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Basically, I'm trying to figure out how PHP can be called from a "web server".

I've read the documentation, but it didn't help much.

As far as I can tell, there are three ways to invoke PHP:

  • via command line (eg: php -f "/path/to/script.php")
  • via CGI(??) / via FastCGI (???)
  • via a web server (eg: Apache) module

So let's start with CGI. Maybe I'm just blind, but the spec doesn't mention how on Earth the web server passes data (headers & callbacks) to the thing implementing CGI. The situation is even worse with FastCGI.

Next up, we have server-specific modules, which, I don't even know what to search for since all leads end up nowhere.

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  • 1
    Have you considered reading the code? All of these things in your question are open source. Commented Aug 12, 2011 at 23:37
  • @Dan I'm trying to do that right now. But it's proving difficult for several reasons: (1) I can't find all the code (2) the code is in c/c++ (3) the code is very old and/or messy. Commented Aug 12, 2011 at 23:44
  • @Dan says who?? I could do it in Assembler or ADA if I wanted to (or FPC, which I'm planning to). Commented Aug 12, 2011 at 23:55
  • Yelling at the wind won't help you. tools.ietf.org/html/draft-robinson-www-interface-00 Commented Aug 13, 2011 at 0:00
  • Here is a CGI module written in PHP, might be easier to follow than the typical guides: code.google.com/p/nanoweb-instant/source/browse/work/five_tani/… - Don't bother with FastCGI, not worth the effort (and PHP doesn't support the simpler SCGI.) Commented Aug 13, 2011 at 0:00

2 Answers 2

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Invoking a CGI script is pretty simple. PHP has a few peculiarities, but you basically only need to setup a list of environment variables, then call the PHP-CGI binary:

setenv GATEWAY_INTERFACE="CGI/1.1"
setenv SCRIPT_FILENAME=/path/to/script.php
setenv QUERY_STRING="id=123&name=title&parm=333"
setenv REQUEST_METHOD="GET"
...

exec /usr/bin/php-cgi

Most of them are boilerplate. SCRIPT_FILENAME is how you pass the actual php filename to the PHP interpreter, not as exec parameter. Crucial for PHP is also the non-standard variable REDIRECT_STATUS=200.

For a GET request you only need the environment variables. For a POST request, you simply pipe the HTTP request body as stdin to the executed php-cgi binary. The returned stdout is the CGI response consisting of an incomplete HTTP header, \r\n\r\n, and the page body.

(Just from memory. There maybe a few more gotchas.)

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I faced the issue then you need to populate PATH_INFO and SCRIPT_PATH variables explicitly. Please check my question for details
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FastCGI is probably the best option since it's so wisely used, it would give you language independence (you could drop in Ruby later, for example) and it's well documented with lots of examples.

You could write your own Server API if you really want, but it's trickier than implementing FastCGI and has several disadvantages.

I wouldn't bother at all with straight CGI, FastCGI exists for a reason.

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3 Comments

OK, how does the web server do IPC with the PHP executable? local(loopback) connection?
@Christian it could be on a different host (an arbitrary TCP/IP connection) or at the other end of a unix pipe. Do read the spec I linked to, it's quite plainly written.
I'll give it a good look after a few hours' sleep. It's 2:30am already :/

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