Question

Does the PHP header function have a limit to the amount of textual or binary output to the browser before it refuses to redirect the browser to the provided URL?

I have noticed that I can output to the browser then do a redirect with header('Location: $url'); exit();, but it seems as though after I have output a certain amount it refuses and outputs this message?

I have never came across anything to suggest this during Zend Certification study, so I wondered if it was a undocumented feature?

Warning: Cannot modify header information – headers already sent by
(output started at /var/www/vhosts/dev/dev_crmpicco/co.php:935) in
/var/www/vhosts/dev/dev_crmpicco/includes/Rangers.inc.php on line 1701

Answer 1

The answer can be found in header() manual

Remember that header() must be called before any actual output is
sent, either by normal HTML tags, blank lines in a file, or from PHP.
It is a very common error to read code with include, or require,
functions, or another file access function, and have spaces or empty
lines that are output before header() is called. The same problem
exists when using a single PHP/HTML file.

You can’t output any text before you set the headers. You might have some sort of output buffering set that allows you to echo anything, if you think you are able to output a certain amount of bytes before header fails.