path: root/jsre/jsre.go

package jsre

import (
    "fmt"
    "io/ioutil"
    "sync"
    "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
    evalQueue     chan *evalReq
    stopEventLoop chan bool
    loopWg        sync.WaitGroup
}

// 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) *JSRE {
    re := &JSRE{
        assetPath:     assetPath,
        evalQueue:     make(chan *evalReq),
        stopEventLoop: make(chan bool),
    }
    re.loopWg.Add(1)
    go re.runEventLoop()
    re.Compile("pp.js", pp_js) // load prettyprint func definition
    re.Set("loadScript", re.loadScript)
    return re
}

// 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() {
    vm := otto.New()
    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.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)
            }
            if timer.interval {
                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)
    }

    self.loopWg.Done()
}

// do schedules the given function on the 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) {
    self.stopEventLoop <- waitForCallbacks
    self.loopWg.Wait()
}

// 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
    }
    self.do(func(vm *otto.Otto) { _, err = vm.Run(code) })
    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()
}

// PrettyPrint writes v to standard output.
func (self *JSRE) PrettyPrint(v interface{}) (val otto.Value, err error) {
    var method otto.Value
    self.do(func(vm *otto.Otto) {
        val, err = vm.ToValue(v)
        if err != nil {
            return
        }
        method, err = vm.Get("prettyPrint")
        if err != nil {
            return
        }
        val, err = method.Call(method, val)
    })
    return val, err
}

// Eval evaluates JS function and returns result in a pretty printed string format.
func (self *JSRE) Eval(code string) (s string, err error) {
    var val otto.Value
    val, err = self.Run(code)
    if err != nil {
        return
    }
    val, err = self.PrettyPrint(val)
    if err != nil {
        return
    }
    return fmt.Sprintf("%v", val), nil
}

// 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)
}