CentOS - May 2020 - xinetd custom service - perl - remote address

Hi all,

I can't believe that I can't find the answer to this one.  I have a perl
script which is called by xinetd.

I want that perl script to be able to detect the remote IP address of the
caller.

I presumed that it would be an environment variable but I could be wrong. 
I've found reference to the ENV and PASSENV arguments for xinetd.conf but no
examples, and no indication of what auguments to use.

In my script I have the following code:

foreach (keys %ENV) { print "$_=$ENV{$_}\n";}


but the only line I get back is:

XINETD_LANG=en_US

On Thu, May 28, 2020 at 04:46:34PM +0100, Gary Stainburn
wrote:
>
> Hi all,
> 
> I can't believe that I can't find the answer to this one.  I have a
> perl script which is called by xinetd. 
> 
> I want that perl script to be able to detect the remote IP address
> of the caller. 
> 
> I presumed that it would be an environment variable but I could be
> wrong.  I've found reference to the ENV and PASSENV arguments for
> xinetd.conf but no examples, and no indication of what auguments to
> use. 
> 
> In my script I have the following code:
> 
> foreach (keys %ENV) { print "$_=$ENV{$_}\n";}
> 
> 
> but the only line I get back is:
> 
> XINETD_LANG=en_US
I don't believe that xinetd tells the underlying processes anything
about IPs, since xinetd handles the network connection and as far as
the process is concerned, it's just filehandles.  

-- 
Jonathan Billings <billings at negate.org>

> Hi all,
>
> I can't believe that I can't find the answer to this one.  I have a
perl
> script which is called by xinetd.
>
> I want that perl script to be able to detect the remote IP address of the
> caller.
>
> I presumed that it would be an environment variable but I could be wrong.
> I've found reference to the ENV and PASSENV arguments for xinetd.conf
but
> no examples, and no indication of what auguments to use.
>
> In my script I have the following code:
>
> foreach (keys %ENV) { print "$_=$ENV{$_}\n";}
>
>
> but the only line I get back is:
The variable you may want is REMOTE_HOST, at least that's what I see on a
host of mine.

Regards,
Simon

On 5/28/2020 8:55 AM, Jonathan Billings wrote:
> I don't believe that xinetd tells the underlying processes anything
> about IPs, since xinetd handles the network connection and as far as
> the process is concerned, it's just filehandles.
Isn't the filehandle just a socket? So can't you use Perl's socket
API
to recover the connection information? So the next problem is to find 
something that wraps an existing filehandle in a Perl socket object.

In article <202005281646.34790.gary.stainburn at ringways.co.uk>,
Gary Stainburn <gary.stainburn at ringways.co.uk>
wrote:
> Hi all,
> 
> I can't believe that I can't find the answer to this one.  I have a
perl script which is called by xinetd.
> 
> I want that perl script to be able to detect the remote IP address of the
caller.
> 
> I presumed that it would be an environment variable but I could be wrong. 
I've found reference to the ENV and PASSENV
> arguments for xinetd.conf but no examples, and no indication of what
auguments to use.
> 
> In my script I have the following code:
> 
> foreach (keys %ENV) { print "$_=$ENV{$_}\n";}
> 
> 
> but the only line I get back is:
> 
> XINETD_LANG=en_US
Works for me. Here are my details:

1. /usr/local/bin/args:

#!/usr/bin/perl

$i=1;
while(defined($_ = shift)) {
        printf "ARGV[%d]=\"%s\"\n",$i++,$_;
}
foreach $env (keys %ENV) {
        printf "ENV{%s}=\"%s\"\n",$env,$ENV{$env};
}

2. /etc/xinetd.d/args:

service args
{
    disable = no
    port = 54321
    type = UNLISTED
    socket_type     = stream
    wait            = no
    user            = root
    server          = /usr/local/bin/args
    server_args     = --test
    log_on_failure  += USERID
}

3. Results of telnet 127.0.0.1 54321:

# telnet 127.0.0.1 54321
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
ARGV[1]="--test"
ENV{CONSOLE}="/dev/console"
ENV{PREVLEVEL}="N"
ENV{SELINUX_INIT}="YES"
ENV{LC_COLLATE}="en_US"
ENV{RUNLEVEL}="3"
ENV{LC_ALL}="en_US"
ENV{previous}="N"
ENV{LC_NUMERIC}="en_US"
ENV{PWD}="/"
ENV{LC_TIME}="en_US"
ENV{LANG}="en_US"
ENV{LC_MESSAGES}="en_US"
ENV{runlevel}="3"
ENV{INIT_VERSION}="sysvinit-2.86"
ENV{SHLVL}="3"
ENV{LC_MONETARY}="en_US"
ENV{_}="/usr/sbin/xinetd"
ENV{PATH}="/sbin:/usr/sbin:/bin:/usr/bin"
ENV{vga}="773"
ENV{REMOTE_HOST}="127.0.0.1"
ENV{TERM}="linux"
Connection closed by foreign host.

Notice the value of ENV{REMOTE_HOST}

Cheers
Tony

-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org

On Thursday 28 May 2020 18:12:55 Tony Mountifield wrote:
> In article <202005281646.34790.gary.stainburn at ringways.co.uk>,
> Works for me. Here are my details:
> 
Thanks for this Tony.  This is exactly what I had expected to happen.  I
subsitiuted your server for mine and got exactly the same results.

The problem was not my server, but the client (Powershell on Win10) losing half
of the data I returned.