exactly know as users aren't terribly detailed on what they did and what happened. Sort of we were doing some updating and it all disappeared)

Anyone have any clue what would cause such a thing to happen and how to prevent it?

Below is the subroutine that does the updating. Not sure how much good it will do anyone without the rest of the file but perhaps.

# update item 
  case'update':
  {
	if (isset($_SESSION['first_name'])) {
			$site_id=$_SESSION['site_id'];
			$site_name=$_SESSION['site_name'];
			$site_opt=$_SESSION['site_opt'];
			echo "<div id=\"Header\"><h1>$site_name website maintenance  welcome";
			echo ", {$_SESSION['first_name']}!";
			echo '</h1></div><br><h4 align=center>Click on a button above to get a menu for that area of your website.</h4>';
	}else {
	echo '<br><br><br><br><br><br><h1> You must be logged in to view this page.</h1><h1><a class=log href="index.php">LOGIN</a></h1>';

	 include("./includes/footer.html");
	 die();
}
echo '<div id="Content">';
echo "<h4 align=center>$page_title -- Edit Item</h4>";
$config="shop/".$site_id."_config.php";

include("includes/menu.php");
include ("$config");

   # check on empty inputs
$error = false;
$fld="";
$reqs = array('Item ID'=>'itemid','Short Description'=>'desc','Long Description'=>'description');
while (list($key,$val) = each($reqs)) {
  if (!isset($_POST["$val"])|| isset($_POST["$val"]) && empty($_POST["$val"])){
	  $error = true;
	$fld.="Fill in the ".$key." <br>";
  }

if ($error == true)
{
  echo "<p align=center><font size=4> Please correct the following errors.<br>".$key." </font>\n";
  echo "<a href=javascript:history.back();><font size=4>GO Back</a></font></p>\n";
  include("includes/footer.html");
  break;
}
}

$d2=eregi_replace("[\n\r\t\n]",' ',$_POST['description']);
$d2=trim($d2);
$d2 = escape_data($d2);
$d = stripslashes($_POST['desc']);
$d=trim($d);
$price=eregi_replace('$',' ',$_POST['price']);
$price=stripslashes($price);
$price=trim($price);
$id=stripslashes($_GET['id']);
$id=trim($id);
$newid=stripslashes($_POST['itemid']);
$newid=trim($newid);
$photo=stripslashes($_POST['photo']);
$photo=trim($photo);
	if (trim($_POST['opt'])!=''){
	$opt="%%OPTION%%";
	$opt=trim($opt);
	$opt.=trim($_POST['opt']);
	$opt=stripslashes($opt);
	$opt=trim($opt);
	$opt =eregi_replace('.html','',$opt);
	$opt =eregi_replace('.htm','',$opt);
	$opt.=".html";
}else{
	$opt="%%OPTION%%blank.html";
}
$entry=$newid."|".$_POST['cat']."|".$price."|".$d."|<img src=\"".$photo."\">|".$d2."|".$opt."\n";
$data=fopen($shop_data_file,"r");
$x=0;
	while (!feof($data)) {
	   $buffer[$x] = fgets($data);
		$x++;
	}
	fclose($data);
	#open data file and check for duplicate ids
	$data=fopen($shop_data_file,"r");
	foreach($buffer as $ke => $val){
	#split items into fields
	$itarray = explode('|', "$val");
		if($itarray[0]==$newid && $id != $newid){
			echo $itarray[0],'&nbsp;'.$newid.'&nbsp;'.$id.'<br>';
			$err=duplicateid;
			fclose($data);
	break;
		}
	}
	#open data file and update
if ($err != duplicateid){
	$data=fopen($shop_data_file,"w");
	foreach($buffer as $ke => $val){
	#split items into fields
	$itarray = explode('|', "$val");
		if($itarray[0]==$id && $newid ==$id){
			fwrite($data,"$entry");
			$itemup= true;
		}
		if($itarray[0] < $newid && $itarray[0] != $id){
			#write buffer
			fwrite($data,"$val");
		}
		if ($itarray[0] >$newid && $itemup != true){
			fwrite($data,"$entry");
			$itemup = true;
		}
		if ($itarray[0] >$newid && $id != $itarray[0] && $itemup == true ){
			fwrite($data,"$val");
			$itemup = true;
			#write buffer;
		}
	}
		if ( $itemup != true){
			fwrite($data,"$entry");
			$itemup = true;
		}
	#close data file
	fclose($data);
}
if($err==duplicateid){
	echo "<p align=center><font color=RED size=4>Duplicate Item ID</font><br>Please use a different ID<br><a href=javascript:history.back();><font size=4>GO Back</a></font></p>\n";
	break;
}else
		echo '<h4 align=center>The file has been updated!</h4>';
break;
  }

[sneakyimp]

You should probably alter the script to first make a backup of the flat file before trying to update it. When your update is complete, check to see if the flat file's size is 0 bytes or whether it's the expected size or whatever. If not, roll back to the backup version of your file.

This won't guarantee anything of course, but might avert catastrophe.

Also, you don't need to re-write the entire file every time you update it. This might keep it nice and clean but it's entirely unnecessary processing that you are doing. The culprit is this line:

        $data=fopen($shop_data_file,"w"); 

That tells php to open the file and EMPTY IT OUT. Look at the manual for [man]fopen[/man]. You should think about using a 2nd arg of 'a' or 'a+' or something like that.

[NogDog]

sneakyimp wrote:

...Also, you don't need to re-write the entire file every time you update it....

Unfortunately, if updating an existing record, then yes, you have to rewrite the whole file. Appending would only be useful (and correct for the reasons you specified) when adding a new record.

Therefore, your suggestion of keeping a backup copy of the file until you are sure everything worked OK is even more sound. 🙂

[minifairy]

Another problem with appending to the file is that the file is kept in a sorted order so appending only would work if the added record would be at the end of the file. So re-writing the file is the only way here. I'm working on phasing out the flat file but can't go there at the moment. After this problem I did decide I would try to implement a backup file which would hopefully avert disaster unless the person decided to try to do it again just to see if it would work the second time. Which they frequently do.

I was just trying to figure out what would cause a problem like this in the first place. Trying to make sure it wasn't something that I overlooked in the code that would cause this. Although I've never had this sort of problem before in at least 2-3 years of running the software. Could it be a server glitch or what would cause this sort of thing? Gremlins??

[NogDog]

Any possibility that it could have been a race condition between two nearly simultaneous requests? (Maybe the second request read the file right after the first request blanked it out with its fopen() write call?)

[minifairy]

That could be a possibility nogg dog but I sort of doubt it as only one user has access to this file for updating. I think it must have been a server glitch of some sort or something. I did have it write out a backup of the file so hopefully we have retrievable data out there.