Move unique name generation and tracking into //content.

content/renderer/unique_name_helper.cc

Index: content/renderer/unique_name_helper.cc
diff --git a/content/renderer/unique_name_helper.cc b/content/renderer/unique_name_helper.cc
new file mode 100644
index 0000000000000000000000000000000000000000..81c8f030f7f67b7226843f2aa6956c9cc8b9b428
--- /dev/null
+++ b/content/renderer/unique_name_helper.cc
@@ -0,0 +1,183 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/renderer/unique_name_helper.h"
+
+#include <vector>
+
+#include "base/containers/adapters.h"
+#include "base/logging.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_piece.h"
+#include "content/renderer/render_frame_impl.h"
+#include "content/renderer/render_frame_proxy.h"
+#include "third_party/WebKit/public/web/WebLocalFrame.h"
+
+namespace content {
+
+namespace {
+
+const std::string& UniqueNameForFrame(blink::WebFrame* frame) {
+  return frame->isWebLocalFrame()
+             ? RenderFrameImpl::FromWebFrame(frame)->unique_name()
+             : RenderFrameProxy::FromWebFrame(frame)->unique_name();
+}
+
+bool UniqueNameExists(blink::WebFrame* top, const std::string& candidate) {
+  // This method is currently O(N), where N = number of frames in the tree.
+
+  // Before recalculating or checking unique name, we set m_uniqueName
+  // to an empty string (so the soon-to-be-removed name does not count
+  // as a collision).  This means that uniqueNameExists would return
+  // false positives when called with an empty |name|.
+  DCHECK(!candidate.empty());
+
+  for (blink::WebFrame* frame = top; frame; frame = frame->traverseNext()) {
+    if (UniqueNameForFrame(frame) == candidate)
+      return true;
+  }
+
+  return false;
+}
+
+std::string GenerateCandidate(blink::WebFrame* parent, blink::WebFrame* child) {
+  constexpr char kFramePathPrefix[] = "<!--framePath ";
+  constexpr int kFramePathPrefixLength = 14;
+  constexpr int kFramePathSuffixLength = 3;
+
+  std::string new_name(kFramePathPrefix);
+
+  // Find the nearest parent that has a frame with a path in it.
+  std::vector<blink::WebFrame*> chain;
+  for (blink::WebFrame* frame = parent; frame; frame = frame->parent()) {
+    base::StringPiece name = UniqueNameForFrame(frame);
+    if (name.starts_with(kFramePathPrefix) && name.ends_with("-->") &&
+        kFramePathPrefixLength + kFramePathSuffixLength < name.size()) {
+      name.substr(kFramePathPrefixLength,
+                  name.size() - kFramePathPrefixLength - kFramePathSuffixLength)
+          .AppendToString(&new_name);
+      break;
+    }
+    chain.push_back(frame);
+  }
+
+  for (auto* frame : base::Reversed(chain)) {
+    new_name += '/';
+    new_name += UniqueNameForFrame(frame);
+  }
+
+  int child_count = 0;
+  for (blink::WebFrame* frame = parent->firstChild(); frame != nullptr;
+       frame = frame->nextSibling()) {
+    ++child_count;
+  }
+
+  // When generating a candidate, a null |child| means that this is the
+  // candidate name for a child frame that's not yet attached.
+  new_name += "/<!--frame";
+  new_name += base::IntToString(child_count - (child ? 1 : 0));
+  new_name += "-->-->";
+
+  // NOTE: This name might not be unique - see http://crbug.com/588800.
+  return new_name;
+}
+
+std::string GenerateFramePosition(blink::WebFrame* parent,
+                                  blink::WebFrame* child) {
+  // This method is currently O(N), where N = number of frames in the tree.
+
+  std::string position_string("<!--framePosition");
+
+  while (parent) {
+    int position_in_parent = 0;
+    blink::WebFrame* sibling = parent->firstChild();
+    while (sibling != child) {
+      sibling = sibling->nextSibling();
+      ++position_in_parent;
+    }
+
+    position_string += '-';
+    position_string += base::IntToString(position_in_parent);
+
+    child = parent;
+    parent = parent->parent();
+  }
+
+  // NOTE: The generated string is not guaranteed to be unique, but should
+  // have a better chance of being unique than the string generated by
+  // GenerateCandidate, because we embed extra information into the string:
+  // 1) we walk the full chain of ancestors, all the way to the main frame
+  // 2) we use frame-position-within-parent (aka |position_in_parent|)
+  //    instead of sibling-count.
+  return position_string;
+}
+
+std::string AppendUniqueSuffix(blink::WebFrame* top,
+                               const std::string& prefix,
+                               const std::string& likely_unique_suffix) {
+  // We want unique name to be stable across page reloads - this is why
+  // we use a deterministic |number_of_tries| rather than a random number
+  // (a random number would be more likely to avoid a collision, but
+  // would change after every page reload).
+  int number_of_retries = 0;
+
+  // Keep trying |prefix| + |likely_unique_suffix| + |number_of_tries|
+  // concatenations until we get a truly unique name.
+  std::string candidate(prefix);
+  candidate += likely_unique_suffix;
+  candidate += '/';
+  while (true) {
+    size_t current_length = candidate.size();
+    candidate += base::IntToString(number_of_retries++);
+    candidate += "-->";
+    if (!UniqueNameExists(top, candidate))
+      break;
+    candidate.resize(current_length);
+  }
+  return candidate;
+}
+
+std::string CalculateNewName(blink::WebFrame* parent,
+                             blink::WebFrame* child,
+                             const std::string& name) {
+  blink::WebFrame* top = parent->top();
+  if (!name.empty() && !UniqueNameExists(top, name) && name != "_blank")
+    return name;
+
+  std::string candidate = GenerateCandidate(parent, child);
+  if (!UniqueNameExists(top, candidate))
+    return candidate;
+
+  std::string likely_unique_suffix = GenerateFramePosition(parent, child);
+  return AppendUniqueSuffix(top, candidate, likely_unique_suffix);
+}
+
+}  // namespace
+
+UniqueNameHelper::UniqueNameHelper(RenderFrameImpl* render_frame)
+    : render_frame_(render_frame) {}
+
+UniqueNameHelper::~UniqueNameHelper() {}
+
+std::string UniqueNameHelper::GenerateNameForNewChildFrame(
+    blink::WebFrame* parent,
+    const std::string& name) {
+  return CalculateNewName(parent, nullptr, name);
+}
+
+void UniqueNameHelper::UpdateName(const std::string& name) {
+  // The unique name of the main frame is always the empty string.
+  if (!GetWebFrame()->parent())
+    return;
+  // It's important to clear this before calculating a new name, as the
+  // calculation checks for collisions with existing unique names.
+  unique_name_.clear();
+  unique_name_ = CalculateNewName(GetWebFrame()->parent(), GetWebFrame(), name);
+}
+
+blink::WebLocalFrame* UniqueNameHelper::GetWebFrame() const {
+  return render_frame_->GetWebFrame();
+}
+
+}  // namespace content