Is it possible to write a peer-to-peer chat application in Python?
I am thinking of this from a hobbyist project point-of-view. Can two machines connect to each other directly without involving a server? I have always wondered this, but never actually seen it implemented anywhere so I am thinking there must be a catch somewhere.
PS: I intend to learn Twisted, so if that is involved, it would be an added advantage!
Yes. You can do this pretty easily with Twisted. Just have one of the peers act like a server and the other one act like a client. In fact, the twisted tutorial will get you most of the way there.
The only problem you're likely to run into is firewalls. Most people run their home machines behind SNAT routers, which make it tougher to connect directly to them from outside. You can get around it with port forwarding though.
Yes, each computer (as long as their on the same network) can establish a server instance with inbound and outbound POST/GET.
I think i am way too late in putting my two bits here, i accidentally stumbled upon here as i was also searching on similar lines. I think you can do this fairly easily using just sockets only, however as mentioned above one of the machines would have to act like a server, to whome the other will connect.
I am not familiar with twisted, but i did achieved this using just sockets. But yes even i am curious to know how would you achieve peer2peer chat communication if there are multiple clients connected to a server. Creating a chat room kind of app is easy but i am having hard time in thinking how to handle peer to peer connections.
Related
I want to make a peer-to-peer program in Python, but I keep running into the same issue of how to get them to communicate. I always run into the same answers.
Use a central server
UDP hole punching, or
use UPnP to tell the router to open a port.
The second and third I haven't gotten to work despite hours of trying. Multiple libraries simply didn't work, and for the second I have no rendezvous server. For the first, I have tried to use the freenode IRC server as the central server, but it is quite unreliable and complicated, and just doesn't feel like a good solution.
Is there any other way? Or solutions to the above problems?
I'm writing a websocket connection between a chrome plugin and a desktop application that exclusively talk to each other locally. I know that you can't have two sockets listening on the same port (is this true for all ports?)
Port clashes won't happen for the majority of my users, but the application will run on a few thousand computers; I think I can reasonably expect there to be clashes in rare situations, where another application already occupies the port.
How do bigger applications deal with this potential issue? I'm fairly unfamiliar with networking and (web)socket programming in general.
I guess there are a few non-technical workarounds like these:
Log the issue well, and let support deal with it
Let the user configure a port
But I'd rather have a sound technical way to deal with it, if possible. I could come up with some algorithm that tries a few preconfigured ports, but I expect that this is a fairly well known problem in the industry, and am hoping to learn what the consensus is for this problem.
The question is primarily technology agnostic, but if it matters, my stack is python with this websockets library on the desktop side, and of course JavaScript on the client side.
I don't think there's a reason to overthink it. A list of seemingly unoccupied fallback ports and finally a prompt to specify a port should be fine. If both parties are capable of HDD IO (I don't know how much can a chrome plugin can do), then it's even easier for the plugin and the app to meet.
For two apps on a same host, you may also add an additional loopback interface. Example.
If to speak about large networks, there's a class of so-called service discovery protocols that may help dealing with this kind of issue. Basically they are IP- or UDP-based multicast protocols that advertise different services across the network. Usually these protocols have a standardized port for communications, so it is unlikely to get occupied by another app. Examples are DHCP, Bonjour.
However, dealing with port conflicts are not their primary function. In large networks machines should be under some sort of control and should not have lots of apps grabbing random ports. If a conflict happens with third party apps, the ideal solution is to look for a setting that allows to set ports manually.
Well I don't know how bigger applications actually do it but a way could be to try till you find a free port?
found_port = False
ports = [port1, port2, port3 ....]
for port in ports
try:
mySocket.bind ( ( ip_address, port ) )
found_port = True
except:
pass
if found_port:
break
I'm working on a project to expose a set of methods from various client machines to a server for the purpose of information gathering and automation. I'm using Python at the moment, and SimpleXMLRPCServer seems to work great on a local network, where I know the addresses of the client machines, and there's no NAT or firewall.
The problem is that the client/server model is backwards for what I want to do. Rather than have an RPC server running on the client machine, exposing a service to the software client, I'd like to have a server listening for connections from clients, which connect and expose the service to the server.
I'd thought about tunneling, remote port forwarding with SSH, or a VPN, but those options don't scale well, and introduce more overhead and complexity than I'd like.
I'm thinking I could write a server and client to reverse the model, but I don't want to reinvent the wheel if it already exists. It seems to me that this would be a common enough problem that there would be a solution for it already.
I'm also just cutting my teeth on Python and networked services, so it's possible I'm asking the wrong question entirely.
What you want is probably WAMP routed RPC.
It seems to address your issue and it's very convenient once you get used to it.
The idea is to put the WAMP router (let's say) in the cloud, and both RPC caller and RPC callee are clients with outbound connections to the router.
I was also using VPN for connecting IoT devices together through the internet, but switching to this router model really simplified things up and it scales pretty well.
By the way WAMP is implemented in different languages, including Python.
Maybe Pyro can be of use? It allows for many forms of distributed computing in Python. You are not very clear in your requirements so it is hard to say if this might work for you, but I advise you to have a look at the documentation or the many examples of Pyro and see if there's something that matches what you want to do.
Pyro abstracts most of the networking intricacy away, you simply invoke a method on a (remote) python object.
I want to write a Python script that will check the users local network for other instances of the script currently running.
For the purposes of this question, let's say that I'm writing an application that runs solely via the command line, and will just update the screen when another instance of the application is "found" on the local network. Sample output below:
$ python question.py
Thanks for running ThisApp! You are 192.168.1.101.
Found 192.168.1.102 running this application.
Found 192.168.1.104 running this application.
What libraries/projects exist to help facilitate something like this?
One of the ways to do this would be the Application under question is broadcasting UDP packets and your application is receiving that from different nodes and then displaying it. Twisted Networking Framework provides facilities for doing such a job. The documentation provides some simple examples too.
Well, you could write something using the socket module. You would have to have two programs though, a server on the users local computer, and then a client program that would interface with the server. The server would also use the select module to listen for multiple connections. You would then have a client program that sends something to the server when it is run, or whenever you want it to. The server could then print out which connections it is maintaining, including the details such as IP address.
This is documented extremely well at this link, more so than you need but it will explain it to you as it did to me. http://ilab.cs.byu.edu/python/
You can try broadcast UDP, I found some example here: http://vizible.wordpress.com/2009/01/31/python-broadcast-udp/
You can have a server-based solution: a central server where clients register themselves, and query for other clients being registered. A server framework like Twisted can help here.
In a peer-to-peer setting, push technologies like UDP broadcasts can be used, where each client is putting out a heartbeat packet ever so often on the network, for others to receive. Basic modules like socket would help with that.
Alternatively, you could go for a pull approach, where the interesting peer would need to discover the others actively. This is probably the least straight-forward. For one, you need to scan the network, i.e. find out which IPs belong to the local network and go through them. Then you would need to contact each IP in turn. If your program opens a TCP port, you could try to connect to this and find out your program is running there. If you want your program to be completely ignorant of these queries, you might need to open an ssh connection to the remote IP and scan the process list for your program. All this might involve various modules and libraries. One you might want to look at is execnet.
I have a program which will be running on multiple devices on a network. These programs will need to send data between each other - to specified devices (not all devices).
server = server.Server('192.168.1.10')
server.identify('device1')
server.send('device2', 'this will be pickled and sent to device2')
That's some basic example code for what I need to do. Of course, it will also need to receive.
I was looking at building my own simple message passing server using Twisted when someone pointed me in the direction of MPI. I've never looked into the MPI protocol before and that website gives rather vague examples.
Is MPI a good approach? Are there better alternatives?
MPI is really good at doing the communications for running a tightly-coupled program accross several or many machines in a cluster. If you're running very loosely coupled programs - only interacting occasionally - or the machines are more distributed than within a cluster, like scattered around a LAN - then MPI is probably not what you're looking for.
There are several Open Source message brokers that already handle this kind of stuff for you, and come with a full API ready to use.
You should take a look at:
ActiveMQ which has a Python Stomp client.
RabbitMQ has a Python client too - see Building RabbitMQ apps using Python.
You could build it yourself, but that would be like reinventing the wheel (and on a side-note: I actually only realised I was half-way building a message broker before I started looking at existing solutions - building one takes a lot of work).
Consider using something like ZeroMQ. It supports the most useful messaging idioms - push/pull, publish/subscribe and so on, and although it's not 100% clear from your question which one you need, I'm pretty sure you will find the answer there.
They have a great user guide here, and the Python bindings are well-developed and supported. Some code samples are here.
You can implement MPI functions in order to create a communication between different codes. In this case the server program should public "MPI ports" with differents IDs. Clients should look for this ports and try to connect to them. Only server can accept each communication. Once the communication is stablished, codes can exchange data between them.
Another posibility is to run different programs in Multiple Instruction MPI option. In this case all programs are executed at the same time, and there is not necessity to create port communicators. After they are executed, you can create particular communicators between groups of programms you select.
Please tell me what kind of method you need and I can provide c code to implement the functions.