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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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  package java.security.cert;
  
  import java.security.AccessController;
  import java.security.InvalidAlgorithmParameterException;
  import java.security.NoSuchAlgorithmException;
  import java.security.NoSuchProviderException;
  import java.security.PrivilegedAction;
  import java.security.Provider;
  import java.security.Security;
  import sun.security.util.Debug;
  
  import sun.security.jca.*;
  import sun.security.jca.GetInstance.Instance;
  
  /**
   * A class for validating certification paths (also known as certificate
   * chains).
   * <p>
   * This class uses a provider-based architecture.
   * To create a {@code CertPathValidator},
   * call one of the static {@code getInstance} methods, passing in the
   * algorithm name of the {@code CertPathValidator} desired and
   * optionally the name of the provider desired.
   *
   * <p>Once a {@code CertPathValidator} object has been created, it can
   * be used to validate certification paths by calling the {@link #validate
   * validate} method and passing it the {@code CertPath} to be validated
   * and an algorithm-specific set of parameters. If successful, the result is
   * returned in an object that implements the
   * {@code CertPathValidatorResult} interface.
   *
   * <p>The {@link #getRevocationChecker} method allows an application to specify
   * additional algorithm-specific parameters and options used by the
   * {@code CertPathValidator} when checking the revocation status of
   * certificates. Here is an example demonstrating how it is used with the PKIX
   * algorithm:
   *
   * <pre>
   * CertPathValidator cpv = CertPathValidator.getInstance("PKIX");
   * PKIXRevocationChecker rc = (PKIXRevocationChecker)cpv.getRevocationChecker();
   * rc.setOptions(EnumSet.of(Option.SOFT_FAIL));
   * params.addCertPathChecker(rc);
   * CertPathValidatorResult cpvr = cpv.validate(path, params);
   * </pre>
   *
   * <p> Android provides the following {@code CertPathValidator} algorithms:
   * <table>
   *   <thead>
   *     <tr>
   *       <th>Algorithm</th>
   *       <th>Supported API Levels</th>
   *     </tr>
   *   </thead>
   *   <tbody>
   *     <tr>
   *       <td>PKIX</td>
   *       <td>1+</td>
   *     </tr>
   *   </tbody>
   * </table>
   *
   * This algorithm is described in the <a href=
   * "{@docRoot}/../technotes/guides/security/StandardNames.html#CertPathValidator">
   * CertPathValidator section</a> of the
   * Java Cryptography Architecture Standard Algorithm Name Documentation.
   *
   * <p>
   * <b>Concurrent Access</b>
   * <p>
   * The static methods of this class are guaranteed to be thread-safe.
   * Multiple threads may concurrently invoke the static methods defined in
   * this class with no ill effects.
   * <p>
   * However, this is not true for the non-static methods defined by this class.
   * Unless otherwise documented by a specific provider, threads that need to
   * access a single {@code CertPathValidator} instance concurrently should
   * synchronize amongst themselves and provide the necessary locking. Multiple
   * threads each manipulating a different {@code CertPathValidator}
   * instance need not synchronize.
   *
   * @see CertPath
   *
   * @since       1.4
   * @author      Yassir Elley
   */
  public class CertPathValidator {
  
      /*
       * Constant to lookup in the Security properties file to determine
       * the default certpathvalidator type. In the Security properties file,
       * the default certpathvalidator type is given as:
       * <pre>
       * certpathvalidator.type=PKIX
       * </pre>
       */
      private static final String CPV_TYPE = "certpathvalidator.type";
      private final CertPathValidatorSpi validatorSpi;
      private final Provider provider;
      private final String algorithm;
  
      /**
       * Creates a {@code CertPathValidator} object of the given algorithm,
       * and encapsulates the given provider implementation (SPI object) in it.
       *
       * @param validatorSpi the provider implementation
       * @param provider the provider
       * @param algorithm the algorithm name
       */
      protected CertPathValidator(CertPathValidatorSpi validatorSpi,
          Provider provider, String algorithm)
      {
          this.validatorSpi = validatorSpi;
          this.provider = provider;
          this.algorithm = algorithm;
      }
  
      /**
       * Returns a {@code CertPathValidator} object that implements the
       * specified algorithm.
       *
       * <p> This method traverses the list of registered security Providers,
       * starting with the most preferred Provider.
       * A new CertPathValidator object encapsulating the
       * CertPathValidatorSpi implementation from the first
       * Provider that supports the specified algorithm is returned.
       *
       * <p> Note that the list of registered providers may be retrieved via
       * the {@link Security#getProviders() Security.getProviders()} method.
       *
       * @param algorithm the name of the requested {@code CertPathValidator}
       *  algorithm. See the CertPathValidator section in the <a href=
       *  "{@docRoot}/../technotes/guides/security/StandardNames.html#CertPathValidator">
       * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
       * for information about standard algorithm names.
       *
       * @return a {@code CertPathValidator} object that implements the
       *          specified algorithm.
       *
       * @exception NoSuchAlgorithmException if no Provider supports a
       *          CertPathValidatorSpi implementation for the
       *          specified algorithm.
       *
       * @see Provider
       */
      public static CertPathValidator getInstance(String algorithm)
              throws NoSuchAlgorithmException {
          Instance instance = GetInstance.getInstance("CertPathValidator",
              CertPathValidatorSpi.class, algorithm);
          return new CertPathValidator((CertPathValidatorSpi)instance.impl,
              instance.provider, algorithm);
      }
  
      /**
       * Returns a {@code CertPathValidator} object that implements the
       * specified algorithm.
       *
       * <p> A new CertPathValidator object encapsulating the
       * CertPathValidatorSpi implementation from the specified provider
       * is returned.  The specified provider must be registered
       * in the security provider list.
       *
       * <p> Note that the list of registered providers may be retrieved via
       * the {@link Security#getProviders() Security.getProviders()} method.
       *
       * @param algorithm the name of the requested {@code CertPathValidator}
       *  algorithm. See the CertPathValidator section in the <a href=
       *  "{@docRoot}/../technotes/guides/security/StandardNames.html#CertPathValidator">
       * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
       * for information about standard algorithm names.
       *
       * @param provider the name of the provider.
       *
       * @return a {@code CertPathValidator} object that implements the
       *          specified algorithm.
       *
       * @exception NoSuchAlgorithmException if a CertPathValidatorSpi
       *          implementation for the specified algorithm is not
       *          available from the specified provider.
       *
       * @exception NoSuchProviderException if the specified provider is not
       *          registered in the security provider list.
       *
       * @exception IllegalArgumentException if the {@code provider} is
       *          null or empty.
       *
       * @see Provider
       */
      public static CertPathValidator getInstance(String algorithm,
              String provider) throws NoSuchAlgorithmException,
              NoSuchProviderException {
          Instance instance = GetInstance.getInstance("CertPathValidator",
              CertPathValidatorSpi.class, algorithm, provider);
          return new CertPathValidator((CertPathValidatorSpi)instance.impl,
              instance.provider, algorithm);
      }
  
      /**
       * Returns a {@code CertPathValidator} object that implements the
       * specified algorithm.
       *
       * <p> A new CertPathValidator object encapsulating the
       * CertPathValidatorSpi implementation from the specified Provider
       * object is returned.  Note that the specified Provider object
       * does not have to be registered in the provider list.
       *
       * @param algorithm the name of the requested {@code CertPathValidator}
       * algorithm. See the CertPathValidator section in the <a href=
       * "{@docRoot}/../technotes/guides/security/StandardNames.html#CertPathValidator">
       * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
       * for information about standard algorithm names.
       *
       * @param provider the provider.
       *
       * @return a {@code CertPathValidator} object that implements the
       *          specified algorithm.
       *
       * @exception NoSuchAlgorithmException if a CertPathValidatorSpi
       *          implementation for the specified algorithm is not available
       *          from the specified Provider object.
       *
       * @exception IllegalArgumentException if the {@code provider} is
       *          null.
       *
       * @see Provider
       */
      public static CertPathValidator getInstance(String algorithm,
              Provider provider) throws NoSuchAlgorithmException {
          Instance instance = GetInstance.getInstance("CertPathValidator",
              CertPathValidatorSpi.class, algorithm, provider);
          return new CertPathValidator((CertPathValidatorSpi)instance.impl,
              instance.provider, algorithm);
      }
  
      /**
       * Returns the {@code Provider} of this
       * {@code CertPathValidator}.
       *
       * @return the {@code Provider} of this {@code CertPathValidator}
       */
      public final Provider getProvider() {
          return this.provider;
      }
  
      /**
       * Returns the algorithm name of this {@code CertPathValidator}.
       *
       * @return the algorithm name of this {@code CertPathValidator}
       */
      public final String getAlgorithm() {
          return this.algorithm;
      }
  
      /**
       * Validates the specified certification path using the specified
       * algorithm parameter set.
       * <p>
       * The {@code CertPath} specified must be of a type that is
       * supported by the validation algorithm, otherwise an
       * {@code InvalidAlgorithmParameterException} will be thrown. For
       * example, a {@code CertPathValidator} that implements the PKIX
       * algorithm validates {@code CertPath} objects of type X.509.
       *
       * @param certPath the {@code CertPath} to be validated
       * @param params the algorithm parameters
       * @return the result of the validation algorithm
       * @exception CertPathValidatorException if the {@code CertPath}
       * does not validate
       * @exception InvalidAlgorithmParameterException if the specified
       * parameters or the type of the specified {@code CertPath} are
       * inappropriate for this {@code CertPathValidator}
       */
      public final CertPathValidatorResult validate(CertPath certPath,
          CertPathParameters params)
          throws CertPathValidatorException, InvalidAlgorithmParameterException
      {
          return validatorSpi.engineValidate(certPath, params);
      }
  
      /**
       * Returns the default {@code CertPathValidator} type as specified by
       * the {@code certpathvalidator.type} security property, or the string
       * {@literal "PKIX"} if no such property exists.
       *
       * <p>The default {@code CertPathValidator} type can be used by
       * applications that do not want to use a hard-coded type when calling one
       * of the {@code getInstance} methods, and want to provide a default
       * type in case a user does not specify its own.
       *
       * <p>The default {@code CertPathValidator} type can be changed by
       * setting the value of the {@code certpathvalidator.type} security
       * property to the desired type.
       *
       * @see Security security properties
       * @return the default {@code CertPathValidator} type as specified
       * by the {@code certpathvalidator.type} security property, or the string
       * {@literal "PKIX"} if no such property exists.
       */
      public final static String getDefaultType() {
          String cpvtype =
              AccessController.doPrivileged(new PrivilegedAction<String>() {
                  public String run() {
                      return Security.getProperty(CPV_TYPE);
                  }
              });
          return (cpvtype == null) ? "PKIX" : cpvtype;
      }
  
      /**
       * Returns a {@code CertPathChecker} that the encapsulated
       * {@code CertPathValidatorSpi} implementation uses to check the revocation
       * status of certificates. A PKIX implementation returns objects of
       * type {@code PKIXRevocationChecker}. Each invocation of this method
       * returns a new instance of {@code CertPathChecker}.
       *
       * <p>The primary purpose of this method is to allow callers to specify
       * additional input parameters and options specific to revocation checking.
       * See the class description for an example.
       *
       * @return a {@code CertPathChecker}
       * @throws UnsupportedOperationException if the service provider does not
       *         support this method
       * @since 1.8
       */
      public final CertPathChecker getRevocationChecker() {
          return validatorSpi.engineGetRevocationChecker();
      }
  }
  