Building a state channel application by Tom Close (Devcon4)

hi so my name's tom close i am the founder of magma and we are a state channel research and development company and today as the title suggests i am going to be talking about building a state channel application so in fact an alternative title of this talk could actually be this we built a state up channel application and we found it really hard it turns out that this is a pretty accurate description of the situation so this talk is going to be partly show and tell it's going to be partly like group therapy and partly a call for help so before I go into that let me tell you a little bit more about who we are because maybe some of this a little bit relevant to why we found it hard but maybe some of it isn't and I'll talk about that later too so we are a team of six researchers and developers so we're all pretty experienced I guess we've got like three or four people who've got like more than five five years experience developing or insecurity half our team have PhDs but we're all new to the blockchain so it's this time last year that I started working the blockchain everyone else is more recent the blockchain than I am and more recent to aetherium obviously so let me now talk a little bit this show-n-tell part so today we have launched this application where you can play rock-paper-scissors in state channel I can see by the like dumbstruck silence that everyone is like utterly amazed by that and to be honest rock-paper-scissors is not the most exciting game let me just quickly take you through it how it works I'm not going to do a live demo but I do have a little video so here somebody is logging into the app they're putting in their name and they're gonna eight a challenge for someone else to join so they're gonna say we're gonna play rock-paper-scissors and we're gonna play for this match each round they put that challenge up on the next left side we've got player to George he's about to login I mean he's gonna accept the first player's challenge first player confirms and then we get into this state where your channel wallet comes out and your channel wallet is something that any state channel application will need if you're exchanging States with someone those states are as almost as important as as real money so like if you lose your state's you can use everything so you need this wallet thing any state channel network will need some sort of channel wallet to manage the states that are being sent across so here you can see they are depositing into an Unchained contract so they're both locking some funds up on chain and those are the funds that we're going to play for in this game so in a moment both those transactions would have gone through and they can return to the game so you can see we've got this state of the game here they've each got five five each as it were and now they're going to play rock-paper-scissors so behind the scenes here this app is implementing a state channel protocol so it is signing States and exchanging those states between the users and I'll talk a little bit more about that how we're actually thinking about those applications so this is built on top of a framework called force move I'll talk a little bit more about how this actually works with force move later we're just going to go through to the end of the game I think George is on a winning streak it's not going to take much longer hopefully yeah he's getting there so yeah at the end of the game one of the things about this sort of state general application is we're playing one game of rock-paper-scissors we needed one on chain deposit the beginning and what we'll see in a minute is another on chain deposit at the end this is something that when we have like virtual channels in state channel networks you'll be able to get away with one deposit at the beginning of the month and then you'll be able to play multiple games like this opening these channels and closing them off chain so that's like an important area of future research which we'll probably be looking at in the future anyway so this is the demo this is the example app that we've put together so you're excited at the beginning you're probably even more overwhelmed now you've seen it in action I'm seeing a lot of stunned faces clearly a winner so what was hard about this so I guess part of the problems where the standard blockchain problems that everyone experiences when they're new to the blockchain and when they're trying to develop on the blockchain and I'm not gonna really talk about that aspect of things so much because that's common to like all the projects so the problems about setting up your app to work with typescript and integrate with truffle or like whichever other developer framework you're using I'm not going to really touch on that I'm not going to really touch on like the problems with meta masks when you're developing and having to flick the network back and forwards and taking a while to realize that stuff and like I'm not going to definitely are going to talk about the eight weeks we spent debugging solidity by omitting events before we realized there was a solidity debugger so a lot of that is just like part and parcel of developing on aetherium we're interested in learning from other people in the room how to better do that we've learnt a lot of this stuff by trial and error but like they're probably still a load of stuff we don't know so one of the things I wanted to spend the last few minutes of this talk talking about is what are the essential things the things essential to state channels that we found difficult and I guess the way I would look at this I'm going to focus on this one problem a hard thing about state channels is state and managing state so what mean by that so we were working we're building this app on top of the force move framework and the force move framework has a very simple way of managing state and thinking about the state of your state channel and your state transitions so this is a representation of rock-paper-scissors in the force move framework you have four different states if you're trying to program this as a developer building on top of the framework you're responsible for writing a single library contract with a valid transition function which defines these states and the valid transitions between them so in the face of that that seems pretty simple and it's pretty conceptually simple to think about what's happening actually in the state channel and what's happening on the chain and that's one of the nice things about what we are working with it's like one of the simpler state channels frameworks to work with but in terms of your app there are like many many more states so we actually came to like interacting with those four states force four types of messages that we're sending back and forth we ended up with this diagram and this doesn't even include the wallet stuff that we showed all of those wallet states have been collapsed into like dates to the top so I guess why is this this complicated and I guess if you think about it like back in the very early days of the web you had like a user who was interacting with a server and that was like pretty simple like the state was the state that was stored on the server there's one way of interacting with it you put it back on the server there's one source of truth now in recent years things have got a bit more complicated so you now have front-end JavaScript apps so you've got like the state your local state and then you've got the updated state on the server and you're interacting with your local state and maybe somebody else is interacting with the server and you like can receive updates and then the blockchain adds an extra dimension into that so the blockchain is like another player and that maybe you've replaced your server with the blockchain maybe you've got a server and you've got a blockchain we've now got multiple places these updates can come from and state channels add yet another place where those dates can come from and in a state channel your whole logic is around I'm receiving these states from my counterparty and therefore I can like reason about what's happening on chain and that just gets very complicated to think about and stuff so like we're now thinking about this thinking about how we can make it simpler thinking about how we can take this thing which seems in some way inherently complex and work with it better think you have better ways to manage this complexity in the applications so final plug so this the code you saw today the demonstration it is currently live on Rob stone so you can visit it at magno calm slash RPS in case you don't find any friends there we have some bots that you can play against they get progressively harder the final bot is the psychic bot and if you can beat the psychic bot we want to hear from you you'll get like I'll give you a Twitter shout-out prizes prizes are limited but you'll get like small fleeting honor in terms of a magnet Twitter shout-out I think I'm out of time though thanks for listening you can follow us at magma HQ on Twitter