How can I see the httpd log for outbound connections?

The access log specified in httpd.conf for a website only shows the information for incoming connections. For outbound connections such as those issued by php file_get_contents function, how can I get the log?

There isn't any solution that can be just switched on, but this functionality has to be implemented.

One possible approach is:

Make a wrapper around the functions that make outgoing requests:

function log_file_get_contents( $url ) {
    log_request( $url ); // A separate logging function that you create
    file_get_contents( $url );
}

Then, use log_file_get_contents() for all requests that you want to be logged.

A similar wrapper function needs to be written for other functions that are used for outgoing requests.

There is no readily available log. You would need a solution specifically catered for your OS.

If you are the programmer then you can look into redeclaring native PHP functions by making use of namespaces and the auto_prepend_file php.ini directive.

<?php
namespace override;
function file_get_contents( string $filename, $use_include_path = false, $context = null, $offset = 0, $length = null )
{
    // If $filename seems like a URL then do log stuff
    if( preg_match( '/^https?:\\/\\//i', $filename ))
    {
        // Do log stuff
        echo 'Doing log stuff for '.$filename;
    }
    
    return \file_get_contents( $filename, $use_include_path, $context, $offset, $length );
}

\override\file_get_contents( 'https://onlinephp.io/' );

Output:

Doing log stuff for https://serverfault.com/

Additionally, you would have to make sure to do this with any other functions or classes which make web requests such as:

curl_init("http://www.example.com/");

curl_setopt($ch, CURLOPT_URL, "http://www.example.com/");

curl_setopt_array($ch, array(CURLOPT_URL => 'http://www.example.com/'));

fopen('http://www.example.com/', 'r');

And possibly more which I am not aware of.

Adapting my answer to How to easily get all HTTPS addresses that an application connects to externally?:

From Monitoring files continuously with lsof, you could use lsof in conjunction with the repeat (-r) option. The following repeats every two seconds

$ lsof -i TCP:80,443 -r 2

which will give you a progressive historical log every 2 seconds:

=======
COMMAND  PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
firefox 9542 user   27u  IPv4 1068219      0t0  TCP user-300V3Z-300V4Z-300V5Z:37360->192.0.78.23:https (ESTABLISHED)
firefox 9542 user   48u  IPv4 1053405      0t0  TCP user-300V3Z-300V4Z-300V5Z:45948->ec2-54-213-37-69.us-west-2.compute.amazonaws.com:https (ESTABLISHED)
=======
COMMAND  PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
firefox 9542 user   27u  IPv4 1068219      0t0  TCP user-300V3Z-300V4Z-300V5Z:37360->192.0.78.23:https (ESTABLISHED)
firefox 9542 user   48u  IPv4 1053405      0t0  TCP user-300V3Z-300V4Z-300V5Z:45948->ec2-54-213-37-69.us-west-2.compute.amazonaws.com:https (ESTABLISHED)
firefox 9542 user   52u  IPv4 1138942      0t0  TCP user-300V3Z-300V4Z-300V5Z:57602->kul08s01-in-f10.1e100.net:https (SYN_SENT)
firefox 9542 user  102u  IPv4 1139934      0t0  TCP user-300V3Z-300V4Z-300V5Z:49102->kul09s13-in-f14.1e100.net:https (ESTABLISHED)
firefox 9542 user  110u  IPv4 1138950      0t0  TCP user-300V3Z-300V4Z-300V5Z:49104->kul09s13-in-f14.1e100.net:https (SYN_SENT)
=======
...
=======
COMMAND  PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
firefox 9542 user   27u  IPv4 1068219      0t0  TCP user-300V3Z-300V4Z-300V5Z:37360->192.0.78.23:https (ESTABLISHED)
firefox 9542 user   48u  IPv4 1053405      0t0  TCP user-300V3Z-300V4Z-300V5Z:45948->ec2-54-213-37-69.us-west-2.compute.amazonaws.com:https (ESTABLISHED)
firefox 9542 user   51u  IPv4 1140129      0t0  TCP user-300V3Z-300V4Z-300V5Z:52284->kul09s13-in-f10.1e100.net:https (ESTABLISHED)
firefox 9542 user  108u  IPv4 1137384      0t0  TCP user-300V3Z-300V4Z-300V5Z:55886->103.229.10.236:https (ESTABLISHED)
firefox 9542 user  122u  IPv4 1137399      0t0  TCP user-300V3Z-300V4Z-300V5Z:55870->kul08s12-in-f1.1e100.net:https (ESTABLISHED)
firefox 9542 user  126u  IPv4 1137402      0t0  TCP user-300V3Z-300V4Z-300V5Z:47370->stackoverflow.com:https (SYN_SENT)

Note: Every two seconds interval is separated by =======.

You could then pipe the output to a file, like so

$ lsof -i TCP:80,443 -r 2 > /tmp/http_out.log

If you don't want to log all outgoing HTTP(S) requests, you could grep for the name of your script/process:

$ lsof -i TCP:80,443 -r 2 | grep <name of your process>

I think that the grep should work, but I'm not able to test it.

Admittedly, the output isn't as pretty as using

watch -n1 lsof -i TCP:80,443 

but this would only give you an instantaneous snapshot of the current outgoing requests:

dropbox    3280 saml   23u  IPv4 56015285      0t0  TCP greeneggs.qmetricstech.local:56003->snt-re3-6c.sjc.dropbox.com:http (ESTABLISHED) 
thunderbi  3306 saml   60u  IPv4 56093767      0t0  TCP greeneggs.qmetricstech.local:34788->ord08s09-in-f20.1e100.net:https (ESTABLISHED) 
mono       3322 saml   15u  IPv4 56012349      0t0  TCP greeneggs.qmetricstech.local:54018->204-62-14-135.static.6sync.net:https (ESTABLISHED) 
chrome    11068 saml  175u  IPv4 56021419      0t0  TCP greeneggs.qmetricstech.local:42182->stackoverflow.com:http (ESTABLISHED) 

Again, to restrict the output to only the PHP process, you might be able to use grep

watch -n1 lsof -i TCP:80,443 | grep <name of your process>