Node dies with unhandled exception on jailed plugin syntax error

[cristiano-belloni]

I'm using

pluginInstance = new jailed.DynamicPlugin(script, api)

and

pluginInstance.whenFailed(function() {
   // Handle plugin failing
 })

but, if script has a syntax error, the process dies with an unhandled exception:

SyntaxError: Unexpected token }
    at Object.exports.runInNewContext (vm.js:48:16)
    at executeJailed (/myDir/node_modules/jailed/lib/_pluginNode.js:194:12)
    at execute (/myDir/node_modules/jailed/lib/_pluginNode.js:143:5)
    at process.<anonymous> (/myDir/node_modules/jailed/lib/_pluginNode.js:36:9)
    at emitTwo (events.js:100:13)
    at process.emit (events.js:185:7)
    at handleMessage (internal/child_process.js:689:10)
    at Pipe.channel.onread (internal/child_process.js:440:11)

Is there a way to handle this without the process dying?

[cristiano-belloni]

(please note that the plugin is submitted by users, and can have a syntax error)

[asvd]

Would it help, if you execute user's code in a try-catch block?

Have a look on how it's implemented in this demo and how it reacts to a syntax error in a user's provided code:

http://asvd.github.io/jailed/demos/web/console/

[cristiano-belloni]

The problem is that I need to call functions on the user code / plugin . Evaluating the user block won't work.

Also, if you specify, for example function(a) { return 'a' } in the Web Console, it returns Unexpected token (

[asvd]

But can you maybe call those functions in try-catch block? What would happen then?

Also, if you specify, for example function(a) { return 'a' } in the Web Console, it returns Unexpected token (

Same happens if you run that code in Chrome Dev-tools. To make it work, you can add an assignment:

b = function(a) { return 'a' }

[cristiano-belloni]

(what I'm doing now is something like):

var log
  , except
  , action
  , next
  , parameters = {}
  , staticData = {}
  , initException = null
  , indexedDB = null
  , location = null
  , navigator = null
  , onerror = null
  , onmessage = null
  , performance = null
  , self = null
  , webkitIndexedDB = null
  , postMessage = null
  , close = null
  , openDatabase = null
  , openDatabaseSync = null
  , webkitRequestFileSystem = null
  , webkitRequestFileSystemSync = null
  , webkitResolveLocalFileSystemSyncURL = null
  , webkitResolveLocalFileSystemURL = null
  , addEventListener = null
  , dispatchEvent = null
  , removeEventListener = null
  , dump = null
  , onoffline = null
  , ononline = null
  , importScripts = null
  , console = null

try {
    application.whenConnected(function() {

      application.remote.start()

      log = application.remote.log
      action = application.remote.action
      except = application.remote.except
      next = application.remote.next

      if (initException) except({type: 'init', e: stringifyException(initException)})

      application.setInterface ({
        callUserFunction: function(data) {
          try {
            onUserFunction(data)
            next()
          }
          catch(e) {
            except({type: 'runtime', e: stringifyException(e)})
          }
        }
      })
      ${script}

    })

}
catch(e) {
  initException = e
  if (except) except({type: 'init', e: stringifyException(e)})
}

var stringifyException = function(err, filter, space) {
  var plainObject = {}
  Object.getOwnPropertyNames(err).forEach(function(key) {
    plainObject[key] = err[key]
  })
  return JSON.stringify(plainObject, filter, space)
}

where ${script} contains the user code, which is like:

function onUserFunction (data) {
  // do something with the data
  log('did something with the data')
}

[cristiano-belloni]

@asvd - btw, if I execute the users's code in a try catch block:

 try {
        ${script}
      }
    catch (e) {
      initException = e
      if (except) except({type: 'init', e: stringifyException(e)}
    }

It still dies with an unhandled exception

[asvd]

so user code is substituted into the plugin code body before creating the plugin instance?

[cristiano-belloni]

Yep, it is.

[cristiano-belloni]

I just can't pass it as a string and then eval it, because I need to call a callback in the user code and it needs to call callbacks in mine.

[asvd]

Not good, user can close the brace and break the structure of the code.

Do the following:

• add the plugin method setUserFunction() which will save user code as a string;
• evaluate it in a try-catch block upon callUserFunction() invocation;
• call whatever callbacks you need afterwards (next()?).

Is there any callbacks you cannot call in this way?

[asvd]

Should work if user's code simply calls log(), since eval() executes code in a current context and has everything available.

But if user-provided code is only intended to process some data, I would suggest simply to let user return the result, and then perform any respective actions on the application site. Why do you need user's code to do something additional?

[asvd]

See another demo concerning processing the data with user-provided code:

http://asvd.github.io/jailed/demos/web/process/

[cristiano-belloni]

Because the user has to send commands to the main application based on the data. Ideally, the user would only have to write something like:

var state = {}

var initialize = function(initData) {
  // This is called once
  state.whatever = initData.whatever
}

var onData = function(data) {
  // This is called repeatedly every time there's a new piece of data
  state.whatever = state + data.whatever
  log('did something with the data')
  action('DO_SOMETHING', calculatedValue)
}

[asvd]

You can also return a string describing which respective action to perform on the application site. Or an array of them in case there might be several actions to be performed. Or a serialized object with properties containing the detailed description concerning what exactly user code wants to happen.

[asvd]

Your example:

var onData = function(data, oldState) {
    return {
        newState: oldState + data.whatever,
        action : {
            name: 'DO_SOMETHING',
            params: [calculatedValue]
        },
        log : 'did something with the data'
    };
}

[cristiano-belloni]

I'll try something similar, thank you. Btw, the last demo doesn't work -- Mixed Content: The page at 'https://asvd.github.io/jailed/lib/_frame.html' was loaded over HTTPS, but requested an insecure Worker script 'blob:null/4abedc87-2d97-45be-9fc6-1c9bc351aa60'. This request has been blocked; the content must be served over HTTPS.

[asvd]

yep, will investigate on this. Should work if you load it by http instead of https

[cristiano-belloni]

@asvd Can I close this or you need it open for the https issue?

[asvd]

We can close it. The https issue is solved on HEAD already.