Updated on 2026-08-14
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Tangem
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12 changed files with 357 additions and 5 deletions
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@ -2,6 +2,9 @@ package com.tangem.domain.transaction
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import com.tangem.domain.models.currency.CryptoCurrency
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import com.tangem.domain.models.network.Network
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import com.tangem.domain.transaction.models.Eip7702Authorization
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import com.tangem.domain.transaction.models.GaslessSignedTransactionResult
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import com.tangem.domain.transaction.models.GaslessTransactionData
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import java.math.BigInteger
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interface GaslessTransactionRepository {
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@ -12,6 +15,50 @@ interface GaslessTransactionRepository {
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fun getTokenFeeReceiverAddress(): String
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/**
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* Sends gasless transaction to the gasless service for signing and returns the signed result.
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*
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* Flow:
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* 1. User signs the gasless transaction data locally with their private key
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* 2. This method submits the transaction + user signature to the gasless service
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* 3. Service validates the signature and transaction data
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* 4. Service adds its own signature for fee delegation (pays gas in tokens)
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* 5. Service constructs the final EIP-1559 transaction with all signatures
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* 6. Service returns the fully signed transaction ready for broadcasting
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*
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* The gasless service acts as a relayer that:
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* - Pays network gas fees on behalf of the user
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* - Receives payment in the specified token from the user's wallet
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* - Ensures atomic execution (either both transfers succeed or both fail)
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*
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* @param gaslessTransactionData domain model containing:
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* - transaction: target contract call data (to, value, data)
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* - fee: token payment configuration (feeToken, maxTokenFee, etc.)
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* - nonce: user's contract nonce to prevent replay attacks
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* @param signature user's ECDSA signature of the gasless transaction in hex format (0x...)
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* Signs keccak256 hash of the transaction data
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* @param userAddress user's Ethereum address (EOA or contract wallet)
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* @param network blockchain network (Ethereum, Polygon, BSC, etc.)
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* Used to determine chainId for the request
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* @param eip7702Auth optional EIP-7702 authorization for EOA delegation to smart contract
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* Required only when user's EOA needs to temporarily act as contract wallet
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* Contains signature authorizing delegation to entry point contract
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* @return [GaslessSignedTransactionResult] containing:
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* - signedTransaction: complete RLP-encoded transaction ready to broadcast
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* - gasLimit: actual gas limit allocated by the service
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* - maxFeePerGas: maximum fee per gas (base + priority) in wei
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* - maxPriorityFeePerGas: tip for validators in wei (EIP-1559)
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* @throws IllegalStateException if network is not supported or chainId cannot be determined
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* @throws Exception if service returns error or network request fails
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*/
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suspend fun sendGaslessTransaction(
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gaslessTransactionData: GaslessTransactionData,
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signature: String,
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userAddress: String,
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network: Network,
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eip7702Auth: Eip7702Authorization? = null,
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): GaslessSignedTransactionResult
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/**
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* Hardcoded value as baseGas
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*/
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@ -0,0 +1,36 @@
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package com.tangem.domain.transaction.models
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import java.math.BigInteger
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/**
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* EIP-7702 authorization for account abstraction.
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* Used for delegating EOA (Externally Owned Account) control to a smart contract.
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*
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* EIP-7702 allows EOAs to temporarily act as smart contract wallets by delegating
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* their authority to a contract address for a specific transaction.
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*
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* @property chainId blockchain network chain ID
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* @property address contract address to delegate authority to (entry point contract)
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* @property nonce authorization nonce to prevent replay attacks
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* @property yParity recovery ID for signature (0 or 1)
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* @property r ECDSA signature component R
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* @property s ECDSA signature component S
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*
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* @see <a href="https://eips.ethereum.org/EIPS/eip-7702">EIP-7702 Specification</a>
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*/
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data class Eip7702Authorization(
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val chainId: Int,
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val address: String,
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val nonce: BigInteger,
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val yParity: Int,
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val r: String,
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val s: String,
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) {
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init {
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require(chainId > 0) { "Chain ID must be positive" }
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require(address.isNotBlank()) { "Address must not be blank" }
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require(yParity in 0..1) { "yParity must be 0 or 1" }
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require(r.isNotBlank()) { "Signature component R must not be blank" }
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require(s.isNotBlank()) { "Signature component S must not be blank" }
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}
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}
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@ -0,0 +1,37 @@
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package com.tangem.domain.transaction.models
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import java.math.BigInteger
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/**
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* Result of gasless transaction signing from the gasless service.
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* Contains the fully signed transaction ready for broadcasting and gas parameters.
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*
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* After the user signs the gasless transaction data locally, the service:
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* 1. Validates the signature
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* 2. Adds its own signature for fee delegation
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* 3. Constructs the final transaction
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* 4. Returns this signed transaction with gas parameters
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*
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* @property signedTransaction complete signed transaction in RLP-encoded hex format (0x...)
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* ready to be broadcast to the blockchain network
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* @property gasLimit maximum amount of gas units allocated for the transaction
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* @property maxFeePerGas maximum total fee per gas unit (base fee + priority fee) in wei
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* @property maxPriorityFeePerGas maximum priority fee (tip) per gas unit in wei for EIP-1559
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*/
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data class GaslessSignedTransactionResult(
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val signedTransaction: String,
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val gasLimit: BigInteger,
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val maxFeePerGas: BigInteger,
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val maxPriorityFeePerGas: BigInteger,
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) {
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init {
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require(signedTransaction.isNotBlank()) { "Signed transaction must not be blank" }
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require(signedTransaction.startsWith("0x")) { "Signed transaction must be in hex format with 0x prefix" }
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require(gasLimit > BigInteger.ZERO) { "Gas limit must be positive" }
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require(maxFeePerGas > BigInteger.ZERO) { "Max fee per gas must be positive" }
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require(maxPriorityFeePerGas >= BigInteger.ZERO) { "Max priority fee per gas must be non-negative" }
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require(maxPriorityFeePerGas <= maxFeePerGas) {
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"Max priority fee per gas cannot exceed max fee per gas"
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}
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}
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}
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@ -0,0 +1,66 @@
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package com.tangem.domain.transaction.models
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import java.math.BigInteger
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/**
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* Domain model for gasless transaction.
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* Represents complete transaction data with fee delegation metadata.
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*/
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data class GaslessTransactionData(
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/** Transaction details */
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val transaction: Transaction,
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/** Fee payment configuration */
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val fee: Fee,
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/** Nonce from user's contract */
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val nonce: BigInteger,
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)
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/**
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* Core transaction data.
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*
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* @property to destination address
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* @property value transaction value in wei (currently always 0 for gasless)
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* @property data encoded transaction data (contract call)
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*/
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data class Transaction(
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val to: String,
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val value: BigInteger,
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val data: ByteArray,
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) {
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override fun equals(other: Any?): Boolean {
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if (this === other) return true
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if (javaClass != other?.javaClass) return false
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other as Transaction
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if (to != other.to) return false
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if (value != other.value) return false
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if (!data.contentEquals(other.data)) return false
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return true
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}
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override fun hashCode(): Int {
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var result = to.hashCode()
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result = 31 * result + value.hashCode()
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result = 31 * result + data.contentHashCode()
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return result
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}
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}
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/**
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* Fee configuration for gasless transaction.
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*
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* @property feeToken token address used for fee payment
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* @property maxTokenFee maximum fee amount in fee token units
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* @property coinPriceInToken price of native coin in fee token units
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* @property feeTransferGasLimit gas limit for fee token transfer
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* @property baseGas base gas cost (currently constant BASE_GAS, may vary in future)
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*/
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data class Fee(
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val feeToken: String,
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val maxTokenFee: BigInteger,
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val coinPriceInToken: BigInteger,
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val feeTransferGasLimit: BigInteger,
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val baseGas: BigInteger,
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)
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@ -0,0 +1,11 @@
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package com.tangem.domain.transaction.usecase.gasless
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import com.tangem.blockchain.common.TransactionData
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import com.tangem.domain.transaction.models.TransactionFeeExtended
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class CreateAndSendGaslessTransactionUseCase {
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operator fun invoke(transactionData: TransactionData, fee: TransactionFeeExtended) {
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// Implementation goes here
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}
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}
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