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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  package org.apache.hadoop.hbase.security.access;
20  
21  import java.io.ByteArrayInputStream;
22  import java.io.DataInput;
23  import java.io.DataInputStream;
24  import java.io.IOException;
25  import java.util.ArrayList;
26  import java.util.Arrays;
27  import java.util.Iterator;
28  import java.util.List;
29  import java.util.Map;
30  import java.util.Set;
31  import java.util.TreeMap;
32  import java.util.TreeSet;
33  
34  import org.apache.commons.logging.Log;
35  import org.apache.commons.logging.LogFactory;
36  import org.apache.hadoop.conf.Configuration;
37  import org.apache.hadoop.hbase.Cell;
38  import org.apache.hadoop.hbase.CellUtil;
39  import org.apache.hadoop.hbase.HColumnDescriptor;
40  import org.apache.hadoop.hbase.HConstants;
41  import org.apache.hadoop.hbase.HTableDescriptor;
42  import org.apache.hadoop.hbase.NamespaceDescriptor;
43  import org.apache.hadoop.hbase.TableName;
44  import org.apache.hadoop.hbase.Tag;
45  import org.apache.hadoop.hbase.TagType;
46  import org.apache.hadoop.hbase.classification.InterfaceAudience;
47  import org.apache.hadoop.hbase.client.Connection;
48  import org.apache.hadoop.hbase.client.ConnectionFactory;
49  import org.apache.hadoop.hbase.client.Delete;
50  import org.apache.hadoop.hbase.client.Get;
51  import org.apache.hadoop.hbase.client.Put;
52  import org.apache.hadoop.hbase.client.Result;
53  import org.apache.hadoop.hbase.client.ResultScanner;
54  import org.apache.hadoop.hbase.client.Scan;
55  import org.apache.hadoop.hbase.client.Table;
56  import org.apache.hadoop.hbase.exceptions.DeserializationException;
57  import org.apache.hadoop.hbase.filter.CompareFilter.CompareOp;
58  import org.apache.hadoop.hbase.filter.QualifierFilter;
59  import org.apache.hadoop.hbase.filter.RegexStringComparator;
60  import org.apache.hadoop.hbase.master.MasterServices;
61  import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
62  import org.apache.hadoop.hbase.protobuf.generated.AccessControlProtos;
63  import org.apache.hadoop.hbase.regionserver.BloomType;
64  import org.apache.hadoop.hbase.regionserver.InternalScanner;
65  import org.apache.hadoop.hbase.regionserver.Region;
66  import org.apache.hadoop.hbase.security.User;
67  import org.apache.hadoop.hbase.util.Bytes;
68  import org.apache.hadoop.hbase.util.Pair;
69  import org.apache.hadoop.io.Text;
70  
71  import com.google.common.collect.ArrayListMultimap;
72  import com.google.common.collect.ListMultimap;
73  import com.google.common.collect.Lists;
74  import com.google.protobuf.InvalidProtocolBufferException;
75  
76  /**
77   * Maintains lists of permission grants to users and groups to allow for
78   * authorization checks by {@link AccessController}.
79   *
80   * <p>
81   * Access control lists are stored in an "internal" metadata table named
82   * {@code _acl_}. Each table's permission grants are stored as a separate row,
83   * keyed by the table name. KeyValues for permissions assignments are stored
84   * in one of the formats:
85   * <pre>
86   * Key                      Desc
87   * --------                 --------
88   * user                     table level permissions for a user [R=read, W=write]
89   * group                    table level permissions for a group
90   * user,family              column family level permissions for a user
91   * group,family             column family level permissions for a group
92   * user,family,qualifier    column qualifier level permissions for a user
93   * group,family,qualifier   column qualifier level permissions for a group
94   * </pre>
95   * All values are encoded as byte arrays containing the codes from the
96   * org.apache.hadoop.hbase.security.access.TablePermission.Action enum.
97   * </p>
98   */
99  @InterfaceAudience.Private
100 public class AccessControlLists {
101   /** Internal storage table for access control lists */
102   public static final TableName ACL_TABLE_NAME =
103       TableName.valueOf(NamespaceDescriptor.SYSTEM_NAMESPACE_NAME_STR, "acl");
104   public static final byte[] ACL_GLOBAL_NAME = ACL_TABLE_NAME.getName();
105   /** Column family used to store ACL grants */
106   public static final String ACL_LIST_FAMILY_STR = "l";
107   public static final byte[] ACL_LIST_FAMILY = Bytes.toBytes(ACL_LIST_FAMILY_STR);
108   /** KV tag to store per cell access control lists */
109   public static final byte ACL_TAG_TYPE = TagType.ACL_TAG_TYPE;
110 
111   public static final char NAMESPACE_PREFIX = '@';
112 
113   /**
114    * Delimiter to separate user, column family, and qualifier in
115    * _acl_ table info: column keys */
116   public static final char ACL_KEY_DELIMITER = ',';
117   /** Prefix character to denote group names */
118   public static final String GROUP_PREFIX = "@";
119   /** Configuration key for superusers */
120   public static final String SUPERUSER_CONF_KEY = "hbase.superuser";
121 
122   private static Log LOG = LogFactory.getLog(AccessControlLists.class);
123 
124   /**
125    * Create the ACL table
126    * @param master
127    * @throws IOException
128    */
129   static void createACLTable(MasterServices master) throws IOException {
130     master.createTable(new HTableDescriptor(ACL_TABLE_NAME)
131       .addFamily(new HColumnDescriptor(ACL_LIST_FAMILY)
132         .setMaxVersions(1)
133         .setInMemory(true)
134         .setBlockCacheEnabled(true)
135         .setBlocksize(8 * 1024)
136         .setBloomFilterType(BloomType.NONE)
137         .setScope(HConstants.REPLICATION_SCOPE_LOCAL)
138         // Set cache data blocks in L1 if more than one cache tier deployed; e.g. this will
139         // be the case if we are using CombinedBlockCache (Bucket Cache).
140         .setCacheDataInL1(true)),
141     null);
142   }
143 
144   /**
145    * Stores a new user permission grant in the access control lists table.
146    * @param conf the configuration
147    * @param userPerm the details of the permission to be granted
148    * @throws IOException in the case of an error accessing the metadata table
149    */
150   static void addUserPermission(Configuration conf, UserPermission userPerm)
151       throws IOException {
152     Permission.Action[] actions = userPerm.getActions();
153     byte[] rowKey = userPermissionRowKey(userPerm);
154     Put p = new Put(rowKey);
155     byte[] key = userPermissionKey(userPerm);
156 
157     if ((actions == null) || (actions.length == 0)) {
158       String msg = "No actions associated with user '" + Bytes.toString(userPerm.getUser()) + "'";
159       LOG.warn(msg);
160       throw new IOException(msg);
161     }
162 
163     byte[] value = new byte[actions.length];
164     for (int i = 0; i < actions.length; i++) {
165       value[i] = actions[i].code();
166     }
167     p.addImmutable(ACL_LIST_FAMILY, key, value);
168     if (LOG.isDebugEnabled()) {
169       LOG.debug("Writing permission with rowKey "+
170           Bytes.toString(rowKey)+" "+
171           Bytes.toString(key)+": "+Bytes.toStringBinary(value)
172       );
173     }
174     // TODO: Pass in a Connection rather than create one each time.
175     try (Connection connection = ConnectionFactory.createConnection(conf)) {
176       try (Table table = connection.getTable(ACL_TABLE_NAME)) {
177         table.put(p);
178       }
179     }
180   }
181 
182   /**
183    * Removes a previously granted permission from the stored access control
184    * lists.  The {@link TablePermission} being removed must exactly match what
185    * is stored -- no wildcard matching is attempted.  Ie, if user "bob" has
186    * been granted "READ" access to the "data" table, but only to column family
187    * plus qualifier "info:colA", then trying to call this method with only
188    * user "bob" and the table name "data" (but without specifying the
189    * column qualifier "info:colA") will have no effect.
190    *
191    * @param conf the configuration
192    * @param userPerm the details of the permission to be revoked
193    * @throws IOException if there is an error accessing the metadata table
194    */
195   static void removeUserPermission(Configuration conf, UserPermission userPerm)
196       throws IOException {
197     Delete d = new Delete(userPermissionRowKey(userPerm));
198     byte[] key = userPermissionKey(userPerm);
199 
200     if (LOG.isDebugEnabled()) {
201       LOG.debug("Removing permission "+ userPerm.toString());
202     }
203     d.addColumns(ACL_LIST_FAMILY, key);
204     // TODO: Pass in a Connection rather than create one each time.
205     try (Connection connection = ConnectionFactory.createConnection(conf)) {
206       try (Table table = connection.getTable(ACL_TABLE_NAME)) {
207         table.delete(d);
208       }
209     }
210   }
211 
212   /**
213    * Remove specified table from the _acl_ table.
214    */
215   static void removeTablePermissions(Configuration conf, TableName tableName)
216       throws IOException{
217     Delete d = new Delete(tableName.getName());
218 
219     if (LOG.isDebugEnabled()) {
220       LOG.debug("Removing permissions of removed table "+ tableName);
221     }
222     // TODO: Pass in a Connection rather than create one each time.
223     try (Connection connection = ConnectionFactory.createConnection(conf)) {
224       try (Table table = connection.getTable(ACL_TABLE_NAME)) {
225         table.delete(d);
226       }
227     }
228   }
229 
230   /**
231    * Remove specified namespace from the acl table.
232    */
233   static void removeNamespacePermissions(Configuration conf, String namespace)
234       throws IOException{
235     Delete d = new Delete(Bytes.toBytes(toNamespaceEntry(namespace)));
236 
237     if (LOG.isDebugEnabled()) {
238       LOG.debug("Removing permissions of removed namespace "+ namespace);
239     }
240 
241     try (Connection connection = ConnectionFactory.createConnection(conf)) {
242       try (Table table = connection.getTable(ACL_TABLE_NAME)) {
243         table.delete(d);
244       }
245     }
246   }
247 
248   /**
249    * Remove specified table column from the acl table.
250    */
251   static void removeTablePermissions(Configuration conf, TableName tableName, byte[] column)
252       throws IOException{
253 
254     if (LOG.isDebugEnabled()) {
255       LOG.debug("Removing permissions of removed column " + Bytes.toString(column) +
256                 " from table "+ tableName);
257     }
258     // TODO: Pass in a Connection rather than create one each time.
259     try (Connection connection = ConnectionFactory.createConnection(conf)) {
260       try (Table table = connection.getTable(ACL_TABLE_NAME)) {
261         Scan scan = new Scan();
262         scan.addFamily(ACL_LIST_FAMILY);
263 
264         String columnName = Bytes.toString(column);
265         scan.setFilter(new QualifierFilter(CompareOp.EQUAL, new RegexStringComparator(
266             String.format("(%s%s%s)|(%s%s)$",
267                 ACL_KEY_DELIMITER, columnName, ACL_KEY_DELIMITER,
268                 ACL_KEY_DELIMITER, columnName))));
269 
270         Set<byte[]> qualifierSet = new TreeSet<byte[]>(Bytes.BYTES_COMPARATOR);
271         ResultScanner scanner = table.getScanner(scan);
272         try {
273           for (Result res : scanner) {
274             for (byte[] q : res.getFamilyMap(ACL_LIST_FAMILY).navigableKeySet()) {
275               qualifierSet.add(q);
276             }
277           }
278         } finally {
279           scanner.close();
280         }
281 
282         if (qualifierSet.size() > 0) {
283           Delete d = new Delete(tableName.getName());
284           for (byte[] qualifier : qualifierSet) {
285             d.addColumns(ACL_LIST_FAMILY, qualifier);
286           }
287           table.delete(d);
288         }
289       }
290     }
291   }
292 
293   static byte[] userPermissionRowKey(UserPermission userPerm) {
294     byte[] row;
295     if(userPerm.hasNamespace()) {
296       row = Bytes.toBytes(toNamespaceEntry(userPerm.getNamespace()));
297     } else if(userPerm.isGlobal()) {
298       row = ACL_GLOBAL_NAME;
299     } else {
300       row = userPerm.getTableName().getName();
301     }
302     return row;
303   }
304 
305   /**
306    * Build qualifier key from user permission:
307    *  username
308    *  username,family
309    *  username,family,qualifier
310    */
311   static byte[] userPermissionKey(UserPermission userPerm) {
312     byte[] qualifier = userPerm.getQualifier();
313     byte[] family = userPerm.getFamily();
314     byte[] key = userPerm.getUser();
315 
316     if (family != null && family.length > 0) {
317       key = Bytes.add(key, Bytes.add(new byte[]{ACL_KEY_DELIMITER}, family));
318       if (qualifier != null && qualifier.length > 0) {
319         key = Bytes.add(key, Bytes.add(new byte[]{ACL_KEY_DELIMITER}, qualifier));
320       }
321     }
322 
323     return key;
324   }
325 
326   /**
327    * Returns {@code true} if the given region is part of the {@code _acl_}
328    * metadata table.
329    */
330   static boolean isAclRegion(Region region) {
331     return ACL_TABLE_NAME.equals(region.getTableDesc().getTableName());
332   }
333 
334   /**
335    * Returns {@code true} if the given table is {@code _acl_} metadata table.
336    */
337   static boolean isAclTable(HTableDescriptor desc) {
338     return ACL_TABLE_NAME.equals(desc.getTableName());
339   }
340 
341   /**
342    * Loads all of the permission grants stored in a region of the {@code _acl_}
343    * table.
344    *
345    * @param aclRegion
346    * @return a map of the permissions for this table.
347    * @throws IOException
348    */
349   static Map<byte[], ListMultimap<String,TablePermission>> loadAll(Region aclRegion)
350     throws IOException {
351 
352     if (!isAclRegion(aclRegion)) {
353       throw new IOException("Can only load permissions from "+ACL_TABLE_NAME);
354     }
355 
356     Map<byte[], ListMultimap<String, TablePermission>> allPerms =
357         new TreeMap<byte[], ListMultimap<String, TablePermission>>(Bytes.BYTES_RAWCOMPARATOR);
358 
359     // do a full scan of _acl_ table
360 
361     Scan scan = new Scan();
362     scan.addFamily(ACL_LIST_FAMILY);
363 
364     InternalScanner iScanner = null;
365     try {
366       iScanner = aclRegion.getScanner(scan);
367 
368       while (true) {
369         List<Cell> row = new ArrayList<Cell>();
370 
371         boolean hasNext = iScanner.next(row);
372         ListMultimap<String,TablePermission> perms = ArrayListMultimap.create();
373         byte[] entry = null;
374         for (Cell kv : row) {
375           if (entry == null) {
376             entry = CellUtil.cloneRow(kv);
377           }
378           Pair<String,TablePermission> permissionsOfUserOnTable =
379               parsePermissionRecord(entry, kv);
380           if (permissionsOfUserOnTable != null) {
381             String username = permissionsOfUserOnTable.getFirst();
382             TablePermission permissions = permissionsOfUserOnTable.getSecond();
383             perms.put(username, permissions);
384           }
385         }
386         if (entry != null) {
387           allPerms.put(entry, perms);
388         }
389         if (!hasNext) {
390           break;
391         }
392       }
393     } finally {
394       if (iScanner != null) {
395         iScanner.close();
396       }
397     }
398 
399     return allPerms;
400   }
401 
402   /**
403    * Load all permissions from the region server holding {@code _acl_},
404    * primarily intended for testing purposes.
405    */
406   static Map<byte[], ListMultimap<String,TablePermission>> loadAll(
407       Configuration conf) throws IOException {
408     Map<byte[], ListMultimap<String,TablePermission>> allPerms =
409         new TreeMap<byte[], ListMultimap<String,TablePermission>>(Bytes.BYTES_RAWCOMPARATOR);
410 
411     // do a full scan of _acl_, filtering on only first table region rows
412 
413     Scan scan = new Scan();
414     scan.addFamily(ACL_LIST_FAMILY);
415 
416     ResultScanner scanner = null;
417     // TODO: Pass in a Connection rather than create one each time.
418     try (Connection connection = ConnectionFactory.createConnection(conf)) {
419       try (Table table = connection.getTable(ACL_TABLE_NAME)) {
420         scanner = table.getScanner(scan);
421         try {
422           for (Result row : scanner) {
423             ListMultimap<String,TablePermission> resultPerms = parsePermissions(row.getRow(), row);
424             allPerms.put(row.getRow(), resultPerms);
425           }
426         } finally {
427           if (scanner != null) scanner.close();
428         }
429       }
430     }
431 
432     return allPerms;
433   }
434 
435   static ListMultimap<String, TablePermission> getTablePermissions(Configuration conf,
436         TableName tableName) throws IOException {
437     return getPermissions(conf, tableName != null ? tableName.getName() : null);
438   }
439 
440   static ListMultimap<String, TablePermission> getNamespacePermissions(Configuration conf,
441         String namespace) throws IOException {
442     return getPermissions(conf, Bytes.toBytes(toNamespaceEntry(namespace)));
443   }
444 
445   /**
446    * Reads user permission assignments stored in the <code>l:</code> column
447    * family of the first table row in <code>_acl_</code>.
448    *
449    * <p>
450    * See {@link AccessControlLists class documentation} for the key structure
451    * used for storage.
452    * </p>
453    */
454   static ListMultimap<String, TablePermission> getPermissions(Configuration conf,
455       byte[] entryName) throws IOException {
456     if (entryName == null) entryName = ACL_GLOBAL_NAME;
457 
458     // for normal user tables, we just read the table row from _acl_
459     ListMultimap<String, TablePermission> perms = ArrayListMultimap.create();
460     // TODO: Pass in a Connection rather than create one each time.
461     try (Connection connection = ConnectionFactory.createConnection(conf)) {
462       try (Table table = connection.getTable(ACL_TABLE_NAME)) {
463         Get get = new Get(entryName);
464         get.addFamily(ACL_LIST_FAMILY);
465         Result row = table.get(get);
466         if (!row.isEmpty()) {
467           perms = parsePermissions(entryName, row);
468         } else {
469           LOG.info("No permissions found in " + ACL_TABLE_NAME + " for acl entry "
470               + Bytes.toString(entryName));
471         }
472       }
473     }
474 
475     return perms;
476   }
477 
478   /**
479    * Returns the currently granted permissions for a given table as a list of
480    * user plus associated permissions.
481    */
482   static List<UserPermission> getUserTablePermissions(
483       Configuration conf, TableName tableName) throws IOException {
484     return getUserPermissions(conf, tableName == null ? null : tableName.getName());
485   }
486 
487   static List<UserPermission> getUserNamespacePermissions(
488       Configuration conf, String namespace) throws IOException {
489     return getUserPermissions(conf, Bytes.toBytes(toNamespaceEntry(namespace)));
490   }
491 
492   static List<UserPermission> getUserPermissions(
493       Configuration conf, byte[] entryName)
494   throws IOException {
495     ListMultimap<String,TablePermission> allPerms = getPermissions(
496       conf, entryName);
497 
498     List<UserPermission> perms = new ArrayList<UserPermission>();
499 
500     for (Map.Entry<String, TablePermission> entry : allPerms.entries()) {
501       UserPermission up = new UserPermission(Bytes.toBytes(entry.getKey()),
502           entry.getValue().getTableName(), entry.getValue().getFamily(),
503           entry.getValue().getQualifier(), entry.getValue().getActions());
504       perms.add(up);
505     }
506     return perms;
507   }
508 
509   private static ListMultimap<String, TablePermission> parsePermissions(
510       byte[] entryName, Result result) {
511     ListMultimap<String, TablePermission> perms = ArrayListMultimap.create();
512     if (result != null && result.size() > 0) {
513       for (Cell kv : result.rawCells()) {
514 
515         Pair<String,TablePermission> permissionsOfUserOnTable =
516             parsePermissionRecord(entryName, kv);
517 
518         if (permissionsOfUserOnTable != null) {
519           String username = permissionsOfUserOnTable.getFirst();
520           TablePermission permissions = permissionsOfUserOnTable.getSecond();
521           perms.put(username, permissions);
522         }
523       }
524     }
525     return perms;
526   }
527 
528   private static Pair<String, TablePermission> parsePermissionRecord(
529       byte[] entryName, Cell kv) {
530     // return X given a set of permissions encoded in the permissionRecord kv.
531     byte[] family = CellUtil.cloneFamily(kv);
532 
533     if (!Bytes.equals(family, ACL_LIST_FAMILY)) {
534       return null;
535     }
536 
537     byte[] key = CellUtil.cloneQualifier(kv);
538     byte[] value = CellUtil.cloneValue(kv);
539     if (LOG.isDebugEnabled()) {
540       LOG.debug("Read acl: kv ["+
541                 Bytes.toStringBinary(key)+": "+
542                 Bytes.toStringBinary(value)+"]");
543     }
544 
545     // check for a column family appended to the key
546     // TODO: avoid the string conversion to make this more efficient
547     String username = Bytes.toString(key);
548 
549     //Handle namespace entry
550     if(isNamespaceEntry(entryName)) {
551       return new Pair<String, TablePermission>(username,
552           new TablePermission(Bytes.toString(fromNamespaceEntry(entryName)), value));
553     }
554 
555     //Handle table and global entry
556     //TODO global entry should be handled differently
557     int idx = username.indexOf(ACL_KEY_DELIMITER);
558     byte[] permFamily = null;
559     byte[] permQualifier = null;
560     if (idx > 0 && idx < username.length()-1) {
561       String remainder = username.substring(idx+1);
562       username = username.substring(0, idx);
563       idx = remainder.indexOf(ACL_KEY_DELIMITER);
564       if (idx > 0 && idx < remainder.length()-1) {
565         permFamily = Bytes.toBytes(remainder.substring(0, idx));
566         permQualifier = Bytes.toBytes(remainder.substring(idx+1));
567       } else {
568         permFamily = Bytes.toBytes(remainder);
569       }
570     }
571 
572     return new Pair<String,TablePermission>(username,
573         new TablePermission(TableName.valueOf(entryName), permFamily, permQualifier, value));
574   }
575 
576   /**
577    * Writes a set of permissions as {@link org.apache.hadoop.io.Writable} instances
578    * and returns the resulting byte array.
579    *
580    * Writes a set of permission [user: table permission]
581    */
582   public static byte[] writePermissionsAsBytes(ListMultimap<String, TablePermission> perms,
583       Configuration conf) {
584     return ProtobufUtil.prependPBMagic(ProtobufUtil.toUserTablePermissions(perms).toByteArray());
585   }
586 
587   /**
588    * Reads a set of permissions as {@link org.apache.hadoop.io.Writable} instances
589    * from the input stream.
590    */
591   public static ListMultimap<String, TablePermission> readPermissions(byte[] data,
592       Configuration conf)
593   throws DeserializationException {
594     if (ProtobufUtil.isPBMagicPrefix(data)) {
595       int pblen = ProtobufUtil.lengthOfPBMagic();
596       try {
597         AccessControlProtos.UsersAndPermissions perms =
598           AccessControlProtos.UsersAndPermissions.newBuilder().mergeFrom(
599             data, pblen, data.length - pblen).build();
600         return ProtobufUtil.toUserTablePermissions(perms);
601       } catch (InvalidProtocolBufferException e) {
602         throw new DeserializationException(e);
603       }
604     } else {
605       ListMultimap<String,TablePermission> perms = ArrayListMultimap.create();
606       try {
607         DataInput in = new DataInputStream(new ByteArrayInputStream(data));
608         int length = in.readInt();
609         for (int i=0; i<length; i++) {
610           String user = Text.readString(in);
611           List<TablePermission> userPerms =
612             (List)HbaseObjectWritableFor96Migration.readObject(in, conf);
613           perms.putAll(user, userPerms);
614         }
615       } catch (IOException e) {
616         throw new DeserializationException(e);
617       }
618       return perms;
619     }
620   }
621 
622   /**
623    * Returns whether or not the given name should be interpreted as a group
624    * principal.  Currently this simply checks if the name starts with the
625    * special group prefix character ("@").
626    */
627   public static boolean isGroupPrincipal(String name) {
628     return name != null && name.startsWith(GROUP_PREFIX);
629   }
630 
631   /**
632    * Returns the actual name for a group principal (stripped of the
633    * group prefix).
634    */
635   public static String getGroupName(String aclKey) {
636     if (!isGroupPrincipal(aclKey)) {
637       return aclKey;
638     }
639 
640     return aclKey.substring(GROUP_PREFIX.length());
641   }
642 
643   /**
644    * Returns the group entry with the group prefix for a group principal.
645    */
646   public static String toGroupEntry(String name) {
647     return GROUP_PREFIX + name;
648   }
649 
650   public static boolean isNamespaceEntry(String entryName) {
651     return entryName.charAt(0) == NAMESPACE_PREFIX;
652   }
653 
654   public static boolean isNamespaceEntry(byte[] entryName) {
655     return entryName[0] == NAMESPACE_PREFIX;
656   }
657 
658   public static String toNamespaceEntry(String namespace) {
659      return NAMESPACE_PREFIX + namespace;
660    }
661 
662    public static String fromNamespaceEntry(String namespace) {
663      if(namespace.charAt(0) != NAMESPACE_PREFIX)
664        throw new IllegalArgumentException("Argument is not a valid namespace entry");
665      return namespace.substring(1);
666    }
667 
668    public static byte[] toNamespaceEntry(byte[] namespace) {
669      byte[] ret = new byte[namespace.length+1];
670      ret[0] = NAMESPACE_PREFIX;
671      System.arraycopy(namespace, 0, ret, 1, namespace.length);
672      return ret;
673    }
674 
675    public static byte[] fromNamespaceEntry(byte[] namespace) {
676      if(namespace[0] != NAMESPACE_PREFIX) {
677        throw new IllegalArgumentException("Argument is not a valid namespace entry: " +
678            Bytes.toString(namespace));
679      }
680      return Arrays.copyOfRange(namespace, 1, namespace.length);
681    }
682 
683    public static List<Permission> getCellPermissionsForUser(User user, Cell cell)
684        throws IOException {
685      // Save an object allocation where we can
686      if (cell.getTagsLength() == 0) {
687        return null;
688      }
689      List<Permission> results = Lists.newArrayList();
690      Iterator<Tag> tagsIterator = CellUtil.tagsIterator(cell.getTagsArray(), cell.getTagsOffset(),
691         cell.getTagsLength());
692      while (tagsIterator.hasNext()) {
693        Tag tag = tagsIterator.next();
694        if (tag.getType() == ACL_TAG_TYPE) {
695          // Deserialize the table permissions from the KV
696          ListMultimap<String,Permission> kvPerms = ProtobufUtil.toUsersAndPermissions(
697            AccessControlProtos.UsersAndPermissions.newBuilder().mergeFrom(
698              tag.getBuffer(), tag.getTagOffset(), tag.getTagLength()).build());
699          // Are there permissions for this user?
700          List<Permission> userPerms = kvPerms.get(user.getShortName());
701          if (userPerms != null) {
702            results.addAll(userPerms);
703          }
704          // Are there permissions for any of the groups this user belongs to?
705          String groupNames[] = user.getGroupNames();
706          if (groupNames != null) {
707            for (String group : groupNames) {
708              List<Permission> groupPerms = kvPerms.get(GROUP_PREFIX + group);
709              if (results != null) {
710                results.addAll(groupPerms);
711              }
712            }
713          }
714        }
715      }
716      return results;
717    }
718 }