Smart Contract Fee Pool is a mechanism that allows users of a contract-based app to use contract calls at the expense of the pool balance that is replenished by someone else. In one case, it could be the owner of the contract and the app itself. This mechanism enables to minimize the threshold for new users running the app, allowing to eliminate the stage when in order to use the contract, the user must first make sure of a non-zero balance on one of the assets by which the commission fee can be paid. In particular, this problem stands out the most when using ERC20 tokens. In this case in order to transfer a token, the user needs to have an additional balance.
By using this operation, any network user has the ability to replenish the contract balance pool. This operation is irreversible - the balance transferred to this contract pool can be spent only when calling the contract. It is impossible to recover (withdraw) the balance from the pool.
A contract pool can only be replenished in Echo.
If there is a non-zero balance on the pool, the get_required_fees
request will return an object having the fee and user fee.
Example1:
If the commission fee is 0.1 echo and the pool holds 0.1 echo
Object1: fee = 0.1 echo, user fee = 0 echo.
Example2:
If the commission fee is 1 echo and the pool holds 0.98 echo
Object2: fee = 1 echo, user fee = 0.02 echo.
The contract has a whitelist and a blacklist. These are lists of accounts edited by the owner of the contract. In the case when at least one account has been added to the whitelist, sending transactions through the fee pool will be available only to the accounts added to the whitelist. If the whitelist is empty, any network account can use the contract's fee pool.
Accounts added to the blacklist cannot use this contract for free, even if there is a non-zero balance on the fee pool.
The contract_whitelist_operation allows to add an account to one of these lists, or exclude it from both of them. Only the owner of the contract (the account that created it) has access to the contract_whitelist_operation.
The get_contract_pool_whitelist method returns both the whitelist and blacklist for the specified contract.
The get_contract_pool_balance method returns the current fee pool balance for the specified contract.