Giving uploaded images a unique name for mysqli - php

Question

I want to allow users to upload images without conflicting problems that may be caused by multiple users uploading images that potentially have the same image name. I am stumped on how to execute this and I have no idea where to start..
Here is my code:
if(isset($_POST['submitimage'])){
move_uploaded_file($_FILES['file']['tmp_name'],"pictures/".$_FILES['file']['name']);
$con = mysqli_connect("localhost","root","","database");
$q = mysqli_query($con,"UPDATE users SET image = '".$_FILES['file']['name']."' WHERE user_id = '".$_SESSION['user']."'");
header("Location: index.php");
}
?>
Any help would be amazing. Thank you!

Answer 1

My solution is to generate a random string for each uploaded file, i.e.:
<?php
if(!empty($_POST['submitimage'])){
//get file extension.
$ext = pathinfo($_FILES['file']['name'])['extension'];
//generate the new random string for filename and append extension.
$nFn = generateRandomString().".$ext";
move_uploaded_file($_FILES['file']['tmp_name'],"pictures/".$nFn);
$con = mysqli_connect("localhost","root","","database");
$q = mysqli_query($con,"UPDATE users SET image = '{$nFn}' WHERE user_id = '{$_SESSION['user']}'");
header("Location: index.php");
}
function generateRandomString($length = 10) {
return substr(str_shuffle("abcdefghijklmnopqrstuvwxyz"), 0, $length);
}
?>

Answer 2

PHP has a build in function to generate unique files on your server. This function is known as tempnam(). If you read the comments on that website carefully though, there is a small chance you'll get unwanted behaviour from that function if to many processes call it at the same time. So a modification to this function would be as follows:
<?php
function tempnam_sfx($path, $suffix){
do {
$file = $path."/".mt_rand().$suffix;
$fp = #fopen($file, 'x');
}
while(!$fp);
fclose($fp);
return $file;
}
?>
Because the file is kept open while it's being created, it can't be accessed by another process and therefor it's impossible to ever create 2 files with the same name simply because a couple of your website visitors happened to upload pictures at the exact same moment. So to implement this in your own code:
<?php
function tempnam_sfx($path, $suffix){
do {
$file = $path."/".mt_rand().$suffix;
$fp = #fopen($file, 'x');
}
while(!$fp);
fclose($fp);
return $file;
}
$uploaddir = 'pictures'; // Upload directory
$file = $_FILES['file']['name']; // Original file
$ext = pathinfo($path, PATHINFO_EXTENSION); // Get file extension
$uploadfile = tempnam_sfx($uploaddir, $ext);
move_uploaded_file($_FILES['file']['tmp_name'], $uploadfile);
$con = mysqli_connect("localhost","root","","database");
$q = mysqli_query($con,"UPDATE users SET image = '".basename($uploadfile)."' WHERE user_id = '{$_SESSION['user']}'");
header("Location: index.php");
?>

Answer 3

One way you could do this, is by generating a few random numbers (and possibly attaching them to current date in number format) and give the image the number sequence.
if(isset($_POST['submitimage'])){
//generate 3 sequences of random numbers,you could do more or less if you wish
$randomNumber=rand().rand().rand();
move_uploaded_file($_FILES['file']['tmp_name'],"pictures/".$randomNumber."jpg");
$con = mysqli_connect("localhost","root","","database");
$q = mysqli_query($con,"UPDATE users SET image = '".$randomNumber.".jpg' WHERE user_id = '".$_SESSION['user']."'");
header("Location: index.php");
}
?>
Note : you could also look into generating random strings if numbers are not your thing.