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bounty dApp - Design Patterns & Decisions

Upgradeability

In this project we separate the data from the logic. The Parent contract is responsible for managing Organisation contracts that are upgradeable by using permanent storage from EntryStorage contract.

By following this pattern it is possible to upgrade the Organisation functionality without having the expenses of also to re-deploy the storage.

It is also created an interface (OrganisationInterface) to decouple inter contract communication and also avoid the Parent to be re-deployed each time there is an upgrade.

This was made possible with this articles:

Fail Early and Fail Loud

Conditions are checked as early as possible (e.g. with require()) and throw exceptions if conditions are not met. These pattern reduce unnecessary code execution in the event that an exception will be thrown.

Restricting Access

Only variables or functions are kept public to only those that require it. It is used function modifiers to manage function restrictions and make them more readable.

By using Ownable from OpenZeppelin library limits the access to certain function to only the owner/creator of the contract.

Mortal

In order to destroy a contract, it is used the destroyAndSend(transferAddress) function in Destructible from OpenZeppelin library. This function receives one parameter (transferAddress) corresponding to the address that will receive all the funds that the contract currently holds.

Only owner/creator of the contract can perform this task.

Pull over Push Payments

In this project if your Submission is accepted by the Entry owner a bounty is made available to be withdrawn by the submission owner, by calling the claimBounty(entryId).

This design pattern protects against re-entrancy and denial of service attacks.

Circuit Breaker

This design pattern allow a contract functionality to be stopped. This would be desirable in situations where there is a live contract where a bug has been detected. Freezing the contract would be beneficial for reducing harm before a fix can be implemented.

In this project we can stop the following functionality:

  • Creation of new entries;
  • Creation of new submissions;
  • Accept submissions;
  • Claim new bounties.

State Machine

In this project the EntryStorage acts as a state machine. An Entry can have differents states:

enum State { Open, Submitted, Done, Canceled }

With the use of function modifiers, different functionalities are made available depending on the state of the Entry (e.g. an entry with Submitted state cannot be canceled).