/**
   * Constructor.
   *
   * @param rq request
   * @param rs response
   * @throws IOException I/O exception
   */
  public HTTPContext(final HttpServletRequest rq, final HttpServletResponse rs) throws IOException {

    req = rq;
    res = rs;
    final String m = rq.getMethod();
    method = HTTPMethod.get(m);

    final StringBuilder uri = new StringBuilder(req.getRequestURL());
    final String qs = req.getQueryString();
    if (qs != null) uri.append('?').append(qs);
    log(false, m, uri);

    // set UTF8 as default encoding (can be overwritten)
    res.setCharacterEncoding(UTF8);

    segments = toSegments(req.getPathInfo());
    path = join(0);

    user = System.getProperty(DBUSER);
    pass = System.getProperty(DBPASS);

    // set session-specific credentials
    final String auth = req.getHeader(AUTHORIZATION);
    if (auth != null) {
      final String[] values = auth.split(" ");
      if (values[0].equals(BASIC)) {
        final String[] cred = Base64.decode(values[1]).split(":", 2);
        if (cred.length != 2) throw new LoginException(NOPASSWD);
        user = cred[0];
        pass = cred[1];
      } else {
        throw new LoginException(WHICHAUTH, values[0]);
      }
    }
  }
  /**
   * Initializes the servlet context, based on the servlet context. Parses all context parameters
   * and passes them on to the database context.
   *
   * @param sc servlet context
   * @throws IOException I/O exception
   */
  static synchronized void init(final ServletContext sc) throws IOException {
    // skip process if context has already been initialized
    if (context != null) return;

    // set servlet path as home directory
    final String path = sc.getRealPath("/");
    System.setProperty(Prop.PATH, path);

    // parse all context parameters
    final HashMap<String, String> map = new HashMap<String, String>();
    // store default web root
    map.put(MainProp.HTTPPATH[0].toString(), path);

    final Enumeration<?> en = sc.getInitParameterNames();
    while (en.hasMoreElements()) {
      final String key = en.nextElement().toString();
      if (!key.startsWith(Prop.DBPREFIX)) continue;

      // only consider parameters that start with "org.basex."
      String val = sc.getInitParameter(key);
      if (eq(key, DBUSER, DBPASS, DBMODE, DBVERBOSE)) {
        // store servlet-specific parameters as system properties
        System.setProperty(key, val);
      } else {
        // prefix relative paths with absolute servlet path
        if (key.endsWith("path") && !new File(val).isAbsolute()) {
          val = path + File.separator + val;
        }
        // store remaining parameters (without project prefix) in map
        map.put(key.substring(Prop.DBPREFIX.length()).toUpperCase(Locale.ENGLISH), val);
      }
    }
    context = new Context(map);

    if (SERVER.equals(System.getProperty(DBMODE))) {
      new BaseXServer(context);
    } else {
      context.log = new Log(context);
    }
  }