path: root/internal/jsre/jsre.go

// Copyright 2015 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 jsre provides execution environment for JavaScript.
package jsre

import (
    crand "crypto/rand"
    "encoding/binary"
    "fmt"
    "io"
    "io/ioutil"
    "math/rand"
    "time"

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

/*
JSRE is a generic JS runtime environment embedding the otto JS interpreter.
It provides some helper functions to
- load code from files
- run code snippets
- require libraries
- bind native go objects
*/
type JSRE struct {
    assetPath     string
    output        io.Writer
    evalQueue     chan *evalReq
    stopEventLoop chan bool
    closed        chan struct{}
}

// jsTimer is a single timer instance with a callback function
type jsTimer struct {
    timer    *time.Timer
    duration time.Duration
    interval bool
    call     otto.FunctionCall
}

// evalReq is a serialized vm execution request processed by runEventLoop.
type evalReq struct {
    fn   func(vm *otto.Otto)
    done chan bool
}

// runtime must be stopped with Stop() after use and cannot be used after stopping
func New(assetPath string, output io.Writer) *JSRE {
    re := &JSRE{
        assetPath:     assetPath,
        output:        output,
        closed:        make(chan struct{}),
        evalQueue:     make(chan *evalReq),
        stopEventLoop: make(chan bool),
    }
    go re.runEventLoop()
    re.Set("loadScript", re.loadScript)
    re.Set("inspect", re.prettyPrintJS)
    return re
}

// randomSource returns a pseudo random value generator.
func randomSource() *rand.Rand {
    bytes := make([]byte, 8)
    seed := time.Now().UnixNano()
    if _, err := crand.Read(bytes); err == nil {
        seed = int64(binary.LittleEndian.Uint64(bytes))
    }

    src := rand.NewSource(seed)
    return rand.New(src)
}

// This function runs the main event loop from a goroutine that is started
// when JSRE is created. Use Stop() before exiting to properly stop it.
// The event loop processes vm access requests from the evalQueue in a
// serialized way and calls timer callback functions at the appropriate time.

// Exported functions always access the vm through the event queue. You can
// call the functions of the otto vm directly to circumvent the queue. These
// functions should be used if and only if running a routine that was already
// called from JS through an RPC call.
func (self *JSRE) runEventLoop() {
    defer close(self.closed)

    vm := otto.New()
    r := randomSource()
    vm.SetRandomSource(r.Float64)

    registry := map[*jsTimer]*jsTimer{}
    ready := make(chan *jsTimer)

    newTimer := func(call otto.FunctionCall, interval bool) (*jsTimer, otto.Value) {
        delay, _ := call.Argument(1).ToInteger()
        if 0 >= delay {
            delay = 1
        }
        timer := &jsTimer{
            duration: time.Duration(delay) * time.Millisecond,
            call:     call,
            interval: interval,
        }
        registry[timer] = timer

        timer.timer = time.AfterFunc(timer.duration, func() {
            ready <- timer
        })

        value, err := call.Otto.ToValue(timer)
        if err != nil {
            panic(err)
        }
        return timer, value
    }

    setTimeout := func(call otto.FunctionCall) otto.Value {
        _, value := newTimer(call, false)
        return value
    }

    setInterval := func(call otto.FunctionCall) otto.Value {
        _, value := newTimer(call, true)
        return value
    }

    clearTimeout := func(call otto.FunctionCall) otto.Value {
        timer, _ := call.Argument(0).Export()
        if timer, ok := timer.(*jsTimer); ok {
            timer.timer.Stop()
            delete(registry, timer)
        }
        return otto.UndefinedValue()
    }
    vm.Set("_setTimeout", setTimeout)
    vm.Set("_setInterval", setInterval)
    vm.Run(`var setTimeout = function(args) {
        if (arguments.length < 1) {
            throw TypeError("Failed to execute 'setTimeout': 1 argument required, but only 0 present.");
        }
        return _setTimeout.apply(this, arguments);
    }`)
    vm.Run(`var setInterval = function(args) {
        if (arguments.length < 1) {
            throw TypeError("Failed to execute 'setInterval': 1 argument required, but only 0 present.");
        }
        return _setInterval.apply(this, arguments);
    }`)
    vm.Set("clearTimeout", clearTimeout)
    vm.Set("clearInterval", clearTimeout)

    var waitForCallbacks bool

loop:
    for {
        select {
        case timer := <-ready:
            // execute callback, remove/reschedule the timer
            var arguments []interface{}
            if len(timer.call.ArgumentList) > 2 {
                tmp := timer.call.ArgumentList[2:]
                arguments = make([]interface{}, 2+len(tmp))
                for i, value := range tmp {
                    arguments[i+2] = value
                }
            } else {
                arguments = make([]interface{}, 1)
            }
            arguments[0] = timer.call.ArgumentList[0]
            _, err := vm.Call(`Function.call.call`, nil, arguments...)
            if err != nil {
                fmt.Println("js error:", err, arguments)
            }

            _, inreg := registry[timer] // when clearInterval is called from within the callback don't reset it
            if timer.interval && inreg {
                timer.timer.Reset(timer.duration)
            } else {
                delete(registry, timer)
                if waitForCallbacks && (len(registry) == 0) {
                    break loop
                }
            }
        case req := <-self.evalQueue:
            // run the code, send the result back
            req.fn(vm)
            close(req.done)
            if waitForCallbacks && (len(registry) == 0) {
                break loop
            }
        case waitForCallbacks = <-self.stopEventLoop:
            if !waitForCallbacks || (len(registry) == 0) {
                break loop
            }
        }
    }

    for _, timer := range registry {
        timer.timer.Stop()
        delete(registry, timer)
    }
}

// Do executes the given function on the JS event loop.
func (self *JSRE) Do(fn func(*otto.Otto)) {
    done := make(chan bool)
    req := &evalReq{fn, done}
    self.evalQueue <- req
    <-done
}

// stops the event loop before exit, optionally waits for all timers to expire
func (self *JSRE) Stop(waitForCallbacks bool) {
    select {
    case <-self.closed:
    case self.stopEventLoop <- waitForCallbacks:
        <-self.closed
    }
}

// Exec(file) loads and runs the contents of a file
// if a relative path is given, the jsre's assetPath is used
func (self *JSRE) Exec(file string) error {
    code, err := ioutil.ReadFile(common.AbsolutePath(self.assetPath, file))
    if err != nil {
        return err
    }
    var script *otto.Script
    self.Do(func(vm *otto.Otto) {
        script, err = vm.Compile(file, code)
        if err != nil {
            return
        }
        _, err = vm.Run(script)
    })
    return err
}

// Bind assigns value v to a variable in the JS environment
// This method is deprecated, use Set.
func (self *JSRE) Bind(name string, v interface{}) error {
    return self.Set(name, v)
}

// Run runs a piece of JS code.
func (self *JSRE) Run(code string) (v otto.Value, err error) {
    self.Do(func(vm *otto.Otto) { v, err = vm.Run(code) })
    return v, err
}

// Get returns the value of a variable in the JS environment.
func (self *JSRE) Get(ns string) (v otto.Value, err error) {
    self.Do(func(vm *otto.Otto) { v, err = vm.Get(ns) })
    return v, err
}

// Set assigns value v to a variable in the JS environment.
func (self *JSRE) Set(ns string, v interface{}) (err error) {
    self.Do(func(vm *otto.Otto) { err = vm.Set(ns, v) })
    return err
}

// loadScript executes a JS script from inside the currently executing JS code.
func (self *JSRE) loadScript(call otto.FunctionCall) otto.Value {
    file, err := call.Argument(0).ToString()
    if err != nil {
        // TODO: throw exception
        return otto.FalseValue()
    }
    file = common.AbsolutePath(self.assetPath, file)
    source, err := ioutil.ReadFile(file)
    if err != nil {
        // TODO: throw exception
        return otto.FalseValue()
    }
    if _, err := compileAndRun(call.Otto, file, source); err != nil {
        // TODO: throw exception
        fmt.Println("err:", err)
        return otto.FalseValue()
    }
    // TODO: return evaluation result
    return otto.TrueValue()
}

// Evaluate executes code and pretty prints the result to the specified output
// stream.
func (self *JSRE) Evaluate(code string, w io.Writer) error {
    var fail error

    self.Do(func(vm *otto.Otto) {
        val, err := vm.Run(code)
        if err != nil {
            prettyError(vm, err, w)
        } else {
            prettyPrint(vm, val, w)
        }
        fmt.Fprintln(w)
    })
    return fail
}

// Compile compiles and then runs a piece of JS code.
func (self *JSRE) Compile(filename string, src interface{}) (err error) {
    self.Do(func(vm *otto.Otto) { _, err = compileAndRun(vm, filename, src) })
    return err
}

func compileAndRun(vm *otto.Otto, filename string, src interface{}) (otto.Value, error) {
    script, err := vm.Compile(filename, src)
    if err != nil {
        return otto.Value{}, err
    }
    return vm.Run(script)
}