php - How to NOT Overwrite a File?

[jebego]

This is my current php script

$fp = fopen('image.jpeg', 'wb');
fwrite($fp, $GLOBALS['HTTP_RAW_POST_DATA']);
fclose($fp); 

I'm using my flash file to send some data to my php file to create and save a .jpeg on my server under the name of "image.jpeg".

If I want to create more the one image, this script overwrites my current image.

How would I not overwrite it, but instead add a number to the end of the image's name, ex: image.jpeg, image-2.jpeg, image-3.jpeg, you get the point.

This is probobly pretty simple, I'm just somewhat of a noobie at php.

Thanks!

[blazes]

The easiest method would to to just add a timestamp to the end.

<?php
$fp = fopen('image'.time().'.jpeg', 'wb');
fwrite($fp, $GLOBALS['HTTP_RAW_POST_DATA']);
fclose($fp);  
?>

[jebego]

that idea occurred to me, but would it be possible for two people to create an image at the exact same time, therefore one overwriting the other? Or is this not possible?

[IQAndreas]

that idea occurred to me, but would it be possible for two people to create an image at the exact same time, therefore one overwriting the other? Or is this not possible?

It depends on how accurate the timestamp is. If it is down to the millisecond (which I am guessing it is, right?) Well, the chances of two people creating an image at the same millisecond are... ... not big. Also, the way PHP works, I could be wrong, but I'm guessing two exact same lines can't be run at the exact same time. Or does PHP use threading for each new page request?

But if you really want to check for this, you could check if the file already exists, and if it does, save the image one millisecond later instead.

[jebego]

It depends on how accurate the timestamp is. If it is down to the millisecond (which I am guessing it is, right?) Well, the chances of two people creating an image at the same millisecond are... ... not big. Also, the way PHP works, I could be wrong, but I'm guessing two exact same lines can't be run at the exact same time. Or does PHP use threading for each new page request?

But if you really want to check for this, you could check if the file already exists, and if it does, save the image one millisecond later instead.

thanks! I'll research timestamping a bit!

[IQAndreas]

Anyway, here is the PHP documentation on time():
http://php.net/manual/en/function.time.php

Sadly, it returns seconds, but if there are a lot of users and it is likely images will be overridden, there is also a command named microtime() which is milliseconds:
http://www.php.net/manual/en/function.microtime.php

[blazes]

If you're in a regular environment time() should be fine. If you want to be sure you can use microtime(). If you expect very heavy usage (or you just want to be as safe as possible), and you don't mind ugly names you can do something like:

<?php
$fp = fopen('image'.sha1(time()).'.jpeg', 'wb');
fwrite($fp, $GLOBALS['HTTP_RAW_POST_DATA']);
fclose($fp);  
?>

Then you're (practically) guaranteed unique names. Or you can do something like:

<?php
$fp = fopen('image'.substr(sha1(time()), 0, 8).'.jpeg', 'wb');
fwrite($fp, $GLOBALS['HTTP_RAW_POST_DATA']);
fclose($fp);  
?>

[lorren.biffin]

Blazes gave a great answer. Though, it seems you want an extra level of assurance (I can relate). Also not perfect or absolute, but a teensie bit less likely to cause conflict:

<?php 
$fp = fopen('image'.sha1(time().rand(0,50000)).'.jpeg', 'wb'); 
fwrite($fp, $GLOBALS['HTTP_RAW_POST_DATA']); 
fclose($fp);   
?>

Though, for the record, in most cases you won't need to be so direct and even a simple time-stamp will do fine to keep you safely unique. Blazes first suggestion will work well enough 98% of the time.

[icio]

<?php
$fp = fopen('image'.sha1(time()).'.jpeg', 'wb');
fwrite($fp, $GLOBALS['HTTP_RAW_POST_DATA']);
fclose($fp);  
?>

Then you're (practically) guaranteed unique names. Or you can do something like:

`sha1(time())` is going to be no more unique than `time()` itself.

[utsav]

time() is what i use and as like others i would sugest tht too. Or you could add time and then generate a random number and add them both to the filename.

[simplistik]

just do a hash on time and the users ip or something that's relatively unique

[jwilliam]

It uses principles already mentioned in this thread, but I thought I'd point out this function:

http://us2.php.net/manual/en/function.uniqid.php