Serialize and Unserializa weird behaviour

From: Alex Malgaroli (lmollea_at_yahoo.it)
Date: 01/09/05 

Date: 9 Jan 2005 06:08:32 -0800

Hello everyone.

I found a strange behaviour using serialize and unserialize to persist
to file a configuration array.

I'm using a flat text file to store configuration information. I have
a function that lets software change the value of a configuration
variable; the function works like this: reads the entire file in a
string, unserialize it into an array, modify the correct variable then
rewrites the entire file serializing back the array.

code is like this:
        function preference_update($name, $val) {
                $fp = fopen('data/preferences.dat', 'r+');
                $ser = fread($fp, filesize('data/preferences.dat'));
                $prefs = unserialize($ser);

                for($i = 0; $i < count($prefs); $i++) {
                        if($prefs[$i]['name'] == $name) {
                                $prefs[$i]['value'] = $val;
                                break;
                        }
                }

                $ser = serialize($prefs);
                fseek($fp, 0);
                fwrite($fp, $ser);
                $this->mylog->debug($ser);
                fflush($fp);
                fclose($fp);
                unset($fp);
                unset($prefs);
                unset($ser);
        }
-----------

fun things I found are:
1) if I dont unset($fp) at the end, when doing multiple
"preference_update" in a single page, the first is written, the others
result in an empty file containing only "b:0;"
2) if I remove fwrite($fp, $ser) at the end, all things are correctly
written back! If I leave this line in the code, when calling multiple
times in the same script "preference_update", it seems that only the
first change gets serialized back.

(I know this is not efficient, but I don't have a database available.
No, either gdbm).

I'm using PHP 4.3.2 under apache 1.3.29 on cygwin both compiled from
source.

Any hint on what I'm doing wrong?

Thanks in advance.

LM

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