can i use the function md5_file to name files when upload without having conflict with names?

问题

all the idea i need to be sure that the file doesn't saved more than one time and don't lose any file because if tow files get the same (md5) the second file will not saved (my goal don't save the same file Twice on hard disk)

In other words, if one user upload image and after that another user upload the same image i need to don't save the the second image because it's already exist in the hard disk all of this because i need to save space on my hard disk this is my code it works fine

$targetFolder = '/test/uploadify/uploads'; // Relative to the root
$tempFile = $_FILES['Filedata']['tmp_name'];
$targetPath = $_SERVER['DOCUMENT_ROOT'] . $targetFolder;

$myhash = md5_file($_FILES['Filedata']['tmp_name']);
$temp = explode(".", $_FILES['Filedata']['name']);
$extension = end($temp);

$targetFile = rtrim($targetPath,'/') . '/' .$myhash.'.'.$extension;
if(file_exists($targetFile)){
    echo 'exist';
}

// Validate the file type
$fileTypes = array('jpg','jpeg','gif','png'); // File extensions
$fileParts = pathinfo($_FILES['Filedata']['name']);
if (in_array($fileParts['extension'],$fileTypes)) {
    move_uploaded_file($tempFile,$targetFile);
} 
else {
    echo 'Invalid file type.';
}

thanks for all of you

回答1:

Well, of course you can do this, in fact this is the way I use to avoid file duplications (and I mean not having two files wit the same content and not just silly name collision).

If you are worried about collisions, then you might take a look at sha1_file:

http://es1.php.net/manual/en/function.sha1-file.php

What are the chances that two messages have the same MD5 digest and the same SHA1 digest?

I've been using the md5 approach the way you are suggesting here for image galleries and it works just fine.

Another thing to take care about is the time it takes to calculate the hash, the more complex the hash, the more time it needs, but I'm talking about processing really big batches.

回答2:

If I understand your question correctly your goal is just to generate unique file names. If so, there is no point in reinventing the wheel - every hash function with fixed output length is going to have collisions - just use built in tempnam function.

Manual states:

Creates a file with a unique filename, with access permission set to 0600, in the specified directory. If the directory does not exist, tempnam() may generate a file in the system's temporary directory, and return the full path to that file, including its name.

Following should work well enough:

$targetDirectory = $_SERVER['DOCUMENT_ROOT'] . '/test/uploadify/uploads';
$uploadedFile = $_FILES['Filedata']['tmp_name'];
$targetFile = tempnam($targetDirectory, '');
move_uploaded_file($uploadedFile, $targetFile);

回答3:

You could always add the systems current time in milliseconds to the filename. That plus the md5, would have a very unlikely chance of returning the same values.

回答4:

It's very small, but the chance is there. You can read more here and here

I suggest you add a salt to the end of the filename to make it practically impossible for files to conflict(You should put the salt in a different md5 function though)

$salt = md5(round(microtime(true) * 1000));
$hash = md5_file($_FILES['Filedata']['tmp_name']);
$targetFile = rtrim($targetPath,'/') . '/' .$hash.$salt.'.'.$extension;

You should then insert the filename in a database so you can access it later.

来源：https://stackoverflow.com/questions/23040824/can-i-use-the-function-md5-file-to-name-files-when-upload-without-having-conflic

标签

php

file-upload

md5

filenames

md5-file