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). 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.
Note that 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.
A file upload screen can be built by creating a special form which
looks something like this:
Example 34-1. File Upload Form <form enctype="multipart/form-data" action="_URL_" method="post">
<input type="hidden" name="MAX_FILE_SIZE" value="30000" />
Send this file: <input name="userfile" type="file" />
<input type="submit" value="Send File" />
</form> |
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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.
Also, be sure your file upload form has
enctype="multipart/form-data" otherwise the file
upload will not work.
| Warning |
The MAX_FILE_SIZE is advisory to the browser, although PHP also checks
it. Changing this on the browser size is quite easy, so you can never
rely on files with a greater size being blocked by this feature. The
PHP-settings for maximum-size, however, cannot be fooled. You should add
the MAX_FILE_SIZE form variable anyway 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 actually failed.
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The Variables defined for uploaded files differs depending on
the PHP version and configuration. The autoglobal
$_FILES
exists as of PHP 4.1.0 The $HTTP_POST_FILES array
has existed since PHP 4.0.0. These arrays will contain all
your uploaded file information. Using $_FILES
is preferred. If the PHP directive
register_globals is
on, related variable names will also exist.
register_globals
defaults to off as of PHP
4.2.0.
The contents of $_FILES
from our example script 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.
- $_FILES['userfile']['name']
The original name of the file on the client machine.
- $_FILES['userfile']['type']
The mime type of the file, if the browser provided this
information. An example would be
"image/gif".
- $_FILES['userfile']['size']
The size, in bytes, of the uploaded file.
- $_FILES['userfile']['tmp_name']
The temporary filename of the file in which the uploaded file
was stored on the server.
- $_FILES['userfile']['error']
The error code
associated with this file upload. ['error']
was added in PHP 4.2.0
Note:
In PHP versions prior to 4.1.0 this was named
$HTTP_POST_FILES and it's not an
autoglobal
variable like $_FILES is. PHP 3 does not
support $HTTP_POST_FILES.
When register_globals
is turned on in php.ini, additional
variables are available. For example,
$userfile_name will equal
$_FILES['userfile']['name'],
$userfile_type will equal
$_FILES['userfile']['type'], etc. Keep in mind
that as of PHP 4.2.0, register_globals defaults to off. It's
preferred to not rely on this directive.
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 34-2. Validating file uploads
See also the function entries for is_uploaded_file()
and move_uploaded_file() for further information. The
following example will process the file upload that came from a form.
<?php
// In PHP versions earlier than 4.1.0, $HTTP_POST_FILES should be used instead
// of $_FILES.
$uploaddir = '/var/www/uploads/';
$uploadfile = $uploaddir . $_FILES['userfile']['name'];
print "<pre>";
if (move_uploaded_file($_FILES['userfile']['tmp_name'], $uploadfile)) {
print "File is valid, and was successfully uploaded. ";
print "Here's some more debugging info:\n";
print_r($_FILES);
} else {
print "Possible file upload attack! Here's some debugging info:\n";
print_r($_FILES);
}
print "</pre>";
?>
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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.
