[Twisted-Python] twisted linux netfilter_log protocol

[Glyph]

On Oct 5, 2013, at 10:50 AM, David Stainton <dstainton415 at gmail.com> wrote:

> 
> Right. I gave my class one of these: implements(interfaces.IPushProducer, interfaces.IReadDescriptor)
> Which means that I can easily write a class that implements IConsumer
> to do something with the packets.
> 
> https://github.com/david415/hushVPN/blob/master/nflog_reader.py

After a brief glance, this stuff looks pretty cool.  Very much in the spirit that these interfaces were developed in.  (And you chose the correct producer interface; the other I*Producer interfaces are pretty much just legacy junk, sorry about that :-))

One thing to note, though: you should switch to this style:

@implementer(IPushProducer, IReadDescriptor)
class NFLogPacket...

because the implements() style won't work in future versions of Python.  (Plus, the implementation of @implementer is much cleaner on older versions too.)

-glyph

> This is basically a packet sniffer which receives packets based on iptables rules.
> 
> After that I wrote proxy consumer/producers too; classes that implement both IConsumer and IPushProducer;
> this allows me to transform the packets before sending them to a transport.
> 
> I was inspired by this doc:
> http://twistedmatrix.com/documents/12.2.0/core/howto/producers.html
> 
> So far I really love Twisted!
> 
> 
> On Wed, Oct 2, 2013 at 3:14 AM, Phil Mayers <p.mayers at imperial.ac.uk> wrote:
> On 02/10/13 09:25, David Stainton wrote:
> 
> In examples of Twisted UDP clients they all do this:
> 
> reactor.listenUDP(3000,MyProtocol())
> 
> What would I do instead?
> reactor.addReader makes sense to me since what I have is a file descriptor,
> and the reactor loop and use select or epoll find out when there is data
> to read...
> and call our doRead() method of the Reader.
> 
> I don't know about implementing this as a Protocol because I do not have any
> equivalent to ReactorUDP. ReactorUDP's listenUDP returns a ListeningPort.
> And I'm not sure how a Transport is related to my Reader... but it seems
> to me
> that there is some abstraction which sets callbacks for io and also
> calls buildProtocol...
> 
> Sorry, maybe I was unclear: you were asking about protocols, so I was merely pointing out that *if* you were to use a protocol, you should copy the approach DatagramProtocol and udp.Port take.
> 
> However as I noted, it *might not* make sense to do this, if there's only ever going to be one socket listening on this "thing", your current approach might be fine.
> 
> 
> If I am going to be using a Twisted Service to drop privileges after
> gaining access to the fd...
> How would I do this? Would I have startService() instantiate a Protocol
> instance?
> 
> As above, it depends. If you're using Protocol instances, then yes. If not, then no.
> 
> Services are just things which start and stop; they may or may not use objects implementing the transport/factory/protocol pattern.
> 
> 
> 
> I don't know about the nflog file descriptor...
> but the nflog generator interface is non-blocking if used like this:
> 
> Ok. Weird API, but if it works...
> 
> 
> My nflog reader seems to work great.
> 
> If it works for you, and you're using documented Twisted interfaces, then there's probably no need to fiddle with it.
> 
> 
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