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05.26.04
 By
Robert Plank
HTACCESS is a remarkable tool you can use for password protection,
error handling (like custom 404 pages), or HTTP redirects. It can
also be used to transform whole folders in seconds: adding headers
to all your HTML documents, watermarking all your images, and more.
A wrapper is like a middleman. Using htaccess you can tell your web
server to "forward" certain files to PHP scripts of yours. When a
visitor tries to load an image in their browser, you could activate
a script that adds a watermark to the image. When an HTML page is
loaded you could query an IP-to-country database and have your HTML
pages translated into the native language of your visitor's country-of-origin.
Every file in a folder, or all files of a certain type in a folder,
can be instructed to go through a PHP script. |
TORTILLA
WRAP
Pretend you host several affiliate sites, or a full-blown hosting
service like Geocities. Most sites running on free hosting services
have some kind of advertisement the owners use to generate revenue.
These aren't applied voluntarily by the users of these services. The
ads don't even show up on their source files, just when displayed
on the web.
It's possible to replicate this feature using less than 10 lines of
PHP and htaccess code. To start off, make a folder on your web host
called "header". Create a new text file and enter the following:
AddHandler headered .htm
AddHandler headered .html
Action headered /header/header.php
This designates files with the extension ".htm" and ".html" to a type
called "headered". The name "headered" can really be anything, it's
just a way of labeling a group of files. The last line there tells
the web server that if any of the file types in the group called "headered"
are called, we should instead execute the script "/header/header.php".
This is the relative path, so if your URL is http://your.host, this
will run http://your.host/header/header.php.
That's all you've got to do for the htaccess file. Save that as "htaccess.txt"
-- we'll get back to it later.
For the actual wrapper, create a new text file with the standard tags,
then assign your header and footer file names to variables called
$header and $footer.
$header = "header.html";
$footer = "footer.html";
Redirecting a user to our script doesn't pass its contents to it,
just the filename. If you call phpinfo() in your script and scroll
to the bottom you can see all the server variables which give us the
name. The element "REQUEST_URI" in $_SERVER gives us the relative
path (/header/sample.html), but we want the full system path since
we're going to be reading the actual file (/home/username/wwwroot/your.host/header/sample.html),
which is "PATH_TRANSLATED".
$file = $_SERVER["PATH_TRANSLATED"];
The name of the file that just tried to be shown is now stored in
the variable $file. Three simple things are left: output the header,
output the actual file, then output the footer.
readfile($header);
readfile($file);
readfile($footer);
That's it. Here's the entire header.php file:
All that, in just nine lines of code. Download it here: http://www.jumpx.com/tutorials/wrapper/header.zip
That contains the htaccess file and PHP wrapper script, along with
a sample header, footer, and a test page. Upload all five files to
your web host, chmod htaccess.txt to 0755 then rename it to ".htaccess".
It might disappear from your directory listing which is okay, it should
still be there.
Load, in your browser, the copy of sample.html residing on your web
server. The text "This is my header" should appear at the top while
"This is my footer" should show on the bottom. If you open up the
actual file called sample.html, you'll see that these actually aren't
there. They've been added in by the script all HTML files in the folder
"header" must now pass through.
This is how wrappers work. Certain things, like adding custom headers
and footers are done "on the fly" without modifying your original
file. You'll get the same effect if you create other HTML files and
upload them to this folder.
Files without ".html" or ".htm" extensions, such as text files or
images, won't show these headers or footers. This is a good thing
because text files aren't part of the presentation on a web site and
adding extra text to images will corrupt them. It affects all HTML
files within your /headers folder, and none of the files outside of
it.
If you wanted, you could add or remove any file extensions you want,
just by adding or taking away those "AddHandler" lines.
To get everything back to normal, either delete your .htaccess file
or upload a blank .htaccess file in that folder, and all will be well
again.
SHRINK-WRAP
The same basic formula can be applied again for other uses -- HTTP
compression, for example. This was an idea that used to be impractical
because computers ran at slower speeds, and is now obsolete because
of broadband technologies (DSL and cable).
It works like this: when an HTML page is loaded, the web server instead
gives the visitor a zipped or compressed version of that page. The
visitor downloads that file, which of course takes up less space than
the real thing and downloads in less time, then unzips it and displays
the original page.
In this age of lighting fast DSL lines, there's almost no noticeable
difference. However, if you have a site that hosts large files whose
audience is mostly dialup users, it might be something to look into.
Make a new folder called "compress". Create your htaccess file again,
just as before, but set the extensions to include .htm, .html, and
.txt. (The group name, folder name, and script name have nothing to
do with one another, you can name any of these whatever you like --
I just like things to match.)
Our wrapper script for this should be called "compress.php". That's
what I'm naming mine. This means the htaccess file you have should
look as follows:
AddHandler compress .html
AddHandler compress .htm
AddHandler compress .txt
Action compress /compress/compress.php
If our wrapper were simply going to pass through the file (in other
words, just read its contents into a variable and display it), our
handler script would look like this:
"GIFT WRAPPING" YOUR OUTPUT
To make the HTTP compression work, we use two functions: ob_start()
and ob_gzhandler(). Output buffering functions are strange. Any time
you try to display something, you can have PHP save up everything
you're trying to output. At the very end it's all dumped into a function
of your choosing where the text can be changed or transformed before
it's output.
There is a built-in PHP function called ob_gzhandler() which takes
one parameter (a string of text), compresses the data according to
the gzip standard and does all the header trickery that's needed to
tell the user's browser that we are transmitting data that needs to
be decompressed once it's downloaded. When this line is used:
ob_start("ob_gzhandler");
It tells PHP: everything displayed afterwards has to go through the
function ob_gzhandler() first. Put that at the top of our script and
here's what we've got:
Save that as compress.php. Upload both files, chmod htaccess.txt to
0755 and rename to .htaccess and you're done. That's all you need
for it to work, and you can just as easily apply HTTP compression
to any script by just adding that line.
To try this puppy out, I got on a dialup connection and put a copy
of "The Decline And Fall Of The Roman Empire Volume 1" on my web host,
a 900 page book, about 1.6 megabytes in size. Without HTTP compression
it took 5 and a half minutes to download. With the compression, only
2 minutes. Internet Explorer told me the download was going at 20
KB per second, impossible with a dialup connection... but since the
file was zipped, I really was downloading 20 KB a second (once the
data was decompressed on my end) over a 5 KB per second connection.
Though HTTP compression will work on sounds, video, and images, the
space you save is negligible, usually only a few bytes. These sorts
of media are already heavily compressed so zipping makes almost no
difference. This is why we've told htaccess to only use compression
on text and HTML, because it's with human languages like English where
a lot of repetition occurs, which means more information can be compressed.
Not all browsers support HTTP compression, but ob_gzhandler() figures
out if a browser can support HTTP compression. If the browser doesn't,
the original file is displayed, no harm done.
You can get a copy of this sample script at: http://www.jumpx.com/tutorials/wrapper/compress.zip
Both of these scripts I've created for you will work only on static
files, files that actually exist such as images or HTML files. If
you tried to apply these wrappers as-is to PHP scripts, Perl scripts
or even HTML pages that use SSI. If your whole site is run by a single
script it's a better idea to hard-code these things right in, anyway.
THE BEST THING SINCE BUBBLE WRAP
This last demonstration of an htaccess wrapper is something that I
think most people with content sites have a use for. On the Internet,
people steal stuff. Theft of HTML source code is a nuisance, sure,
but the lifting of images is more common. Someone likes a logo on
your page, or an e-book cover, or a picture of a physical product
you're selling, and it becomes theirs to use.
A practical way to keep this from happening is to add a watermark
to all your images, which is your logo or name on a corner somewhere,
forcing anyone who takes your graphic to either unwillingly give you
credit, or chop off a part of that picture.
Lucky for us, PHP has a set of functions to handle images, and in
version 4.3 and above, it's included by default. Wrappers come in
handy here because you might have an entire site full of images and
would rather not spend three weeks watermarking tons of images by
hand. Maybe you just don't want to have to juggle two sets of images,
one watermarked and one normal.
Download this script from: http://www.jumpx.com/tutorials/wrapper/watermark.zip
The only files you need to worry about in that zip are htaccess.txt
and wrapper.php. Upload them to a folder called "watermark", chmod
htaccess.txt to 0755 and rename to ".htaccess".
The file wrapper.php remain as is. I've put comments in the file regarding
most of what it does, so if you're curious go ahead and take a peek.
What the script does is this: It figures out the original image that
was supposed to be called. Then it loads the watermark, which I've
set in wrapper.php to be "watermark.png" which is just a PNG image
containing the text "THIS IS WATER MARKED". The watermark is placed
on top of the original, in the lower right corner, and output in the
same format (i.e., JPEG) as the original.
You can tell the difference by looking at these two images:
http://www.jumpx.com/tutorials/wrapper/thomas.jpg
http://www.jumpx.com/tutorials/wrapper/thomas-watermarked.jpg
I've included several types of images (GIFs, JPGs, and PNGs) in the
zip file for you to test out. Once you've got everything setup, upload
those images and see how they look with the watermark.
This script will work with GIFs, JPEGs, and PNGs. Due to a patent
issue (which expires worldwide in July 2004) GIFs can only be read,
and not output. To make up for this, any of your GIFs will be output
as PNGs, which should still work.
THE WRAP-UP
If you think about it, a watermark script like this could also be
used for a number of things. For example, if you decide to run an
image hosting service like AuctionWatch does for eBay users, you could
watermark your site's URL to the bottom. Your users get a free service
and everyone else sees a possible place to get free image hosting,
there's some nice viral promotion right there.
You could also adapt the script to check the HTTP referer (in the
variable $_SERVER["HTTP_REFERER"]) to see if the image was called
offsite. If it was, the script would put the watermark on there but
if you called it from a page on your own site, the image would be
shown without one.
Even I have put wrappers to good use. Last year I wrote a product
for Teresa King called Codewarden, which uses htaccess wrappers to
display all the files of a directory in an encoded JavaScript string
in an effort to hide HTML source.
About the Author:
Robert Plank is the creator of Lightning Track, Redirect Pro, Rotatorblaze,
and other useful tools. Want to pick up more programming skills? Then
purchase the e-book "Simple PHP" at http://www.simplephp.com
You may reprint this article in full in your newsletter or web site.
Read this newsletter at:
http://www.thedevweb.com/2004/0526.html |
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| From
the Forum: |
| How
can i stop others copying text from my site? |
Hi folks, i have a large directory which
has taken hours to type up etc and people are now copying
it. How can I stop them? I have the copyright logo etc at
the bottom of each page but this doesn't stop them. Please
help. ...
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