hosts parser

gistfile1.scala

import scala.util.parsing.combinator._

/**
 * <hosts> ::= { <line> }
 * <line> ::= <entry> | [ <comment> ] <eol>
 * <entry> ::= <ip-address> <hostnames> [ <comment> ] <eol>
 * <ip-address> ::= <ipv4-address> | <ipv6-address>
 * <ipv4-address> ::= "[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}"
 * <ipv6-address> ::= ...
 * <hostnames> ::= <hostname> { <hostname> }
 * <hostname> ::= [a-zA-Z\.]+
 * <eol> ::= "\r?\n"
 * <comment> ::= #.*
 */
class HostsParser extends RegexParsers {
  import java.net.InetAddress

  case class Comment(text: String = "")

  override val whiteSpace = """[ \t]+""".r

  def hosts: Parser[Map[InetAddress, Set[String]]] = (line*) ^^ { lines =>
    val map = new collection.mutable.HashMap[InetAddress, Set[String]]
    lines.flatMap(e => e).foreach[Any] {
      case (key,  value) => {
  if (map.contains(key)) map(key) = map(key) ++ value
  else map += (key -> value)
      }
    }
    map.toMap
  }

  def line: Parser[Option[Pair[InetAddress, Set[String]]]]
    = (entry | opt(comment)~eol) ^^ {
    case entry : Pair[InetAddress, Set[String]] => Some(entry)
    case _ => None
  }
  def entry: Parser[Pair[InetAddress, Set[String]]]
    = ipAddress~(hostname*)~opt(comment)~eol ^^
    {
      case ipAddress~hostnames~_~eol => (ipAddress -> hostnames.toSet)
    }
  def ipAddress: Parser[InetAddress] = ipv4Address | ipv6Address
  def ipv4Address: Parser[InetAddress] = """[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}""".r ^^ (s => InetAddress.getByName(s))
  def ipv6Address: Parser[InetAddress] = """[:%a-z0-9]+""".r ^^ (s => InetAddress.getByName(s))
  def hostname: Parser[String] = """[a-zA-Z0-9\.]+""".r
  def eol: Parser[Any] = """\r?\n""".r ^^ (s => "")
  def comment: Parser[Comment] = """#.*""".r ^^ (s => Comment(s))
}

object Main extends HostsParser with App {
  import scala.io.Source
  val hostsFile = Source.fromFile(args(0)).mkString
  println("=====================================")
  println(hostsFile)
  println("=====================================")
  println(parseAll(hosts, hostsFile))
}