WpadProxySearchStrategy.java

package com.github.markusbernhardt.proxy.search.wpad;

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.InetAddress;
import java.net.Proxy;
import java.net.ProxySelector;
import java.net.URL;
import java.net.UnknownHostException;
import java.util.Properties;

import com.github.markusbernhardt.proxy.ProxySearchStrategy;
import com.github.markusbernhardt.proxy.util.Logger;
import com.github.markusbernhardt.proxy.util.Logger.LogLevel;
import com.github.markusbernhardt.proxy.util.ProxyException;
import com.github.markusbernhardt.proxy.util.ProxyUtil;

/*****************************************************************************
 * Uses automatic proxy script search (WPAD) to find an PAC file automatically.
 * <p>
 * Note: at the moment only the DNS name guessing schema is implemented. All
 * others are missing.
 * </p>
 * <p>
 * For more information about WPAD:
 * <a href="http://en.wikipedia.org/wiki/Web_Proxy_Autodiscovery_Protocol">
 * Web_Proxy_Autodiscovery_Protocol</a>
 * </p>
 * <p>
 * Outdated RFC draft: <a href=
 * "http://www.web-cache.com/Writings/Internet-Drafts/draft-ietf-wrec-wpad-01.txt">
 * draft-ietf-wrec-wpad-01.txt</a>
 * </p>
 * 
 * @author Markus Bernhardt, Copyright 2016
 * @author Bernd Rosstauscher, Copyright 2009
 ****************************************************************************/

public class WpadProxySearchStrategy implements ProxySearchStrategy {

  /*************************************************************************
   * Constructor
   ************************************************************************/

  public WpadProxySearchStrategy() {
    super();
  }

  /*************************************************************************
   * Loads the proxy settings from a PAC file. The location of the PAC file is
   * determined automatically.
   * 
   * @return a configured ProxySelector, null if none is found.
   * @throws ProxyException
   *           on error.
   ************************************************************************/

  @Override
  public ProxySelector getProxySelector() throws ProxyException {
    try {
      Logger.log(getClass(), LogLevel.TRACE, "Using WPAD to find a proxy");

      String pacScriptUrl = detectScriptUrlPerDHCP();
      if (pacScriptUrl == null) {
        pacScriptUrl = detectScriptUrlPerDNS();
      }
      if (pacScriptUrl == null) {
        return null;
      }
      Logger.log(getClass(), LogLevel.TRACE, "PAC script url found: {0}", pacScriptUrl);
      return ProxyUtil.buildPacSelectorForUrl(pacScriptUrl);
    } catch (IOException e) {
      Logger.log(getClass(), LogLevel.ERROR, "Error during WPAD search.", e);
      throw new ProxyException(e);
    }
  }

  /*************************************************************************
   * Gets the printable name of the search strategy.
   * 
   * @return the printable name of the search strategy
   ************************************************************************/

  @Override
  public String getName() {
    return "wpad";
  }

  /*************************************************************************
   * Loads the settings and stores them in a properties map.
   * 
   * @return the settings.
   ************************************************************************/

  public Properties readSettings() {
    try {
      String pacScriptUrl = detectScriptUrlPerDHCP();
      if (pacScriptUrl == null) {
        pacScriptUrl = detectScriptUrlPerDNS();
      }
      if (pacScriptUrl == null) {
        return null;
      }
      Properties result = new Properties();
      result.setProperty("url", pacScriptUrl);
      return result;
    } catch (IOException e) {
      // Ignore and return empty properties.
      return new Properties();
    }
  }

  /*************************************************************************
   * Uses DNS to find the script URL. Attention: this detection method is known
   * to have some severe security issues.
   * 
   * @return the URL, null if not found.
   ************************************************************************/

  private String detectScriptUrlPerDNS() throws IOException {

    String fqdn = InetAddress.getLocalHost().getCanonicalHostName();
    if (fqdn.equalsIgnoreCase("localhost") || fqdn.length() == 0 || Character.isDigit(fqdn.charAt(0))) {
      return null;
    }

    Logger.log(getClass(), LogLevel.TRACE, "Searching per DNS guessing.");

    String[] fqdnParts = fqdn.split("\\.");
    for (int i = 0; i < fqdnParts.length; i++) {
      // Build URL
      StringBuilder stringBuilder = new StringBuilder("http://wpad");
      for (int j = i + 1; j < fqdnParts.length; j++) {
        stringBuilder.append('.');
        stringBuilder.append(fqdnParts[j]);
      }
      stringBuilder.append("/wpad.dat");

      // Try to connect to URL
      try {
        URL lookupURL = new URL(stringBuilder.toString());
        Logger.log(getClass(), LogLevel.TRACE, "Trying url: {0}", lookupURL);

        HttpURLConnection con = (HttpURLConnection) lookupURL.openConnection(Proxy.NO_PROXY);
        con.setInstanceFollowRedirects(true);
        con.setRequestProperty("accept", "application/x-ns-proxy-autoconfig");
        if (con.getResponseCode() == 200) {
          return lookupURL.toString();
        }
        con.disconnect();
      } catch (UnknownHostException e) {
        Logger.log(getClass(), LogLevel.DEBUG, "Not available!");
        // Not a real error, try next address
      }
    }

    return null;
  }

  /*************************************************************************
   * Uses DHCP to find the script URL.
   * 
   * @return the URL, null if not found.
   ************************************************************************/

  private String detectScriptUrlPerDHCP() {
    Logger.log(getClass(), LogLevel.DEBUG, "Searching per DHCP not supported yet.");
    // TODO Rossi 28.04.2009 Not implemented yet.
    return null;
  }

}