Dynamic Code Execution

Dynamic code execution

For real Java code, this is possible using the JavaCompiler interface. However, it's very inconvenient to use since it's just an interface to a real Java compiler that expects to compile entire class definitions found in files.

The easiest way to execute code supplied at runtime would be to use the Rhino JavaScript engine.

Both of these options have been only in Java 6, though I believe the scripting interface existed before, so you could use Rhino in an earlier JRE if you download and add it to the classpath.

What is wrong with this dynamic code execution?

The code fails / can't be compiled because it contains three issues:

1. The method needs to be public
2. The return value is not a string like specified
3. Missing semicolon in the method

Fix it like this to get it running:

var code = @"using System; public class Abc { public static string Get() { return System.DateTime.Now.ToString(); } }";

You should check the errors after compiling your code compile.Errors.

How do I execute dynamic code in a container?

1. THIS IS A VERY BAD IDEA DO NOT DO IT
2. You would want to run each snippet in a new container for maximum isolation.

Dynamic C# code execution

You didn't explicitly state if you're looking for guidance on implementing your own solution or what, but if you're open to using a third party utility then LINQPad is pretty much exactly what you're describing.

Dynamic code evaluation in scala

You could use either scala-lang API for that or twitter-eval. Here is the snippet of a simple use case of scala-lang

import scala.tools.nsc.Settings
import scala.tools.nsc.interpreter.IMain

object ScalaReflectEvaluator {

  def evaluate() = {
    val clazz = prepareClass
    val settings = new Settings
    settings.usejavacp.value = true
    settings.deprecation.value = true

    val eval = new IMain(settings)
    val evaluated = eval.interpret(clazz)
    val res = eval.valueOfTerm("res0").get.asInstanceOf[Int]
    println(res) //yields 9
  }

  private def prepareClass: String = {
    s"""
       |val x = 4
       |val y = 5
       |x + y
       |""".stripMargin
  }
}

or with twitter:

import com.twitter.util.Eval

object TwitterUtilEvaluator {

  def evaluate() = {
    val clazz = prepareClass
    val eval = new Eval
    eval.apply[Int](clazz)
  }

  private def prepareClass: String = {
    s"""
       |val x = 4
       |val y = 5
       |x + y
       |""".stripMargin
  }
}

I am not able to compile it at the moment to check whether I have missed something but you should get the idea.

AWS Lambda execute dynamic code

eval works fine in Lambda. Remove the 'use strict' and it will work fine, outputting 10.

strict mode doesn't allow creating global variables, that's why you're getting the error.

A second option is to explicity add the function to the global context:

'use strict';

exports.handler = (event, context, callback) => {
    var body = "global.test = function() { return 10; };";
    console.log("body", body);

    eval(body);

    var result = test();

    callback(null, result);
};

R: dynamic construction and execution of commands

You want to evaluate the parsed text:

> eval(parse(text="gray.colors(n=10)"))
 [1] "#4D4D4D" "#6C6C6C" "#838383" "#969696" "#A7A7A7" "#B5B5B5" "#C3C3C3"
 [8] "#CFCFCF" "#DBDBDB" "#E6E6E6"

Any text can be evaluated and run this way. Note that if this string can be set by a user and sent to a server there may be a way for them to run arbitrary code on your server. Make sure you validate the allowed palette functions on the server before running code from clients like this (search for "XKCD Bobby Tables" for more).

Another option is using do.call, which works with character strings of function names:

> do.call("gray.colors",list(n=10))
 [1] "#4D4D4D" "#6C6C6C" "#838383" "#969696" "#A7A7A7" "#B5B5B5" "#C3C3C3"
 [8] "#CFCFCF" "#DBDBDB" "#E6E6E6"

and is probably less vulnerable to code injection vulnerabilities.

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