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Scala example source code file (ClassFileParser.scala)

This example Scala source code file (ClassFileParser.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Scala tags/keywords

any, array, bytecode, bytecode, constantpool, constantpool, elementvalue, int, int, io, seq, seq, string, t, x

The Scala ClassFileParser.scala source code

package scala.tools.scalap
package scalax
package rules
package scalasig


import java.io.IOException

import scala._
import scala.Predef._

object ByteCode {
  def apply(bytes : Array[Byte]) = new ByteCode(bytes, 0, bytes.length)

  def forClass(clazz : Class[_]) = {
    val name = clazz.getName
    val subPath = name.substring(name.lastIndexOf('.') + 1) + ".class"
    val in = clazz.getResourceAsStream(subPath)
    
    try {
      var rest = in.available()
      val bytes = new Array[Byte](rest)
      while (rest > 0) {
        val res = in.read(bytes, bytes.length - rest, rest)
        if (res == -1) throw new IOException("read error")
        rest -= res
      }
      ByteCode(bytes)
      
    } finally { 
      in.close() 
    }
  }
}

/** Represents a chunk of raw bytecode.  Used as input for the parsers
 */
class ByteCode(val bytes : Array[Byte], val pos : Int, val length : Int) {
  
  assert(pos >= 0 && length >= 0 && pos + length <= bytes.length)
  
  def nextByte = if (length == 0) Failure else Success(drop(1), bytes(pos))
  def next(n : Int) = if (length >= n) Success(drop(n), take(n)) else Failure
  
  def take(n : Int) = new ByteCode(bytes, pos, n)
  def drop(n : Int) = new ByteCode(bytes, pos + n, length - n)
  
  def fold[X](x : X)(f : (X, Byte) => X) : X = {
    var result = x
    var i = pos
    while (i < pos + length) {
      result = f(result, bytes(i))
      i += 1
    }
    result
  }
  
  override def toString = length + " bytes"

  def toInt = fold(0) { (x, b) => (x << 8) + (b & 0xFF)}
  def toLong = fold(0L) { (x, b) => (x << 8) + (b & 0xFF)}

  /**
   * Transforms array subsequence of the current buffer into the UTF8 String and
   * stores and array of bytes for the decompiler
   */
  def fromUTF8StringAndBytes = {
    val chunk: Array[Byte] = bytes drop pos take length
    StringBytesPair(io.Codec.fromUTF8(chunk).mkString, chunk)
  }

  def byte(i : Int) = bytes(pos) & 0xFF
}

/**
 * The wrapper for decode UTF-8 string
 */
case class StringBytesPair(string: String, bytes: Array[Byte])

/** Provides rules for parsing byte-code.
*/
trait ByteCodeReader extends RulesWithState {
  type S = ByteCode
  type Parser[A] = Rule[A, String]
    
  val byte = apply(_ nextByte)
  
  val u1 = byte ^^ (_ & 0xFF)
  val u2 = bytes(2) ^^ (_ toInt)
  val u4 = bytes(4) ^^ (_ toInt) // should map to Long??
  
  def bytes(n : Int) = apply(_ next n)  
}

object ClassFileParser extends ByteCodeReader {
  def parse(byteCode : ByteCode) = expect(classFile)(byteCode)
  def parseAnnotations(byteCode: ByteCode) = expect(annotations)(byteCode)
  
  val magicNumber = (u4 filter (_ == 0xCAFEBABE)) | error("Not a valid class file")
  val version = u2 ~ u2 ^^ { case minor ~ major => (major,  minor) }
  val constantPool = (u2 ^^ ConstantPool) >> repeatUntil(constantPoolEntry)(_ isFull)
  
  // NOTE currently most constants just evaluate to a string description
  // TODO evaluate to useful values
  val utf8String = (u2 >> bytes) ^^ add1 { raw => pool => raw.fromUTF8StringAndBytes }
  val intConstant = u4 ^^ add1 { x => pool => x }
  val floatConstant = bytes(4) ^^ add1 { raw => pool => "Float: TODO" }
  val longConstant = bytes(8) ^^ add2 { raw => pool => raw.toLong }
  val doubleConstant = bytes(8) ^^ add2 { raw => pool => "Double: TODO" }
  val classRef = u2 ^^ add1 { x => pool => "Class: " + pool(x) }
  val stringRef = u2 ^^ add1 { x => pool => "String: " + pool(x) }
  val fieldRef = memberRef("Field")
  val methodRef = memberRef("Method")
  val interfaceMethodRef = memberRef("InterfaceMethod")
  val nameAndType = u2 ~ u2 ^^ add1 { case name ~ descriptor => pool => "NameAndType: " + pool(name) + ", " + pool(descriptor) }
  
  val constantPoolEntry = u1 >> {
    case 1 => utf8String
    case 3 => intConstant
    case 4 => floatConstant
    case 5 => longConstant
    case 6 => doubleConstant
    case 7 => classRef
    case 8 => stringRef
    case 9 => fieldRef
    case 10 => methodRef
    case 11 => interfaceMethodRef
    case 12 => nameAndType
  }
  
  val interfaces = u2 >> u2.times
  
  // bytes are parametrizes by the length, declared in u4 section
  val attribute = u2 ~ (u4 >> bytes) ^~^ Attribute
  // parse attributes u2 times
  val attributes = u2 >> attribute.times

  // parse runtime-visible annotations
  abstract class ElementValue
  case class AnnotationElement(elementNameIndex: Int, elementValue: ElementValue)
  case class ConstValueIndex(index: Int) extends ElementValue
  case class EnumConstValue(typeNameIndex: Int, constNameIndex: Int) extends ElementValue
  case class ClassInfoIndex(index: Int) extends ElementValue
  case class Annotation(typeIndex: Int, elementValuePairs: Seq[AnnotationElement]) extends ElementValue
  case class ArrayValue(values: Seq[ElementValue]) extends ElementValue

  def element_value: Parser[ElementValue] = u1 >> {
    case 'B'|'C'|'D'|'F'|'I'|'J'|'S'|'Z'|'s' => u2 ^^ ConstValueIndex
    case 'e' => u2 ~ u2 ^~^ EnumConstValue
    case 'c' => u2 ^^ ClassInfoIndex
    case '@' => annotation //nested annotation
    case '[' => u2 >> element_value.times ^^ ArrayValue
  }

  val element_value_pair = u2 ~ element_value ^~^ AnnotationElement
  val annotation: Parser[Annotation] = u2 ~ (u2 >> element_value_pair.times) ^~^ Annotation
  val annotations = u2 >> annotation.times

  val field = u2 ~ u2 ~ u2 ~ attributes ^~~~^ Field
  val fields = u2 >> field.times
  
  val method = u2 ~ u2 ~ u2 ~ attributes ^~~~^ Method
  val methods = u2 >> method.times
  
  val header = magicNumber -~ u2 ~ u2 ~ constantPool ~ u2 ~ u2 ~ u2 ~ interfaces ^~~~~~~^ ClassFileHeader
  val classFile = header ~ fields ~ methods ~ attributes ~- !u1 ^~~~^ ClassFile 

  // TODO create a useful object, not just a string
  def memberRef(description : String) = u2 ~ u2 ^^ add1 {
    case classRef ~ nameAndTypeRef => pool => description + ": " + pool(classRef) + ", " + pool(nameAndTypeRef)
  }

  def add1[T](f : T => ConstantPool => Any)(raw : T)(pool : ConstantPool) = pool add f(raw)
  def add2[T](f : T => ConstantPool => Any)(raw : T)(pool : ConstantPool) = pool add f(raw) add { pool => "<empty>" }
}

case class ClassFile(
    header : ClassFileHeader,
    fields : Seq[Field],
    methods : Seq[Method],
    attributes : Seq[Attribute]) {
  
  def majorVersion = header.major
  def minorVersion = header.minor
  
  def className = constant(header.classIndex)
  def superClass = constant(header.superClassIndex)
  def interfaces = header.interfaces.map(constant)
    
  def constant(index : Int) = header.constants(index) match {
    case StringBytesPair(str, _) => str
    case z => z
  }

  def constantWrapped(index: Int) = header.constants(index)
    
  def attribute(name : String) = attributes.find {attrib => constant(attrib.nameIndex) == name }

  val RUNTIME_VISIBLE_ANNOTATIONS = "RuntimeVisibleAnnotations"
  def annotations = (attributes.find(attr => constant(attr.nameIndex) == RUNTIME_VISIBLE_ANNOTATIONS)
          .map(attr => ClassFileParser.parseAnnotations(attr.byteCode)))

  def annotation(name: String) = annotations.flatMap(seq => seq.find(annot => constant(annot.typeIndex) == name))
}
  
case class Attribute(nameIndex : Int, byteCode : ByteCode)
case class Field(flags : Int, nameIndex : Int, descriptorIndex : Int, attributes : Seq[Attribute])
case class Method(flags : Int, nameIndex : Int, descriptorIndex : Int, attributes : Seq[Attribute])
  
case class ClassFileHeader(
    minor : Int, 
    major : Int, 
    constants : ConstantPool, 
    flags : Int,
    classIndex : Int,
    superClassIndex : Int,
    interfaces : Seq[Int]) {
    
  def constant(index : Int) = constants(index)
}
  
case class ConstantPool(len : Int) {
  val size = len - 1
  
  private val buffer = new scala.collection.mutable.ArrayBuffer[ConstantPool => Any]
  private val values = Array.fill[Option[Any]](size)(None)
    
  def isFull = buffer.length >= size
  
  def apply(index : Int) = {
    // Note constant pool indices are 1-based
    val i = index - 1
    values(i) getOrElse {
      val value = buffer(i)(this)
      buffer(i) = null
      values(i) = Some(value)
      value
    }
  }
    
  def add(f : ConstantPool => Any) = {
    buffer += f
    this
  }
}

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