Overview of req4c

The main requirements of the req4c PHP extension were:

Allow the PHP program to call 4C Update programs and get a return value.
Allow the PHP program to call 4C Report programs and get results from the 4C report program.
Allow the PHP program to get info messages and error messages generated by the 4C program.
Allow the PHP program full control over formatting the data.
Allow low to high level security.
Minimize network traffic.
Allow the main 4C application accessed through the normal 4C Client/Server interface to work without interference.
Make the req4c extension as PHP like as possible so that it would feel natural to the PHP programmer.

There are three parts to the req4c PHP extension.

The req4c extension itself. This is a standard PHP extension written in C and linked with the lib4cphp.so library. The req4c extension provides all the funtions that a PHP program needs to interact with 4C programs.
A new server daemon, 4creqd, that runs in the background and receives requests from the PHP program and forwards them to a 4csrvr. 4creqd then waits for the results from the 4csrvr and returns them to the PHP program. Though it is not necessary, the 4creqd daemon will typically run on the same machine as the Web Server.
The 4csrvr program. This is the normal 4csrvr process with a few modifications to allow it to interact with the 4creqd daemon. Only version 4.8.0 and higher of 4csrvr can interact with the 4creqd process.