Sockets Help

P_Ferreira

Hi,

I'm trying to read data from a logger... I have the logger ip address and port. And I have to give the logger a command like 555555#STATUS# in order for him to output the needed information.

I'm used to PHP but I'm not very experienced in socket programmation, I've been trying the follow code but without success:

$context = stream_context_create();
stream_context_set_option($context, 'tcp', 'content', '555555#STATUS#');

$fp = stream_socket_client(IP:PORT', $err, $errstr, 120, STREAM_CLIENT_CONNECT, $context);

$socket_name = stream_socket_get_name($fp,true);

if (!$fp)
{
    ....
} 
else 
{
    ....
}

I would appreciate any help you could give...
Thanks.

sneakyimp

Your code has a syntax error (the single quote after IP😛ORT).

If you are not having success, perhaps you could describe the problem exactly?

P_Ferreira

Sorry about the error but that was when I copied the code here, the script itself doesn't have that error...

I'm need to connect and retrieve data from a socket.
I have the socket's IP adress and port and for the socket to output the data I need I have to first send the command 555555#STATUS#.

So the problem is how do I connect and send the command to the socket correctly... I'm using the code I put in my previous post but that isn't working... I'm not really experienced in working with sockets...

sneakyimp

I'm not familiar with [man]stream_context_set_option[/man] and what it does exactly -- and unfortunately the documentation is not particularly informative -- however, I suspect that trying to send the command you want to send by calling it is not correct.

[man]stream_socket_client[/man] opens a socket and returns a stream resource (a file pointer you can use to write the socket). There's an example on that page where they do this:


<?php
$fp = stream_socket_client("tcp://www.example.com:80", $errno, $errstr, 30);
if (!$fp) {
    echo "$errstr ($errno)<br />\n";
} else {
    fwrite($fp, "GET / HTTP/1.0\r\nHost: www.example.com\r\nAccept: */*\r\n\r\n");
    while (!feof($fp)) {
        echo fgets($fp, 1024);
    }
    fclose($fp);
}
?>

You should probably use fwrite to write the command on your $fp just like that example does. You might want to follow it with a newline char.

Then, once you've written that command to the socket, you are going to have to read data off the same socket until you reach the end of it. You'll probably have to use fread for that -- possibly in a loop unless you know exactly how much data you are supposed to read.

P_Ferreira

So it will be something along these lines, correct?

$fp = stream_socket_client("tcp://my_ip:my_port", $errno, $errstr, 30);
if (!$fp) {
    echo "$errstr ($errno)<br />\n";
} else {
    fwrite($fp, "555555#STATUS#\n");
    while (!feof($fp)) {
        echo fgets($fp, 1024);
    }
    fclose($fp);
}

Thank you for all the help...

sneakyimp

I'm not certain, but that looks pretty good to me. Working with sockets can be pretty weird because a lot depends on communication protocol -- what is the computer on the other end of the socket expecting? What commands does it understand? Does it keep listening until I send a newline or null char or something? What if my data contains newlines or null chars? How do I know when it is finished sending data? At what point should I just stop reading data to prevent security problems like a buffer overload?

P_Ferreira

Understood, thanks for the help...

By the way if the connection were udp instead of tcp I just needed to change the line

$fp = stream_socket_client("tcp://my_ip:my_port", $errno, $errstr, 30);

$fp = stream_socket_client("udp://my_ip:my_port", $errno, $errstr, 30);

Correct?

P_Ferreira

Now I have another problem... Apparently after the socket receive the command 555555#STATUS# requesting data it sends the requested data to another ip adress, so I have to create another socket in that ip address to receive the data. What is the correct way to create this socket?

P_Ferreira

Here is my current code...

/ SEND COMMAND TO SOCKET /

$fp = stream_socket_client("udp://my_ip:my_port", $errno, $errstr, 30);
if (!$fp) 
{
    echo "$errstr ($errno)<br />\n";
}
else 
{
    fwrite($fp, "555555#STATUS#\n");
    /*while (!feof($fp)) 
	{
        echo fgets($fp, 1024);
	}*/
    fclose($fp);
}  

/* NEW SOCKET TO RECEIVE DATA */
$fp_r = stream_socket_client("udp://localhost:receive_port", $errno, $errstr, 30);
if (!$fp_r) 
{
    echo "$errstr ($errno)<br />\n";
} 
else 
{
    while (!feof($fp_r))
	{
        var_dump(fgets($fp_r, 1024));
    }
    fclose($fp_r);
}

Like I said in my previous post I need a new socket to receive tha data.
But I'm not sure this is correct way to create a socket to receive the data...

sneakyimp

Simply switching your parameter from TCP:BLAH to UDP:BLAH ignores the difference between the TCP and UDP protocol. From the Wikipedia page on UDP:

UDP uses a simple transmission model without implicit handshaking dialogues for providing reliability, ordering, or data integrity. Thus, UDP provides an unreliable service and datagrams may arrive out of order, appear duplicated, or go missing without notice. UDP assumes that error checking and correction is either not necessary or performed in the application, avoiding the overhead of such processing at the network interface level.

In short, your packets may not get through and you would have to take care in your PHP script of constructing the data you transmit such that you handle sequencing and error checking and resending of packets and so on. I wouldn't use it for this application unless I absolutely had to.

Apparently after the socket receive the command 555555#STATUS# requesting data it sends the requested data to another ip adress, so I have to create another socket in that ip address to receive the data. What is the correct way to create this socket?

What makes you say that? You need to share the technical details with us if we are to understand exactly what's going on. I suspect this may be a problem with using UDP -- you are being exposed to the sequencing/routing/error stuff that is automatically handled with TCP.

P_Ferreira

sneakyimp;11009539 wrote:
What makes you say that? You need to share the technical details with us if we are to understand exactly what's going on. I suspect this may be a problem with using UDP -- you are being exposed to the sequencing/routing/error stuff that is automatically handled with TCP.

Let's see if I can make the situation clearer...

I'm trying to insert temperature values in a DB. Said temperature values are provided by a probe. To retrieve the temperature values I have to send a command (555555#STATUS#) to the probe. That's why:

$fp = stream_socket_client("udp://my_ip:my_port", $errno, $errstr, 30);
if (!$fp) 
{
    echo "$errstr ($errno)<br />\n";
}
else 
{
    fwrite($fp, "555555#STATUS#\n");
    /*while (!feof($fp)) 
    {
        echo fgets($fp, 1024);
    }*/
    fclose($fp);
}

I know this code is working for a fact.
But the probe send the data (temperature values) not to ip that send the command (555555#STATUS#) but to the IP and Port that is set in the probe SETUP. So I have to create another socket in that IP address (IP that is set in the probe SETUP) to receive the data. That's why

$fp_r = stream_socket_client("udp://localhost:receive_port", $errno, $errstr, 30);
if (!$fp_r) 
{
    echo "$errstr ($errno)<br />\n";
} 
else 
{
    while (!feof($fp_r))
    {
        var_dump(fgets($fp_r, 1024));
    }
    fclose($fp_r);
}

So adding those two parts, sending the command and receiving the data in the determined IP adress I currently have:

$fp_r = stream_socket_client("udp://receive_ip:receive_port", $errno, $errstr, 30);
if (!$fp_r) 
{
	echo "$errstr ($errno)<br />\n";
} 
else 
{
	$fp = stream_socket_client("udp://my_ip:my_port", $errno, $errstr, 30);
	if (!$fp) 
	{
		echo "Socket Send Message: $errstr ($errno)<br />\n";
	}
	else 
	{
		fwrite($fp, "555555#STATUS#\n");
	}

while (!feof($fp_r))
{
	var_dump(fgets($fp_r, 1024));
}
fclose($fp_r);
}

This code is sending the command correctly but not receiving correctly but I'm not entirely sure about the receive_ip so that could be the problem... Unless you find something else wrong with the previous code...

Thanks for the help...

sneakyimp

These details (i.e, the probe has two ports, one for commands, one for data) sound like they are specific to the probe and I cannot provide answers about how the probe works. I can see that you are first connecting to the port from which you hope to receive information and then you connect to the port to which you send the command. Then, you once you connect to the command port, you immediately send the command and start looping using feof which I don't think is correct. If the probe takes a mere millisecond to respond, your script may attempt to read the $fp_r port before the probe has any data, resulting in feof and then your script ends.

You might want to look at [man]stream_select[/man] and [man]stream_set_blocking[/man].

P_Ferreira

sneakyimp;11009573 wrote:
If the probe takes a mere millisecond to respond, your script may attempt to read the $fp_r port before the probe has any data, resulting in feof and then your script ends.

The script doesn't end... The page just keeps processing... processing...
I think the page stays stuck in the feof loop...

P_Ferreira

sneakyimp;11009573 wrote:
If the probe takes a mere millisecond to respond, your script may attempt to read the $fp_r port before the probe has any data, resulting in feof and then your script ends.

The script doesn't end... The page just keeps processing... processing...
I think the page stays stuck in the feof loop...

sneakyimp

Well the docs on [man]feof[/man] say this:

Returns TRUE if the file pointer is at EOF or an error occurs (including socket timeout); otherwise returns FALSE.

Which means that there is no error and the file pointer returned by $fp_r is not at EOF. Admittedly, the documentation is not particularly helpful here, but some things occur to me:

1) Perhaps you shouldn't open the response port until after you send the command?
2) Does this probe have any documentation that might tell you something about how it should work?
3) Why UDP? Have you tried TCP instead? I already pointed out why UDP kinda sucks.
4) Instead of fgets maybe you could try fread?

Does var_dump output anything in your loop?
Did you read the docs on stream_select? stream_set_blocking?
Are you sure you are connecting to the right ports?
Maybe you should use is_resource to check the validity of $fp or $fp_r before trying to read/write?
What the hell is the data format you expect to find on the probe?

P_Ferreira

sneakyimp;11009585 wrote:
Well the docs on [man]feof[/man] say this:

Which means that there is no error and the file pointer returned by $fp_r is not at EOF. Admittedly, the documentation is not particularly helpful here, but some things occur to me:

1) Perhaps you shouldn't open the response port until after you send the command?
2) Does this probe have any documentation that might tell you something about how it should work?
3) Why UDP? Have you tried TCP instead? I already pointed out why UDP kinda sucks.
4) Instead of fgets maybe you could try fread?

Does var_dump output anything in your loop?
Did you read the docs on stream_select? stream_set_blocking?
Are you sure you are connecting to the right ports?
Maybe you should use is_resource to check the validity of $fp or $fp_r before trying to read/write?
What the hell is the data format you expect to find on the probe?

1) Same situation... The page just keeps processing... processing...
2) No.
3) Because according to the manufacturer the logger only accepts UDP.
4) Same situation... The page just keeps processing... processing...

Does var_dump output anything in your loop? No.
Did you read the docs on stream_select? stream_set_blocking? Yes.
Are you sure you are connecting to the right ports? Yes.
Maybe you should use is_resource to check the validity of $fp or $fp_r before trying to read/write? It's valid.
What the hell is the data format you expect to find on the probe? String: #STC1:000000,00;L:395;TM:...etc...

sneakyimp

If you know the data format you expect to read from the probe, does it have a fixed length? If so, you can read the exact number of bytes you expect rather than checking for EOF like example #2 onthis page. I'm not at all certain but I suspect that checking for FEOF with a UDP connection might not be the right thing to do.

You've also contradicted yourself in your response a bit -- you say there is no documentation but then say "according to the manufacturer the logger only accepts UDP." Any additional information you have from the manufacturer would be helpful.

P_Ferreira

You were right on when you said checking for FEOF with a UDP connection might not be the right thing to do. I finally had success receiving data from the probe.

$sd_cmd_socket = stream_socket_client("udp://logger_ip:logger_port", $errno, $errstr, 30);
if (!$sd_cmd_socket) 
{
    echo "$errstr ($errno)<br />\n";
}
else 
{
    fwrite($sd_cmd_socket, "999999#STATUS#\n");

$rc_resp_socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
socket_bind($rc_resp_socket, 'receive_ip', 'receive_port');

$rc_from = 'logger_ip';
$rc_port = 'logger_port';
socket_recvfrom($rc_resp_socket, $buf, 300, 0, $rc_from, $rc_port);

echo "Received $buf from remote address $from and remote port $port" . PHP_EOL;

fclose($rc_resp_socket);	
fclose($sd_cmd_socket);
}

I put the script (that is working...) here in case you were curious since you helped me a lot with this problem...
I want to apologize for any gramatical errors but english isn't my primary language (I'm portuguese...) and thank you for all time you spent helping me...
I really appreciated... Thanks sneakyimp.

sneakyimp

Glad it's working. Interesting that you chose to use the other socket commands. Any particular reason?

P_Ferreira

No particular reason, total fluke!! Following your sugestion that FEOF might no be right I experimented other commands for the receiver socket... I saw an example with those commands and tried it out...