git ssb

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/**
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 * This implements the Ethereum Kernel
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 * Kernels must implement two methods `codeHandler` and `callHandler` (and `linkHandler` for sharding)
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 * The Kernel Contract handles the following
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 * - Interprocess communications
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 * - Intializing the VM and exposes ROM to it (codeHandler)
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 * - Expose namespace which VM instance exists and Intializes the Environment (callHandler)
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 * - Provides some built in contract (runTx, runBlock)
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 * - Provides resource sharing and limiting via gas
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 *
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 *   All State should be stored in the Environment.
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 *
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 */
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// The Kernel Exposes this Interface to VM instances it makes
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const Interface = require('./interface.js')
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// The Kernel Stores all of its state in the Environment. The Interface is used
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// to by the VM to retrive infromation from the Environment.
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const Environment = require('./environment.js')
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const DebugInterface = require('./debugInterface.js')
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const Address = require('./address.js')
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const U256 = require('./u256.js')
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const Utils = require('./utils.js')
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const Transaction = require('./transaction.js')
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const Precompile = require('./precompile.js')
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const identityContract = new Address('0x0000000000000000000000000000000000000004')
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const meteringContract = new Address('0x000000000000000000000000000000000000000A')
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const transcompilerContract = new Address('0x000000000000000000000000000000000000000B')
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module.exports = class Kernel {
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  // runs some code in the VM
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  constructor (environment = new Environment()) {
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    this.environment = environment
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    this.environment.addAccount(identityContract, {})
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    this.environment.addAccount(meteringContract, {})
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    this.environment.addAccount(transcompilerContract, {})
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  }
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  // handles running code.
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  // NOTE: it assumes that wasm will raise an exception if something went wrong,
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  //       otherwise execution succeeded
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  codeHandler (code, ethInterface = new Interface(new Environment())) {
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    const debugInterface = new DebugInterface(ethInterface.environment)
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    const module = WebAssembly.Module(code)
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    const imports = {
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      'ethereum': ethInterface.exportTable,
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      'debug': debugInterface.exportTable,
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      // export this for Rust
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      // FIXME: remove once Rust has proper imports, see https://github.com/ethereum/evm2.0-design/issues/15
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      'spectest': ethInterface.exportTable,
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      // export this for Binaryen
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      // FIXME: remove once C has proper imports, see https://github.com/ethereum/evm2.0-design/issues/16
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      'env': ethInterface.exportTable
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    }
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    // add shims
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    imports.ethereum.useGas = ethInterface.shims.exports.useGas
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    imports.ethereum.getGasLeft = ethInterface.shims.exports.getGasLeft
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    imports.ethereum.call = ethInterface.shims.exports.call
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    const instance = WebAssembly.Instance(module, imports)
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    ethInterface.setModule(instance)
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    debugInterface.setModule(instance)
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    if (instance.exports.main) {
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      instance.exports.main()
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    }
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    return instance
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  }
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  // loads code from the merkle trie and delegates the message
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  // Detects if code is EVM or WASM
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  // Detects if the code injection is needed
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  // Detects if transcompilation is needed
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  callHandler (call) {
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    // FIXME: this is here until these two contracts are compiled to WASM
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    // The two special contracts (precompiles now, but will be real ones later)
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    if (call.to.equals(meteringContract)) {
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      return Precompile.meteringInjector(call)
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    } else if (call.to.equals(transcompilerContract)) {
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      return Precompile.transcompiler(call)
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    } else if (call.to.equals(identityContract)) {
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      return Precompile.identity(call)
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    }
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    let account = this.environment.state.get(call.to.toString())
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    if (!account) {
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      throw new Error('Account not found: ' + call.to.toString())
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    }
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    let code = Uint8Array.from(account.get('code'))
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    if (code.length === 0) {
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      throw new Error('Contract not found')
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    }
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    if (!Utils.isWASMCode(code)) {
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      // throw new Error('Not an eWASM contract')
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      // Transcompile code
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      // FIXME: decide if these are the right values here: from: 0, gasLimit: 0, value: 0
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      code = this.callHandler({ from: Address.zero(), to: transcompilerContract, gasLimit: 0, value: new U256(0), data: code }).returnValue
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      if (code[0] === 0) {
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        code = code.slice(1)
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      } else {
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        throw new Error('Transcompilation failed: ' + Buffer.from(code).slice(1).toString())
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      }
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    }
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    // creats a new Kernel
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    const environment = new Environment()
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    environment.parent = this
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    // copy the transaction details
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    environment.code = code
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    environment.address = call.to
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    // FIXME: make distinction between origin and caller
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    environment.origin = call.from
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    environment.caller = call.from
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    environment.callData = call.data
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    environment.callValue = call.value
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    environment.gasLeft = call.gasLimit
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    environment.callHandler = this.callHandler.bind(this)
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    environment.createHandler = this.createHandler.bind(this)
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    const kernel = new Kernel(environment)
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    kernel.codeHandler(code, new Interface(environment))
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    // self destructed
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    if (environment.selfDestruct) {
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      const balance = this.state.get(call.to.toString()).get('balance')
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      const beneficiary = this.state.get(environment.selfDestructAddress)
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      beneficiary.set('balance', beneficiary.get('balance').add(balance))
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      this.state.delete(call.to.toString())
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    }
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    // generate new stateroot
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    // this.environment.state.set(address, { stateRoot: stateRoot })
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    return {
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      executionOutcome: 1, // success
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      gasLeft: new U256(environment.gasLeft),
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      gasRefund: new U256(environment.gasRefund),
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      returnValue: environment.returnValue,
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      selfDestruct: environment.selfDestruct,
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      selfDestructAddress: environment.selfDestructAddress,
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      logs: environment.logs
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    }
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  }
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  createHandler (create) {
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    let code = create.data
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    // Inject metering
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    if (Utils.isWASMCode(code)) {
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      // FIXME: decide if these are the right values here: from: 0, gasLimit: 0, value: 0
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      code = this.callHandler({ from: Address.zero(), to: meteringContract, gasLimit: 0, value: new U256(0), data: code }).returnValue
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      if (code[0] === 0) {
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        code = code.slice(1)
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      } else {
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        throw new Error('Metering injection failed: ' + Buffer.from(code).slice(1).toString())
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      }
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    }
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    let account = this.environment.state.get(create.from.toString())
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    if (!account) {
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      throw new Error('Account not found: ' + create.from.toString())
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    }
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    let address = Utils.newAccountAddress(create.from, account.get('nonce'))
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    this.environment.addAccount(address.toString(), {
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      balance: create.value,
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      code: code
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    })
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    // Run code and take return value as contract code
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    // FIXME: decide if these are the right values here: value: 0, data: ''
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    code = this.callHandler({ from: create.from, to: address, gasLimit: create.gasLimit, value: new U256(0), data: new Uint8Array() }).returnValue
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    // FIXME: special handling for selfdestruct
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    this.environment.state.get(address.toString()).set('code', code)
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    return {
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      executionOutcome: 1, // success
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      gasLeft: new U256(this.environment.gasLeft),
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      gasRefund: new U256(this.environment.gasRefund),
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      accountCreated: address,
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      logs: this.environment.logs
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    }
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  }
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  // run tx; the tx message handler
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  runTx (tx, environment = new Environment()) {
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    this.environment = environment
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    if (Buffer.isBuffer(tx) || typeof tx === 'string') {
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      tx = new Transaction(tx)
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      if (!tx.valid) {
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        throw new Error('Invalid transaction signature')
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      }
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    }
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    // look up sender
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    let fromAccount = this.environment.state.get(tx.from.toString())
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    if (!fromAccount) {
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      throw new Error('Sender account not found: ' + tx.from.toString())
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    }
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    if (fromAccount.get('nonce').gt(tx.nonce)) {
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      throw new Error(`Invalid nonce: ${fromAccount.get('nonce')} > ${tx.nonce}`)
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    }
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    fromAccount.set('nonce', fromAccount.get('nonce').add(new U256(1)))
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    let isCreation = false
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    // Special case: contract deployment
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    if (tx.to.isZero() && (tx.data.length !== 0)) {
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      console.log('This is a contract deployment transaction')
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      isCreation = true
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    }
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    // This cost will not be refunded
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    let txCost = 21000 + (isCreation ? 32000 : 0)
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    tx.data.forEach((item) => {
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      if (item === 0) {
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        txCost += 4
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      } else {
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        txCost += 68
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      }
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    })
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    if (tx.gasLimit.lt(new U256(txCost))) {
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      throw new Error(`Minimum transaction gas limit not met: ${txCost}`)
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    }
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    if (fromAccount.get('balance').lt(tx.gasLimit.mul(tx.gasPrice))) {
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      throw new Error(`Insufficient account balance: ${fromAccount.get('balance').toString()} < ${tx.gasLimit.mul(tx.gasPrice).toString()}`)
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    }
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    // deduct gasLimit * gasPrice from sender
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    fromAccount.set('balance', fromAccount.get('balance').sub(tx.gasLimit.mul(tx.gasPrice)))
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    const handler = isCreation ? this.createHandler.bind(this) : this.callHandler.bind(this)
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    let ret = handler({
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      to: tx.to,
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      from: tx.from,
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      gasLimit: tx.gasLimit - txCost,
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      value: tx.value,
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      data: tx.data
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    })
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    // refund unused gas
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    if (ret.executionOutcome === 1) {
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      fromAccount.set('balance', fromAccount.get('balance').add(tx.gasPrice.mul(ret.gasLeft.add(ret.gasRefund))))
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    }
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    // save new state?
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    return {
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      executionOutcome: ret.executionOutcome,
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      accountCreated: isCreation ? ret.accountCreated : undefined,
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      returnValue: isCreation ? undefined : ret.returnValue,
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      gasLeft: ret.gasLeft,
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      logs: ret.logs
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    }
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  }
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  // run block; the block message handler
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  runBlock (block, environment = new Environment()) {
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    // verify block then run each tx
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    block.tx.forEach((tx) => {
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      this.runTx(tx, environment)
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    })
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  }
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  // run blockchain
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  // runBlockchain () {}
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}
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