horizontalsystems / ethereum-kit-android

Comprehensive EVM SDK (Ethereum, Binance Smart Chain, Avalanche, Arbitrum, Optimism, Polygon) for Android, implemented on Kotlin. Create wallets, watch wallets (read-only), sync transactions, filter transactions by type (erc20, bep20, swap transactions etc.), swap using native DEX protocols, connect to DeFi smart contracts using WalletConnect. Easily extendable to work with custom smart contracts. Full support for EIP1159.

EthereumKit

EthereumKit is a native(Kotlin) toolkit for EVM compatible networks. It's implemented and used by Unstoppable Wallet, a multi-currency crypto wallet. It implements a lot of features of the DeFi world natively (no need for WalletConnect) out-of-the-box.

Core Features

• Restore with mnemonic phrase, BIP39 Seed, EVM private key, or simply an Ethereum address
• Local storage of account data (ETH, Token/NFT balance and transactions)
• Synchronization over HTTP/WebSocket
• Watch accounts. Restore with any address
• Ethereum Name Service (ENS) support
• EIP-1559 Gas Prices with live updates
• Reactive-functional API by RxAndroid
• Implementation of Ethereum's JSON-RPC API
• Support for Infura and Etherscan
• Can be extended to natively support any smart contract
• EIP20 token standard support
• EIP721 and EIP1155 non-fungible tokens(NFT)
• Uniswap (PancakeSwap, QuickSwap, Trader Joe) support
• 1Inch support

Blockchains supported

Any EVM blockchain that supports the Ethereum's RPC API and has an Etherscan-like block explorer can be easily integrated to your wallet using EthereumKit. The following blockchains are currently integrated to Unstoppable Wallet:

• Ethereum
• Binance Smart Chain
• Polygon
• ArbitrumOne
• Optimism
• Avalanche C-Chain

Usage

Initialization

First you need to initialize an EthereumKit instance

val context = Application()
val address = Address("0x..your..address")

val evmKit = EthereumKit.getInstance(
    context,
    address,
    Chain.Ethereum,
    RpcSource.ethereumInfuraHttp("projectId", "projectSecret"),
    TransactionSource.ethereumEtherscan("apiKey"),
    "unique_wallet_id"
)

Starting and Stopping

EthereumKit instance requires to be started with start command. This start the process of synchronization with the blockchain state.

evmKit.start()
evmKit.stop()

Get wallet data

You can get account state, last block height, sync state, transactions sync state and some others synchronously:

evmKit.accountState?.let { state ->
    state.balance
    state.nonce
}

evmKit.lastBlockHeight

You also can subscribe to Rx observables of those and more:

evmKit.accountStateFlowable.subscribe { state -> println("balance: ${state.balance}); nonce: ${state.nonce}") }
evmKit.lastBlockHeightFlowable.subscribe { height -> println(height) }
evmKit.syncStateFlowable.subscribe { state -> println(state) }
evmKit.transactionsSyncStateFlowable.subscribe { state -> println(state) }

// Subscribe to ETH transactions synced by the kit
evmKit.getFullTransactionsFlowable(listOf(listOf("ETH"))).subscribe { transactions -> 
    println(transactions.size) 
}

// Subscribe to all EVM transactions
evmKit.allTransactionsFlowable.subscribe { transactionsPair -> 
    println(transactionsPair.first.size) 
}

Send Transaction

To send a transaction you need a Signer object. Here's how you can create it using Mnemonic seed phrase:

val seed = Mnemonic().toSeed(listOf("mnemonic", "phrase"), "passphrase_if_exists'")
val signer = Signer.getInstance(seed, Chain.Ethereum)

Now you can use it to sign an Ethereum transaction:

val toAddress = Address("0x..recipient..address..here")
val amount = BigInteger("100000000000000000")                         // 0.1 ETH in WEIs
val gasPrice = GasPrice.Legacy(50_000_000_000)

// Construct TransactionData which is the key payload of any EVM transaction
val transactionData = ethereumKit.transferTransactionData(toAddress, amount)

// Estimate gas for the transaction
val estimateGasSingle = ethereumKit.estimateGas(transactionData, gasPrice)

// Generate a raw transaction which is ready to be signed. This step also synchronizes the nonce
val rawTransactionSingle = estimateGasSingle.flatMap { estimateGasSingle ->
    ethereumKit.rawTransaction(transactionData, gasPrice, estimateGasSingle)
}

val sendSingle = rawTransactionSingle.flatMap { rawTransaction ->
    // Sign the transaction
    val signature = signer.signature(rawTransaction)

    // Send the transaction to RPC node
    ethereumKit.send(rawTransaction, signature)
}

// This step is needed for Rx reactive code to run
val disposables = CompositeDisposable()

sendSingle.subscribe { fullTransaction ->
    // ethereumKit.send returns FullTransaction object that contains transaction and a transaction decoration
    val transaction = fullTransaction.transaction

    println("Transaction sent: ${transaction.hash.toHexString()}")
    println("To: ${transaction.to?.let { it.eip55 }}")
    println("Amount: ${transaction.value?.let { it.toString(10) }}")
}.let {
    disposables.add(it)
}

Get ETH transactions

The following code retrieves the transactions that have ETH coin incoming or outgoing, including the transactions where ETH is received in internal transactions.

ethereumKit.getFullTransactionsAsync(listOf(listOf("ETH")))
        .subscribe { fullTransactions ->
            for (fullTransaction in fullTransactions) {
                println("Transaction hash: ${fullTransaction.transaction.hash.toHexString()}")

                when (val decoration = fullTransaction.decoration) {
                    is IncomingDecoration -> {
                        println("From: ${decoration.from.eip55}")
                        println("Amount: ${decoration.value.toString(10)}")
                    }

                    is OutgoingDecoration -> {
                        println("To: ${decoration.to.eip55}")
                        println("Amount: ${decoration.value.toString(10)}")
                    }
                    
                    else -> {}
                }
            }
        }.let {
            disposables.add(it)
        }

EIP20 tokens

Initialization

val contractAddress = Address("0x..token..contract..address..")
val erc20Kit = Erc20Kit.getInstance(context, ethereumKit, contractAddress)

// Decorators are needed to detect transactions as `Erc20` transfer/approve transactions
Erc20Kit.addTransactionSyncer(ethereumKit)
        
// Erc20 transactions syncer is needed to pull Eip20 transfer transactions from Etherscan
Erc20Kit.addDecorators(ethereumKit)

Get token balance

erc20Kit.balance?.let { balance ->
    println(balance.toString(10))
}

Send Erc20 transfer transaction

val toAddress = Address("0x..recipient..address..here")
val amount = BigInteger("100000000000000000")
val gasPrice = GasPrice.Legacy(50_000_000_000)

// Construct TransactionData which calls a `Transfer` method of the EIP20 compatible smart contract
val transactionData = erc20Kit.buildTransferTransactionData(toAddress, amount)

ethereumKit.estimateGas(transactionData, gasPrice)
        .flatMap { estimateGasSingle ->
            ethereumKit.rawTransaction(transactionData, gasPrice, estimateGasSingle)
        }
        .flatMap { rawTransaction ->
            val signature = signer.signature(rawTransaction)
            ethereumKit.send(rawTransaction, signature)
        }
        .subscribe { fullTransaction ->
            println("Transaction sent: ${fullTransaction.transaction.hash.toHexString()}")

            val decoration = fullTransaction.decoration as? OutgoingDecoration ?: return@subscribe
                    
            println("To: ${decoration.to.eip55}")
            println("Amount: ${decoration.value.toString(10)}")
        }.let {
            disposables.add(it)
        }

Get Erc20 transactions

ethereumKit.getFullTransactionsAsync(listOf(listOf(contractAddress.eip55)))
        .subscribe { fullTransactions ->
            for (fullTransaction in fullTransactions) {
                println("Transaction sent: ${fullTransaction.transaction.hash.toHexString()}")

                when (val decoration = fullTransaction.decoration) {
                    is IncomingDecoration -> {
                        println("From: ${decoration.from.eip55}")
                        println("Amount: ${decoration.value.toString(10)}")
                    }

                    is OutgoingDecoration -> {
                        println("To: ${decoration.to.eip55}")
                        println("Amount: ${decoration.value.toString(10)}")
                    }

                    else -> {}
                }
            }
        }.let {
            disposables.add(it)
        }

Uniswap

Initialization

val uniswapKit = UniswapKit.getInstance(ethereumKit)

// Decorators are needed to detect and decorate transactions as `Uniswap` transactions
UniswapKit.addDecorators(ethereumKit)

Send sample swap transaction

// Sample swap data
val tokenIn = uniswapKit.etherToken()
val tokenOut = uniswapKit.token(Address("0x..token..address"), 18)
val amount = BigDecimal(1)
val gasPrice = GasPrice.Legacy(50_000_000_000)

// Get SwapData. SwapData is a list of pairs available in Uniswap smart contract at the moment
uniswapKit.swapData(tokenIn, tokenOut)
        .map { swapData ->
            // Get TradeData. TradeData is the best swap route evaluated by UniswapKit
            val tradeData = uniswapKit.bestTradeExactIn(swapData, amount)

            // Convert TradeData to EvmKit TransactionData
            uniswapKit.transactionData(tradeData)
        }
        .flatMap { transactionData ->
            ethereumKit.estimateGas(transactionData, gasPrice)
                    .flatMap { estimateGasSingle ->
                        ethereumKit.rawTransaction(transactionData, gasPrice, estimateGasSingle)
                    }
        }
        .flatMap { rawTransaction ->
            val signature = signer.signature(rawTransaction)
            ethereumKit.send(rawTransaction, signature)
        }
        .subscribe { fullTransaction ->
            println("Transaction sent: ${fullTransaction.transaction.hash.toHexString()}")
        }.let {
            disposables.add(it)
        }

ExactIn/ExactOut

With UniswapKit you can build swap transaction that either has an exact In or exact Out amount. That is, if you want to swap exactly 1 ETH to USDT, you get TradeData using bestTradeExactIn method. Similarly, if you want to swap ETH to USDT and you want to get exactly 1000 USDT, then you get TradeData using bestTradeExactOut

Trade Options

UniswapKit supports Price Impact/Deadline/Recipient options. You can set them in TradeOptions object passed to bestTradeExactIn/bestTradeExactOut methods. Please, look at official Uniswap app documentation to learn about those options.

1Inch

OneInchKit is an extension that wraps interactions with 1Inch API.

Initialization

val oneInchKit = OneInchKit.getInstance(ethereumKit)
OneInchKit.addDecorators(ethereumKit)

Sample code to get swap data from 1Inch API, sign it and send to RPC node

// Sample swap data
val tokenFromAddress = Address("0x..from..token..address")
val tokenToAddress = Address("0x..to..token..address")
val amount = BigInteger("100000000000000000")
val gasPrice = GasPrice.Legacy(50_000_000_000)

// Get Swap object, evaluated transaction data by 1Inch aggregator
oneInchKit.getSwapAsync(
        fromToken = tokenFromAddress,
        toToken = tokenToAddress,
        amount = amount,
        slippagePercentage = 1F,
        recipient = null,
        gasPrice = gasPrice
)
        .flatMap { swap ->
            val tx = swap.transaction
            val transactionData = TransactionData(tx.to, tx.value, tx.data)

            ethereumKit.rawTransaction(transactionData, gasPrice, tx.gasLimit)
        }
        .flatMap { rawTransaction ->
            val signature = signer.signature(rawTransaction)
            ethereumKit.send(rawTransaction, signature)
        }
        .subscribe { fullTransaction ->
            println("Transaction sent: ${fullTransaction.transaction.hash.toHexString()}")
        }.let {
            disposables.add(it)
        }

NFTs

NftKit support EIP721 and EIP1155

Initialization

val nftKit = NftKit.getInstance(App.instance, ethereumKit)

nftKit.addEip721Decorators()
nftKit.addEip1155Decorators()

nftKit.addEip721TransactionSyncer()
nftKit.addEip1155TransactionSyncer()

Get NFTs owned by the user

val nftBalances = nftKit.nftBalances

for (nftBalance in nftBalances) {
    println("---- ${nftBalance.balance} pieces of ${nftBalance.nft.tokenName} ---")
    println("Contract Address: ${nftBalance.nft.contractAddress.eip55}")
    println("TokenID: ${nftBalance.nft.tokenId.toString(10)}")
}

Send an NFT

val nftContractAddress = Address("0x..contract..address")
val tokenId = BigInteger("234123894712031638516723498")
val to = Address("0x..recipient..address")
val gasPrice = GasPrice.Legacy(50_000_000_000)

// Construct a TransactionData
val transactionData = nftKit.transferEip721TransactionData(nftContractAddress, to, tokenId)

ethereumKit.estimateGas(transactionData, gasPrice)
        .flatMap { estimateGasSingle ->
            ethereumKit.rawTransaction(transactionData, gasPrice, estimateGasSingle)
        }
        .flatMap { rawTransaction ->
            val signature = signer.signature(rawTransaction)
            ethereumKit.send(rawTransaction, signature)
        }
        .subscribe { fullTransaction ->
            println("Transaction sent: ${fullTransaction.transaction.hash.toHexString()}")
        }.let {
            disposables.add(it)
        }

Extending

Smart contract call

In order to send an EVM smart contract call transaction, you need to create an instance of TransactionData object. Then you can sign and send it as seen above.

Prerequisites

• JDK >= 11
• Android 8 (minSdkVersion 26) or greater

Installation

Add the JitPack to module build.gradle

repositories {
    maven { url 'https://jitpack.io' }
}

Add the following dependency to your build.gradle file:

dependencies {
    implementation 'com.github.horizontalsystems:ethereum-kit-android:master-SNAPSHOT'
}

Example App

All features of the library are used in example project. It can be referred as a starting point for usage of the library.

• Example App

License

The EthereumKit is open source and available under the terms of the MIT License