Chapter 4 Day 2.md

Quest Chapter 4 Day 2 🆗

1. What does .link() do?

.link() allows a developer to "link" resources in the /storage/ path to the /public/ or /private/ paths so the resource can be publically accessible or viewable in the case of /public/ OR accessible/viewable to whoever the developer wants to give access to /storage/ in the case of /private/.

2. In your own words (no code), explain how we can use resource interfaces to only expose certain things to the /public/ path.

We can use resource interfaces to only expose certain things to the /public/ path by only exposing the fields we want to expose to the pubic and then by linking that resource interface to the /public/ path using .link(). That will restrict that reference to only use the resource interface that we defined and make it secure from any hackers that want to change our info.

3. Deploy a contract that contains a resource that implements a resource interface. Then, do the following:

pub contract SportsCars {

    pub resource interface IDrive {
        pub var auto: String
    }

    pub resource Drive: IDrive {
        pub var auto: String

        pub fun changeAuto(newAuto: String) {
            self.auto = newAuto
        }

        init () {
            self.auto = "Lotus Exige"
        }
    }

    pub fun createDrive(): @Drive {
        return <- create Drive()
    }

}

i. In a transaction, save the resource to storage and link it to the public with the restrictive interface.

import SportsCars from 0x01
transaction () {
prepare(signer: AuthAccount) {

  signer.save(<- SportsCars.createDrive(), to: /storage/MyScenicDriveResource)

  signer.link<&SportsCars.Drive{SportsCars.IDrive}>(/public/MyScenicDriveResource, target: /storage/MyScenicDriveResource)
}

execute {

}
}

ii. Run a script that tries to access a non-exposed field in the resource interface, and see the error pop up.

I ran a transaction instead of a script here, I think there's a typo.

import SportsCars from 0x01
transaction(address: Address) {
  prepare(signer: AuthAccount) {

  }

  execute {
      let publicCapability: Capability<&SportsCars.Drive> = 
          getAccount(address).getCapability<&SportsCars.Drive>(/public/MyScenicDriveResource)

      let driveResource: &SportsCars.Drive = publicCapability.borrow() ?? panic("The capability does not exist or you did not specify the right type when you got the capability.")

      driveResource.changeAuto(newAuto: "Ferrari Enzo")
  }
}

iii. Run the script and access something you CAN read from. Return it from the script.

import SportsCars from 0x01
pub fun main(address: Address): String {
  let publicCapability: Capability<&SportsCars.Drive{SportsCars.IDrive}> =
      getAccount(address).getCapability<&SportsCars.Drive{SportsCars.IDrive}>(/public/MyScenicDriveResource)

  let driveResource: &SportsCars.Drive{SportsCars.IDrive} = publicCapability.borrow() ?? panic("The capability does not exist or you did not specify the right type when you got the capability.")

  return driveResource.auto 
}