Disable echo and print in PHP

Question

This may seem like a funny question but in fact it's not, I would like to disable echo, print and other functions that may output to the buffer such as readfile.

The reason why I would like to do this is to prevent the client from using echo or print outside the rules of my application, forcing them to compile their contents and send it to the output class, so that the whole buffer is managed.

Now I know I can set up an output buffer at the start of my script and throw away any content, but this will not include things such as header and set_cookie, so my question may be interpreted as How can I control the buffer for the head of the response

Is there any possible way to manage all aspects of PHP's outputting, such as assign a callback to the main buffer rather then just the body of response?

Answer 1

At the end there is no effective way to achieve this, because at least echo is not a function, but a language construct, that cannot get disabled. You may play around with output buffering (ob_start() and such), but that will not prevent other code to disable the output buffering again.

In my eyes there is no way around but to make sure, there is only "good code". I don't know, what you mean by "prevent the client", but I would not execute arbitrary code anyway. And if its written by disciplined developers and its tested, there should be no problem then.

Answer 2

Other than editing and recompiling, I don't believe you can disable functions that output. For functions that bypass output buffering, your SOL.

You can, however, use inline output buffering to control non-header output. The best part is it's nesting capability:

ob_start();
echo 'The first output!',"\n";

ob_start();
echo 'The second output.';

$output2 = ob_get_clean();

ob_flush();

echo $output2;

will output:

The first output!
The second output.