Publius content type

The file name extension of a particular file usually determines the way in which a Web browser interprets the file's content. For example, a file that has a name ending with the extension ``.htm'' usually contains HTML. Similarly a file that has a name ending with the extension ``.jpg'' usually contains a JPEG image. The Publius URL does not retain the file extension of the file it represents. Therefore the Publius URL gives no hint to the browser, or anyone else for that matter, as to the type of file it points to. Indeed, this is the desired behavior as we do not wish to give the hosting server the slightest hint as to the type of content being hosted. However, in order for the browser to correctly interpret the byte stream sent to it by the proxy, the proxy must properly identify the type of data it is sending. Therefore before publishing a file we prepend the first three letters of the file's name extension to the file. We prepend the three letter file extension rather than the actual MIME type because MIME types are of variable length (An alternative implementation could store the actual MIME type prepended with two characters that represented the length of the MIME type string). The file is then published as described in Section 3.2. When the proxy is ready to send the requested file back to the browser the three letter extension is removed from the file. This three letter extension is used by the proxy to determine an appropriate MIME type for the document. The MIME type is sent in an HTTP ``Content-type'' header. If the three letter extension is not helpful in determining the MIME type a default type of ``text/plain'' is sent for text files. The default MIME type for binary files is ``octet/stream''.