An Open Source Proxy Checker

 

Main Course

You did read every single line up to this point, didn't you?

Peculiarities

Let's assume for a moment that the reader knows how to read C code, 'cause that alleviates the task of explaining the more occult twists of PHP3.
Here follows a short list of differences to C and other peculiarities:

1. PHP is a server side scripting language. Please don't expect any interactive features as known from Java or JavaScript. Those cute tricks done with OnMouseOver event handlers are run on the clients machine. PHP scripts are always run on the server. Each and every interaction will always go through a page fetch, a page refresh or a form submission.
   There are even some nasty tricks which can be implemented in PHP3, aided by some nice features found on Apache servers in the .htacces file. But that is stuff for another essay.
2. PHP code goes embedded anywhere in the normal html flow, enclosed within <?php and ?> tags. At the start, in the middle or at the end, it's just the same. The code is executed by the PHP module, and replaced by any output (print() and printf() functions) during that execution.
3. Variables are easy to recognize, as all of them are prepended by $. There's no difference between strings, chars, ints or reals, even more, each variable can be cast into any mode, mostly dependand on the context. But don't worry, I did not use any typecasting in the sources.
   A nice feature of PHP is that all environment strings are automagically available as variables. Same is valid for passed form fields.
4. Associative arrays are a nice extension to any language. Let me try to explain this feature with the following example:
   Instead of creating two arrays, one for christian names and one with matching lastnames, we just create a single array, using the lastnames as indices and filling in each slot with the corresponding christian name:

   /* 'outdated' style */
   $christname[0]='John';
     $lastname[0]='Doe';
   $christname[1]='Don';
     $lastname[1]='Quijote';
   
   /* 'slick' style */
   $name['Doe']='John';
   $name['Quijote']='Don';

   Yes, I know, don't tell me that this doesn't work when you have a huge tribe of Doe brothers or Quijotes.
   Another way to initialize associative arrays is by using the array keyword. You may look it up in the Quick Reference section at the PHP site.

   There are many ways to browse through these associative array. I use this code snippet:

   reset($name);
   while(list($last,$first)=each($name)) print("Hello $first $last\n");

5. Surely you have observed that even strings are parsed and any variables found replaced by their values. Nice, isn't it?
   This only applies to "double quoted" strings. You can embed newlines (\n) as well as most other ASCII codes as known from C.
   Single quoted strings are not checked nor transformed, and probably render quicklier.
6. Some words regarding variable scope. Variables are always local to the surrounding function. To access global variables, you need to create an explicit reference to them with a global $variable; line.
   Another advantage (or disadvantage for the cunning old C devils) is the free use (and misuse) of variables: there are no possibilities to declare them before actual use. Reminds me of good old BASIC times.
   There's also no int main() entrypoint. You just start coding with the actual code, no need for bureaucratic crap ;-)

Core Code

<?php // Open Source Proxy Checker, severely stripped down
  error_reporting(0);  // no error reporting
  if(isset($PATH_INFO)&&($PATH_INFO=='/feedback.txt')) { // asked to behave like a mirror?
    Header('Content-Type: text/plain');
    $headers=getallheaders();
    reset($headers);
    while(list($header,$value)=each($headers)) print("$header === $value\n");
  } else { // testing the proxy
    $SockAdr='proxy.spaceproxy.com';
    $SockPort=80;
    $HL=array(
      'User-Agent' => 'Mozilla/4.0 (Windows 98;US) Opera 3.62 [en]',
      'Accept' => 'image/gif, image/x-xbitmap, image/jpeg, image/png, */*',
      'Pragma' => 'no-cache',
      'Connection' => 'keep-alive');
    print('<html><body><h1>Stripped down version of OSPC</h1>');
    printf('Sending request to proxy %s, port %s<br><pre>',$SockAdr,$SockPort);
    print("  GET http://$HTTP_HOST$SCRIPT_NAME/feedback.txt HTTP/1.1\n");
    print("  Host: $HTTP_HOST:80\n");
    reset($HL);
    while(list($header,$value)=each($HL)) print("  $header: $value\n");
    printf("</pre>Connecting to %s, port %s...<br>",$SockAdr,$SockPort);
    flush(); // force flushing of "printf" buffers.
    $fp=fsockopen($SockAdr,$SockPort);
    if($fp) { // you are reading this code? Wow, I'm proud of you!
      // start outputting our header
      fputs($fp,"GET http://$HTTP_HOST$SCRIPT_NAME/feedback.txt HTTP/1.1\r\n");
      fputs($fp,"Host: $HTTP_HOST:80\r\n");
      reset($HL);
      while(list($header,$value)=each($HL)) fputs($fp,"$header: $value\r\n");
      fputs($fp,"\r\n"); // terminate header structure by appending a blank line
      while(!feof($fp)) {
        $line=fgets($fp,4096); // I suppose no line will be longer than this
        if($line=="\r\n") break; // reached end of header
      } // end while
      if(!feof($fp)) {
        print('<br>Receiving...<pre>');
        while(!feof($fp)) {
          $line=trim(fgets($fp,4096));
          list($name,$value)=split(' === ',$line,2);
          if((strlen($name)>0)&&(strlen($value)>0)) print("  $name: $value\n");
        } // end while() (end of "file" reached)
        print("</pre>That's all!");
      } // end if
      fclose($fp);
    } // end if: end processing with a valid socket handle ($fp)
    print('</body></html>');
  } // end else: testing proxy
?>

Functional View

Anyway, let's have a short glimpse at a typical run of previous script:

Stripped down version of OSPC Sending request to proxy proxy.spaceproxy.com, port 80 GET http://dq.linuxave.net/stripped.php3/feedback.txt HTTP/1.1 Host: dq.linuxave.net:80 User-Agent: Mozilla/4.0 (Windows 98;US) Opera 3.62 [en] Accept: image/gif, image/x-xbitmap, image/jpeg, image/png, */* Pragma: no-cache Connection: keep-alive Connecting to proxy.spaceproxy.com, port 80... Receiving Accept: image/gif, image/x-xbitmap, image/jpeg, image/png, */* Host: dq.linuxave.net Pragma: no-cache User-Agent: Mozilla/4.0 (Windows 98;US) Opera 3.62 [en] Via: 1.1 - (DeleGate/6.1.0) That's all!

Let's take that Core Code apart, and analyse what's supposed to be going on under the PHP hood.

The indentation already gives some nice hints about the overall structure: The whole code is separated by an if statement in two sections.

The variable $PATH_INFO is defined when the URL to this page includes something more in the path, right after this scripts name.
If this code was stored on a server as http://somewhere.com/stripped.php3 and we call up this URL:
http://somewhere.com/stripped.php3/test,
then $PATH_INFO will be /test.

The first part of this script just tells the client browser to expect plain text and not the default, avoiding an unfitting HTML rendering of a pure textual feedback page.
getallheaders() returns an array with all those bits of information sent from your browser through a proxy to arrive finally at a greedy logging bot on some web server. You better watch out what you're willing to send. IP disguise is not the only thing to do when you care at least a bit about anonymity.
The next two lines just traverse this array ($headers) and print out this information.

So much for that first and easy part. Let's have a look at the second part.
From the previous discussion, you should be able to figure out everything until that flush() line. Hint: Variable definitions, $HL being an array, some print statements starting to render the HTML page.

All print statements will at some time arrive at your clients browser, but first they have to be send by the server. This process is normally buffered to avoid sending too many small packets of info.
If, for some reason, you want to push the already buffered info to the client, you use the flush() function.

The most important part of this script is IMO the fsockopen() functionality: PHP tries to open a socket to a certain port ($SockPort) on a certain address ($SockAdr). You can also express that address in IPv4 format (4 groups of non-negative decimal numbers lower than 256, separated by dots).
I/O to this socket is done with fgets() and fputs().

I'm not that good at casting my own code into english words, so bear with me ;-)

I'm sending out a HTTP order to fetch a certain page (http://$HTTP_HOST$SCRIPT_NAME/feedback.txt) on the host $HTTP_HOST, port 80. You should know that 80 is the port commonly associated with HTML traffic.

Q: All nice and fun. But what the heck are $HTTP_HOST and $SCRIPTNAME supposed to be??

A: They are part of the environment variables. Please write yourself a little PHP script to print out the contents of these variables among some more info:

<?php
  phpinfo();
?>

Next block of code just fetches the remaining data on that socket (belonging to the HTML body) and prints them out.

That's all!!

Not quite. There are many cute little functions making up the spicy flavor of PHP and helping at every corner. You should look them up in that Quick Reference section on the PHP site. Or even better, start downloading sources, binaries and manuals and install PHP on your machine and begin experimenting right away, you won't regret it!

Open Paths

Sources are available, lucky you, so you can take them and enhance the app, adding your own bells and whistles. Please be so kind and mail me any use or changes you do.

 

Dessert

Final Notes

All these examples will run on a server, and not on your own machine, thus, not having the bandwidth limitation of your dial-up telephone line.
This narrow-bandwidth-line is only used to trigger the execution of the PHP3 script.

There's a very wide field of application for PHP3, most of what is known deals only with the commercial crap, i.e., web based shopping carts and related stuff.

PHP3 is also very helpful when implementing any client/server protocol. I wrote a client to retrieve files from a CVS server, implementing the whole client-server CVS handshaking in PHP3.

Hopefully there will be more essays dealing with these scripting languages. Besides PHP3 there's also Perl, Rebol and Python. Each of them has its own advantages/disadvantages, shallow or steeper learning curves, function or object oriented approach. In the end, it's just a matter of personal taste which language is your preferred one.

I can't resist the temptation of including some fly outs ;-)

• svd, you got me started on this stuff. Shall I be angry with you? Do you know how much time I'm wasting instead of earning money like all other ants?
• Laurent, an incredibly quick learner, pushing me with his questions into this. Thanks for your proofreading, the idea with the dishes and for teaching me how to use smileys ;-)
• Fravia, for your trust in friends and strangers. And for being patient!

You might provide me with some of your feedback through Fravia's messageboard (preferred way of sharing knowledge) or through my email (dq at altern dot org).

Good Netiquette

Relevant Links

• PHP, server side scripting language
• PHP Homepage
• PHP 4.0 Version 4 Downloads (betas)
• PHP Downloads: source and Windows binaries
• PHP Annotated Online Manual
• PHP Manual Quick Reference
• Download manuals (tgz, zip, pdf, rtf, etc.)
• Frequently Asked Questions
• Some more or less useful books
• Sites with PHP code snippets and tutorials.
• The Resource For PHP Developers
• Developer Shed
• Where PHP meets eBusiness :-(
• 'Free' web space providers
• Altern french spoken
• XodoX german spoken
• LinuxAve linux spoken
• Best provider please send me feedback on other PHP3 enabled free web space providers
• Miscellanea
• Open Source Proxy Checker & Full Sources
• Web Searchlores
• Fravia's messageboard
• Request For Comments
• RFC 2068 - HTTP/1.1 -- Hypertext Transfer Protocol