path: root/internal/ethapi/tracer.go

// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package ethapi

import (
    "errors"
    "fmt"
    "math/big"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/vm"
    "github.com/robertkrimen/otto"
)

// fakeBig is used to provide an interface to Javascript for 'big.NewInt'
type fakeBig struct{}

// NewInt creates a new big.Int with the specified int64 value.
func (fb *fakeBig) NewInt(x int64) *big.Int {
    return big.NewInt(x)
}

// OpCodeWrapper provides a JavaScript-friendly wrapper around OpCode, to convince Otto to treat it
// as an object, instead of a number.
type opCodeWrapper struct {
    op vm.OpCode
}

// toNumber returns the ID of this opcode as an integer
func (ocw *opCodeWrapper) toNumber() int {
    return int(ocw.op)
}

// toString returns the string representation of the opcode
func (ocw *opCodeWrapper) toString() string {
    return ocw.op.String()
}

// isPush returns true if the op is a Push
func (ocw *opCodeWrapper) isPush() bool {
    return ocw.op.IsPush()
}

// toValue returns an otto.Value for the opCodeWrapper
func (ocw *opCodeWrapper) toValue(vm *otto.Otto) otto.Value {
    value, _ := vm.ToValue(ocw)
    obj := value.Object()
    obj.Set("toNumber", ocw.toNumber)
    obj.Set("toString", ocw.toString)
    obj.Set("isPush", ocw.isPush)
    return value
}

// memoryWrapper provides a JS wrapper around vm.Memory
type memoryWrapper struct {
    memory *vm.Memory
}

// slice returns the requested range of memory as a byte slice
func (mw *memoryWrapper) slice(begin, end int64) []byte {
    return mw.memory.Get(begin, end-begin)
}

// getUint returns the 32 bytes at the specified address interpreted
// as an unsigned integer
func (mw *memoryWrapper) getUint(addr int64) *big.Int {
    ret := big.NewInt(0)
    ret.SetBytes(mw.memory.GetPtr(addr, 32))
    return ret
}

// toValue returns an otto.Value for the memoryWrapper
func (mw *memoryWrapper) toValue(vm *otto.Otto) otto.Value {
    value, _ := vm.ToValue(mw)
    obj := value.Object()
    obj.Set("slice", mw.slice)
    obj.Set("getUint", mw.getUint)
    return value
}

// stackWrapper provides a JS wrapper around vm.Stack
type stackWrapper struct {
    stack *vm.Stack
}

// peek returns the nth-from-the-top element of the stack.
func (sw *stackWrapper) peek(idx int) *big.Int {
    return sw.stack.Data()[len(sw.stack.Data())-idx-1]
}

// length returns the length of the stack
func (sw *stackWrapper) length() int {
    return len(sw.stack.Data())
}

// toValue returns an otto.Value for the stackWrapper
func (sw *stackWrapper) toValue(vm *otto.Otto) otto.Value {
    value, _ := vm.ToValue(sw)
    obj := value.Object()
    obj.Set("peek", sw.peek)
    obj.Set("length", sw.length)
    return value
}

// dbWrapper provides a JS wrapper around vm.Database
type dbWrapper struct {
    db vm.Database
}

// getBalance retrieves an account's balance
func (dw *dbWrapper) getBalance(addr common.Address) *big.Int {
    return dw.db.GetBalance(addr)
}

// getNonce retrieves an account's nonce
func (dw *dbWrapper) getNonce(addr common.Address) uint64 {
    return dw.db.GetNonce(addr)
}

// getCode retrieves an account's code
func (dw *dbWrapper) getCode(addr common.Address) []byte {
    return dw.db.GetCode(addr)
}

// getState retrieves an account's state data for the given hash
func (dw *dbWrapper) getState(addr common.Address, hash common.Hash) common.Hash {
    return dw.db.GetState(addr, hash)
}

// exists returns true iff the account exists
func (dw *dbWrapper) exists(addr common.Address) bool {
    return dw.db.Exist(addr)
}

// toValue returns an otto.Value for the dbWrapper
func (dw *dbWrapper) toValue(vm *otto.Otto) otto.Value {
    value, _ := vm.ToValue(dw)
    obj := value.Object()
    obj.Set("getBalance", dw.getBalance)
    obj.Set("getNonce", dw.getNonce)
    obj.Set("getCode", dw.getCode)
    obj.Set("getState", dw.getState)
    obj.Set("exists", dw.exists)
    return value
}

// JavascriptTracer provides an implementation of Tracer that evaluates a
// Javascript function for each VM execution step.
type JavascriptTracer struct {
    vm          *otto.Otto             // Javascript VM instance
    traceobj    *otto.Object           // User-supplied object to call
    log         map[string]interface{} // (Reusable) map for the `log` arg to `step`
    logvalue    otto.Value             // JS view of `log`
    opcode      *opCodeWrapper         // Wrapper around the opcode
    opcodevalue otto.Value             // JS view of 'opcode'
    memory      *memoryWrapper         // Wrapper around the VM memory
    memvalue    otto.Value             // JS view of `memory`
    stack       *stackWrapper          // Wrapper around the VM stack
    stackvalue  otto.Value             // JS view of `stack`
    db          *dbWrapper             // Wrapper around the VM environment
    dbvalue     otto.Value             // JS view of `db`
    err         error                  // Error, if one has occurred
}

// NewJavascriptTracer instantiates a new JavascriptTracer instance.
// code specifies a Javascript snippet, which must evaluate to an expression
// returning an object with 'step' and 'result' functions.
func NewJavascriptTracer(code string) (*JavascriptTracer, error) {
    vm := otto.New()
    vm.Interrupt = make(chan func(), 1)

    // Set up builtins for this environment
    vm.Set("big", &fakeBig{})

    jstracer, err := vm.Object("(" + code + ")")
    if err != nil {
        return nil, err
    }

    // Check the required functions exist
    step, err := jstracer.Get("step")
    if err != nil {
        return nil, err
    }
    if !step.IsFunction() {
        return nil, fmt.Errorf("Trace object must expose a function step()")
    }

    result, err := jstracer.Get("result")
    if err != nil {
        return nil, err
    }
    if !result.IsFunction() {
        return nil, fmt.Errorf("Trace object must expose a function result()")
    }

    // Create the persistent log object
    log := make(map[string]interface{})
    logvalue, _ := vm.ToValue(log)

    // Create persistent wrappers for memory and stack
    opcode := &opCodeWrapper{}
    mem := &memoryWrapper{}
    stack := &stackWrapper{}
    db := &dbWrapper{}

    return &JavascriptTracer{
        vm:          vm,
        traceobj:    jstracer,
        log:         log,
        logvalue:    logvalue,
        opcode:      opcode,
        opcodevalue: opcode.toValue(vm),
        memory:      mem,
        memvalue:    mem.toValue(vm),
        stack:       stack,
        stackvalue:  stack.toValue(vm),
        db:          db,
        dbvalue:     db.toValue(vm),
        err:         nil,
    }, nil
}

// Stop terminates execution of any JavaScript
func (jst *JavascriptTracer) Stop(err error) {
    jst.vm.Interrupt <- func() {
        panic(err)
    }
}

// callSafely executes a method on a JS object, catching any panics and
// returning them as error objects.
func (jst *JavascriptTracer) callSafely(method string, argumentList ...interface{}) (ret interface{}, err error) {
    defer func() {
        if caught := recover(); caught != nil {
            switch caught := caught.(type) {
            case error:
                err = caught
            case string:
                err = errors.New(caught)
            case fmt.Stringer:
                err = errors.New(caught.String())
            default:
                panic(caught)
            }
        }
    }()

    value, err := jst.traceobj.Call(method, argumentList...)
    ret, _ = value.Export()
    return ret, err
}

// CaptureState implements the Tracer interface to trace a single step of VM execution
func (jst *JavascriptTracer) CaptureState(env vm.Environment, pc uint64, op vm.OpCode, gas, cost *big.Int, memory *vm.Memory, stack *vm.Stack, contract *vm.Contract, depth int, err error) {
    if jst.err == nil {
        jst.opcode.op = op
        jst.memory.memory = memory
        jst.stack.stack = stack
        jst.db.db = env.Db()

        jst.log["pc"] = pc
        jst.log["op"] = jst.opcodevalue
        jst.log["gas"] = gas.Int64()
        jst.log["gasPrice"] = cost.Int64()
        jst.log["memory"] = jst.memvalue
        jst.log["stack"] = jst.stackvalue
        jst.log["depth"] = depth
        jst.log["account"] = contract.Address()
        jst.log["err"] = err

        _, err := jst.callSafely("step", jst.logvalue, jst.dbvalue)
        if err != nil {
            jst.err = err
        }
    }
}

// GetResult calls the Javascript 'result' function and returns its value, or any accumulated error
func (jst *JavascriptTracer) GetResult() (result interface{}, err error) {
    if jst.err != nil {
        return nil, jst.err
    }

    return jst.callSafely("result")
}