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Binding

Binding is an important process in Aspect-based development. An Aspect can only be triggered at certain join points when it is bound to a specific smart contract. EoA can also bind with Aspect, Aspect can provide customized transaction verification process for EoA.

Steps​

Binding

  1. Initiating Binding: The account owner initiates the binding process by signing a binding transaction using their Externally Owned Account (EOA).
  2. Contract Ownership Verification (Only required for contract accounts): The Aspect Core system contract invokes the isOwner(address) returns (bool) method of the smart contract to verify the sender's address. If the validation fails (e.g., due to an unimplemented validation method or address verification failure), the binding transaction will be reverted.
  3. Aspect Allowance Check: Upon successful contract ownership verification, the onContractBinding(address) bool method of the given Aspect is called. This checks if the current smart contract can bind with the given Aspect. If this validation fails, the transaction will be reverted.
  4. Finalizing Binding: If all checks pass, the Aspect Core system contract saves the relationship in the global state. Subsequently, the Aspect will be triggered at the designated join points when the smart contract is invoked.
note

The binding relationship can only be established when both the given version of the Aspect and the smart contract are deployed. You cannot bind with a non-existent Aspect or smart contract.

Contract Ownership Verification​

To support binding with an Aspect, the smart contract must implement the isOwner(address) returns (bool) method. This method is essential for verifying the ownership of the smart contract. If the method fails to invoke or returns false, the binding transaction will not succeed. Implementing custom logic in this method allows for more complex ownership verification, such as multi-signature verification.

Contract Address Validation​

Aspects have the ability to reject binding from certain contracts. The onContractBinding(address) bool hook is invoked when a smart contract attempts to bind with the Aspect. The binding transaction will fail if this method returns false or is not implemented. To restrict your Aspect to certain contracts, you can implement a whitelist check in this method. Alternatively, for public accessibility, simply return true.

Priority​

The priority in a binding request is an unsigned 8-bit integer. It determines the order of Aspect execution, with the Aspect having the lowest priority number being executed first. If multiple Aspects have the same priority, the one with the earliest binding time is executed first.

Aspect Execution Order Diagram

Aspect Number Limitations​

The maximum number of Aspects that an account can bind is 255, but this differs on the Aspect type. The special case here is the transaction verifier Aspect, if you are binding such Aspect for a Contract Account, you can only bind one Aspect per account.