PHP file_exists With Contents Instead of Name? - php

Question

Is there a function built into PHP that acts like file_exists, but given file contents instead of the file name?
I need this because I have a site where people can upload an image. The image is stored in a file with a name determined by my program (image_0.png image_1.png image_2.png image_3.png image_4.png ...). I do not want my site to have multiple images with the same contents. This could happen if multiple people found a picture on the internet and all of them uploaded it to my site. I would like to check if there is already a file with the contents of the uploaded file to save on storage.

Answer 1

This is how you can compare exactly two files with PHP:
function compareFiles($file_a, $file_b)
{
if (filesize($file_a) == filesize($file_b))
{
$fp_a = fopen($file_a, 'rb');
$fp_b = fopen($file_b, 'rb');
while (($b = fread($fp_a, 4096)) !== false)
{
$b_b = fread($fp_b, 4096);
if ($b !== $b_b)
{
fclose($fp_a);
fclose($fp_b);
return false;
}
}
fclose($fp_a);
fclose($fp_b);
return true;
}
return false;
}
If you keep the sha1 sum of each file you accept you can simply:
if ($known_sha1 == sha1_file($new_file))

Answer 2

You can use a while loop to look look through the contents of all of your files. This is shown in the example below :
function content_exists($file){
$image = file_get_contents($file);
$counter = 0;
while(file_exists('image_' . $counter . '.png')){
$check = file_get_contents('image_' . $counter . '.png');
if($image === $check){
return true;
}
else{
$counter ++;
}
}
return false;
}
The above function looks through all of your files and checks to see if the given image matches an image that is already stored. If the image already exists, true is returned and if the image does not exist false is returned. An example of how you can use this function shown is below :
if(content_exists($_FILES['file']['tmp_name'])){
// upload
}
else{
// do not upload
}

Answer 3

You could store hashed files in a .txt file separated by a \n so that you could use the function below :
function content_exists($file){
$file = hash('sha256', file_get_contents($file));
$files = explode("\n", rtrim(file_get_contents('files.txt')));
if(in_array($file, $files)){
return true;
}
else{
return false;
}
}
You could then use it to determine whether or not you should save the file as shown below :
if(content_exists($_FILES['file']['tmp_name'])){
// upload
}
else{
// do not upload
}
Just make sure that when a file IS stored, you use the following line of code :
file_put_contents('files.txt', hash('sha256', file_get_contents($file)) . "\n");