content/renderer/unique_name_helper.h

// 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.

#ifndef CONTENT_RENDERER_UNIQUE_NAME_HELPER_H_
#define CONTENT_RENDERER_UNIQUE_NAME_HELPER_H_

#include <string>

#include "base/macros.h"

namespace blink {
class WebFrame;
class WebLocalFrame;
}  // namespace blink

namespace content {

class RenderFrameImpl;

// Frame helper that manages the details of generating a quasi-stable unique
// name for the frame. The name is unique within a page, and is used for:
// - matching up session history items with recreated frames
// - layout test results
//
// Description of the current unique name format
// ---------------------------------------------
// Changing the format of unique name has a high cost, because it breaks
// backwards compatibility of session history (which stores unique names
// generated in the past on user's disk). The evolution of unique name in a
// mostly backwards-compatible way has resulted in the rather baroque format...
//
// uniqueName ::= <nullForMainFrame> | <assignedName> | <generatedName>
// Note: generatedName is used if assignedName is non-unique / conflicts with
// other frame's unique name.
//
// assignedName ::= value of iframe's name attribute
//                  or value assigned to window.name
// Note: The name must be assigned *before* the first real commit: afterwards,
// the unique name is immutable.
//
// generatedName ::= oldGeneratedName newUniqueSuffix?
// Note: newUniqueSuffix is only present if oldGeneratedName is not unique.
//
// oldGeneratedName ::= "<!--framePath //" ancestorChain
//                      "/<!--frame" childCount "-->-->"
// Note: oldGeneratedName is generated by the internal GenerateCandidate()
// method.
//
// childCount ::= current number of siblings
//
// ancestorChain ::= concatenated unique names of ancestor chain,
//                   terminated on the first ancestor (if any) starting with
//                   "<!--framePath"; each ancestor's unique name is
//                   separated by "/" character
// Note: Two examples are provided below, with each portion of the name from a
// distinct ancestor annotated.
//
// Example ancestor chain #1:
//     "grandparent/parent"
//     |    #1     |  #2  |
// Example ancestor chain #2:
//     "<!--framePath //foo/bar/<!--frame42-->-->/blah/foobar"
//     |                    #1                   | #2 |  #3  |
//
// newUniqueSuffix ::= "<!--framePosition" framePosition "/" retryNumber "-->"
//
// framePosition ::= "-" numberOfSiblingsBeforeChild
//                   [ framePosition-forParent? ]
//
// retryNumber ::= smallest non-negative integer resulting in unique name
class UniqueNameHelper {
 public:
  explicit UniqueNameHelper(RenderFrameImpl* render_frame);
  ~UniqueNameHelper();

  // Returns the generated unique name.
  const std::string& value() const { return unique_name_; }

  // Used to propagate an already calculated unique name.
  //
  // TODO(lukasza): It would be nice to assert uniqueness of the propagated
  // name here but:
  // 1) uniqueness is currently violated by provisional/old frame pairs.
  // 2) there is an unresolved race between 2 OOPIFs, that can result in a
  //    non-unique unique name: see https://crbug.com/558680#c14.
  void set_propagated_name(const std::string& name) { unique_name_ = name; }

  // Note: when creating a new child frame, the unique name needs to be
  // calculated before the RenderFrameImpl is created. To avoid this chicken and
  // egg problem, this method is static, which means that |parent| needs to be
  // passed as a parameter.
  static std::string GenerateNameForNewChildFrame(blink::WebFrame* parent,
                                                  const std::string& name);

  // Called after a browsing context name change to generate a new name. Note
  // that this should not be called if the frame is no longer displaying the
  // initial empty document, as unique name changes after that point will break
  // history navigations. See https://crbug.com/607205.
  void UpdateName(const std::string& name);

 private:
  blink::WebLocalFrame* GetWebFrame() const;

  RenderFrameImpl* const render_frame_;
  std::string unique_name_;

  DISALLOW_COPY_AND_ASSIGN(UniqueNameHelper);
};

}  // namespace content

#endif  // CONTENT_RENDERER_UNIQUE_NAME_HELPER_H_