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package javax.security.auth.kerberos;

import java.io.File;
import java.util.Objects;
import sun.misc.SharedSecrets;
import sun.security.krb5.EncryptionKey;
import sun.security.krb5.PrincipalName;
import sun.security.krb5.RealmException;

/**
 * This class encapsulates a keytab file.
 * <p>
 * A Kerberos JAAS login module that obtains long term secret keys from a
 * keytab file should use this class. The login module will store
 * an instance of this class in the private credential set of a
 * {@link javax.security.auth.Subject Subject} during the commit phase of the
 * authentication process.
 * <p>
 * It might be necessary for the application to be granted a
 * {@link javax.security.auth.PrivateCredentialPermission
 * PrivateCredentialPermission} if it needs to access the KeyTab
 * instance from a Subject. This permission is not needed when the
 * application depends on the default JGSS Kerberos mechanism to access the
 * KeyTab. In that case, however, the application will need an appropriate
 * {@link javax.security.auth.kerberos.ServicePermission ServicePermission}.
 * <p>
 * The keytab file format is described at
 * <a href="http://www.ioplex.com/utilities/keytab.txt">
 * http://www.ioplex.com/utilities/keytab.txt</a>.
 *
 * @since 1.7
 */
public final class KeyTab {

    /*
     * Impl notes:
     *
     * This class is only a name, a permanent link to the keytab source
     * (can be missing). Itself has no content. In order to read content,
     * take a snapshot and read from it.
     *
     * The snapshot is of type sun.security.krb5.internal.ktab.KeyTab, which
     * contains the content of the keytab file when the snapshot is taken.
     * Itself has no refresh function and mostly an immutable class (except
     * for the create/add/save methods only used by the ktab command).
     */

    // Source, null if using the default one. Note that the default name
    // is maintained in snapshot, this field is never "resolved".
    private final File file;

    // Set up JavaxSecurityAuthKerberosAccess in SharedSecrets
    static {
        SharedSecrets.setJavaxSecurityAuthKerberosAccess(
                new JavaxSecurityAuthKerberosAccessImpl());
    }

    private KeyTab(File file) {
        this.file = file;
    }

    /**
     * Returns a {@code KeyTab} instance from a {@code File} object.
     * <p>
     * The result of this method is never null. This method only associates
     * the returned {@code KeyTab} object with the file and does not read it.
     * @param file the keytab {@code File} object, must not be null
     * @return the keytab instance
     * @throws NullPointerException if the {@code file} argument is null
     */
    public static KeyTab getInstance(File file) {
        if (file == null) {
            throw new NullPointerException("file must be non null");
        }
        return new KeyTab(file);
    }

    /**
     * Returns the default {@code KeyTab} instance.
     * <p>
     * The result of this method is never null. This method only associates
     * the returned {@code KeyTab} object with the default keytab file and
     * does not read it.
     * @return the default keytab instance.
     */
    public static KeyTab getInstance() {
        return new KeyTab(null);
    }

    //Takes a snapshot of the keytab content
    private sun.security.krb5.internal.ktab.KeyTab takeSnapshot() {
        return sun.security.krb5.internal.ktab.KeyTab.getInstance(file);
    }

    /**
     * Returns fresh keys for the given Kerberos principal.
     * <p>
     * Implementation of this method should make sure the returned keys match
     * the latest content of the keytab file. The result is a newly created
     * copy that can be modified by the caller without modifying the keytab
     * object. The caller should {@link KerberosKey#destroy() destroy} the
     * result keys after they are used.
     * <p>
     * Please note that the keytab file can be created after the
     * {@code KeyTab} object is instantiated and its content may change over
     * time. Therefore, an application should call this method only when it
     * needs to use the keys. Any previous result from an earlier invocation
     * could potentially be expired.
     * <p>
     * If there is any error (say, I/O error or format error)
     * during the reading process of the KeyTab file, a saved result should be
     * returned. If there is no saved result (say, this is the first time this
     * method is called, or, all previous read attempts failed), an empty array
     * should be returned. This can make sure the result is not drastically
     * changed during the (probably slow) update of the keytab file.
     * <p>
     * Each time this method is called and the reading of the file succeeds
     * with no exception (say, I/O error or file format error),
     * the result should be saved for {@code principal}. The implementation can
     * also save keys for other principals having keys in the same keytab object
     * if convenient.
     * <p>
     * Any unsupported key read from the keytab is ignored and not included
     * in the result.
     *
     * @param principal the Kerberos principal, must not be null.
     * @return the keys (never null, may be empty)
     * @throws NullPointerException if the {@code principal}
     * argument is null
     * @throws SecurityException if a security manager exists and the read
     * access to the keytab file is not permitted
     */
    public KerberosKey[] getKeys(KerberosPrincipal principal) {
        try {
            EncryptionKey[] keys = takeSnapshot().readServiceKeys(
                    new PrincipalName(principal.getName()));
            KerberosKey[] kks = new KerberosKey[keys.length];
            for (int i=0; i<kks.length; i++) {
                Integer tmp = keys[i].getKeyVersionNumber();
                kks[i] = new KerberosKey(
                        principal,
                        keys[i].getBytes(),
                        keys[i].getEType(),
                        tmp == null ? 0 : tmp.intValue());
                keys[i].destroy();
            }
            return kks;
        } catch (RealmException re) {
            return new KerberosKey[0];
        }
    }

    EncryptionKey[] getEncryptionKeys(PrincipalName principal) {
        return takeSnapshot().readServiceKeys(principal);
    }

    /**
     * Checks if the keytab file exists. Implementation of this method
     * should make sure that the result matches the latest status of the
     * keytab file.
     * <p>
     * The caller can use the result to determine if it should fallback to
     * another mechanism to read the keys.
     * @return true if the keytab file exists; false otherwise.
     * @throws SecurityException if a security manager exists and the read
     * access to the keytab file is not permitted
     */
    public boolean exists() {
        return !takeSnapshot().isMissing();
    }

    public String toString() {
        return file == null ? "Default keytab" : file.toString();
    }

    /**
     * Returns a hashcode for this KeyTab.
     *
     * @return a hashCode() for the <code>KeyTab</code>
     */
    public int hashCode() {
        return Objects.hash(file);
    }

    /**
     * Compares the specified Object with this KeyTab for equality.
     * Returns true if the given object is also a
     * <code>KeyTab</code> and the two
     * <code>KeyTab</code> instances are equivalent.
     *
     * @param other the Object to compare to
     * @return true if the specified object is equal to this KeyTab
     */
    public boolean equals(Object other) {
        if (other == this)
            return true;

        if (! (other instanceof KeyTab)) {
            return false;
        }

        KeyTab otherKtab = (KeyTab) other;
        return Objects.equals(otherKtab.file, file);
    }
}
