Overview

This section explains how reactive contracts pay for execution and cross-chain callbacks, including REACT funding, transaction fees, and callback pricing. Contracts must maintain sufficient balances to remain active.

Reactive Transactions

Reactive transaction fees are charged synchronously when the system contract executes the react() call. The fee is calculated as:

$$fee = BaseFee ⋅ GasUsed$$

Where:

• BaseFee — base fee per gas unit in the current block
• GasUsed — gas consumed during execution

Max Gas Limit

The maximum gas limit for reactive transactions is 900,000 units.

Direct Transfers

Reactive contracts must be funded in REACT before executing reactive transactions.

Fund a contract:

cast send $CONTRACT_ADDR \
  --rpc-url $REACTIVE_RPC \
  --private-key $REACTIVE_PRIVATE_KEY \
  --value 0.1ether

Then settle outstanding debt:

cast send \
  --rpc-url $REACTIVE_RPC \
  --private-key $REACTIVE_PRIVATE_KEY \
  $CONTRACT_ADDR "coverDebt()"

Contract Status

Contract status is available on Reactscan.

• active — contract executes normally
• inactive — outstanding debt must be settled

System Contract Deposits

Contracts can be funded through the system contract using depositTo(). The sender pays the transaction fee, and any outstanding debt is settled automatically.

cast send \
  --rpc-url $REACTIVE_RPC \
  --private-key $REACTIVE_PRIVATE_KEY \
  $SYSTEM_CONTRACT_ADDR "depositTo(address)" \
  $CONTRACT_ADDR \
  --value 0.1ether

Callback Pricing

Callback costs depend on the destination network and current base fees. The callback price $p_{callback}$ is calculated as:

$$p_{callback} = p_{base} ⋅ C ⋅ (g_{callback} + K)$$

Where:

• $p_{base}$ — base gas price (tx.gasprice or block.basefee)
• $C$ — destination-network pricing coefficient
• $g_{callback}$ — callback gas usage
• $K$ — fixed gas surcharge

Callback Payment

Callbacks use the same payment model as reactive transactions. Contracts without sufficient funds are blocklisted and can't execute transactions or callbacks.

Callback Gas Limit

Reactive Network enforces a minimum callback gas limit of 100,000 gas. Callback requests below this threshold are ignored, as this minimum ensures sufficient gas for internal audits and computations required to process the callback.

Direct Transfers

Fund a callback contract:

cast send $CALLBACK_ADDR \
  --rpc-url $DESTINATION_RPC \
  --private-key $DESTINATION_PRIVATE_KEY \
  --value 0.1ether

Then settle outstanding debt:

cast send \
  --rpc-url $DESTINATION_RPC \
  --private-key $DESTINATION_PRIVATE_KEY \
  $CALLBACK_ADDR "coverDebt()"

Callback Proxy Deposits

Callback contracts can be funded through the callback proxy using depositTo(). Debt is settled automatically.

cast send \
  --rpc-url $DESTINATION_RPC \
  --private-key $DESTINATION_PRIVATE_KEY \
  $CALLBACK_PROXY_ADDR "depositTo(address)" \
  $CALLBACK_ADDR \
  --value 0.1ether

On-The-Spot Payment

Implementing pay() or inheriting from AbstractPayer enables automatic settlement. The callback proxy calls pay() when a callback creates debt. The standard implementation verifies the caller, checks balances, and settles the debt.

Callback Contract Balance

Balance

Retrieve the balance of a callback contract:

cast balance $CONTRACT_ADDR --rpc-url $DESTINATION_RPC

Debt

Query the debt recorded by the callback proxy:

cast call $CALLBACK_PROXY_ADDR "debts(address)" $CONTRACT_ADDR --rpc-url $DESTINATION_RPC | cast to-dec

Reserves

Retrieve reserves held by the callback proxy:

cast call $CALLBACK_PROXY_ADDR "reserves(address)" $CONTRACT_ADDR --rpc-url $DESTINATION_RPC | cast to-dec

Reactive Contract Balance

Balance

Retrieve the REACT balance of a reactive contract:

cast balance $CONTRACT_ADDR --rpc-url $REACTIVE_RPC

Debt

Query the debt recorded by the system contract:

cast call $SYSTEM_CONTRACT_ADDR "debts(address)" $CONTRACT_ADDR --rpc-url $REACTIVE_RPC | cast to-dec

Reserves

Retrieve reserves held by the system contract:

cast call $SYSTEM_CONTRACT_ADDR "reserves(address)" $CONTRACT_ADDR --rpc-url $REACTIVE_RPC | cast to-dec