Casper Weekly Workshops, 28 Jun 2020

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From YouTube: CasperLabs Weekly Workshop 6/19: Contract Headers

Description

During this workshop, we will introduce how contract headers work.
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A

Okay, it's recording I, don't know how! Well you remember when we talked about zesting contract and that was while ago so today, I want you I want to show you a feature. We call contract headers, and this is a step with it towards being more developer-friendly for writing. Smart contracts and I rewrote my fasting contract to support this feature and.

A

So in the past, or as it is now because this is still a feature on a feature event- we haven't matched it to the main repository, but that's ongoing progress now so so in the past, when you wanted to similar, have functions in your smart contract like.

A

You so many times that you had to parse it by your own and assume that the first argument is the method name and then, based on this decide which actual function you want to call and that that wasn't very good, because that's not something developers should be doing it would be rather than the system gives this to you and that what we did, we focused a lot on. What's the next big thing, we want the improvements on, and that was our. This is to get rid of this and introduce functions function name.

A

So now, when you call the smart contract, you need to specify a method so.

A

Okay, so let's start with.

A

Okay, this method- and this is a testing framework site. So when you want to test contract want to deploy it, and then you can call it, and this is how.

A

How to call the function now, so you have the sender which is an address wrapped around center struct. You have a method string and you have runtime arguments and.

A

This code is the change so now, when you produce what you want to call you, just you don't just say, I want to call a contract under this hash.

A

You also have to say this is the method I want to call, and then everything goes normal normally, so you create a session, and then you use the context to run the session and that's how your contract we get executed and when you specify the method name.

A

When you specify the method name, the host will take during the execution, they have to take the wasn't file and it will take a look.

A

It will try to execute this method, name you provided so in the past there was only one method expected that was called still expected.

A

So it's still expected to call so when you send the worsen file to the network in order to execute one file, the call method is called and but then this method should do the deploy. So it should save the smart contract under under a hat and then it's possible to call it by the hash.

A

So, let's assume that we already have this deployed and I'll show you later how to deploy it, but that, let's assume that this is deployed, and now someone want to can call it by name. So if we put a name in it,.

A

Then the host function, the host environment, let's say we'll call the virtual machine and it will put the wasn't file inside the virtual machine and it will call the method to you specified. That's why every method that you want to specify should be no mangled function, which means the compiler will not change its name inside the world. It wasn't filed.

A

And indeed, if you do this, then the heart will be able to tell virtual machine to call it to call in.

B

A

And then the execution happen.

A

So this way we don't have to specify this method parsing function, and this is this is nice. We also did one more one. More change.

A

Instead of having positional arguments, we changed to the named arguments, which means it's no longer relevant. What's the name of the position of document, we only focus Python names of the first, so you should do runtime get named arc and specify a string in this case. It's admin here. It's just a string, admin and expected and again, if you, when I, call something that's that's not there or something that has the wrong type, then you then the system will handle this for you, you don't have to specify by your own okay.

A

So let's take a look. What happens in the init in the init? We create a vesting contract instance.

A

Just to remind you what what it does.

A

So when you have the my vesting in testing, contract implements vesting trait and those functions are setters and getters for specific time. The types that I use in that trait, which means that every time the vesting trait wants to save or read something from the memory, it will use one those functions, and this is the building with the with the blockchain.

A

So I am able to define all my logic and the plain rest, assuming that those functions are right thinking in a way that those functions are abstract and to remind what the best things you can do is it can in it, which means it's going to set a bunch of bunch of settings.

A

These are cliff timestamp, some at some point point of time. Users should be able to withdraw some amount, and this is amount is cliff amount, and then we have drip duration and drip amount means after after so after the cliff timestamp moment is reached every dripped duration. The user can withdraw additional drip amount.

A

Also, we have a total amount, which is the amount of tokens locked in this in this contract and some admin admin think that allows admin to release tokens after some some period of time of the contract being tossed so situation, where this is the besting contract for the employee.

A

That gets additional bonus every month, but the employee gets leaves the company and the admin should pause. The should pause the system because album can do it and after this time, I mean can release all of the all of remaining tokens.

A

Okay. So what we have here is available amount is not public, so we withdraw. This should be called by the recipient. So, in the scenario I'll talk about, that would be the employee, polka, polka and unpause should be called by admin. That's pausing to contract.

A

Admin release is this admin releasing function? I talked so these are the functions here and.

A

Let's come back here, so the semantics here is I, create the vesting contract and I can call a function on it. So in this case, that's vault in it. So here I'm gathering this arguments, I do set admin account and set recipient account. Those functions.

A

These are just set safe value under a key which is admin or recipient, and then I can use it in verify. Admin account and verify recipient account, which is this get the admin account. That was calling the contract and compare and if it's not the same thing, return error simple check, but that allows me to to guard functions so, for example, post someone will call pause.

A

Verify admin account will show up, it will be executed and, if start an admin tent will revert with error and again we create a vault of vault can do something in this case. Pause handle the result and pretty much that's it. This is the this is how the contract can be, can be done.

A

Okay, to achieve that, the system should know what kind of what are those functions available for the user to code and not only the functions, but we have a bunch of meta data around those functions like arguments so the list of arguments so, for example, when the get named arc is called with something like in this case that would be string amount.

A

Then it's good for the contract to know that this is allowed allowed argument. That's one thing, and the second thing is that it should have a specific type, because we don't want the contract to accept arguments that are random or that could be anything we want to specify what we want. So that's the one one thing we want to do and how we do it so.

A

In the lip, so in the code I have contract deploy, so this is going to be executed as the admin akka as the account, and it has the accounts accounts context.

A

Keep in mind that for later so right now, if you want to deploy the contract, you don't simply deploy the contract you want to. You need to actually create a package, we call contract package and then you can be adding multiple versions of the contract contracts to this package. So this package will be your starting point for managing contracts. So that's that's for the updates reason.

B

A

If you create a new pack contract package, you'll get two things: one is the contract package hash, which is identifier the package, and here you get something should be called contract package.

A

Access- and this is a token I- don't do anything with it because I didn't need it for now, but this talk and allows you to do all of the operations on top of the package, which means which are like adding new versions of the contracts, removing old versions of the contracts, editing groups and I'll gonna talk tell you about groups in the month, so this is the master key to the to the system to the contract, and if you want to be an admin, you need to hold this there's an option to pass this into the contract itself, so the contract could manage itself.

A

That would be interesting to see.

A

Okay, so what I do now? What I do here contract package has I have the contract package has I, can manage this contract package hash, because my access Europe is still in scope, but if I, don't I, don't save it anywhere. So after this code is executed, then the admin will no longer have the access, but I simply don't need it that way. I haven't done anything with it and okay. Next thing is a group start which create contract user group.

A

That's a that's the function to add a group create a few you rats and we turn those URIs okay. So the first argument is the contract packet hash. Then, because this is the contract package we work with and we want to add group into then I specify a string need group. This is, is it so that's just string name of the group in your group, then I specify number of new Europe's I want to create, and then, if I want to other existing curious I can using bit reset.

A

So this is the Europe, as you might remember, us is the pointer in this is in our system, but also it is treated as a access token. So, if you have Europe, then the contract could check. If you have this Europe and let you in you can do about it. For example, you can have a Europe that points on the and the purse that holds tokens. So if you have it, you can access it. If you don't, you cannot so in this case after this call is done.

A

This package has should have a new group, that's called init group, and then each group should have one your.

A

F1 you ref and what I do is I extract. This you Ref first I call unwrap or Ravel, because I'm getting back the result result of a factor of Europe's, so I do pop to extract the face. You read: I only have one so that's all I need and that also returns result.

A

So I can do unwrapped everywhere. I have to do an Rapid River again, but again I, don't use it.

A

It's here on me like I use it in the I will gonna use this in this call, but I will not use it later, because this is the you ref and the group. That's that why I called in it group, because this, the I'm, the goal of this group is to set access rights to the init function and the init function in my example needs to be called only once during this call. So that's the constructor, so you cannot call the constructor multiple times shouldn't be so I created this group.

A

So later, I can call the I can add access rights to call in it only to this group and then call the in it and then revoke the access.

A

I'll remove this in it access URF from this group, but we'll share it. I'll show you life so for now. Just keep in mind that we have a group that we call in each group and we have the access token for it. So in it access, Europe, okay, then I need to define entry points.

A

There is a trait called a struct entry points. That's the wrapper for multiple entry point. So entry points, add entry point and you specify new entry point. First, you have to set n a simple string.

A

Then you have to specify a list of types.

A

List of arguments, and so for example, first argument is here an admin. This is string and you specify CL type so program for here below this. You 5 1 2, it's a simple sale type, but you can pass a more complex types and every every type that can be accepted by the system should implement a trade called CL typed, the has CL type function and it will return some sort of CL type combination, so that could be like. Maybe that could be this here.

A

We have a list fix this of 32 elements of bytes, and so we don't have to type it manually. We can reuse this and that says, accept an argument called admin with this type, all right. So that's the list of arguments and then I specify the return type for now. Here, every type every function returns nothing.

A

This is unit. And then then you specify entry point access, and here it so here it can be groups or, as you see below it can be public. If it's public, then everyone can access this method. If it groups, then only their group can so here we inserted in.

B

A

That's a proper on top of string, so only you reps, that are only accounts that helps you reps, that are in the in each group. Can access this and in this call, because we just created it, we still have it in the scope, so we can access it here during this deploy function, execution, okay, so later, I specify I, also specify entry point type, and this is something I'm really excited about, because that solves a lot of problems in the past.

A

When you wanted to call and implement and call smart contract, you had to first call the function as a account. So you have you need to have a type context of the account and then the account should call the contract, because only this way you could gain the contracts own context, so some time ago requested that it was very helpful just to be able to call the contracts by its own and directly.

A

So now, it's possible to specify whether this entry point should be treated as a smart contract or session code session code is the code that should be that will be executed as the as the session code. As they accounting so I could also type session.

B

A

But in this example, every entry point is a contract so because I'm writing smart contract here. Okay, so that's all you know: let's go a bit further three documents, so we want. We want to know some arguments here. We expect this to be passed to the along with the Watson file, so we extract admin. We extract recipient and the best in config and the best in config.

A

That was in contact.

A

So that's just the best in conflict right, that's composed out of multiple multiple arguments that specify cranked up quick amount and and others. So this this part is reading arguments and what next repair contractors so again as I did in the past, so it's required to pass the purse with tokens to the contract. How do you do it? You create you, take the main parts of the account that has a positive balance.

A

You create a new purse empty purse. You do the transfer from the main purse to the new purse and put it as a create a b-tree map and put it there under under a name first name, and this way you can. You have fasting keys, that.

A

That are the name keys for the contract and if you pass it so you pass it here, the contract will have those name please, and this is where the contract gets actually deployed and so storage at contract version, and that will add the first version of our contract to the contract package so yeah. So you need to put package hash entry points of the list of we created and the vesting keys and the second list we created this way gives you contract hash.

A

Then you have to save save it, to the scope, to the name keys of the account, so people can or you can use it I.

A

First, you can save the best in contract, but also for the regions of smart free testing. Testing frame would not be able to exactly extract it from from this one. The half of the contract is good to wrap it under a UF and store it under a different key. So that will give you the hash and that will give you the instance of the contract but will be used in the testing framework and the end of this method is actually calling the in it. And so you specify you do a runtime call contract.

A

Let's fight the hash, specify the method and specify arguments, and here we introduced runtime arcs macro, that's defined. As you see it's a very nice, so you specify the key and the value, and this should be all of the arguments required by in it. So dislike admin, recipient, cliffs, drip total on this duration, and this is the same list as you saw here, and then the function ends and two elements.

A

That was so two elements are not safe, so first, this contract package, access token that that should be here is not saved and in it, access Europe for the faulty group is also not site, so the init method will not cannot be accessed again.

A

A

In the contract, I also have an error so before the lip implements, the call utils.

A

Is a generic getter and setter for the keys and transfer clx and the vesting is the implementation of the vesting trait.

A

So, as you can see the amount of code you need to write went down, so it's left last code and I think it's more readable now and with that. I would like to end this part. And here, if you have any questions.

A

So there are no questions, then I hope I explained it good way.

A

This picture will be available soon on our tablet. So if you want to use it.

A

I use it directly from the branch so contract, ID and contract, catalog, contract and Castrol lapse. Types comes from, the branch features contract headers soon it will be deaf and and then it will be deployed and you can use it by version.

A

So that when you undo this is on the branch so I'll send you.

A

The link to it so you can play with it.

A

That's also under review, but some it will be merged.

A

Okay, this is it if you wanna play with this, is to copy the link and remember to use this branch for now.

A

Okay, so thank you very much for showing up and I wish you a good weekend.

A

Thank you very much so if you have any questions, feel free to to reach out to me on slack and.

B

Also soon we will release the updated documentation. We are now working to include contract headers in our places that they used to be that they should be so we'll also inform you when this will be available.

A

Yeah. Thank you very much.

B

So I think we can stop the recording.