1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
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  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
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  20  *
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  25 
  26 package java.security.acl;
  27 
  28 import java.util.Enumeration;
  29 import java.security.Principal;
  30 
  31 /**
  32  * Interface representing an Access Control List (ACL).  An Access
  33  * Control List is a data structure used to guard access to
  34  * resources.<p>
  35  *
  36  * An ACL can be thought of as a data structure with multiple ACL
  37  * entries.  Each ACL entry, of interface type AclEntry, contains a
  38  * set of permissions associated with a particular principal. (A
  39  * principal represents an entity such as an individual user or a
  40  * group). Additionally, each ACL entry is specified as being either
  41  * positive or negative. If positive, the permissions are to be
  42  * granted to the associated principal. If negative, the permissions
  43  * are to be denied.<p>
  44  *
  45  * The ACL Entries in each ACL observe the following rules:<p>
  46  *
  47  * <ul> <li>Each principal can have at most one positive ACL entry and
  48  * one negative entry; that is, multiple positive or negative ACL
  49  * entries are not allowed for any principal.  Each entry specifies
  50  * the set of permissions that are to be granted (if positive) or
  51  * denied (if negative). <p>
  52  *
  53  * <li>If there is no entry for a particular principal, then the
  54  * principal is considered to have a null (empty) permission set.<p>
  55  *
  56  * <li>If there is a positive entry that grants a principal a
  57  * particular permission, and a negative entry that denies the
  58  * principal the same permission, the result is as though the
  59  * permission was never granted or denied. <p>
  60  *
  61  * <li>Individual permissions always override permissions of the
  62  * group(s) to which the individual belongs. That is, individual
  63  * negative permissions (specific denial of permissions) override the
  64  * groups' positive permissions. And individual positive permissions
  65  * override the groups' negative permissions.<p>
  66  *
  67  * </ul>
  68  *
  69  * The <code> java.security.acl </code> package provides the
  70  * interfaces to the ACL and related data structures (ACL entries,
  71  * groups, permissions, etc.), and the <code> sun.security.acl </code>
  72  * classes provide a default implementation of the interfaces. For
  73  * example, <code> java.security.acl.Acl </code> provides the
  74  * interface to an ACL and the <code> sun.security.acl.AclImpl </code>
  75  * class provides the default implementation of the interface.<p>
  76  *
  77  * The <code> java.security.acl.Acl </code> interface extends the
  78  * <code> java.security.acl.Owner </code> interface. The Owner
  79  * interface is used to maintain a list of owners for each ACL.  Only
  80  * owners are allowed to modify an ACL. For example, only an owner can
  81  * call the ACL's <code>addEntry</code> method to add a new ACL entry
  82  * to the ACL.
  83  *
  84  * @see java.security.acl.AclEntry
  85  * @see java.security.acl.Owner
  86  * @see java.security.acl.Acl#getPermissions
  87  *
  88  * @author Satish Dharmaraj
  89  */
  90 
  91 public interface Acl extends Owner {
  92 
  93     /**
  94      * Sets the name of this ACL.
  95      *
  96      * @param caller the principal invoking this method. It must be an
  97      * owner of this ACL.
  98      *
  99      * @param name the name to be given to this ACL.
 100      *
 101      * @exception NotOwnerException if the caller principal
 102      * is not an owner of this ACL.
 103      *
 104      * @see #getName
 105      */
 106     public void setName(Principal caller, String name)
 107       throws NotOwnerException;
 108 
 109     /**
 110      * Returns the name of this ACL.
 111      *
 112      * @return the name of this ACL.
 113      *
 114      * @see #setName
 115      */
 116     public String getName();
 117 
 118     /**
 119      * Adds an ACL entry to this ACL. An entry associates a principal
 120      * (e.g., an individual or a group) with a set of
 121      * permissions. Each principal can have at most one positive ACL
 122      * entry (specifying permissions to be granted to the principal)
 123      * and one negative ACL entry (specifying permissions to be
 124      * denied). If there is already an ACL entry of the same type
 125      * (negative or positive) already in the ACL, false is returned.
 126      *
 127      * @param caller the principal invoking this method. It must be an
 128      * owner of this ACL.
 129      *
 130      * @param entry the ACL entry to be added to this ACL.
 131      *
 132      * @return true on success, false if an entry of the same type
 133      * (positive or negative) for the same principal is already
 134      * present in this ACL.
 135      *
 136      * @exception NotOwnerException if the caller principal
 137      *  is not an owner of this ACL.
 138      */
 139     public boolean addEntry(Principal caller, AclEntry entry)
 140       throws NotOwnerException;
 141 
 142     /**
 143      * Removes an ACL entry from this ACL.
 144      *
 145      * @param caller the principal invoking this method. It must be an
 146      * owner of this ACL.
 147      *
 148      * @param entry the ACL entry to be removed from this ACL.
 149      *
 150      * @return true on success, false if the entry is not part of this ACL.
 151      *
 152      * @exception NotOwnerException if the caller principal is not
 153      * an owner of this Acl.
 154      */
 155     public boolean removeEntry(Principal caller, AclEntry entry)
 156           throws NotOwnerException;
 157 
 158     /**
 159      * Returns an enumeration for the set of allowed permissions for the
 160      * specified principal (representing an entity such as an individual or
 161      * a group). This set of allowed permissions is calculated as
 162      * follows:<p>
 163      *
 164      * <ul>
 165      *
 166      * <li>If there is no entry in this Access Control List for the
 167      * specified principal, an empty permission set is returned.<p>
 168      *
 169      * <li>Otherwise, the principal's group permission sets are determined.
 170      * (A principal can belong to one or more groups, where a group is a
 171      * group of principals, represented by the Group interface.)
 172      * The group positive permission set is the union of all
 173      * the positive permissions of each group that the principal belongs to.
 174      * The group negative permission set is the union of all
 175      * the negative permissions of each group that the principal belongs to.
 176      * If there is a specific permission that occurs in both
 177      * the positive permission set and the negative permission set,
 178      * it is removed from both.<p>
 179      *
 180      * The individual positive and negative permission sets are also
 181      * determined. The positive permission set contains the permissions
 182      * specified in the positive ACL entry (if any) for the principal.
 183      * Similarly, the negative permission set contains the permissions
 184      * specified in the negative ACL entry (if any) for the principal.
 185      * The individual positive (or negative) permission set is considered
 186      * to be null if there is not a positive (negative) ACL entry for the
 187      * principal in this ACL.<p>
 188      *
 189      * The set of permissions granted to the principal is then calculated
 190      * using the simple rule that individual permissions always override
 191      * the group permissions. That is, the principal's individual negative
 192      * permission set (specific denial of permissions) overrides the group
 193      * positive permission set, and the principal's individual positive
 194      * permission set overrides the group negative permission set.
 195      *
 196      * </ul>
 197      *
 198      * @param user the principal whose permission set is to be returned.
 199      *
 200      * @return the permission set specifying the permissions the principal
 201      * is allowed.
 202      */
 203     public Enumeration<Permission> getPermissions(Principal user);
 204 
 205     /**
 206      * Returns an enumeration of the entries in this ACL. Each element in
 207      * the enumeration is of type AclEntry.
 208      *
 209      * @return an enumeration of the entries in this ACL.
 210      */
 211     public Enumeration<AclEntry> entries();
 212 
 213     /**
 214      * Checks whether or not the specified principal has the specified
 215      * permission. If it does, true is returned, otherwise false is returned.
 216      *
 217      * More specifically, this method checks whether the passed permission
 218      * is a member of the allowed permission set of the specified principal.
 219      * The allowed permission set is determined by the same algorithm as is
 220      * used by the <code>getPermissions</code> method.
 221      *
 222      * @param principal the principal, assumed to be a valid authenticated
 223      * Principal.
 224      *
 225      * @param permission the permission to be checked for.
 226      *
 227      * @return true if the principal has the specified permission, false
 228      * otherwise.
 229      *
 230      * @see #getPermissions
 231      */
 232     public boolean checkPermission(Principal principal, Permission permission);
 233 
 234     /**
 235      * Returns a string representation of the
 236      * ACL contents.
 237      *
 238      * @return a string representation of the ACL contents.
 239      */
 240     public String toString();
 241 }