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package com.twitter.util
import scala.tools.nsc.{Global, Settings}
import scala.tools.nsc.reporters.ConsoleReporter
import scala.runtime._
import java.io.{File, FileWriter}
import java.net.{URL, URLClassLoader}
import scala.io.Source
import java.util.jar._
/**
* Eval is a utility function to evaluate a file and return its results.
* It is intended to be used for application configuration (rather than Configgy, XML, YAML files, etc.)
* and anything else.
*
* Consider this example. You have the following configuration trait Config.scala.
*
* package com.mycompany
*
* import com.twitter.util.Duration
* import com.twitter.util.StorageUnit
*
* trait Config {
* def myValue: Int
* def myTimeout: Duration
* def myBufferSize: StorageUnit
* }
*
* You have the following configuration file (specific values) in config/Development.scala:
*
* import com.mycompany.Config
* import com.twitter.util.TimeConversions._
* import com.twitter.util.StorageUnitConversions._
*
* new Config {
* val myValue = 1
* val myTimeout = 2.seconds
* val myBufferSize = 14.kilobytes
* }
*
* And finally, in Main.scala:
*
* package com.mycompany
*
* object Main {
* def main(args: Array[String]) {
* val config = Eval[Config](new File(args(0)))
* ...
* }
* }
*
* Note that in this example there is no need for any configuration format like Configgy, YAML, etc.
*
* So how does this work? Eval takes a file or string and generates a new scala class that has an apply method that
* evaluates that string. The newly generated file is then compiled. All generated .scala and .class
* files are stored, by default, in System.getProperty("java.io.tmpdir").
*
* After compilation, a new class loader is created with the temporary dir as the classPath.
* The generated class is loaded and then apply() is called.
*
* This implementation is inspired by
* http://scala-programming-language.1934581.n4.nabble.com/Compiler-API-td1992165.html
*
*/
object Eval {
private val compilerPath = jarPathOfClass("scala.tools.nsc.Interpreter")
private val libPath = jarPathOfClass("scala.ScalaObject")
/**
* Eval[Int]("1 + 1") // => 2
*/
def apply[T](stringToEval: String): T = {
val className = "Evaluator"
val targetDir = new File(System.getProperty("java.io.tmpdir"))
val wrappedFile = wrapInClass(stringToEval, className, targetDir)
compile(wrappedFile, targetDir)
val clazz = loadClass(targetDir, className)
val constructor = clazz.getConstructor()
val evaluator = constructor.newInstance().asInstanceOf[() => Any]
evaluator().asInstanceOf[T]
}
/**
* Eval[Int](new File("..."))
*/
def apply[T](fileToEval: File): T = {
val stringToEval = scala.io.Source.fromFile(fileToEval).mkString
apply(stringToEval)
}
/**
* Wrap sourceCode in a new class that has an apply method that evaluates that sourceCode.
* Write generated (temporary) classes to targetDir
*/
private def wrapInClass(sourceCode: String, className: String, targetDir: File) = {
val targetFile = File.createTempFile(className, ".scala", targetDir)
targetFile.deleteOnExit()
val writer = new FileWriter(targetFile)
writer.write("class " + className + " extends (() => Any) {\n")
writer.write(" def apply() = {\n")
writer.write(sourceCode)
writer.write("\n }\n")
writer.write("}\n")
writer.close()
targetFile
}
val JarFile = """\.jar$""".r
/**
* Compile a given file into the targetDir
*/
private def compile(file: File, targetDir: File) {
val settings = new Settings
val origBootclasspath = settings.bootclasspath.value
// Figure out our app classpath.
// TODO: there are likely a ton of corner cases waiting here
val configulousClassLoader = this.getClass.getClassLoader.asInstanceOf[URLClassLoader]
val configulousClasspath = configulousClassLoader.getURLs.map { url =>
val urlStr = url.toString
urlStr.substring(5, urlStr.length)
}.toList
// It's not clear how many nested jars we should open.
val classPathAndClassPathsNestedInJars = configulousClasspath.flatMap { fileName =>
val nestedClassPath = if (JarFile.findFirstMatchIn(fileName).isDefined) {
val nestedClassPathAttribute = new JarFile(fileName).getManifest.getMainAttributes.getValue("Class-Path")
if (nestedClassPathAttribute != null) {
nestedClassPathAttribute.split(" ").toList
} else Nil
} else Nil
List(fileName) ::: nestedClassPath
}
val bootClassPath = origBootclasspath.split(java.io.File.pathSeparator).toList
// the classpath for compile is our app path + boot path + make sure we have compiler/lib there
val pathList = bootClassPath ::: (classPathAndClassPathsNestedInJars ::: List(compilerPath, libPath))
val pathString = pathList.mkString(java.io.File.pathSeparator)
settings.bootclasspath.value = pathString
settings.classpath.value = pathString
settings.deprecation.value = true // enable detailed deprecation warnings
settings.unchecked.value = true // enable detailed unchecked warnings
settings.outdir.value = targetDir.toString
val reporter = new ConsoleReporter(settings)
val compiler = new Global(settings, reporter)
(new compiler.Run).compile(List(file.toString))
if (reporter.hasErrors || reporter.WARNING.count > 0) {
// FIXME: use proper logging
System.err.println("reporter has warnings attempting to compile")
reporter.printSummary()
}
}
/**
* Create a new classLoader with the targetDir as the classPath.
* Load the class with className
*/
private def loadClass(targetDir: File, className: String) = {
// set up the new classloader in targetDir
val scalaClassLoader = this.getClass.getClassLoader
val targetDirURL = targetDir.toURL
val newClassLoader = URLClassLoader.newInstance(Array(targetDir.toURL), scalaClassLoader)
newClassLoader.loadClass(className)
}
private def jarPathOfClass(className: String) = {
val resource = className.split('.').mkString("/", "/", ".class")
//println("resource for %s is %s".format(className, resource))
val path = getClass.getResource(resource).getPath
val indexOfFile = path.indexOf("file:")
val indexOfSeparator = path.lastIndexOf('!')
path.substring(indexOfFile, indexOfSeparator)
}
}
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