Codeigniter REQUEST_URI gets wrong value when app loaded from Internet

Question

I've installed latest Apache, PHP7 and codeigniter in a Ubuntu 17.04 server. I've assigned it a local IP, let's say 10.20.30.40 .
This codeigniter app should work locally and also should work from outside (internet). There is also an intermediary nginx server (which I cannot access) that redirects everything from outside (Internet) to my server, so I've made some test and debugging with xdebug:

Locally

http://10.20.30.40/ciapp/index.php/test
works fine

$_SERVER['REQUEST_URI'] = string '/ciapp/index.php/test'

From Internet

http://www.subdomain.company.xxx/ciapp/index.php/test
does not work (it throws the codeigniter 404 page)

$_SERVER['REQUEST_URI'] = string '//ciapp/index.php/test'

(note the double slash preceding)

Also, I've tested the following

http://10.20.30.40//ciapp/index.php/test
(note the double slash on purpose) didn't work, got the CI's 404

Is there something I could do with REQUEST_URI so it works from outside? Or maybe it is another problem...?

PS: config suggested elsewhere:

$config['base_url'] = $_SERVER['HTTP_HOST'] == '10.20.30.40' ? 'http://10.20.30.40/ciapp/' : 'http://www.subdomain.company.xxx/ciapp/'; 

Answer 1

Finally solved by setting uri_protocol = PATH_INFO

file: application/config/config.php

$config['base_url'] = $_SERVER['HTTP_HOST'] == '10.20.30.40' ? 'http://10.20.30.40/ci/' : 'http://www.subdomain.company.xxx/ciapp/'; 
$config['index_page'] = '';
$config['uri_protocol'] = 'PATH_INFO'; 

file: .htaccess (to remove index.php from url)

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]

Now it is working perfect locally and loading from Internet