com.autonomousapps.internal.ConstantPoolParser.kt Maven / Gradle / Ivy

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// Copyright (c) 2024. Tony Robalik.
// SPDX-License-Identifier: Apache-2.0
package com.autonomousapps.internal

import com.autonomousapps.internal.utils.mapNotNullToSet
import java.nio.Buffer
import java.nio.ByteBuffer
import java.nio.ByteOrder
import kotlin.experimental.and

/**
 * A small parser to read the constant pool directly, in case it contains references ASM does not support.
 *
 * 
 *
 * Adapted from [stack overflow](http://stackoverflow.com/a/32278587/23691)
 *
 * @see The Constant Pool
 * @see maven-dependency-analyzer
 */
internal object ConstantPoolParser {

  private const val HEAD = 0xcafebabe.toInt()

  // Constant pool types
  private const val CONSTANT_UTF8: Byte = 1
  private const val CONSTANT_INTEGER: Byte = 3
  private const val CONSTANT_FLOAT: Byte = 4
  private const val CONSTANT_LONG: Byte = 5
  private const val CONSTANT_DOUBLE: Byte = 6
  private const val CONSTANT_CLASS: Byte = 7
  private const val CONSTANT_STRING: Byte = 8
  private const val CONSTANT_FIELDREF: Byte = 9
  private const val CONSTANT_METHODREF: Byte = 10
  private const val CONSTANT_INTERFACEMETHODREF: Byte = 11
  private const val CONSTANT_NAME_AND_TYPE: Byte = 12
  private const val CONSTANT_METHODHANDLE: Byte = 15
  private const val CONSTANT_METHOD_TYPE: Byte = 16
  private const val CONSTANT_DYNAMIC: Byte = 17
  private const val CONSTANT_INVOKE_DYNAMIC: Byte = 18

  private const val OXF0 = 0xf0
  private const val OXE0 = 0xe0
  private const val OX3F = 0x3F

  internal fun getConstantPoolClassReferences(b: ByteArray, classFilePath: String): Set {
    return parseConstantPoolClassReferences(ByteBuffer.wrap(b), classFilePath)
  }

  private fun parseConstantPoolClassReferences(buf: ByteBuffer, classFilePath: String): Set {
    if (buf.order(ByteOrder.BIG_ENDIAN).int != HEAD) {
      return emptySet()
    }

    buf.char
    buf.char // minor + ver
    val classes = HashSet()
    val stringConstants = HashMap()

    var ix = 1
    val num: Int = buf.char.code

    while (ix < num) {
      when (val b = buf.get()) {
        CONSTANT_UTF8 -> stringConstants[ix] = decodeString(buf)
        CONSTANT_CLASS, CONSTANT_STRING, CONSTANT_METHOD_TYPE -> classes.add(buf.char.code)
        CONSTANT_FIELDREF, CONSTANT_METHODREF, CONSTANT_INTERFACEMETHODREF, CONSTANT_NAME_AND_TYPE, CONSTANT_DYNAMIC, CONSTANT_INVOKE_DYNAMIC -> {
          buf.char
          buf.char
        }

        CONSTANT_INTEGER -> buf.int
        CONSTANT_FLOAT -> buf.float
        CONSTANT_DOUBLE -> {
          buf.double
          ix++
        }

        CONSTANT_LONG -> {
          buf.long
          ix++
        }

        CONSTANT_METHODHANDLE -> {
          buf.get()
          buf.char
        }

        else -> throw RuntimeException(
          "Unknown constant pool type: byte '$b' at pos '$ix', in class file '$classFilePath'"
        )
      }
      ix++
    }

    return classes.mapNotNullToSet {
      stringConstants[it]
    }
  }

  private fun decodeString(buf: ByteBuffer): String {
    val size = buf.char.code
    val oldLimit = buf.limit()

    (buf as Buffer).limit(buf.position() + size)
    val sb = StringBuilder(size + (size shr 1) + 16)
    while (buf.hasRemaining()) {
      val b = buf.get()
      if (b > 0) {
        sb.append(b.toInt().toChar())
      } else {
        val b2 = buf.get()
        if (b and OXF0.toByte() != OXE0.toByte()) {
          sb.append(((b and 0x1F).toInt() shl 6 or (b2.toInt() and OX3F)).toChar())
        } else {
          val b3: Int = buf.get().toInt()
          sb.append(((b and 0x0F).toInt() shl 12 or (b2.toInt() and OX3F shl 6) or (b3 and OX3F)).toChar())
        }
      }
    }
    (buf as Buffer).limit(oldLimit)
    return sb.toString()
  }
}