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DESPITE THE HYPE, glory, and often rumors of magical powers bestowed upon it almost from birth, the Web is really nothing more than a global file server. More specifically, it's a global file server farm. And although HTML files of course make up the vast majority of all files transferred via the HTTP protocol, it has become quite commonplace to make Word documents, PDFs, executables, MPEGs, and any number of other file types accessible via the Web. Although FTP has historically been the common means for uploading files to a server, such file transfers are becoming increasingly prevalent via a Web-based interface. In this chapter, you'll learn all about PHP's fileupload handling capabilities. In particular, chapter topics include:

• PHP's file upload configuration directives
• PHP's Array superglobal array, used to handle file upload data
• PHP's built-in upload functions: is_uploaded_file() and move_uploaded_file()
• A review of possible values returned from an upload script

As always, numerous real-world examples are offered throughout this chapter, providing you with applicable insight into this topic.

Uploading Files via the HTTP Protocol

The way files are uploaded via a Web browser was officially formalized in around November 1995, when Ernesto Nebel and Larry Masinter of the Xerox Corporation proposed a standardized methodology for doing so within RFC 1867 (http://www.ietf.org/rfc/rfc1867.txt.). This memo, which formulated the groundwork for making the additions necessary to HTML to allow for file uploads (subsequently incorporated into HTML 3.0), also offered the specification for a new Internet Media Type, multipart/form-data. This new media type was desired, because the standard type used to encode "normal" form values, application/x-www-form-urlencoded, is considered too inefficient to handle large quantities of binary data such as that which might be uploaded via such a form interface.

<form action="uploadmanager.html" enctype="multipart/form-data" method="post">

Name:<br /> <input type="text" name="name" value="" /><br />

Email:<br /> <input type="text" name="email" value="" /><br />

Homework:<br /> <input type="file" name="homework" value="" /><br />

<p><input type="submit" name="submit" value="Submit Homework" /></p>

</form>

Understand that this offers only half of the desired result; whereas the file input type and other upload-related attributes standardize the way files are sent to the server via an HTML page, no capabilities are offered for determining what happens once that file gets there! The reception and subsequent handling of the uploaded files is a function of an upload handler, created using some server process, or capable server-side language, like Perl, Java, or PHP. We'll devote the remainder of this chapter to this aspect of the upload process.