This feature lets people upload both text and binary files. With PHP's authentication and file manipulation functions, you have full control over who is allowed to upload and what is to be done with the file once it has been uploaded.
PHP is capable of receiving file uploads from any RFC-1867 compliant browser (which includes Netscape Navigator 3 or later, Microsoft Internet Explorer 3 with a patch from Microsoft, or later without a patch).
PHP also supports PUT-method file uploads as used by Netscape Composer and W3C's Amaya clients. See the PUT Method Support for more details.
Example 38-1. File Upload Form
A file upload screen can be built by creating a special form which looks something like this:
The __URL__ in the above example should be replaced, and point to a PHP file.
The MAX_FILE_SIZE hidden field (measured in bytes) must precede the file input field, and its value is the maximum filesize accepted. This is an advisory to the browser, PHP also checks it. Fooling this setting on the browser side is quite easy, so never rely on files with a greater size being blocked by this feature. The PHP settings for maximum-size, however, cannot be fooled. This form element should always be used as it saves users the trouble of waiting for a big file being transferred only to find that it was too big and the transfer failed.
Note: Be sure your file upload form has attribute enctype="multipart/form-data" otherwise the file upload will not work.
The global $_FILES exists as of PHP 4.1.0 (Use $HTTP_POST_FILES instead if using an earlier version). These arrays will contain all the uploaded file information.
The contents of $_FILES from the example form is as follows. Note that this assumes the use of the file upload name userfile, as used in the example script above. This can be any name.
The original name of the file on the client machine.
The mime type of the file, if the browser provided this information. An example would be "image/gif".
The size, in bytes, of the uploaded file.
The temporary filename of the file in which the uploaded file was stored on the server.
The error code associated with this file upload. This element was added in PHP 4.2.0
Files will, by default be stored in the server's default temporary directory, unless another location has been given with the upload_tmp_dir directive in php.ini. The server's default directory can be changed by setting the environment variable TMPDIR in the environment in which PHP runs. Setting it using putenv() from within a PHP script will not work. This environment variable can also be used to make sure that other operations are working on uploaded files, as well.
Example 38-2. Validating file uploads
The PHP script which receives the uploaded file should implement whatever logic is necessary for determining what should be done with the uploaded file. You can, for example, use the $_FILES['userfile']['size'] variable to throw away any files that are either too small or too big. You could use the $_FILES['userfile']['type'] variable to throw away any files that didn't match a certain type criteria. As of PHP 4.2.0, you could use $_FILES['userfile']['error'] and plan your logic according to the error codes. Whatever the logic, you should either delete the file from the temporary directory or move it elsewhere.
If no file is selected for upload in your form, PHP will return $_FILES['userfile']['size'] as 0, and $_FILES['userfile']['tmp_name'] as none.
The file will be deleted from the temporary directory at the end of the request if it has not been moved away or renamed.