/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999,2000 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xerces" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, iClick Inc., 
 * http://www.apache.org.  For more information on the Apache Software 
 * Foundation, please see <http://www.apache.org/>.
 */

package org.apache.xerces.utils;

import java.io.IOException;
import java.io.Serializable;

/**********************************************************************
* A class to represent a Uniform Resource Identifier (URI). This class
* is designed to handle the parsing of URIs and provide access to 
* the various components (scheme, host, port, userinfo, path, query
* string and fragment) that may constitute a URI. 
* <p>
* Parsing of a URI specification is done according to the URI 
* syntax described in RFC 2396 
* <http://www.ietf.org/rfc/rfc2396.txt?number=2396>. Every URI consists 
* of a scheme, followed by a colon (':'), followed by a scheme-specific
* part. For URIs that follow the "generic URI" syntax, the scheme-
* specific part begins with two slashes ("//") and may be followed
* by an authority segment (comprised of user information, host, and 
* port), path segment, query segment and fragment. Note that RFC 2396
* no longer specifies the use of the parameters segment and excludes
* the "user:password" syntax as part of the authority segment. If 
* "user:password" appears in a URI, the entire user/password string
* is stored as userinfo.
* <p>
* For URIs that do not follow the "generic URI" syntax (e.g. mailto),
* the entire scheme-specific part is treated as the "path" portion
* of the URI.
* <p>
* Note that, unlike the java.net.URL class, this class does not provide
* any built-in network access functionality nor does it provide any 
* scheme-specific functionality (for example, it does not know a 
* default port for a specific scheme). Rather, it only knows the 
* grammar and basic set of operations that can be applied to a URI.
*
* @version  $Id$
*
**********************************************************************/
 public class URI implements Serializable {

  /*******************************************************************
  * MalformedURIExceptions are thrown in the process of building a URI
  * or setting fields on a URI when an operation would result in an 
  * invalid URI specification. 
  *
  ********************************************************************/
  public static class MalformedURIException extends IOException {

   /******************************************************************
    * Constructs a <code>MalformedURIException</code> with no specified
    * detail message.
    ******************************************************************/
    public MalformedURIException() {
      super();
    }

    /*****************************************************************
    * Constructs a <code>MalformedURIException</code> with the 
    * specified detail message. 
    *
    * @param p_msg the detail message.
    ******************************************************************/
    public MalformedURIException(String p_msg) {
      super(p_msg);
    }
  }

  /** reserved characters */
  private static final String RESERVED_CHARACTERS = ";/?:@&=+$,";

  /** URI punctuation mark characters - these, combined with 
      alphanumerics, constitute the "unreserved" characters */
  private static final String MARK_CHARACTERS = "-_.!~*'() ";

  /** scheme can be composed of alphanumerics and these characters */
  private static final String SCHEME_CHARACTERS = "+-.";

  /** userinfo can be composed of unreserved, escaped and these 
      characters */
  private static final String USERINFO_CHARACTERS = ";:&=+$,";

  /** Stores the scheme (usually the protocol) for this URI. */
  private String m_scheme = null;

  /** If specified, stores the userinfo for this URI; otherwise null */
  private String m_userinfo = null;

  /** If specified, stores the host for this URI; otherwise null */
  private String m_host = null;

  /** If specified, stores the port for this URI; otherwise -1 */
  private int m_port = -1;

  /** If specified, stores the path for this URI; otherwise null */
  private String m_path = null;

  /** If specified, stores the query string for this URI; otherwise 
      null.  */
  private String m_queryString = null;

  /** If specified, stores the fragment for this URI; otherwise null */
  private String m_fragment = null;

  private static boolean DEBUG = false;

  /**
  * Construct a new and uninitialized URI.
  */
  public URI() {
  }

 /**
  * Construct a new URI from another URI. All fields for this URI are 
  * set equal to the fields of the URI passed in.
  *
  * @param p_other the URI to copy (cannot be null)
  */
  public URI(URI p_other) {
    initialize(p_other);
  }

 /**
  * Construct a new URI from a URI specification string. If the 
  * specification follows the "generic URI" syntax, (two slashes 
  * following the first colon), the specification will be parsed 
  * accordingly - setting the scheme, userinfo, host,port, path, query
  * string and fragment fields as necessary. If the specification does 
  * not follow the "generic URI" syntax, the specification is parsed 
  * into a scheme and scheme-specific part (stored as the path) only.
  *
  * @param p_uriSpec the URI specification string (cannot be null or
  *                  empty)
  *
  * @exception MalformedURIException if p_uriSpec violates any syntax
  *                                   rules
  */
  public URI(String p_uriSpec) throws MalformedURIException {
    this((URI)null, p_uriSpec);
  }

 /**
  * Construct a new URI from a base URI and a URI specification string.
  * The URI specification string may be a relative URI. 
  *
  * @param p_base the base URI (cannot be null if p_uriSpec is null or
  *               empty)
  * @param p_uriSpec the URI specification string (cannot be null or
  *                  empty if p_base is null)
  *
  * @exception MalformedURIException if p_uriSpec violates any syntax
  *                                  rules
  */
  public URI(URI p_base, String p_uriSpec) throws MalformedURIException {
    initialize(p_base, p_uriSpec);
  }

 /**
  * Construct a new URI that does not follow the generic URI syntax.
  * Only the scheme and scheme-specific part (stored as the path) are
  * initialized.
  *
  * @param p_scheme the URI scheme (cannot be null or empty)
  * @param p_schemeSpecificPart the scheme-specific part (cannot be
  *                             null or empty)
  *
  * @exception MalformedURIException if p_scheme violates any 
  *                                  syntax rules
  */
  public URI(String p_scheme, String p_schemeSpecificPart) 
             throws MalformedURIException {
    if (p_scheme == null || p_scheme.trim().length() == 0) {
      throw new MalformedURIException(
            "Cannot construct URI with null/empty scheme!");
    }
    if (p_schemeSpecificPart == null || 
        p_schemeSpecificPart.trim().length() == 0) {
      throw new MalformedURIException(
          "Cannot construct URI with null/empty scheme-specific part!");
    }
    setScheme(p_scheme);
    setPath(p_schemeSpecificPart);
  }

 /**
  * Construct a new URI that follows the generic URI syntax from its
  * component parts. Each component is validated for syntax and some
  * basic semantic checks are performed as well.  See the individual
  * setter methods for specifics.
  *
  * @param p_scheme the URI scheme (cannot be null or empty)
  * @param p_host the hostname or IPv4 address for the URI
  * @param p_path the URI path - if the path contains '?' or '#',
  *               then the query string and/or fragment will be
  *               set from the path; however, if the query and 
  *               fragment are specified both in the path and as 
  *               separate parameters, an exception is thrown
  * @param p_queryString the URI query string (cannot be specified
  *                      if path is null)
  * @param p_fragment the URI fragment (cannot be specified if path
  *                   is null)
  *
  * @exception MalformedURIException if any of the parameters violates 
  *                                  syntax rules or semantic rules
  */
  public URI(String p_scheme, String p_host, String p_path,
             String p_queryString, String p_fragment) 
         throws MalformedURIException {
    this(p_scheme, null, p_host, -1, p_path, p_queryString, p_fragment);
  }

 /**
  * Construct a new URI that follows the generic URI syntax from its
  * component parts. Each component is validated for syntax and some
  * basic semantic checks are performed as well.  See the individual
  * setter methods for specifics.
  *
  * @param p_scheme the URI scheme (cannot be null or empty)
  * @param p_userinfo the URI userinfo (cannot be specified if host 
  *                   is null)
  * @param p_host the hostname or IPv4 address for the URI
  * @param p_port the URI port (may be -1 for "unspecified"; cannot 
  *               be specified if host is null)
  * @param p_path the URI path - if the path contains '?' or '#',
  *               then the query string and/or fragment will be
  *               set from the path; however, if the query and 
  *               fragment are specified both in the path and as 
  *               separate parameters, an exception is thrown
  * @param p_queryString the URI query string (cannot be specified
  *                      if path is null)
  * @param p_fragment the URI fragment (cannot be specified if path
  *                   is null)
  *
  * @exception MalformedURIException if any of the parameters violates 
  *                                  syntax rules or semantic rules
  */
  public URI(String p_scheme, String p_userinfo, 
             String p_host, int p_port, String p_path,
             String p_queryString, String p_fragment) 
         throws MalformedURIException {
    if (p_scheme == null || p_scheme.trim().length() == 0) {
      throw new MalformedURIException("Scheme is required!");
    }

    if (p_host == null) {
      if (p_userinfo != null) {
        throw new MalformedURIException(
             "Userinfo may not be specified if host is not specified!");
      }
      if (p_port != -1) {
        throw new MalformedURIException(      
             "Port may not be specified if host is not specified!");
      }
    }

    if (p_path != null) { 
      if (p_path.indexOf('?') != -1 && p_queryString != null) {
        throw new MalformedURIException(
          "Query string cannot be specified in path and query string!");
      }

      if (p_path.indexOf('#') != -1 && p_fragment != null) {
        throw new MalformedURIException(
          "Fragment cannot be specified in both the path and fragment!");
      }
    }

    setScheme(p_scheme);
    setHost(p_host);
    setPort(p_port);
    setUserinfo(p_userinfo);
    setPath(p_path);
    setQueryString(p_queryString);
    setFragment(p_fragment);
  }

 /**
  * Initialize all fields of this URI from another URI.
  *
  * @param p_other the URI to copy (cannot be null)
  */
  private void initialize(URI p_other) {
    m_scheme = p_other.getScheme();
    m_userinfo = p_other.getUserinfo();
    m_host = p_other.getHost();
    m_port = p_other.getPort();
    m_path = p_other.getPath();
    m_queryString = p_other.getQueryString();
    m_fragment = p_other.getFragment();
  }

 /**
  * Initializes this URI from a base URI and a URI specification string.
  * See RFC 2396 Section 4 and Appendix B for specifications on parsing
  * the URI and Section 5 for specifications on resolving relative URIs
  * and relative paths.
  *
  * @param p_base the base URI (may be null if p_uriSpec is an absolute
  *               URI)
  * @param p_uriSpec the URI spec string which may be an absolute or
  *                  relative URI (can only be null/empty if p_base
  *                  is not null)
  *
  * @exception MalformedURIException if p_base is null and p_uriSpec
  *                                  is not an absolute URI or if
  *                                  p_uriSpec violates syntax rules 
  */
  private void initialize(URI p_base, String p_uriSpec) 
                         throws MalformedURIException {
    if (p_base == null && 
        (p_uriSpec == null || p_uriSpec.trim().length() == 0)) {
      throw new MalformedURIException(
                  "Cannot initialize URI with empty parameters.");
      }

    // just make a copy of the base if spec is empty
    if (p_uriSpec == null || p_uriSpec.trim().length() == 0) {
      initialize(p_base);
      return;
    }

    String uriSpec = p_uriSpec.trim();
    int uriSpecLen = uriSpec.length();
    int index = 0;

    // check for scheme
    if (uriSpec.indexOf(':') == -1) {
      int fragmentIdx = uriSpec.indexOf('#');
      if (p_base == null && fragmentIdx != 0 ) {//A standalone base is a valid URI according to spec
        throw new MalformedURIException("No scheme found in URI.");
      }
    }
    else {
      initializeScheme(uriSpec);
      index = m_scheme.length()+1;
    }

    // two slashes means generic URI syntax, so we get the authority
    if (((index+1) < uriSpecLen) && 
        (uriSpec.substring(index).startsWith("//"))) {
      index += 2;
      int startPos = index;

      // get authority - everything up to path, query or fragment
      char testChar = '\0';
      while (index < uriSpecLen) {
        testChar = uriSpec.charAt(index);
        if (testChar == '/' || testChar == '?' || testChar == '#') {
          break;
        }
        index++;
      }

      // if we found authority, parse it out, otherwise we set the
      // host to empty string
      if (index > startPos) {
        initializeAuthority(uriSpec.substring(startPos, index));
      }
      else {
        m_host = "";
      }
    }

    initializePath(uriSpec.substring(index));

    // Resolve relative URI to base URI - see RFC 2396 Section 5.2
    // In some cases, it might make more sense to throw an exception
    // (when scheme is specified is the string spec and the base URI
    // is also specified, for example), but we're just following the
    // RFC specifications 
    if (p_base != null) {

      // check to see if this is the current doc - RFC 2396 5.2 #2
      // note that this is slightly different from the RFC spec in that
      // we don't include the check for query string being null
      // - this handles cases where the urispec is just a query
      // string or a fragment (e.g. "?y" or "#s") - 
      // see <http://www.ics.uci.edu/~fielding/url/test1.html> which
      // identified this as a bug in the RFC
      if (m_path.length() == 0 && m_scheme == null && 
          m_host == null) {
        m_scheme = p_base.getScheme();
        m_userinfo = p_base.getUserinfo();
        m_host = p_base.getHost();
        m_port = p_base.getPort();
        m_path = p_base.getPath();

        if (m_queryString == null) {
          m_queryString = p_base.getQueryString();
        }
        return;
      }

      // check for scheme - RFC 2396 5.2 #3
      // if we found a scheme, it means absolute URI, so we're done
      if (m_scheme == null) {
        m_scheme = p_base.getScheme();
      }
      else {
        return;
      }

      // check for authority - RFC 2396 5.2 #4
      // if we found a host, then we've got a network path, so we're done
      if (m_host == null) {
        m_userinfo = p_base.getUserinfo();
        m_host = p_base.getHost();
        m_port = p_base.getPort();
      }
      else {
        return;
      }

      // check for absolute path - RFC 2396 5.2 #5
      if (m_path.length() > 0 && 
          m_path.startsWith("/")) {
        return;
      }

      // if we get to this point, we need to resolve relative path
      // RFC 2396 5.2 #6
      String path = new String();
      String basePath = p_base.getPath();

      // 6a - get all but the last segment of the base URI path
      if (basePath != null) {
        int lastSlash = basePath.lastIndexOf('/');
        if (lastSlash != -1) {
          path = basePath.substring(0, lastSlash+1);
        }
      }

      // 6b - append the relative URI path
      path = path.concat(m_path);

      // 6c - remove all "./" where "." is a complete path segment
      index = -1;
      while ((index = path.indexOf("/./")) != -1) {
        path = path.substring(0, index+1).concat(path.substring(index+3));
      }

      // 6d - remove "." if path ends with "." as a complete path segment
      if (path.endsWith("/.")) {
        path = path.substring(0, path.length()-1);
      }

      // 6e - remove all "<segment>/../" where "<segment>" is a complete 
      // path segment not equal to ".."
      index = -1;
      int segIndex = -1;
      String tempString = null;

      while ((index = path.indexOf("/../")) > 0) {
        tempString = path.substring(0, path.indexOf("/../"));
        segIndex = tempString.lastIndexOf('/');
        if (segIndex != -1) {
          if (!tempString.substring(segIndex++).equals("..")) {
            path = path.substring(0, segIndex).concat(path.substring(index+4));
           }
        }
      }

      // 6f - remove ending "<segment>/.." where "<segment>" is a 
      // complete path segment
      if (path.endsWith("/..")) {
        tempString = path.substring(0, path.length()-3);
        segIndex = tempString.lastIndexOf('/');
        if (segIndex != -1) {
          path = path.substring(0, segIndex+1);
        }
      }
      m_path = path;
    }
  }

 /**
  * Initialize the scheme for this URI from a URI string spec.
  *
  * @param p_uriSpec the URI specification (cannot be null)
  *
  * @exception MalformedURIException if URI does not have a conformant
  *                                  scheme
  */
  private void initializeScheme(String p_uriSpec) 
                 throws MalformedURIException {
    int uriSpecLen = p_uriSpec.length();
    int index = 0;
    String scheme = null;
    char testChar = '\0';

    while (index < uriSpecLen) {
      testChar = p_uriSpec.charAt(index);
      if (testChar == ':' || testChar == '/' || 
          testChar == '?' || testChar == '#') {
        break;
      }
      index++;
    }
    scheme = p_uriSpec.substring(0, index);

    if (scheme.length() == 0) {
      throw new MalformedURIException("No scheme found in URI.");
    }
    else {
      setScheme(scheme);
    }
  }

 /**
  * Initialize the authority (userinfo, host and port) for this 
  * URI from a URI string spec.
  *
  * @param p_uriSpec the URI specification (cannot be null)
  *
  * @exception MalformedURIException if p_uriSpec violates syntax rules
  */
  private void initializeAuthority(String p_uriSpec) 
                 throws MalformedURIException {
    int index = 0;
    int start = 0;
    int end = p_uriSpec.length();
    char testChar = '\0';
    String userinfo = null;

    // userinfo is everything up @
    if (p_uriSpec.indexOf('@', start) != -1) {
      while (index < end) {
        testChar = p_uriSpec.charAt(index);
        if (testChar == '@') {
          break;
        }
        index++;
      }
      userinfo = p_uriSpec.substring(start, index);
      index++;
    }

    // host is everything up to ':'
    String host = null;
    start = index;
    while (index < end) { 
      testChar = p_uriSpec.charAt(index);
      if (testChar == ':') {
        break;
      }
      index++;
    }
    host = p_uriSpec.substring(start, index);
    int port = -1;
    if (host.length() > 0) {
      // port
      if (testChar == ':') {
        index++;
        start = index;
        while (index < end) {
          index++;
        }
        String portStr = p_uriSpec.substring(start, index);
        if (portStr.length() > 0) {
          for (int i = 0; i < portStr.length(); i++) {
            if (!isDigit(portStr.charAt(i))) {
              throw new MalformedURIException(
                   portStr + 
                   " is invalid. Port should only contain digits!");
            }
          } 
          try {
            port = Integer.parseInt(portStr);
          }
          catch (NumberFormatException nfe) {
            // can't happen
          }
        }
      }
    }
    setHost(host);
    setPort(port);
    setUserinfo(userinfo);
  }

 /**
  * Initialize the path for this URI from a URI string spec.
  *
  * @param p_uriSpec the URI specification (cannot be null)
  *
  * @exception MalformedURIException if p_uriSpec violates syntax rules
  */
  private void initializePath(String p_uriSpec) 
                 throws MalformedURIException {
    if (p_uriSpec == null) {
      throw new MalformedURIException(
                "Cannot initialize path from null string!");
    }

    int index = 0;
    int start = 0;
    int end = p_uriSpec.length();
    char testChar = '\0';

    // path - everything up to query string or fragment
    while (index < end) {
      testChar = p_uriSpec.charAt(index);
      if (testChar == '?' || testChar == '#') {
        break;
      }
      // check for valid escape sequence
      if (testChar == '%') { 
         if (index+2 >= end ||
            !isHex(p_uriSpec.charAt(index+1)) ||
            !isHex(p_uriSpec.charAt(index+2))) {
          throw new MalformedURIException(
                "Path contains invalid escape sequence!");
         }
      }
      else if (!isReservedCharacter(testChar) && 
               !isUnreservedCharacter(testChar)) {
        throw new MalformedURIException(
                  "Path contains invalid character: " + testChar);
      }
      index++;
    }
    m_path = p_uriSpec.substring(start, index);

    // query - starts with ? and up to fragment or end
    if (testChar == '?') { 
      index++;
      start = index;
      while (index < end) {
        testChar = p_uriSpec.charAt(index);
        if (testChar == '#') {
          break;
        }
        if (testChar == '%') { 
           if (index+2 >= end ||
              !isHex(p_uriSpec.charAt(index+1)) ||
              !isHex(p_uriSpec.charAt(index+2))) {
            throw new MalformedURIException(
                    "Query string contains invalid escape sequence!");
           }
        }
        else if (!isReservedCharacter(testChar) && 
                 !isUnreservedCharacter(testChar)) {
          throw new MalformedURIException(
                "Query string contains invalid character:" + testChar);
        }
        index++;
      }
      m_queryString = p_uriSpec.substring(start, index);
    }

    // fragment - starts with #
    if (testChar == '#') { 
      index++;
      start = index;
      while (index < end) {
        testChar = p_uriSpec.charAt(index);

        if (testChar == '%') { 
           if (index+2 >= end ||
              !isHex(p_uriSpec.charAt(index+1)) ||
              !isHex(p_uriSpec.charAt(index+2))) {
            throw new MalformedURIException(
                    "Fragment contains invalid escape sequence!");
           }
        }
        else if (!isReservedCharacter(testChar) && 
                 !isUnreservedCharacter(testChar)) {
          throw new MalformedURIException(
                "Fragment contains invalid character:"+testChar);
        }
        index++;
      }
      m_fragment = p_uriSpec.substring(start, index);
    }
  }

 /**
  * Get the scheme for this URI.
  *
  * @return the scheme for this URI
  */
  public String getScheme() {
    return m_scheme;
  }

 /**
  * Get the scheme-specific part for this URI (everything following the
  * scheme and the first colon). See RFC 2396 Section 5.2 for spec.
  *
  * @return the scheme-specific part for this URI
  */
  public String getSchemeSpecificPart() {
    StringBuffer schemespec = new StringBuffer();

    if (m_userinfo != null || m_host != null || m_port != -1) {
      schemespec.append("//");
    }

    if (m_userinfo != null) {
      schemespec.append(m_userinfo);
      schemespec.append('@');
    }

    if (m_host != null) {
      schemespec.append(m_host);
    }

    if (m_port != -1) {
      schemespec.append(':');
      schemespec.append(m_port);
    }

    if (m_path != null) {
      schemespec.append((m_path));
    }

    if (m_queryString != null) {
      schemespec.append('?');
      schemespec.append(m_queryString);
    }

    if (m_fragment != null) {
      schemespec.append('#');
      schemespec.append(m_fragment);
    }

    return schemespec.toString();
  }

 /**
  * Get the userinfo for this URI.
  *
  * @return the userinfo for this URI (null if not specified).
  */
  public String getUserinfo() {
    return m_userinfo;
  }

  /**
  * Get the host for this URI.
  *
  * @return the host for this URI (null if not specified).
  */
  public String getHost() {
    return m_host;
  }

 /**
  * Get the port for this URI.
  *
  * @return the port for this URI (-1 if not specified).
  */
  public int getPort() {
    return m_port;
  }

 /**
  * Get the path for this URI (optionally with the query string and
  * fragment). 
  *
  * @param p_includeQueryString if true (and query string is not null),
  *                             then a "?" followed by the query string 
  *                             will be appended 
  * @param p_includeFragment if true (and fragment is not null),
  *                             then a "#" followed by the fragment
  *                             will be appended
  *
  * @return the path for this URI possibly including the query string
  *         and fragment
  */
  public String getPath(boolean p_includeQueryString, 
                        boolean p_includeFragment) {
    StringBuffer pathString = new StringBuffer(m_path);

    if (p_includeQueryString && m_queryString != null) {
      pathString.append('?');
      pathString.append(m_queryString);
    }

    if (p_includeFragment && m_fragment != null) {
      pathString.append('#');
      pathString.append(m_fragment);
    }
    return pathString.toString();
  }

 /**
  * Get the path for this URI. Note that the value returned is the path
  * only and does not include the query string or fragment.
  *
  * @return the path for this URI.
  */
  public String getPath() {
    return m_path;
  }

 /**
  * Get the query string for this URI.
  *
  * @return the query string for this URI. Null is returned if there
  *         was no "?" in the URI spec, empty string if there was a 
  *         "?" but no query string following it.
  */
  public String getQueryString() {
    return m_queryString;
  }

 /**
  * Get the fragment for this URI.
  *
  * @return the fragment for this URI. Null is returned if there
  *         was no "#" in the URI spec, empty string if there was a 
  *         "#" but no fragment following it.
  */
  public String getFragment() {
    return m_fragment;
  }

 /**
  * Set the scheme for this URI. The scheme is converted to lowercase
  * before it is set.
  *
  * @param p_scheme the scheme for this URI (cannot be null)
  *
  * @exception MalformedURIException if p_scheme is not a conformant
  *                                  scheme name
  */
  public void setScheme(String p_scheme) throws MalformedURIException {
    if (p_scheme == null) {
      throw new MalformedURIException(
                "Cannot set scheme from null string!");
    }
    if (!isConformantSchemeName(p_scheme)) {
      throw new MalformedURIException("The scheme is not conformant.");
    }

    m_scheme = p_scheme.toLowerCase();
  }

 /**
  * Set the userinfo for this URI. If a non-null value is passed in and 
  * the host value is null, then an exception is thrown.
  *
  * @param p_userinfo the userinfo for this URI
  *
  * @exception MalformedURIException if p_userinfo contains invalid
  *                                  characters
  */
  public void setUserinfo(String p_userinfo) throws MalformedURIException {
    if (p_userinfo == null) {
      m_userinfo = null;
    }
    else {
      if (m_host == null) {
        throw new MalformedURIException(
                     "Userinfo cannot be set when host is null!");
      }

      // userinfo can contain alphanumerics, mark characters, escaped
      // and ';',':','&','=','+','$',','
      int index = 0;
      int end = p_userinfo.length();
      char testChar = '\0';
      while (index < end) {
        testChar = p_userinfo.charAt(index);
        if (testChar == '%') {
          if (index+2 >= end ||
              !isHex(p_userinfo.charAt(index+1)) ||
              !isHex(p_userinfo.charAt(index+2))) {
            throw new MalformedURIException(
                  "Userinfo contains invalid escape sequence!");
          }
        }
        else if (!isUnreservedCharacter(testChar) &&
                 USERINFO_CHARACTERS.indexOf(testChar) == -1) {
          throw new MalformedURIException(
                  "Userinfo contains invalid character:"+testChar);
        }
        index++;
      }
    }
    m_userinfo = p_userinfo;
  }

  /**
  * Set the host for this URI. If null is passed in, the userinfo
  * field is also set to null and the port is set to -1.
  *
  * @param p_host the host for this URI
  *
  * @exception MalformedURIException if p_host is not a valid IP 
  *                                  address or DNS hostname.
  */
  public void setHost(String p_host) throws MalformedURIException {
    if (p_host == null || p_host.trim().length() == 0) {
      m_host = p_host;
      m_userinfo = null;
      m_port = -1;
    }
    else if (!isWellFormedAddress(p_host)) {
      throw new MalformedURIException("Host is not a well formed address!");
    } 
    m_host = p_host;
  }

 /**
  * Set the port for this URI. -1 is used to indicate that the port is
  * not specified, otherwise valid port numbers are  between 0 and 65535.
  * If a valid port number is passed in and the host field is null,
  * an exception is thrown.
  *
  * @param p_port the port number for this URI
  *
  * @exception MalformedURIException if p_port is not -1 and not a 
  *                                  valid port number 
  */
  public void setPort(int p_port) throws MalformedURIException {
    if (p_port >= 0 && p_port <= 65535) {
      if (m_host == null) {
        throw new MalformedURIException(
                      "Port cannot be set when host is null!");
      }
    }
    else if (p_port != -1) {
      throw new MalformedURIException("Invalid port number!");
    }
    m_port = p_port;
  }

 /**
  * Set the path for this URI. If the supplied path is null, then the
  * query string and fragment are set to null as well. If the supplied 
  * path includes a query string and/or fragment, these fields will be
  * parsed and set as well. Note that, for URIs following the "generic
  * URI" syntax, the path specified should start with a slash.
  * For URIs that do not follow the generic URI syntax, this method 
  * sets the scheme-specific part.
  *
  * @param p_path the path for this URI (may be null)
  *
  * @exception MalformedURIException if p_path contains invalid
  *                                  characters
  */
  public void setPath(String p_path) throws MalformedURIException {
    if (p_path == null) {
      m_path = null;
      m_queryString = null;
      m_fragment = null;
    }
    else {
      initializePath(p_path);
    }
  }

 /**
  * Append to the end of the path of this URI. If the current path does
  * not end in a slash and the path to be appended does not begin with 
  * a slash, a slash will be appended to the current path before the 
  * new segment is added. Also, if the current path ends in a slash
  * and the new segment begins with a slash, the extra slash will be
  * removed before the new segment is appended.
  *
  * @param p_addToPath the new segment to be added to the current path
  *
  * @exception MalformedURIException if p_addToPath contains syntax
  *                                  errors
  */
  public void appendPath(String p_addToPath) 
                         throws MalformedURIException {
    if (p_addToPath == null || p_addToPath.trim().length() == 0) {
      return;
    }

    if (!isURIString(p_addToPath)) {
      throw new MalformedURIException(
              "Path contains invalid character!");
    }

    if (m_path == null || m_path.trim().length() == 0) {
      if (p_addToPath.startsWith("/")) {
        m_path = p_addToPath;
      }
      else {
        m_path = "/" + p_addToPath;
      }
    }
    else if (m_path.endsWith("/")) {
      if (p_addToPath.startsWith("/")) {
        m_path = m_path.concat(p_addToPath.substring(1));
      }
      else {
        m_path = m_path.concat(p_addToPath);
      }
    }
    else {
      if (p_addToPath.startsWith("/")) {
        m_path = m_path.concat(p_addToPath);
      }
      else {
        m_path = m_path.concat("/" + p_addToPath);
      }
    }
  }

 /**
  * Set the query string for this URI. A non-null value is valid only
  * if this is an URI conforming to the generic URI syntax and 
  * the path value is not null.
  *
  * @param p_queryString the query string for this URI
  *
  * @exception MalformedURIException if p_queryString is not null and this  
  *                                  URI does not conform to the generic
  *                                  URI syntax or if the path is null
  */
  public void setQueryString(String p_queryString) throws MalformedURIException {
    if (p_queryString == null) {
      m_queryString = null;
    }
    else if (!isGenericURI()) {
      throw new MalformedURIException(
              "Query string can only be set for a generic URI!");
    }
    else if (getPath() == null) {
      throw new MalformedURIException(
              "Query string cannot be set when path is null!");
    }
    else if (!isURIString(p_queryString)) {
      throw new MalformedURIException(
              "Query string contains invalid character!");
    }
    else {
      m_queryString = p_queryString;
    }
  }

 /**
  * Set the fragment for this URI. A non-null value is valid only
  * if this is a URI conforming to the generic URI syntax and 
  * the path value is not null.
  *
  * @param p_fragment the fragment for this URI
  *
  * @exception MalformedURIException if p_fragment is not null and this  
  *                                  URI does not conform to the generic
  *                                  URI syntax or if the path is null
  */
  public void setFragment(String p_fragment) throws MalformedURIException {
    if (p_fragment == null) {
      m_fragment = null;
    }
    else if (!isGenericURI()) {
      throw new MalformedURIException(
         "Fragment can only be set for a generic URI!");
    }
    else if (getPath() == null) {
      throw new MalformedURIException(
              "Fragment cannot be set when path is null!");
    }
    else if (!isURIString(p_fragment)) {
      throw new MalformedURIException(
              "Fragment contains invalid character!");
    }
    else {
      m_fragment = p_fragment;
    }
  }

 /**
  * Determines if the passed-in Object is equivalent to this URI.
  *
  * @param p_test the Object to test for equality.
  *
  * @return true if p_test is a URI with all values equal to this
  *         URI, false otherwise
  */
  public boolean equals(Object p_test) {
    if (p_test instanceof URI) {
      URI testURI = (URI) p_test;
      if (((m_scheme == null && testURI.m_scheme == null) ||
           (m_scheme != null && testURI.m_scheme != null &&
            m_scheme.equals(testURI.m_scheme))) &&
          ((m_userinfo == null && testURI.m_userinfo == null) ||
           (m_userinfo != null && testURI.m_userinfo != null &&
            m_userinfo.equals(testURI.m_userinfo))) &&
          ((m_host == null && testURI.m_host == null) ||
           (m_host != null && testURI.m_host != null &&
            m_host.equals(testURI.m_host))) &&
            m_port == testURI.m_port &&
          ((m_path == null && testURI.m_path == null) ||
           (m_path != null && testURI.m_path != null &&
            m_path.equals(testURI.m_path))) &&
          ((m_queryString == null && testURI.m_queryString == null) ||
           (m_queryString != null && testURI.m_queryString != null &&
            m_queryString.equals(testURI.m_queryString))) &&
          ((m_fragment == null && testURI.m_fragment == null) ||
           (m_fragment != null && testURI.m_fragment != null &&
            m_fragment.equals(testURI.m_fragment)))) {
        return true;
      }
    }
    return false;
  }

 /**
  * Get the URI as a string specification. See RFC 2396 Section 5.2.
  *
  * @return the URI string specification
  */
  public String toString() {
    StringBuffer uriSpecString = new StringBuffer();

    if (m_scheme != null) {
      uriSpecString.append(m_scheme);
      uriSpecString.append(':');
    }
    uriSpecString.append(getSchemeSpecificPart());
    return uriSpecString.toString();
  }

 /**
  * Get the indicator as to whether this URI uses the "generic URI"
  * syntax.
  *
  * @return true if this URI uses the "generic URI" syntax, false
  *         otherwise
  */
  public boolean isGenericURI() {
    // presence of the host (whether valid or empty) means 
    // double-slashes which means generic uri
    return (m_host != null);
  }

 /**
  * Determine whether a scheme conforms to the rules for a scheme name.
  * A scheme is conformant if it starts with an alphanumeric, and 
  * contains only alphanumerics, '+','-' and '.'.
  *
  * @return true if the scheme is conformant, false otherwise
  */
  public static boolean isConformantSchemeName(String p_scheme) {
    if (p_scheme == null || p_scheme.trim().length() == 0) {
      return false;
    }

    if (!isAlpha(p_scheme.charAt(0))) {
      return false;
    }

    char testChar;
    for (int i = 1; i < p_scheme.length(); i++) {
      testChar = p_scheme.charAt(i);
      if (!isAlphanum(testChar) && 
          SCHEME_CHARACTERS.indexOf(testChar) == -1) {
        return false;
      }
    }

    return true;
  }

 /**
  * Determine whether a string is syntactically capable of representing
  * a valid IPv4 address or the domain name of a network host. A valid
  * IPv4 address consists of four decimal digit groups separated by a
  * '.'. A hostname consists of domain labels (each of which must 
  * begin and end with an alphanumeric but may contain '-') separated
  & by a '.'. See RFC 2396 Section 3.2.2.
  *
  * @return true if the string is a syntactically valid IPv4 address 
  *              or hostname
  */
  public static boolean isWellFormedAddress(String p_address) {
    if (p_address == null) {
      return false;
    }

    String address = p_address.trim();
    int addrLength = address.length();
    if (addrLength == 0 || addrLength > 255) {
      return false;
    }

    if (address.startsWith(".") || address.startsWith("-")) {
      return false;
    }

    // rightmost domain label starting with digit indicates IP address
    // since top level domain label can only start with an alpha
    // see RFC 2396 Section 3.2.2
    int index = address.lastIndexOf('.');
    if (address.endsWith(".")) {
      index = address.substring(0, index).lastIndexOf('.');
    }

    if (index+1 < addrLength && isDigit(p_address.charAt(index+1))) {
      char testChar;
      int numDots = 0;

      // make sure that 1) we see only digits and dot separators, 2) that
      // any dot separator is preceded and followed by a digit and 
      // 3) that we find 3 dots
      for (int i = 0; i < addrLength; i++) {
        testChar = address.charAt(i);
        if (testChar == '.') {
          if (!isDigit(address.charAt(i-1)) || 
              (i+1 < addrLength && !isDigit(address.charAt(i+1)))) {
            return false;
          }
          numDots++;
        }
        else if (!isDigit(testChar)) {
          return false;
        }
      }
      if (numDots != 3) {
        return false;
      }
    }
    else {
      // domain labels can contain alphanumerics and '-"
      // but must start and end with an alphanumeric
      char testChar;
  
      for (int i = 0; i < addrLength; i++) {
        testChar = address.charAt(i);
        if (testChar == '.') {
          if (!isAlphanum(address.charAt(i-1))) {
            return false;
          } 
          if (i+1 < addrLength && !isAlphanum(address.charAt(i+1))) {
            return false;
          }
        }
        else if (!isAlphanum(testChar) && testChar != '-') {
          return false;
        }
      }
    }
    return true;
  }


 /**
  * Determine whether a char is a digit.
  *
  * @return true if the char is betweeen '0' and '9', false otherwise
  */
  private static boolean isDigit(char p_char) {
    return p_char >= '0' && p_char <= '9';
  }

 /**
  * Determine whether a character is a hexadecimal character.
  *
  * @return true if the char is betweeen '0' and '9', 'a' and 'f'
  *         or 'A' and 'F', false otherwise
  */
  private static boolean isHex(char p_char) {
    return (isDigit(p_char) || 
            (p_char >= 'a' && p_char <= 'f') || 
            (p_char >= 'A' && p_char <= 'F'));
  }

 /**
  * Determine whether a char is an alphabetic character: a-z or A-Z
  *
  * @return true if the char is alphabetic, false otherwise
  */
  private static boolean isAlpha(char p_char) {
    return ((p_char >= 'a' && p_char <= 'z') || 
            (p_char >= 'A' && p_char <= 'Z' )); 
  }

 /**
  * Determine whether a char is an alphanumeric: 0-9, a-z or A-Z
  *
  * @return true if the char is alphanumeric, false otherwise
  */
  private static boolean isAlphanum(char p_char) {
    return (isAlpha(p_char) || isDigit(p_char)); 
  }

 /**
  * Determine whether a character is a reserved character:
  * ';', '/', '?', ':', '@', '&', '=', '+', '$' or ',' 
  *
  * @return true if the string contains any reserved characters
  */
  private static boolean isReservedCharacter(char p_char) {
    return RESERVED_CHARACTERS.indexOf(p_char) != -1;
  }

 /**
  * Determine whether a char is an unreserved character.
  *
  * @return true if the char is unreserved, false otherwise
  */
  private static boolean isUnreservedCharacter(char p_char) {
    return (isAlphanum(p_char) || 
            MARK_CHARACTERS.indexOf(p_char) != -1);
  }

 /**
  * Determine whether a given string contains only URI characters (also
  * called "uric" in RFC 2396). uric consist of all reserved
  * characters, unreserved characters and escaped characters.
  *
  * @return true if the string is comprised of uric, false otherwise
  */
  private static boolean isURIString(String p_uric) {
    if (p_uric == null) {
      return false;
    }
    int end = p_uric.length();
    char testChar = '\0';
    for (int i = 0; i < end; i++) {
      testChar = p_uric.charAt(i);
      if (testChar == '%') {
        if (i+2 >= end ||
            !isHex(p_uric.charAt(i+1)) ||
            !isHex(p_uric.charAt(i+2))) {
          return false;
        }
        else {
          i += 2;
          continue;
        }
      }
      if (isReservedCharacter(testChar) || 
          isUnreservedCharacter(testChar)) {
          continue;
      }
      else {
        return false;
      }
    }
    return true;
  }
}