Add CPDF_ObjectWalker.

It is allow us to walk on all non-null sub-objects 
in an object in depth, include itself,

Change-Id: Ia23051073984411668112422b47cf7a4460aa078
Reviewed-on: https://pdfium-review.googlesource.com/8910
Commit-Queue: Art Snake <art-snake@yandex-team.ru>
Reviewed-by: dsinclair <dsinclair@chromium.org>

1 files changed, 69 insertions, 0 deletions

diff --git a/core/fpdfapi/parser/cpdf_object_walker.h b/core/fpdfapi/parser/cpdf_object_walker.h
new file mode 100644
index 0000000000..5590440f8f
--- /dev/null
+++ b/core/fpdfapi/parser/cpdf_object_walker.h
@@ -0,0 +1,69 @@
+// Copyright 2017 PDFium 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 CORE_FPDFAPI_PARSER_CPDF_OBJECT_WALKER_H_
+#define CORE_FPDFAPI_PARSER_CPDF_OBJECT_WALKER_H_
+
+#include <memory>
+#include <stack>
+
+#include "core/fpdfapi/parser/cpdf_dictionary.h"
+
+// Walk on all non-null sub-objects in an object in depth, include itself,
+// like in flat list.
+class CPDF_ObjectWalker {
+ public:
+  class SubobjectIterator {
+   public:
+    virtual ~SubobjectIterator();
+    bool IsStarted() const { return is_started_; }
+    bool virtual IsFinished() const = 0;
+    const CPDF_Object* Increment();
+    const CPDF_Object* object() const { return object_; }
+
+   protected:
+    explicit SubobjectIterator(const CPDF_Object* object);
+
+    virtual const CPDF_Object* IncrementImpl() = 0;
+    virtual void Start() = 0;
+
+   private:
+    const CPDF_Object* object_;
+    bool is_started_ = false;
+  };
+
+  explicit CPDF_ObjectWalker(const CPDF_Object* root);
+  ~CPDF_ObjectWalker();
+
+  const CPDF_Object* GetNext();
+  void SkipWalkIntoCurrentObject();
+
+  size_t current_depth() const { return current_depth_; }
+  const CPDF_Object* GetParent() const { return parent_object_; }
+  const CFX_ByteString& dictionary_key() const { return dict_key_; }
+
+ private:
+  static std::unique_ptr<SubobjectIterator> MakeIterator(
+      const CPDF_Object* object);
+
+  const CPDF_Object* next_object_;
+  const CPDF_Object* parent_object_;
+
+  CFX_ByteString dict_key_;
+  size_t current_depth_;
+
+  std::stack<std::unique_ptr<SubobjectIterator>> stack_;
+};
+
+class CPDF_NonConstObjectWalker : public CPDF_ObjectWalker {
+ public:
+  explicit CPDF_NonConstObjectWalker(CPDF_Object* root)
+      : CPDF_ObjectWalker(root) {}
+
+  CPDF_Object* GetNext() {
+    return const_cast<CPDF_Object*>(CPDF_ObjectWalker::GetNext());
+  }
+};
+
+#endif  // CORE_FPDFAPI_PARSER_CPDF_OBJECT_WALKER_H_