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diff --git a/java/com/google/gerrit/reviewdb/client/RefNames.java b/java/com/google/gerrit/reviewdb/client/RefNames.java
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+++ b/java/com/google/gerrit/reviewdb/client/RefNames.java
@@ -0,0 +1,443 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.reviewdb.client;
+
+/** Constants and utilities for Gerrit-specific ref names. */
+public class RefNames {
+  public static final String HEAD = "HEAD";
+
+  public static final String REFS = "refs/";
+
+  public static final String REFS_HEADS = "refs/heads/";
+
+  public static final String REFS_TAGS = "refs/tags/";
+
+  public static final String REFS_CHANGES = "refs/changes/";
+
+  public static final String REFS_META = "refs/meta/";
+
+  /** Note tree listing commits we refuse {@code refs/meta/reject-commits} */
+  public static final String REFS_REJECT_COMMITS = "refs/meta/reject-commits";
+
+  /** Configuration settings for a project {@code refs/meta/config} */
+  public static final String REFS_CONFIG = "refs/meta/config";
+
+  /** Note tree listing external IDs */
+  public static final String REFS_EXTERNAL_IDS = "refs/meta/external-ids";
+
+  /** Magic user branch in All-Users {@code refs/users/self} */
+  public static final String REFS_USERS_SELF = "refs/users/self";
+
+  /** Default user preference settings */
+  public static final String REFS_USERS_DEFAULT = RefNames.REFS_USERS + "default";
+
+  /** Configurations of project-specific dashboards (canned search queries). */
+  public static final String REFS_DASHBOARDS = "refs/meta/dashboards/";
+
+  /** Sequence counters in NoteDb. */
+  public static final String REFS_SEQUENCES = "refs/sequences/";
+
+  /**
+   * Prefix applied to merge commit base nodes.
+   *
+   * <p>References in this directory should take the form {@code refs/cache-automerge/xx/yyyy...}
+   * where xx is the first two digits of the merge commit's object name, and yyyyy... is the
+   * remaining 38. The reference should point to a treeish that is the automatic merge result of the
+   * merge commit's parents.
+   */
+  public static final String REFS_CACHE_AUTOMERGE = "refs/cache-automerge/";
+
+  /** Suffix of a meta ref in the NoteDb. */
+  public static final String META_SUFFIX = "/meta";
+
+  /** Suffix of a ref that stores robot comments in the NoteDb. */
+  public static final String ROBOT_COMMENTS_SUFFIX = "/robot-comments";
+
+  public static final String EDIT_PREFIX = "edit-";
+
+  /*
+   * The following refs contain an account ID and should be visible only to that account.
+   *
+   * Parsing the account ID from the ref is implemented in Account.Id#fromRef(String). This ensures
+   * that VisibleRefFilter hides those refs from other users.
+   *
+   * This applies to:
+   * - User branches (e.g. 'refs/users/23/1011123')
+   * - Draft comment refs (e.g. 'refs/draft-comments/73/67473/1011123')
+   * - Starred changes refs (e.g. 'refs/starred-changes/73/67473/1011123')
+   */
+
+  /** Preference settings for a user {@code refs/users} */
+  public static final String REFS_USERS = "refs/users/";
+
+  /** NoteDb ref for a group {@code refs/groups} */
+  public static final String REFS_GROUPS = "refs/groups/";
+
+  /** NoteDb ref for the NoteMap of all group names */
+  public static final String REFS_GROUPNAMES = "refs/meta/group-names";
+
+  /**
+   * NoteDb ref for deleted groups {@code refs/deleted-groups}. This ref namespace is foreseen as an
+   * attic for deleted groups (it's reserved but not used yet)
+   */
+  public static final String REFS_DELETED_GROUPS = "refs/deleted-groups/";
+
+  /** Draft inline comments of a user on a change */
+  public static final String REFS_DRAFT_COMMENTS = "refs/draft-comments/";
+
+  /** A change starred by a user */
+  public static final String REFS_STARRED_CHANGES = "refs/starred-changes/";
+
+  public static String fullName(String ref) {
+    return (ref.startsWith(REFS) || ref.equals(HEAD)) ? ref : REFS_HEADS + ref;
+  }
+
+  public static final String shortName(String ref) {
+    if (ref.startsWith(REFS_HEADS)) {
+      return ref.substring(REFS_HEADS.length());
+    } else if (ref.startsWith(REFS_TAGS)) {
+      return ref.substring(REFS_TAGS.length());
+    }
+    return ref;
+  }
+
+  public static String changeMetaRef(Change.Id id) {
+    StringBuilder r = newStringBuilder().append(REFS_CHANGES);
+    return shard(id.get(), r).append(META_SUFFIX).toString();
+  }
+
+  public static String robotCommentsRef(Change.Id id) {
+    StringBuilder r = newStringBuilder().append(REFS_CHANGES);
+    return shard(id.get(), r).append(ROBOT_COMMENTS_SUFFIX).toString();
+  }
+
+  public static boolean isNoteDbMetaRef(String ref) {
+    if (ref.startsWith(REFS_CHANGES)
+        && (ref.endsWith(META_SUFFIX) || ref.endsWith(ROBOT_COMMENTS_SUFFIX))) {
+      return true;
+    }
+    if (ref.startsWith(REFS_DRAFT_COMMENTS) || ref.startsWith(REFS_STARRED_CHANGES)) {
+      return true;
+    }
+    return false;
+  }
+
+  public static String refsGroups(AccountGroup.UUID groupUuid) {
+    return REFS_GROUPS + shardUuid(groupUuid.get());
+  }
+
+  public static String refsDeletedGroups(AccountGroup.UUID groupUuid) {
+    return REFS_DELETED_GROUPS + shardUuid(groupUuid.get());
+  }
+
+  public static String refsUsers(Account.Id accountId) {
+    StringBuilder r = newStringBuilder().append(REFS_USERS);
+    return shard(accountId.get(), r).toString();
+  }
+
+  public static String refsDraftComments(Change.Id changeId, Account.Id accountId) {
+    return buildRefsPrefix(REFS_DRAFT_COMMENTS, changeId.get()).append(accountId.get()).toString();
+  }
+
+  public static String refsDraftCommentsPrefix(Change.Id changeId) {
+    return buildRefsPrefix(REFS_DRAFT_COMMENTS, changeId.get()).toString();
+  }
+
+  public static String refsStarredChanges(Change.Id changeId, Account.Id accountId) {
+    return buildRefsPrefix(REFS_STARRED_CHANGES, changeId.get()).append(accountId.get()).toString();
+  }
+
+  public static String refsStarredChangesPrefix(Change.Id changeId) {
+    return buildRefsPrefix(REFS_STARRED_CHANGES, changeId.get()).toString();
+  }
+
+  private static StringBuilder buildRefsPrefix(String prefix, int id) {
+    StringBuilder r = newStringBuilder().append(prefix);
+    return shard(id, r).append('/');
+  }
+
+  public static String refsCacheAutomerge(String hash) {
+    return REFS_CACHE_AUTOMERGE + hash.substring(0, 2) + '/' + hash.substring(2);
+  }
+
+  public static String shard(int id) {
+    if (id < 0) {
+      return null;
+    }
+    return shard(id, newStringBuilder()).toString();
+  }
+
+  private static StringBuilder shard(int id, StringBuilder sb) {
+    int n = id % 100;
+    if (n < 10) {
+      sb.append('0');
+    }
+    sb.append(n);
+    sb.append('/');
+    sb.append(id);
+    return sb;
+  }
+
+  private static String shardUuid(String uuid) {
+    if (uuid == null || uuid.length() < 2) {
+      throw new IllegalArgumentException("UUIDs must consist of at least two characters");
+    }
+    return uuid.substring(0, 2) + '/' + uuid;
+  }
+
+  /**
+   * Returns reference for this change edit with sharded user and change number:
+   * refs/users/UU/UUUU/edit-CCCC/P.
+   *
+   * @param accountId account id
+   * @param changeId change number
+   * @param psId patch set number
+   * @return reference for this change edit
+   */
+  public static String refsEdit(Account.Id accountId, Change.Id changeId, PatchSet.Id psId) {
+    return refsEditPrefix(accountId, changeId) + psId.get();
+  }
+
+  /**
+   * Returns reference prefix for this change edit with sharded user and change number:
+   * refs/users/UU/UUUU/edit-CCCC/.
+   *
+   * @param accountId account id
+   * @param changeId change number
+   * @return reference prefix for this change edit
+   */
+  public static String refsEditPrefix(Account.Id accountId, Change.Id changeId) {
+    return refsEditPrefix(accountId) + changeId.get() + '/';
+  }
+
+  public static String refsEditPrefix(Account.Id accountId) {
+    return refsUsers(accountId) + '/' + EDIT_PREFIX;
+  }
+
+  public static boolean isRefsEdit(String ref) {
+    return ref != null && ref.startsWith(REFS_USERS) && ref.contains(EDIT_PREFIX);
+  }
+
+  public static boolean isRefsUsers(String ref) {
+    return ref.startsWith(REFS_USERS);
+  }
+
+  /**
+   * Whether the ref is a group branch that stores NoteDb data of a group. Returns {@code true} for
+   * all refs that start with {@code refs/groups/}.
+   */
+  public static boolean isRefsGroups(String ref) {
+    return ref.startsWith(REFS_GROUPS);
+  }
+
+  /**
+   * Whether the ref is a group branch that stores NoteDb data of a deleted group. Returns {@code
+   * true} for all refs that start with {@code refs/deleted-groups/}.
+   */
+  public static boolean isRefsDeletedGroups(String ref) {
+    return ref.startsWith(REFS_DELETED_GROUPS);
+  }
+
+  /**
+   * Whether the ref is used for storing group data in NoteDb. Returns {@code true} for all group
+   * branches, refs/meta/group-names and deleted group branches.
+   */
+  public static boolean isGroupRef(String ref) {
+    return isRefsGroups(ref) || isRefsDeletedGroups(ref) || REFS_GROUPNAMES.equals(ref);
+  }
+
+  /** Whether the ref is the configuration branch, i.e. {@code refs/meta/config}, for a project. */
+  public static boolean isConfigRef(String ref) {
+    return REFS_CONFIG.equals(ref);
+  }
+
+  static Integer parseShardedRefPart(String name) {
+    if (name == null) {
+      return null;
+    }
+
+    String[] parts = name.split("/");
+    int n = parts.length;
+    if (n < 2) {
+      return null;
+    }
+
+    // Last 2 digits.
+    int le;
+    for (le = 0; le < parts[0].length(); le++) {
+      if (!Character.isDigit(parts[0].charAt(le))) {
+        return null;
+      }
+    }
+    if (le != 2) {
+      return null;
+    }
+
+    // Full ID.
+    int ie;
+    for (ie = 0; ie < parts[1].length(); ie++) {
+      if (!Character.isDigit(parts[1].charAt(ie))) {
+        if (ie == 0) {
+          return null;
+        }
+        break;
+      }
+    }
+
+    int shard = Integer.parseInt(parts[0]);
+    int id = Integer.parseInt(parts[1].substring(0, ie));
+
+    if (id % 100 != shard) {
+      return null;
+    }
+    return id;
+  }
+
+  static String parseShardedUuidFromRefPart(String name) {
+    if (name == null) {
+      return null;
+    }
+
+    String[] parts = name.split("/");
+    int n = parts.length;
+    if (n != 2) {
+      return null;
+    }
+
+    // First 2 chars.
+    if (parts[0].length() != 2) {
+      return null;
+    }
+
+    // Full UUID.
+    String uuid = parts[1];
+    if (!uuid.startsWith(parts[0])) {
+      return null;
+    }
+
+    return uuid;
+  }
+
+  /**
+   * Skips a sharded ref part at the beginning of the name.
+   *
+   * <p>E.g.: "01/1" -> "", "01/1/" -> "/", "01/1/2" -> "/2", "01/1-edit" -> "-edit"
+   *
+   * @param name ref part name
+   * @return the rest of the name, {@code null} if the ref name part doesn't start with a valid
+   *     sharded ID
+   */
+  static String skipShardedRefPart(String name) {
+    if (name == null) {
+      return null;
+    }
+
+    String[] parts = name.split("/");
+    int n = parts.length;
+    if (n < 2) {
+      return null;
+    }
+
+    // Last 2 digits.
+    int le;
+    for (le = 0; le < parts[0].length(); le++) {
+      if (!Character.isDigit(parts[0].charAt(le))) {
+        return null;
+      }
+    }
+    if (le != 2) {
+      return null;
+    }
+
+    // Full ID.
+    int ie;
+    for (ie = 0; ie < parts[1].length(); ie++) {
+      if (!Character.isDigit(parts[1].charAt(ie))) {
+        if (ie == 0) {
+          return null;
+        }
+        break;
+      }
+    }
+
+    int shard = Integer.parseInt(parts[0]);
+    int id = Integer.parseInt(parts[1].substring(0, ie));
+
+    if (id % 100 != shard) {
+      return null;
+    }
+
+    return name.substring(2 + 1 + ie); // 2 for the length of the shard, 1 for the '/'
+  }
+
+  /**
+   * Parses an ID that follows a sharded ref part at the beginning of the name.
+   *
+   * <p>E.g.: "01/1/2" -> 2, "01/1/2/4" -> 2, ""01/1/2-edit" -> 2
+   *
+   * @param name ref part name
+   * @return ID that follows the sharded ref part at the beginning of the name, {@code null} if the
+   *     ref name part doesn't start with a valid sharded ID or if no valid ID follows the sharded
+   *     ref part
+   */
+  static Integer parseAfterShardedRefPart(String name) {
+    String rest = skipShardedRefPart(name);
+    if (rest == null || !rest.startsWith("/")) {
+      return null;
+    }
+
+    rest = rest.substring(1);
+
+    int ie;
+    for (ie = 0; ie < rest.length(); ie++) {
+      if (!Character.isDigit(rest.charAt(ie))) {
+        break;
+      }
+    }
+    if (ie == 0) {
+      return null;
+    }
+    return Integer.parseInt(rest.substring(0, ie));
+  }
+
+  static Integer parseRefSuffix(String name) {
+    if (name == null) {
+      return null;
+    }
+    int i = name.length();
+    while (i > 0) {
+      char c = name.charAt(i - 1);
+      if (c == '/') {
+        break;
+      } else if (!Character.isDigit(c)) {
+        return null;
+      }
+      i--;
+    }
+    if (i == 0) {
+      return null;
+    }
+    return Integer.valueOf(name.substring(i, name.length()));
+  }
+
+  private static StringBuilder newStringBuilder() {
+    // Many refname types in this file are always are longer than the default of 16 chars, so
+    // presize StringBuilders larger by default. This hurts readability less than accurate
+    // calculations would, at a negligible cost to memory overhead.
+    return new StringBuilder(64);
+  }
+
+  private RefNames() {}
+}