Question

I’m looking to write a PHP script to act as a mini “daemon” to receive data from a remote socket. The remote server is an Asterisk VoIP server and I’ll be connecting to the Asterisk Management Interface (AMI) in an attempt to receive AMI Event notifications. The connection will be through an always-on SSH tunnel (using autossh) which has been stable enough for our use so far.

Here’s the plan…

• A PHP script connecting to the local port of the SSH tunnel which forwards to the remote port at the other end using fsockopen() or most likely pfsockopen()
• The PHP script will be run from CLI and I guess I should have some sort of shell script on a cron job to check that the PHP script hasn’t stopped for any reason
• I’ll need this PHP script to be running permanently, and permanently connected to the socket to receive data whenever it’s published by the other end
• Memory and CPU is not a problem as we have plenty of resources on our intranet server (criminally under used) but equally I don’t want this script spiralling out of control
• The PHP script will hopefully react to occasional data appearing at the other end of the socket and sometimes inserting or updating data in a MySQL database. Obviously I’ll open/close the MySQL connection when necessary, not just leave it hanging.

First of all, is this a terrible idea that will never work?

I realise PHP’s probably not the best language for a sort of small daemon like this but I’ve had success with PHP on CLI before and it’s the language I’m most comfortable with these days.

Are there any PHP functions that can spring into action when data is published at the other end of the socket?
Or would I just loop using fread() like this…

while (!feof($socket)) {
$output .= fread($socket, 8192);
}

The loop option seems a bit of a mess so I’m just wondering if there’s another way that will mean the script stays connected to the socket but basically idle until some data appears.

What cons/pitfalls should I be aware of when thinking about having a permanently running PHP script connected to a socket?

Cheers, B

Answer 1

• you should be aware of memory consumption when writing a PHP daemon.
  If not carefully unset()/free()d, your daemon may eat more and more memory over time.

• as you already said, PHP is not the best language for this, but it will definitely work. i already did that “hack” a few times.

• be aware that fread() on a TCP socket will be non-blocking. As each line is CR/LF terminated (\r\n) and two CR/LF mark the end of an AMI event/command, you may want to read until “\r\n\r\n” occurs, then process this event and then begin reading again. i’d set the socket blocking and use fgets() instead of fread(). that way its much easier to detect the end of an AMI event – without needing to do string magic / splitting.