Building a Reliable Crypto Deposit Monitor: Finality, Idempotency, and Spendable Balance Checks

A reliable crypto deposit monitor must distinguish between the blockchain's processing state and the exchange's accounting state. A two-layer settlement model is recommended, with one layer tracking the blockchain lifecycle and the other tracking the exchange's credit lifecycle. These two layers should be kept separate to avoid incorrectly treating blockchain observations as proof of account availability.

When monitoring TRC-20 transfers on the TRON network, it's crucial to verify the transaction status through solidified receipts rather than relying solely on the initial broadcast response. This ensures that the transaction has been successfully executed and included in the final chain state. Key verification steps include confirming the intended blockchain network, token contract, smart contract execution, and the presence of the expected Transfer event with the correct recipient and amount.

The event identity (network, transaction_id, log_index) should be used for accurate record-keeping, as a single transaction can contain multiple transfer events.

The deposit monitoring system should be designed to handle potential duplicate records due to network issues or retries. Implementing an idempotent record-keeping process using a composite primary key in a database ensures that the same transfer event is only recorded once, preventing multiple credits to the exchange balance. The Python example demonstrates this principle using an SQLite database, where a new deposit record is inserted only if it has not been inserted before, based on the network, transaction ID, and log index.

This approach safeguards against incorrectly crediting the exchange multiple times for a single transfer.