Smart Contract Demonstration Part-2

Aptos Smart Contract Tutorial – Claim and Withdraw Token Functions

In this video, we’ll continue building our Aptos smart contract by implementing two essential entry functions: claim tokens and withdraw tokens.

1. Claim Tokens Function

This function allows users to claim their allocated tokens from the Vault.

Function Declaration

public entry fun claim_tokens(account: &signer, admin_address: address)

acquires Vault, VaultSignerCapability

Key Steps:

• Check Allocation: Verify that the account address exists in the Vault’s allocation table. If not, return a NoAllocation error.
• Remove Allocation: Remove the allocation from the table. The remove method returns the allocated amount.
• Validate Balance: Ensure the Vault’s total balance is greater than or equal to the claimed amount. If not, return InsufficientBalance.
• Update Vault Records:
• Decrease total_allocated by the claimed amount.
• Decrease total_balance accordingly.
• Create Vault Signer:
• Retrieve signer capability from the admin address.
• Use this to create a signer for the Vault.
• Ensure Account Registration:
• Check if the recipient account is registered to receive Aptos coins.
• If not, register it.
• Transfer Tokens:
• Transfer the claimed tokens using the Vault signer.
• Emit Event:
• Emit AllocationClaimedEvent with the account address and amount.

2. Withdraw Tokens Function

This function enables the admin to withdraw unallocated tokens from the Vault.

Function Declaration

public entry fun withdraw_tokens(admin: &signer, amount: u64)

acquires Vault, VaultSignerCapability

Key Steps:

• Admin Verification:
• Retrieve the Vault and check if the signer matches the stored admin address.
• If not, return NotAdmin.
• Calculate Available Balance:
• available_balance = total_balance - total_allocated
• Only this amount is withdrawable by the admin.
• Check Withdrawable Amount:
• Ensure the requested amount does not exceed the available_balance.
• If it does, return InsufficientBalance.
• Create Vault Signer:
• Use the signer capability from the admin to create the Vault signer.
• Transfer Tokens:
• Transfer the specified amount from the Vault to the admin’s address.
• Emit Event:
• Emit a WithdrawEvent recording the withdrawal.

Summary

In both functions, the process follows a clear pattern:

1. Retrieve the Vault.
2. Validate permissions and conditions.
3. Update Vault state (balances and allocations).
4. Transfer coins using the Vault signer.
5. Emit relevant events.

This structure ensures consistency and security in handling token transfers.