/* SaslClient.java --
   Copyright (C) 2003, 2004 Free Software Foundation, Inc.

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package javax.security.sasl;

/**
 * <p>Performs SASL authentication as a client.</p>
 *
 * <p>A protocol library such as one for LDAP gets an instance of this class in
 * order to perform authentication defined by a specific SASL mechanism.
 * Invoking methods on the <code>SaslClient</code> instance process challenges
 * and create responses according to the SASL mechanism implemented by the
 * <code>SaslClient</code>. As the authentication proceeds, the instance
 * encapsulates the state of a SASL client's authentication exchange.</p>
 *
 * <p>Here's an example of how an LDAP library might use a <code>SaslClient</code>.
 * It first gets an instance of a SaslClient:</p>
 * <pre>
 *SaslClient sc =
 *      Sasl.createSaslClient(mechanisms, authorizationID, protocol,
 *                            serverName, props, callbackHandler);
 * </pre>
 *
 * <p>It can then proceed to use the client for authentication. For example, an
 * LDAP library might use the client as follows:</p>
 * <pre>
 * // Get initial response and send to server
 *byte[] response = sc.hasInitialResponse()
 *      ? sc.evaluateChallenge(new byte[0]) : null;
 *LdapResult res = ldap.sendBindRequest(dn, sc.getName(), response);
 *while (!sc.isComplete()
 *       && ((res.status == SASL_BIND_IN_PROGRESS) || (res.status == SUCCESS))) {
 *   response = sc.evaluateChallenge( res.getBytes() );
 *   if (res.status == SUCCESS) {
 *      // we're done; don't expect to send another BIND
 *      if ( response != null ) {
 *         throw new SaslException(
 *               "Protocol error: attempting to send response after completion");
 *      }
 *      break;
 *   }
 *   res = ldap.sendBindRequest(dn, sc.getName(), response);
 *}
 *if (sc.isComplete() && (res.status == SUCCESS) ) {
 *   String qop = (String)sc.getNegotiatedProperty(Sasl.QOP);
 *   if ((qop != null)
 *         && (qop.equalsIgnoreCase("auth-int")
 *            || qop.equalsIgnoreCase("auth-conf"))) {
 *      // Use SaslClient.wrap() and SaslClient.unwrap() for future
 *      // communication with server
 *      ldap.in = new SecureInputStream(sc, ldap.in);
 *      ldap.out = new SecureOutputStream(sc, ldap.out);
 *   }
 *}
 * </pre>
 *
 * <p>If the mechanism has an initial response, the library invokes
 * {@link #evaluateChallenge(byte[])} with an empty challenge to get the initial
 * response. Protocols such as IMAP4, which do not include an initial response
 * with their first authentication command to the server, initiate the
 * authentication without first calling {@link #hasInitialResponse()} or
 * {@link #evaluateChallenge(byte[])}. When the server responds to the command,
 * it sends an initial challenge. For a SASL mechanism in which the client sends
 * data first, the server should have issued a challenge with no data. This will
 * then result in a call (on the client) to {@link #evaluateChallenge(byte[])}
 * with an empty challenge.</p>
 *
 * @see Sasl
 * @see SaslClientFactory
 */
public interface SaslClient
{

  /**
   * Returns the IANA-registered mechanism name of this SASL client. (e.g.
   * "CRAM-MD5", "GSSAPI").
   *
   * @return a non-null string representing the IANA-registered mechanism name.
   */
  String getMechanismName();

  /**
   * Determines if this mechanism has an optional initial response. If
   * <code>true</code>, caller should call {@link #evaluateChallenge(byte[])}
   * with an empty array to get the initial response.
   *
   * @return <code>true</code> if this mechanism has an initial response.
   */
  boolean hasInitialResponse();

  /**
   * Evaluates the challenge data and generates a response. If a challenge is
   * received from the server during the authentication process, this method is
   * called to prepare an appropriate next response to submit to the server.
   *
   * @param challenge the non-null challenge sent from the server. The
   * challenge array may have zero length.
   * @return the possibly <code>null</code> reponse to send to the server. It
   * is <code>null</code> if the challenge accompanied a "SUCCESS" status and
   * the challenge only contains data for the client to update its state and no
   * response needs to be sent to the server. The response is a zero-length
   * byte array if the client is to send a response with no data.
   * @throws SaslException if an error occurred while processing the challenge
   * or generating a response.
   */
  byte[] evaluateChallenge(byte[] challenge) throws SaslException;

  /**
   * Determines if the authentication exchange has completed. This method may
   * be called at any time, but typically, it will not be called until the
   * caller has received indication from the server (in a protocol-specific
   * manner) that the exchange has completed.
   *
   * @return <code>true</code> if the authentication exchange has completed;
   * <code>false</code> otherwise.
   */
  boolean isComplete();

  /**
   * <p>Unwraps a byte array received from the server. This method can be
   * called only after the authentication exchange has completed (i.e., when
   * {@link #isComplete()} returns <code>true</code>) and only if the
   * authentication exchange has negotiated integrity and/or privacy as the
   * quality of protection; otherwise, an {@link IllegalStateException} is
   * thrown.</p>
   *
   * <p><code>incoming</code> is the contents of the SASL buffer as defined in
   * RFC 2222 without the leading four octet field that represents the length.
   * <code>offset</code> and <code>len</code> specify the portion of incoming
   * to use.</p>
   *
   * @param incoming a non-null byte array containing the encoded bytes from
   * the server.
   * @param offset the starting position at <code>incoming</code> of the bytes
   * to use.
   * @param len the number of bytes from <code>incoming</code> to use.
   * @return a non-null byte array containing the decoded bytes.
   * @throws SaslException if <code>incoming</code> cannot be successfully
   * unwrapped.
   * @throws IllegalStateException if the authentication exchange has not
   * completed, or if the negotiated quality of protection has neither
   * integrity nor privacy.
   */
  byte[] unwrap(byte[] incoming, int offset, int len) throws SaslException;

  /**
   * <p>Wraps a byte array to be sent to the server. This method can be called
   * only after the authentication exchange has completed (i.e., when
   * {@link #isComplete()} returns <code>true</code>) and only if the
   * authentication exchange has negotiated integrity and/or privacy as the
   * quality of protection; otherwise, an {@link IllegalStateException} is
   * thrown.</p>
   *
   * <p>The result of this method will make up the contents of the SASL buffer
   * as defined in RFC 2222 without the leading four octet field that
   * represents the length. <code>offset</code> and <code>len</code> specify
   * the portion of <code>outgoing</code> to use.</p>
   *
   * @param outgoing a non-null byte array containing the bytes to encode.
   * @param offset the starting position at <code>outgoing</code> of the bytes
   * to use.
   * @param len the number of bytes from <code>outgoing</code> to use.
   * @return a non-null byte array containing the encoded bytes.
   * @throws SaslException if <code>outgoing</code> cannot be successfully
   * wrapped.
   * @throws IllegalStateException if the authentication exchange has not
   * completed, or if the negotiated quality of protection has neither
   * integrity nor privacy.
   */
  byte[] wrap(byte[] outgoing, int offset, int len) throws SaslException;

  /**
   * Retrieves the negotiated property. This method can be called only after
   * the authentication exchange has completed (i.e., when {@link #isComplete()}
   * returns <code>true</code>); otherwise, an {@link IllegalStateException} is
   * thrown.
   *
   * @param propName the non-null property name.
   * @return the value of the negotiated property. If <code>null</code>, the
   * property was not negotiated or is not applicable to this mechanism.
   * @throws IllegalStateException if this authentication exchange has not
   * completed.
   */
  Object getNegotiatedProperty(String propName) throws SaslException;

  /**
   * Disposes of any system resources or security-sensitive information the
   * <code>SaslClient</code> might be using. Invoking this method invalidates
   * the <code>SaslClient</code> instance. This method is idempotent.
   *
   * @throws SaslException if a problem was encountered while disposing of the
   * resources.
   */
  void dispose() throws SaslException;
}