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PHP Foundations Working with Forms in PHP, Part 2

by John Coggeshall
05/01/2003

Welcome back to PHP Foundations. In my previous column, I explained how to retrieve form data with a PHP script via the superglobal arrays ($_GET, $_POST, and $_REQUEST) and the import_request_variables() function. In today's column, I'll be looking at how to accept HTTP file uploads via PHP in a web page.

Before showing any code, it is important that I acknowledge that there are a number of PHP configuration directives that affect the behavior of file uploads to PHP. Specifically, the file_uploads, uploads_max_filesize, upload_tmp_dir, and post_max_size configuration directives have a direct bearing on PHP's ability to accept file uploads. If you are unsure what these directives do (or how to tell if they are set properly), please consult the PHP manual.

Uploading Files with PHP

The first step to a successful file upload is to ensure that your form is constructed properly. When dealing with files in HTML, there are a couple of rules regarding the attributes the <form> tag uses. Specifically, the enctype attribute must be set to the MIME type multipart/form-data and the method attribute must be set to post. As always, the action attribute should point to the PHP script that will process the file upload. This example HTML form uploads a file to a script named uploadproc.php:

<form method="post" action="uploadproc.php" enctype="multipart/form-data">
	<input type="file" name="myfile"><br />
	<input type="submit" value="Upload File">
</form>

If you haven't explored the file-uploading capabilities of HTML forms, notice above the form element whose type attribute is set to file. When rendered, this <input> tag will create a text field (showing the path and file to upload) and a button (used to browse the file system to select a file). Although not shown above, a hidden HTML form element named MAX_FILE_SIZE can be used to limit the size of the file the browser will allow the client to upload (with the value in bytes). For instance, to limit the size of any uploaded file to no more than one kilobyte, the following hidden element should be included:

<input type="hidden" name="MAX_FILE_SIZE" value="1024">

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Please note that this method of limiting the accepted file size is in no way a fool-proof method to ensure the maximum size of uploaded files. A buggy browser or malicious client may ignore this field entirely. If there is a real need to limit uploaded files to a certain size, see the upload_max_filesize PHP configuration directive in the PHP manual.

Once a form containing a uploaded file is submitted to PHP, the file will be stored in the temporary directory specified by the upload_tmp_dir PHP configuration directive. PHP populates the $_FILES superglobal array with information on the uploaded file. As with the other superglobal arrays I discussed in my previous column, $_FILES is an associative array. It contains a key corresponding to the name attribute of each file uploaded. When PHP receives our example form above, it will create $_FILES['myfile'], which actually represents a sub-array populated with information about the file that was uploaded. This information is:

nameThe name of the file as it was saved on the client machine
typeThe MIME type for the file
sizeThe size of the uploaded file (in bytes)
tmp_nameThe temporary name given to the file by PHP
errorAn integer error code (if something went wrong)

Although all of the above keys will be created, they may or may not actually contain useful values. If the client does not provide a MIME type for the uploaded file, the type key will not have a value. Any errors that occur during the file-uploading process are represented as one of the following integer constants stored in the error key:

UPLOAD_ERR_OKNo error occurred.
UPLOAD_ERR_INI_SIZEThe file was larger than PHP will accept, based on the upload_max_filesize configuration directive.
UPLOAD_ERR_FORM_SIZEThe file was larger than the maximum value specified by the MAX_FILE_SIZE hidden form element.
UPLOAD_ERR_PARTIALThe file upload was cancelled before it was complete.
UPLOAD_ERR_NOFILEThe form was submitted, but no file was uploaded.

Assuming that the file was successfully uploaded, it will be stored in the temporary directory specified by the upload_tmp_dir PHP directive using the temporary name given in the value stored under the tmp_name array key. PHP will automatically delete this file when the script terminates, so you must move it if you want to keep it. To move an uploaded file, use the move_uploaded_file() function. Although you could use other PHP file functions, this specialized function can be more secure. Its syntax is as follows:

move_uploaded_file($tmp_name, $newfile)

$tmp_name represents the temporary name of the uploaded file (taken from the tmp_name array key). $newfile represents the complete path and new filename of the uploaded file. There is no need to specify the temporary upload directory in $tmp_name, as PHP will automatically assume this directory. When executed, this function will move the file and return a Boolean indicating if the file was successfully moved or not. Below is an example script that could be used as the uploadproc.php script in our initial HTML form for uploading a file.

<?php
if(!isset($_FILES['myfile'])) {
 	die "Error! The expected file wasn't a part of the submitted form";
} 

if($_FILES['myfile']['error'] != UPLOAD_ERR_OK) {
 	die "Error! The file uploaded failed.";
}

if(!move_uploaded_file($_FILES['myfile']['tmp_name'], 
   "/path/to/dir/newmyfile")) {
 	die "Error! Moving the uploaded file failed.";
}

echo "File successfully uploaded.";
?>

Until Next Time

That's about all there is to uploading files from HTML forms into PHP. Of course, the example I've discussed doesn't make use of a number of the pieces of information provided in the $_FILES array (such as the file size, stored in the size key), but feel free to use those values in your scripts. This column also concludes my discussion of working with form-submitted data in PHP. In future columns, I'll be discussing some data validation methods--so check back soon!

John Coggeshall is a a PHP consultant and author who started losing sleep over PHP around five years ago.


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