How to do GetHostByAddr via other means?

whr76

I'm brand spanking new to this...

Have an applic that I've installed on my host and I suspect they have limited the GetHostByAddr function due to what I've read in docs as much overhead...

I've read the alternative codings suggested but have NO idea on how to adapt this one usage to any of them...as examples in docs are much simpler...

$hostname       = ($ip)       ? @getHostByAddr($ip)       : '';

Would someone give me some pointers, please? Thanks!
If I get this adapted, I think that should be all I need...

justsomeone

There is no neat algorithm that can convert an IP to a FQDN. It has to be a database lookup. You need to query a DNS server to get it. This will involve a some socket level coding to opena connection to a DNS server/port, issue the request and parse the result.

Fairly messy stuff. Have you done any socket coding before?

whr76

no socket coding...but in http://us2.php.net/manual/en/function.gethostbyaddr.php
there are some things listed there such as

<?php
// For Linux...

function gethost ($ip) {
 $host = `host $ip`;
 return (($host ? end ( explode (' ', $host)) : $ip));
}

that's the type of code what I'm wanting to try out... but I've been unable to find what the statement in existing code does...such as that "?" and the ": ' ' " stuff and why is there a "@" before it...and what is this new code doing? Can you explain? Thanks!

And there are warnings in the manual replies about the backquotes...what about that?

Wynder

[QUOTE=whr76
...I've been unable to find what the statement in existing code does...such as that "?" and the ": ' ' " stuff and why is there a "@" before it...and what is this new code doing? Can you explain? Thanks!
QUOTE]

The ?/: is an inline if/else -- shorthand basically. The return statement is saying...

if($host)
   return end ( explode (' ', $host));
else
   return $ip;

A @ before a function tells that function to supress any errors that might be caused as a result of the operation.

whr76

Wynder, Thanks for that clear description!
It's almost impossible to find those shorthand codes in manual when they are such common one-char values.

But I'm still wondering...what does the "$host = host $ip;" stmt do?
And the backtick issue...is that a cause for concern? (
It appears to my untrained eye that safe mode is off at my host)

Wynder

whr76 wrote:
But I'm still wondering...what does the "$host = host $ip;" stmt do?
And the backtick issue...is that a cause for concern? (
It appears to my untrained eye that safe mode is off at my host)

That's an execution operator: http://us2.php.net/language.operators.execution

Basically tries to run the command 'host 192.168.1.1' (for example) in linux. Wouldn't work on a windows machine. The reason the backtick is an issue of concern is, if someone somehow is able to modify the $ip variable, it's still executing a command on your server -- always good to scrub input (if it's user entered).

whr76

OH! Well...now the veil has been lifted and I can see a bit more...it would have been nice if in the post by "Matt AKA junkie" in GetAddr docs, it would have said "backtick operator" instead of "backticked variables" so I could have found it via search...

In this case, the $ip variable is extracted from headers so it's fairly safe, I think...

It would have been somewhat more helpful if user contributed notes to manual were a bit more descriptive, especially when they use shortcuts...but that's NOT your problem!

I'll take what you have given me and do some more research so I better follow it...and then try it maybe...thanks for now...may post a followup later, ok?

Wynder

Sounds good. 🙂

whr76

Well...guess what? My host had limited my account from accessing a socket! That was the entire problem...I got access turned on and the original code worked...but nice to know what that strange syntax really did!