This week was quite busy, despite not having committed any code, I had to do a lot of research with regards to broadcasting the Freeseer server across networks. Right now, it is trivial to set up our REST api endpoint so that anyone on our network who knows the IP address of the computer running the server, as well as the port number the server is broadcasting over, they can send api requests from some client. For example, if the Freeseer host machine has an local ip address of 192.168.0.11, and the Freeseer server is running on port 5000, any other computer connected to that network should be able to send api requests to that box with "curl -i -X GET http://192.168.0.11:5000/<endpoint>".
This is only one part of the puzzle however. We want Freeseer servers and clients to be able to be set up and run by people without too much knowledge of ip addresses and networking. What would be ideal is if we could configure things so that Freeseer clients were aware of all instances of Freeseer servers running on a network merely by being connected to it. Even better if we can do this without any configuration necessary. We were aware of at least one way to accomplish this: Zerconf (Zero-configuration networking), implemented by Bonjour on Mac and Windows, and Avahi on Linux. In the most basic terms, Zeroconf is what allows your iTunes to be aware of all iTunes libraries shared on your network auto-magically. So this week I spent researching and prototyping existing implementations of Zeroconf on Python to determine which one was the best to be used by Freeseer.
We had a few critieria for choosing which would be the best:
- Code must work well.
- Must work without any configuration necessary on the part of the user.
- Should refrain from making calls to shell.
- Should be cross platform compatible.
- Should be available through pip.
Basically all we needed was some solution that would broadcast an IP address, a port number, and some other information (name and description of the Freeseer server, for example).
Avahi
Avahi worked really well and painlessly. The only problem is that Avahi is only available for linux, and while headless Freeseer servers are probably only going to be used on linux boxes, we want to run clients on Windows boxes. Therefore, we would need a separate implementation for Windows boxes, and we should be able to accomplish this with only one library.
pybonjour
This library is cross platform, unlike the Avahi solution. I didn't try to make a prototype solution because the code is apparently is very old and unmaintained (last commit 2009), and not particularly well designed according to mtomwing.
mtomwing talked about the possibility of forking and improving.
python-zeroconf
This library actually manages to work fairly well without any external dependencies (relies entirely on socket programming). It caused me a lot of headaches this weekend because Avahi was able to run on a host-only network and python-zeroconf could only work in bridge mode. I have the feeling that even though I managed to get it to work, my gut feeling is that it may only play well with very specific types of network configurations, basically home networks. For example, it makes a call to ip address '4.2.2.1' to get an ip address to bind to. If some network had no DNS server, there is no route to that host and python-zeroconf would falls back to the host IP, (on debian boxes, the host ip is always '127.0.1.1', which useless for us). Avahi has worked extremely well in all the network configurations I've used thus far, including those with no DNS.
I think, the best use for this library would be to use it for clients that don't run avahi. It is just a little too low-level and lacks the robustness of avahi or bonjour to be used for servers.
zeroconf (python module)
This module would work cross platform (ostensibly from looking at the code, I don't have a Windows box to test against). My prototype worked very well. The two biggest issues is that it relies on a number of calls to shell, and it is not installable from pip, meaning we'd have to bring the whole module into our code base.
non-Zeroconf solutions (multicasting, ssdp)
When considering all the problems these three solutions had we tried looking in a different direction and to move away from Zeroconf, and look for some other solution. Without getting into too many details, they all worked well, but they were all held back by the fact that you needed to specify the interface you wished to broadcast over, which infringes on our first 'must' which is that it must be runnable without dealing with ip addresses and interfaces.
I tried both multicast with socket programming and ssdp (simple service discovery platform) with a small python module, and there was no way that they would be without zero configuration unless we went way beyond the scope of our current project.
Winner? Avahi + python-zeroconf?
So, essentially all of them have their own positives and heavy drawbacks. I think what will probably happen is we use avahi bindings to create our headless server, and avahi/python-zeroconf for our clients? Perhaps we may just need to fork and refactor pybonjour for our own use.
NEXT WEEK:
Hopefully I will be in the spot where I can put together an implementation this week. I have to discuss where we will go next with the Freeseer mentors. Until next week!
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