import java.net.*;
import java.io.*;

// A pure 1.1 variation of a class that appears in
// Core Web Programming from Prentice Hall Publishers.
// May be freely used or adapted.
// 1998 Marty Hall, http://www.apl.jhu.edu/~hall/java/.


//----------------------------------------------------
/** Given an email address of the form user@host,
 *  connect to port 25 of the host and issue an
 *  'expn' request for the user. Print the results.
 */

public class AddressVerifier extends NetworkClient {
  private String username;

  //----------------------------------------------------

  public static void main(String[] args) {
    if (args.length != 1)
      usage();
    MailAddress address = new MailAddress(args[0]);
    AddressVerifier verifier
      = new AddressVerifier(address.getUsername(),
                            address.getHostname(),
                            25);
    verifier.connect();
  }

  //----------------------------------------------------

  public AddressVerifier(String username,
                         String hostname,
                         int port) {
    super(hostname, port);
    this.username = username;
  }

  //----------------------------------------------------
  /** NetworkClient, the parent class, automatically
   *  establishes the connection and then passes
   *  the Socket to handleConnection. So this method
   *  does all the real work of talking to the mail
   *  server.
   */

  // You can't use readLine, since it blocks.
  // Blocking IO via readLine is only appropriate
  // when you know how many lines to read (but mail
  // servers send a varying number of lines when
  // you first connect) or when they close the
  // connection when done (as HTTP servers do,
  // yielding null for readLine. Also, we'll
  // be lazy and assume that 1000 bytes is
  // more than enough to handle any server
  // welcome message and the actual EXPN response.

  protected void handleConnection(Socket client) {
    try {
      PrintWriter out = SocketUtil.getPrintWriter(client);
      InputStream in = client.getInputStream();
      byte[] response = new byte[1000];
      // Clear out mail server's welcome message.
      in.read(response);
      out.println("EXPN " + username);
      // Read the response to the EXPN command.
      int numBytes = in.read(response);
      // The 0 means to use normal ASCII encoding.
      System.out.write(response, 0, numBytes);
      out.println("QUIT");
      client.close();
    } catch(IOException ioe) {
      System.out.println("Couldn't make connection: "
                         + ioe);
    }
  }
  //----------------------------------------------------
  /** Warn user if they supplied the wrong arguments. */

  public static void usage() {
    System.out.println
      ("You must supply an email address " +
       "of the form 'username@hostname'.");
    System.exit(-1);
  }
}