Sockets: Problem Reading Responses

TGK

Greetings all. I've been working on a project dealing with sockets and sending out some kind of broadcast message. I have used many various methods and I am able to send out a broadcast and I can see the responses being sent, however, I am never able to retrieve the responses with any socket read functions.

I've tried the fsockopen() method, using fwrite/fputs and fread/fgets, as well as the socket_write and socket_read methods. Since I am using UDP I recently decided to try to use socket_sendmsg and socket_sendto. With sendto() I am able to send the message out but I am still unable to get any responses using recvfrom. I also have a hard time running the UDP examples on the PHP site, and it seems that everything is configured correctly. I am currently running PHP 4.3.6. I know the newer .7 version was released yesterday, but haven't gotten around to trying it out on it yet.

Basically what I've been doing is something like:

<?php

$buf = "this will be the broadcast message";

$socket = fsockopen('udp://255.255.255.255', $port, $errno, $errstr) or die ("Error creating socket");

fwrite($socket, $buf);  // this works fine when i check ports with a scan utility, I can see the responses.

// I generally set the sockets to blocking at this point since it will hang indefinitly.

fread($socket, 80);     // will hang here since nothing is being returned to the buffer.  

// I can see error responses being sent to those devices that are
// sending me the initial response, saying the destination can not be reached.

fclose($socket);

?>

This isn't my actual code at the moment and I haven't been using the fsockopen() method, but in all cases I am unable to get a response back. By watching the ports, as I've said, I can see the responses are unable to make it back to my destination. But they show up as making it to the computer, and the actual computer IP responding back, and not a router IP.

All I'm trying to do at this point is successfully read the responses sent back to me in a very basic form.

Sorry the post isn't too elaborate I don't have the code on me at the moment to reference to. Any ideas from anyone?

Thanks.

drew010

the problems might be
$fwrite($socket, $buf);
and
$fread($socket);

they are functions so you dont want the dollar sign in front

fwrite($socket, $buf);

while(!feof($fp)) {
$data .= fgets($fp);
}

TGK

Thanks for the response.

Yeah, I just fixed that in my post. I typed it up quickly without referencing anything to give a quick example of where it was going wrong. I don't actually use the $ when accessing the functions, sorry about that.

AstroTeg

What might help is if you explained what your goal is. From the look of it, you're sending a UDP broadcast message out (not sure on what port though) and then listening for a response on port 80.

I don't know if this quote from php.net has anything to do with your problem:

"UDP sockets will sometimes appear to have opened without an error, even if the remote host is unreachable. The error will only become apparent when you read or write data to/from the socket. The reason for this is because UDP is a "connectionless" protocol, which means that the operating system does not try to establish a link for the socket until it actually needs to send or receive data."

TGK

The 80 is the fread() isn't a port, it's the length you want to read from the receive buffer. Anyhow, I was able to fix that actual code on my other machine today (I had to do it from memory when posting since I didn't have access to it at the time).

My goal was to accept the responses that were given to me from other devices on the network after doing a broadcast, but nothing would be returned to the receive buffer when the responses were sent, or so it seemed. Apparently there was just a problem having to read the the exact number (or more) of the bytes that were being sent. Long story short, unless the read length was more than about 85-90 I was unable to read anything from the buffer.

So I managed to get it to work, thanks for the replies though. I'm sorry my post wasn't very straight forward, had a hard time remembering what it was I had written for code.