maintain tcp socket

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

some time ago I asked similar question. Now I got some clues how to do this properly, but I can't find any decent docs or tutorials on this matter in Perl.

I want to write TCP client, that will automatically maintaint TCP socket to server and reconnect if necessary...

I got following sockopt options to use:

#KeepAlive<br>
setsockopt($sck,SOL_SOCKET, SO_KEEPALIVE, pack("l", 1));
<br>
#After 30 secs idle send KeepAlive probe<br>
setsockopt($sck,IPPROTO_TCP,TCP_KEEPIDLE, pack("l", 30));
 <br>
#Rest probes after 30 secs.<br>
setsockopt($sck,IPPROTO_TCP,TCP_KEEPINTVL,pack("l", 30));
 <br><br>
[download]

Now I have no clue how to include this in Perl program - do I have to write in event-driven manner or just collect state of socket in ordinary manner. I'd just like a program that will reconnect/maintain socket connection (with those socket options)and will not loose data sent to tcp connection - will continue only if write was succesful and rewrite on broken socket ...

I'd kindly ask for more info, pointers or working examples....

Thanks in advance,

Rob.

Comment on maintain tcp socket Download Code

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Re: maintain tcp socket by 5mi11er (Deacon) on Apr 12, 2005 at 15:37 UTC
I'm a network engineer, meaning I build and support the infrastructure of my place of employment. I've not done this type of programming, but... I implore you, don't take the easy or cheap way out. Do the networking stuff, properly! I've had to defend our network many, many, many times against programers who've not bothered to write the socket handling software correctly, then thought it was "the network's fault". Tip 1: No, it's not ok to assume that you can create a connection and leave it up forever. We have to maintain the network, and failures can and do happen. You need to open the connection when you have traffic to send, and close it when you're done, then open it again when you have the next batch of stuff to send. Tip 2: It's also not ok to assume that you'll never have to deal with a network failure. Most of the time the failure will be a failure to open the connection, but occasionally it will happen that you'll have to deal with the failure of an already open connection. Deal with those failures properly. Tip 3: CPAN is your friend. There are lots of very smart people who've been down this road before, I'm sure there are modules on CPAN to make most of this pretty painless. Posting this question was also a good thing, I'm sure you'll find good examples of code from other monks who have experience doing this stuff. I will thank you in advance for your Network Support group for your future attention to these details. -Scott	[reply]
Re^2: maintain tcp socket by Anonymous Monk on Apr 12, 2005 at 16:00 UTC
Hi, thanks for response. I agree, but maintaining TCP connection always up is a requirement in my situation - connected TCP socket is a sign of my client being alive. I've searched CPAN all the way but got no single explanation to socket options I described. There are some packages that deal with TCP sockets, but no one has functionality to keep TCP connection alive in this manner (I could be wrong in this one...) ... So perl monks are my last hope to find some solution to this. I've searched Internet and found only C library references (almost no Perl sources) that I don't know how to use under Perl... From other functionality I just want to resend data if something failed and that's it... Thanks in advance for Perl wisdom, regards, Rob.	[reply]
Re^3: maintain tcp socket by 5mi11er (Deacon) on Apr 12, 2005 at 16:35 UTC
Granted there are situations that seem to require an "always up" connection, but really the only one that I can think of that really requires one is Telnet, because it's simply a window waiting for user input, and you can't assume anything about how the user is going to work. I tend to leave myself connected to my unix workstations for weeks at a time. Almost everything else is some form of 'batch' processing. Wait for data to come in, send it out. Most of the time, the waiting for data part is generally MUCH longer than the sending part. Why hold open the connection forever if you're rarely sending data (on average). Opening and closing TCP connections is a relatively fast operation. If you are having to rely on something to keep the connection alive, then you're describing a situation where you should be opening and closing the connection as needed. At least most of the time that's going to be true. So, I don't know what you're writing, it may be that "always up" is really a requirement, I'm just asking that you think hard about this question, because I'll contend that it's actually easier, once it's written, to support & maintain a program that opens and closes the connections as needed than it is for one that tries to keep the connection alive. The reason is that you'll already have the error handling routines well tested to insure that the connection is opened and closed correctly before trying to send the data. If the connection is assumed to always be there, the error handling routines will be viewed more as being in the way, and will likely not be very robust, rather than as an important and integral part of the program. While I've never had the need to program this type of thing, I do program quite a lot, so understand that while doing it the right way is seen as a pain right now, the reward is worth the more difficult path. -Scott	[reply]
Re: maintain tcp socket by johnnywang (Priest) on Apr 12, 2005 at 17:25 UTC
Try POE, http://poe.perl.org, it contains what you need and some more.	[reply]
Re^2: maintain tcp socket by 5mi11er (Deacon) on Apr 13, 2005 at 15:24 UTC
Given the overwhelming number of areas that POE extends into, you might want to point him to an area that is specific to his needs. Not being familiar with POE myself, I went and looked around. Rob, these POE links might be helpful to you: Evolution of a POE server - Looks like a good introduction to POE itself while building a fairly complex server. POE Cookbook - Lots of little, well commented POE implementations POE Whitepaper - introduction in PDF form Hope these help, -Scott	[reply]