/*
 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 *
 */

package javax.security.auth.kerberos;

import java.util.*;
import java.security.Permission;
import java.security.PermissionCollection;
import java.io.ObjectStreamField;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.IOException;

/**
 * This class is used to protect Kerberos services and the
 * credentials necessary to access those services. There is a one to
 * one mapping of a service principal and the credentials necessary
 * to access the service. Therefore granting access to a service
 * principal implicitly grants access to the credential necessary to
 * establish a security context with the service principal. This
 * applies regardless of whether the credentials are in a cache
 * or acquired via an exchange with the KDC. The credential can
 * be either a ticket granting ticket, a service ticket or a secret
 * key from a key table.
 * <p>
 * A ServicePermission contains a service principal name and
 * a list of actions which specify the context the credential can be
 * used within.
 * <p>
 * The service principal name is the canonical name of the
 * {@code KerberosPrincipal} supplying the service, that is
 * the KerberosPrincipal represents a Kerberos service
 * principal. This name is treated in a case sensitive manner.
 * An asterisk may appear by itself, to signify any service principal.
 * <p>
 * Granting this permission implies that the caller can use a cached
 * credential (TGT, service ticket or secret key) within the context
 * designated by the action. In the case of the TGT, granting this
 * permission also implies that the TGT can be obtained by an
 * Authentication Service exchange.
 * <p>
 * The possible actions are:
 *
 * <pre>
 *    initiate -              allow the caller to use the credential to
 *                            initiate a security context with a service
 *                            principal.
 *
 *    accept -                allow the caller to use the credential to
 *                            accept security context as a particular
 *                            principal.
 * </pre>
 *
 * For example, to specify the permission to access to the TGT to
 * initiate a security context the permission is constructed as follows:
 *
 * <pre>
 *     ServicePermission("krbtgt/EXAMPLE.COM@EXAMPLE.COM", "initiate");
 * </pre>
 * <p>
 * To obtain a service ticket to initiate a context with the "host"
 * service the permission is constructed as follows:
 * <pre>
 *     ServicePermission("host/foo.example.com@EXAMPLE.COM", "initiate");
 * </pre>
 * <p>
 * For a Kerberized server the action is "accept". For example, the permission
 * necessary to access and use the secret key of the  Kerberized "host"
 * service (telnet and the likes)  would be constructed as follows:
 *
 * <pre>
 *     ServicePermission("host/foo.example.com@EXAMPLE.COM", "accept");
 * </pre>
 *
 * @since 1.4
 */

public final class ServicePermission extends Permission
    implements java.io.Serializable {

    private static final long serialVersionUID = -1227585031618624935L;

    /**
     * Initiate a security context to the specified service
     */
    private final static int INITIATE   = 0x1;

    /**
     * Accept a security context
     */
    private final static int ACCEPT     = 0x2;

    /**
     * All actions
     */
    private final static int ALL        = INITIATE|ACCEPT;

    /**
     * No actions.
     */
    private final static int NONE    = 0x0;

    // the actions mask
    private transient int mask;

    /**
     * the actions string.
     *
     * @serial
     */

    private String actions; // Left null as long as possible, then
                            // created and re-used in the getAction function.

    /**
     * Create a new {@code ServicePermission}
     * with the specified {@code servicePrincipal}
     * and {@code action}.
     *
     * @param servicePrincipal the name of the service principal.
     * An asterisk may appear by itself, to signify any service principal.
     * <p>
     * @param action the action string
     */
    public ServicePermission(String servicePrincipal, String action) {
        // Note: servicePrincipal can be "@REALM" which means any principal in
        // this realm implies it. action can be "-" which means any
        // action implies it.
        super(servicePrincipal);
        init(servicePrincipal, getMask(action));
    }


    /**
     * Initialize the ServicePermission object.
     */
    private void init(String servicePrincipal, int mask) {

        if (servicePrincipal == null)
                throw new NullPointerException("service principal can't be null");

        if ((mask & ALL) != mask)
            throw new IllegalArgumentException("invalid actions mask");

        this.mask = mask;
    }


    /**
     * Checks if this Kerberos service permission object "implies" the
     * specified permission.
     * <P>
     * If none of the above are true, {@code implies} returns false.
     * @param p the permission to check against.
     *
     * @return true if the specified permission is implied by this object,
     * false if not.
     */
    public boolean implies(Permission p) {
        if (!(p instanceof ServicePermission))
            return false;

        ServicePermission that = (ServicePermission) p;

        return ((this.mask & that.mask) == that.mask) &&
            impliesIgnoreMask(that);
    }


    boolean impliesIgnoreMask(ServicePermission p) {
        return ((this.getName().equals("*")) ||
                this.getName().equals(p.getName()) ||
                (p.getName().startsWith("@") &&
                        this.getName().endsWith(p.getName())));
    }

    /**
     * Checks two ServicePermission objects for equality.
     * <P>
     * @param obj the object to test for equality with this object.
     *
     * @return true if <i>obj</i> is a ServicePermission, and has the
     *  same service principal, and actions as this
     * ServicePermission object.
     */
    public boolean equals(Object obj) {
        if (obj == this)
            return true;

        if (! (obj instanceof ServicePermission))
            return false;

        ServicePermission that = (ServicePermission) obj;
        return ((this.mask & that.mask) == that.mask) &&
            this.getName().equals(that.getName());


    }

    /**
     * Returns the hash code value for this object.
     *
     * @return a hash code value for this object.
     */

    public int hashCode() {
        return (getName().hashCode() ^ mask);
    }


    /**
     * Returns the "canonical string representation" of the actions in the
     * specified mask.
     * Always returns present actions in the following order:
     * initiate, accept.
     *
     * @param mask a specific integer action mask to translate into a string
     * @return the canonical string representation of the actions
     */
    private static String getActions(int mask)
    {
        StringBuilder sb = new StringBuilder();
        boolean comma = false;

        if ((mask & INITIATE) == INITIATE) {
            if (comma) sb.append(',');
            else comma = true;
            sb.append("initiate");
        }

        if ((mask & ACCEPT) == ACCEPT) {
            if (comma) sb.append(',');
            else comma = true;
            sb.append("accept");
        }

        return sb.toString();
    }

    /**
     * Returns the canonical string representation of the actions.
     * Always returns present actions in the following order:
     * initiate, accept.
     */
    public String getActions() {
        if (actions == null)
            actions = getActions(this.mask);

        return actions;
    }


    /**
     * Returns a PermissionCollection object for storing
     * ServicePermission objects.
     * <br>
     * ServicePermission objects must be stored in a manner that
     * allows them to be inserted into the collection in any order, but
     * that also enables the PermissionCollection implies method to
     * be implemented in an efficient (and consistent) manner.
     *
     * @return a new PermissionCollection object suitable for storing
     * ServicePermissions.
     */
    public PermissionCollection newPermissionCollection() {
        return new KrbServicePermissionCollection();
    }

    /**
     * Return the current action mask.
     *
     * @return the actions mask.
     */
    int getMask() {
        return mask;
    }

    /**
     * Convert an action string to an integer actions mask.
     *
     * Note: if action is "-", action will be NONE, which means any
     * action implies it.
     *
     * @param action the action string.
     * @return the action mask
     */
    private static int getMask(String action) {

        if (action == null) {
            throw new NullPointerException("action can't be null");
        }

        if (action.equals("")) {
            throw new IllegalArgumentException("action can't be empty");
        }

        int mask = NONE;

        char[] a = action.toCharArray();

        if (a.length == 1 && a[0] == '-') {
            return mask;
        }

        int i = a.length - 1;

        while (i != -1) {
            char c;

            // skip whitespace
            while ((i!=-1) && ((c = a[i]) == ' ' ||
                               c == '\r' ||
                               c == '\n' ||
                               c == '\f' ||
                               c == '\t'))
                i--;

            // check for the known strings
            int matchlen;

            if (i >= 7 && (a[i-7] == 'i' || a[i-7] == 'I') &&
                          (a[i-6] == 'n' || a[i-6] == 'N') &&
                          (a[i-5] == 'i' || a[i-5] == 'I') &&
                          (a[i-4] == 't' || a[i-4] == 'T') &&
                          (a[i-3] == 'i' || a[i-3] == 'I') &&
                          (a[i-2] == 'a' || a[i-2] == 'A') &&
                          (a[i-1] == 't' || a[i-1] == 'T') &&
                          (a[i] == 'e' || a[i] == 'E'))
            {
                matchlen = 8;
                mask |= INITIATE;

            } else if (i >= 5 && (a[i-5] == 'a' || a[i-5] == 'A') &&
                                 (a[i-4] == 'c' || a[i-4] == 'C') &&
                                 (a[i-3] == 'c' || a[i-3] == 'C') &&
                                 (a[i-2] == 'e' || a[i-2] == 'E') &&
                                 (a[i-1] == 'p' || a[i-1] == 'P') &&
                                 (a[i] == 't' || a[i] == 'T'))
            {
                matchlen = 6;
                mask |= ACCEPT;

            } else {
                // parse error
                throw new IllegalArgumentException(
                        "invalid permission: " + action);
            }

            // make sure we didn't just match the tail of a word
            // like "ackbarfaccept".  Also, skip to the comma.
            boolean seencomma = false;
            while (i >= matchlen && !seencomma) {
                switch(a[i-matchlen]) {
                case ',':
                    seencomma = true;
                    break;
                case ' ': case '\r': case '\n':
                case '\f': case '\t':
                    break;
                default:
                    throw new IllegalArgumentException(
                            "invalid permission: " + action);
                }
                i--;
            }

            // point i at the location of the comma minus one (or -1).
            i -= matchlen;
        }

        return mask;
    }


    /**
     * WriteObject is called to save the state of the ServicePermission
     * to a stream. The actions are serialized, and the superclass
     * takes care of the name.
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws IOException
    {
        // Write out the actions. The superclass takes care of the name
        // call getActions to make sure actions field is initialized
        if (actions == null)
            getActions();
        s.defaultWriteObject();
    }

    /**
     * readObject is called to restore the state of the
     * ServicePermission from a stream.
     */
    private void readObject(java.io.ObjectInputStream s)
         throws IOException, ClassNotFoundException
    {
        // Read in the action, then initialize the rest
        s.defaultReadObject();
        init(getName(),getMask(actions));
    }


    /*
      public static void main(String args[]) throws Exception {
      ServicePermission this_ =
      new ServicePermission(args[0], "accept");
      ServicePermission that_ =
      new ServicePermission(args[1], "accept,initiate");
      System.out.println("-----\n");
      System.out.println("this.implies(that) = " + this_.implies(that_));
      System.out.println("-----\n");
      System.out.println("this = "+this_);
      System.out.println("-----\n");
      System.out.println("that = "+that_);
      System.out.println("-----\n");

      KrbServicePermissionCollection nps =
      new KrbServicePermissionCollection();
      nps.add(this_);
      nps.add(new ServicePermission("nfs/example.com@EXAMPLE.COM",
      "accept"));
      nps.add(new ServicePermission("host/example.com@EXAMPLE.COM",
      "initiate"));
      System.out.println("nps.implies(that) = " + nps.implies(that_));
      System.out.println("-----\n");

      Enumeration e = nps.elements();

      while (e.hasMoreElements()) {
      ServicePermission x =
      (ServicePermission) e.nextElement();
      System.out.println("nps.e = " + x);
      }

      }
    */

}


final class KrbServicePermissionCollection extends PermissionCollection
    implements java.io.Serializable {

    // Not serialized; see serialization section at end of class
    private transient List<Permission> perms;

    public KrbServicePermissionCollection() {
        perms = new ArrayList<Permission>();
    }

    /**
     * Check and see if this collection of permissions implies the permissions
     * expressed in "permission".
     *
     * @param permission the Permission object to compare
     *
     * @return true if "permission" is a proper subset of a permission in
     * the collection, false if not.
     */
    public boolean implies(Permission permission) {
        if (! (permission instanceof ServicePermission))
                return false;

        ServicePermission np = (ServicePermission) permission;
        int desired = np.getMask();

        if (desired == 0) {
            for (Permission p: perms) {
                ServicePermission sp = (ServicePermission)p;
                if (sp.impliesIgnoreMask(np)) {
                    return true;
                }
            }
            return false;
        }

        int effective = 0;
        int needed = desired;

        synchronized (this) {
            int len = perms.size();

            // need to deal with the case where the needed permission has
            // more than one action and the collection has individual permissions
            // that sum up to the needed.

            for (int i = 0; i < len; i++) {
                ServicePermission x = (ServicePermission) perms.get(i);

                //System.out.println("  trying "+x);
                if (((needed & x.getMask()) != 0) && x.impliesIgnoreMask(np)) {
                    effective |=  x.getMask();
                    if ((effective & desired) == desired)
                        return true;
                    needed = (desired ^ effective);
                }
            }
        }
        return false;
    }

    /**
     * Adds a permission to the ServicePermissions. The key for
     * the hash is the name.
     *
     * @param permission the Permission object to add.
     *
     * @exception IllegalArgumentException - if the permission is not a
     *                                       ServicePermission
     *
     * @exception SecurityException - if this PermissionCollection object
     *                                has been marked readonly
     */
    public void add(Permission permission) {
        if (! (permission instanceof ServicePermission))
            throw new IllegalArgumentException("invalid permission: "+
                                               permission);
        if (isReadOnly())
            throw new SecurityException("attempt to add a Permission to a readonly PermissionCollection");

        synchronized (this) {
            perms.add(0, permission);
        }
    }

    /**
     * Returns an enumeration of all the ServicePermission objects
     * in the container.
     *
     * @return an enumeration of all the ServicePermission objects.
     */

    public Enumeration<Permission> elements() {
        // Convert Iterator into Enumeration
        synchronized (this) {
            return Collections.enumeration(perms);
        }
    }

    private static final long serialVersionUID = -4118834211490102011L;

    // Need to maintain serialization interoperability with earlier releases,
    // which had the serializable field:
    // private Vector permissions;

    /**
     * @serialField permissions java.util.Vector
     *     A list of ServicePermission objects.
     */
    private static final ObjectStreamField[] serialPersistentFields = {
        new ObjectStreamField("permissions", Vector.class),
    };

    /**
     * @serialData "permissions" field (a Vector containing the ServicePermissions).
     */
    /*
     * Writes the contents of the perms field out as a Vector for
     * serialization compatibility with earlier releases.
     */
    private void writeObject(ObjectOutputStream out) throws IOException {
        // Don't call out.defaultWriteObject()

        // Write out Vector
        Vector<Permission> permissions = new Vector<>(perms.size());

        synchronized (this) {
            permissions.addAll(perms);
        }

        ObjectOutputStream.PutField pfields = out.putFields();
        pfields.put("permissions", permissions);
        out.writeFields();
    }

    /*
     * Reads in a Vector of ServicePermissions and saves them in the perms field.
     */
    @SuppressWarnings("unchecked")
    private void readObject(ObjectInputStream in)
        throws IOException, ClassNotFoundException
    {
        // Don't call defaultReadObject()

        // Read in serialized fields
        ObjectInputStream.GetField gfields = in.readFields();

        // Get the one we want
        Vector<Permission> permissions =
                (Vector<Permission>)gfields.get("permissions", null);
        perms = new ArrayList<Permission>(permissions.size());
        perms.addAll(permissions);
    }
}
