Superfluid Host Overview

Superfluid host contract (Superfluid.sol) is the central contract that provides the following functionalities in the Superfluid Framework:

Super Agreement

Key features:

• Allow new agreement class to be whitelisted.
• callAgreement (contextless + contextual).
• IAgreementFramework:
  • for callbacks: callAppBeforeCallback, callAppAfterCallback, appCallbackPush, appCallbackPop
  • ctxUseAllowance: for app credit.
  • jailApp: for jail rules.

Design Points:

• Agreement Whitelisting:

  • No choice.

• Polymorphic agreement support:

  • No polymorphic approach: always add new entry functions for new agreement in host contract.
    • Pros: avoid duck tapes (hence type-safe)
    • Cons: more boiler plate.
  • callAgreement: duck tape "polymorphic" solution.
    • Pros: extremely flexible.
    • Cons: type-unsafe, may have security implications when handling calldata.
  • Better approach, e.g. "spec-haskell" type class, define AgreementOperation instances.
    • Pros: CORRECT WAY OF DOING THINGS.
    • Cons: not supported by dumb languages.

• App Jail:

  • Main objective: make sure that agreement is always destructible.
  • Zero tolerance jail:fdd
    • assuming hostile app,
    • being over protective to users so that they don't continue to interact with the callbacks.

Super App

Key Features:

• App Registry

  • Whitelisting modes:
    • registerAppWithKey
    • registerAppByFactory
    • [TODO] whitelistedDeployerWithExpirationDate

• Composability:

  • App Level
  • Callbacks
  • App Credit

• Ctx: transactional secure heap-memory in EVM

Design Points:

• App Registry:

  • whitelisting: to be removed as soon as we feel fit.

• Composability:

  • State Sync: Callbacks vs Async
  • App Credit:
    • objective: zero balance super app requirement for reasonable cases.
    • benchmark case: 1to1 flow forwarding.
  • App Level:
    • 1-level ~= global re-entrance protection

Extra Notes

• function overload: use or not use?
• function pointer: worth exploring a bit.
• more usage of user types: worth exploring in the future.
• generics: let's wait and see.