PHP: I get a completely blank page, I don't know how to debug this in PHP

Question

I'm having some issues to debug this in php. When I include this line:

require_once("http://" . $_SERVER["HTTP_HOST"] . "/dompdf/dompdf_config.inc.php");

what I get is just a blank page, I don't get any html code as response. Maybe the error messages are hidden ?

Answer 1

Quite often, when you get a WSOD (white screen of death) , it's because there's a Fatal Error, and it's not displayed on the standard output -- ie the generated page.

To have it displayed, you need to :

• set error_reporting to the right level
• and enable display_errors

An easy way is to do that at the top of your PHP script, with a portion of code like this one :

error_reporting(E_ALL);
ini_set('display_errors', 'On');

In your specific case, you are trying to include/require something via HTTP ; which is often disabled.

See the allow_url_include directive, about that.

A possibility would be to enable that one in your PHP's configuration... But it's generally not considered as a good idea : it's disabled for security reasons.
And sending an HTTP request to include a file is slow -- and means your application will not work anymore if the remote server doesn't answer !

Also, here, you are trying to include a file from a remote server that is $_SERVER["HTTP_HOST"] ...

... So, you are trying to include a file from a remote server that is, in fact, your own server ? ie not a remote one ?

If so, you should not try to include via HTTP ; instead, you should work with a local file ; this way (will need some tunning) :

require_once dirname(__FILE__) . "/dompdf/dompdf_config.inc.php";

This way :

• No network un-needed request (you'll just read from the local disk) => faster and safer
• And no need to enable allow_url_include

I should also add :

• When including a local .php file, the content of the .php file is included in your page ; like if it's copy-pasted
• When including a .php file via HTTP, chances are that the remote server will interpret the PHP code, and only send you the output back
  • Which means it's not the PHP code that will get included by your script
  • But only the output you'd get by executing that PHP code !

Answer 2

You should not require/include a remote file like this. Instead provide the local absolute or relative path.

Though insecure and not recommended, it is technically possible to do if certain configuration options are set. (allow_url_include)

See other answers below regarding display_errors for future debugging concerns. I often use the PHP command line interpreter to get the real error, without allowing error details to be presented to web visitors.

Answer 3

这是一种非常不寻常且不安全的方式来包含文件，但是如果您仍然想要使用它，请确保您所包含的文件未在远程服务器上执行，因为您可能在require_once上定位php源代码这里不是它的最终输出。

Answer 4

尝试将其添加为脚本的第一行（显然在<？php之后）：

error_reporting(E_ALL);

Answer 5

The parameter to the require_once statement should be a file path, not a URL.

You are telling the web server to import a file from the file system, not the client to import the file from the web.

It is documented on the include statement page.