ui/accessibility/ax_tree.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "ui/accessibility/ax_tree.h"
   6
   7 #include <set>
   8
   9 #include "base/logging.h"
  10 #include "base/strings/stringprintf.h"
  11 #include "ui/accessibility/ax_node.h"
  12
  13 namespace ui {
  14
  15 namespace {
  16
  17 std::string TreeToStringHelper(AXNode* node, int indent) {
  18   std::string result = std::string(2 * indent, ' ');
  19   result += node->data().ToString() + "\n";
  20   for (int i = 0; i < node->child_count(); ++i)
  21     result += TreeToStringHelper(node->ChildAtIndex(i), indent + 1);
  22   return result;
  23 }
  24
  25 }  // namespace
  26
  27 // Intermediate state to keep track of during a tree update.
  28 struct AXTreeUpdateState {
  29   AXTreeUpdateState() : new_root(nullptr) {}
  30
  31   // During an update, this keeps track of all nodes that have been
  32   // implicitly referenced as part of this update, but haven't been
  33   // updated yet. It's an error if there are any pending nodes at the
  34   // end of Unserialize.
  35   std::set<AXNode*> pending_nodes;
  36
  37   // Keeps track of new nodes created during this update.
  38   std::set<AXNode*> new_nodes;
  39
  40   // The new root in this update, if any.
  41   AXNode* new_root;
  42 };
  43
  44 AXTreeDelegate::AXTreeDelegate() {
  45 }
  46
  47 AXTreeDelegate::~AXTreeDelegate() {
  48 }
  49
  50 AXTree::AXTree()
  51     : delegate_(NULL), root_(NULL) {
  52   AXNodeData root;
  53   root.id = -1;
  54   root.role = AX_ROLE_ROOT_WEB_AREA;
  55
  56   AXTreeUpdate initial_state;
  57   initial_state.nodes.push_back(root);
  58   CHECK(Unserialize(initial_state)) << error();
  59 }
  60
  61 AXTree::AXTree(const AXTreeUpdate& initial_state)
  62     : delegate_(NULL), root_(NULL) {
  63   CHECK(Unserialize(initial_state)) << error();
  64 }
  65
  66 AXTree::~AXTree() {
  67   if (root_)
  68     DestroyNodeAndSubtree(root_, nullptr);
  69 }
  70
  71 void AXTree::SetDelegate(AXTreeDelegate* delegate) {
  72   delegate_ = delegate;
  73 }
  74
  75 AXNode* AXTree::GetFromId(int32 id) const {
  76   base::hash_map<int32, AXNode*>::const_iterator iter = id_map_.find(id);
  77   return iter != id_map_.end() ? iter->second : NULL;
  78 }
  79
  80 bool AXTree::Unserialize(const AXTreeUpdate& update) {
  81   AXTreeUpdateState update_state;
  82   int32 old_root_id = root_ ? root_->id() : 0;
  83
  84   if (update.node_id_to_clear != 0) {
  85     AXNode* node = GetFromId(update.node_id_to_clear);
  86     if (!node) {
  87       error_ = base::StringPrintf("Bad node_id_to_clear: %d",
  88                                   update.node_id_to_clear);
  89       return false;
  90     }
  91     if (node == root_) {
  92       DestroySubtree(root_, &update_state);
  93       root_ = NULL;
  94     } else {
  95       for (int i = 0; i < node->child_count(); ++i)
  96         DestroySubtree(node->ChildAtIndex(i), &update_state);
  97       std::vector<AXNode*> children;
  98       node->SwapChildren(children);
  99       update_state.pending_nodes.insert(node);
 100     }
 101   }
 102
 103   for (size_t i = 0; i < update.nodes.size(); ++i) {
 104     if (!UpdateNode(update.nodes[i], &update_state))
 105       return false;
 106   }
 107
 108   if (!update_state.pending_nodes.empty()) {
 109     error_ = "Nodes left pending by the update:";
 110     for (std::set<AXNode*>::iterator iter = update_state.pending_nodes.begin();
 111          iter != update_state.pending_nodes.end(); ++iter) {
 112       error_ += base::StringPrintf(" %d", (*iter)->id());
 113     }
 114     return false;
 115   }
 116
 117   if (delegate_) {
 118     std::set<AXNode*>& new_nodes = update_state.new_nodes;
 119     std::vector<AXTreeDelegate::Change> changes;
 120     changes.reserve(update.nodes.size());
 121     for (size_t i = 0; i < update.nodes.size(); ++i) {
 122       AXNode* node = GetFromId(update.nodes[i].id);
 123       if (new_nodes.find(node) != new_nodes.end()) {
 124         if (new_nodes.find(node->parent()) == new_nodes.end()) {
 125           changes.push_back(
 126               AXTreeDelegate::Change(node, AXTreeDelegate::SUBTREE_CREATED));
 127         } else {
 128           changes.push_back(
 129               AXTreeDelegate::Change(node, AXTreeDelegate::NODE_CREATED));
 130         }
 131       } else {
 132         changes.push_back(
 133             AXTreeDelegate::Change(node, AXTreeDelegate::NODE_CHANGED));
 134       }
 135     }
 136     delegate_->OnAtomicUpdateFinished(
 137         this, root_->id() != old_root_id, changes);
 138   }
 139
 140   return true;
 141 }
 142
 143 std::string AXTree::ToString() const {
 144   return TreeToStringHelper(root_, 0);
 145 }
 146
 147 AXNode* AXTree::CreateNode(AXNode* parent, int32 id, int32 index_in_parent) {
 148   AXNode* new_node = new AXNode(parent, id, index_in_parent);
 149   id_map_[new_node->id()] = new_node;
 150   if (delegate_)
 151     delegate_->OnNodeCreated(this, new_node);
 152   return new_node;
 153 }
 154
 155 bool AXTree::UpdateNode(const AXNodeData& src,
 156                         AXTreeUpdateState* update_state) {
 157   // This method updates one node in the tree based on serialized data
 158   // received in an AXTreeUpdate. See AXTreeUpdate for pre and post
 159   // conditions.
 160
 161   // Look up the node by id. If it's not found, then either the root
 162   // of the tree is being swapped, or we're out of sync with the source
 163   // and this is a serious error.
 164   AXNode* node = GetFromId(src.id);
 165   if (node) {
 166     update_state->pending_nodes.erase(node);
 167     node->SetData(src);
 168   } else {
 169     if (src.role != AX_ROLE_ROOT_WEB_AREA &&
 170         src.role != AX_ROLE_DESKTOP) {
 171       error_ = base::StringPrintf(
 172           "%d is not in the tree and not the new root", src.id);
 173       return false;
 174     }
 175     if (update_state->new_root) {
 176       error_ = "Tree update contains two new roots";
 177       return false;
 178     }
 179
 180     update_state->new_root = CreateNode(NULL, src.id, 0);
 181     node = update_state->new_root;
 182     update_state->new_nodes.insert(node);
 183     node->SetData(src);
 184   }
 185
 186   if (delegate_)
 187     delegate_->OnNodeChanged(this, node);
 188
 189   // First, delete nodes that used to be children of this node but aren't
 190   // anymore.
 191   if (!DeleteOldChildren(node, src.child_ids, update_state)) {
 192     if (update_state->new_root)
 193       DestroySubtree(update_state->new_root, update_state);
 194     return false;
 195   }
 196
 197   // Now build a new children vector, reusing nodes when possible,
 198   // and swap it in.
 199   std::vector<AXNode*> new_children;
 200   bool success = CreateNewChildVector(
 201       node, src.child_ids, &new_children, update_state);
 202   node->SwapChildren(new_children);
 203
 204   // Update the root of the tree if needed.
 205   if ((src.role == AX_ROLE_ROOT_WEB_AREA || src.role == AX_ROLE_DESKTOP) &&
 206       (!root_ || root_->id() != src.id)) {
 207     if (root_)
 208       DestroySubtree(root_, update_state);
 209     root_ = node;
 210   }
 211
 212   return success;
 213 }
 214
 215 void AXTree::DestroySubtree(AXNode* node,
 216                             AXTreeUpdateState* update_state) {
 217   if (delegate_)
 218     delegate_->OnSubtreeWillBeDeleted(this, node);
 219   DestroyNodeAndSubtree(node, update_state);
 220 }
 221
 222 void AXTree::DestroyNodeAndSubtree(AXNode* node,
 223                                    AXTreeUpdateState* update_state) {
 224   id_map_.erase(node->id());
 225   for (int i = 0; i < node->child_count(); ++i)
 226     DestroyNodeAndSubtree(node->ChildAtIndex(i), update_state);
 227   if (delegate_)
 228     delegate_->OnNodeWillBeDeleted(this, node);
 229   if (update_state) {
 230     update_state->pending_nodes.erase(node);
 231   }
 232   node->Destroy();
 233 }
 234
 235 bool AXTree::DeleteOldChildren(AXNode* node,
 236                                const std::vector<int32>& new_child_ids,
 237                                AXTreeUpdateState* update_state) {
 238   // Create a set of child ids in |src| for fast lookup, and return false
 239   // if a duplicate is found;
 240   std::set<int32> new_child_id_set;
 241   for (size_t i = 0; i < new_child_ids.size(); ++i) {
 242     if (new_child_id_set.find(new_child_ids[i]) != new_child_id_set.end()) {
 243       error_ = base::StringPrintf("Node %d has duplicate child id %d",
 244                                   node->id(), new_child_ids[i]);
 245       return false;
 246     }
 247     new_child_id_set.insert(new_child_ids[i]);
 248   }
 249
 250   // Delete the old children.
 251   const std::vector<AXNode*>& old_children = node->children();
 252   for (size_t i = 0; i < old_children.size(); ++i) {
 253     int old_id = old_children[i]->id();
 254     if (new_child_id_set.find(old_id) == new_child_id_set.end())
 255       DestroySubtree(old_children[i], update_state);
 256   }
 257
 258   return true;
 259 }
 260
 261 bool AXTree::CreateNewChildVector(AXNode* node,
 262                                   const std::vector<int32>& new_child_ids,
 263                                   std::vector<AXNode*>* new_children,
 264                                   AXTreeUpdateState* update_state) {
 265   bool success = true;
 266   for (size_t i = 0; i < new_child_ids.size(); ++i) {
 267     int32 child_id = new_child_ids[i];
 268     int32 index_in_parent = static_cast<int32>(i);
 269     AXNode* child = GetFromId(child_id);
 270     if (child) {
 271       if (child->parent() != node) {
 272         // This is a serious error - nodes should never be reparented.
 273         // If this case occurs, continue so this node isn't left in an
 274         // inconsistent state, but return failure at the end.
 275         error_ = base::StringPrintf(
 276             "Node %d reparented from %d to %d",
 277             child->id(),
 278             child->parent() ? child->parent()->id() : 0,
 279             node->id());
 280         success = false;
 281         continue;
 282       }
 283       child->SetIndexInParent(index_in_parent);
 284     } else {
 285       child = CreateNode(node, child_id, index_in_parent);
 286       update_state->pending_nodes.insert(child);
 287       update_state->new_nodes.insert(child);
 288     }
 289     new_children->push_back(child);
 290   }
 291
 292   return success;
 293 }
 294
 295 }  // namespace ui