AJAX technology based on PHP to implement asynchronous file upload_PHP tutorial

Asynchronous file upload is a problem that is often encountered and must be solved in modern AJAX-implemented web applications. However, the standard AJAX class (XmlHttpRequest) cannot realize the function of transferring files. Therefore, what is discussed here is how to build an asynchronous file upload function based on AJAX technology. In this function, you need to use the built-in frame and (IFRAME) to transfer files. The effect of this function is that when the page is uploading files, users can also use the page and fill in the file description.

This example is analyzed by citing a classic case of AJAX.

System environment

　· Newer version of browser. For example Opera, Firefox or Internet Explorer.

　· PHP 4.3.0 or higher

　· PHP 5 version

· The 'short_open_tag' option in PHP is turned on (otherwise a parsing error will occur).

Functional analysis

File upload through built-in IFRAME (framework). It consists of three parts.

　· There is a simple control in the middle of the page. The target link of this form is a hidden IFRAME (implemented by the CSS style "display: none;") and the OnChange event of the only control in the form is used to trigger the JavaScript function. The purpose of this function is to check the extension submitted by the user and then submit the form.

　·Written a processing process using PHP on the server side (annotated with FILEFRAME). This process is used to check the files uploaded from the client, save them on the server, and return them to the user in the form of Javascript code. The Javascript returned to the user changes the page the user is now viewing via "parent.window.document", sets the name of the file and enables the button that lets the user submit the form. The operation of enabling the button is implemented through the getElementById function.

· There is also a form on the main page that contains the user-submitted description and hidden file name. Users can fill in the description of the file while uploading it. When the file upload is completed, the user clicks the button to view the file information returned to the user after uploading. (The file information is composed of the returned file name and the description entered by the user).

Maybe you will say that this operation is unreasonable: the file has been submitted before the user confirms it. What will happen if the user does not submit. You can handle files abandoned by the user yourself in the extension.

This example stores the file in a file system directory. You need to configure this directory when the script starts running. The specific variables containing this directory information are $upload_dir and $web_upload_dir. There is a permission check to see if the directory is writable.

Here we use the following PHP functions:

· move_uploaded_file - Move a file once uploaded to the server

· fopen - open a file

· fwrite - write content to file

· fclose - close the file

· str_replace - replace string

· filesize - Returns the file size

· filemtime - returns processing time

You can find out how to use these functions through the manual. Please note that HTM (<, >, &) tags should be replaced with (<, > and &).

Source code

　$upload_dir = "/var/www/anyexample/aeu"; // The path where the file is stored

　$web_upload_dir = "/aeu"; // The path of the file in the Web directory

$tf = $upload_dir.'/'.md5(rand()).".test";

　$f = @fopen($tf, "w");

　if ($f == false)

　die("Fatal error! {$upload_dir} is not writable. Set 'chmod 777 {$upload_dir}'

or something like this");

　fclose($f);

unlink($tf);

// Process uploaded files

　if (isset($_POST['fileframe']))

　{

$result = 'ERROR';

　$result_msg = 'No FILE field found';

　if (isset($_FILES['file'])) // Accept files from the browser

　{

　if ($_FILES['file']['error'] == UPLOAD_ERR_OK) // No error

　{

$filename = $_FILES['file']['name']; // File name

move_uploaded_file($_FILES['file']['tmp_name'], $upload_dir.'/'.$filename);

// Main process of processing - transfer files to $upload_dir

$result = 'OK';

　}

elseif ($_FILES['file']['error'] == UPLOAD_ERR_INI_SIZE)

　$result_msg = 'The uploaded file exceeds the upload_max_filesize directive in php.ini';

else

$result_msg = 'Unknown error';

　}

echo '';

echo '