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+// Copyright (c) 2009 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 CHROMEOS_PLATFORM_UPDATE_ENGINE_DELTA_DIFF_PARSER_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_DELTA_DIFF_PARSER_H__
+
+#include <string>
+#include <vector>
+#include "chromeos/obsolete_logging.h"
+#include "base/basictypes.h"
+#include "update_engine/update_metadata.pb.h"
+
+// The DeltaDiffParser class is used to parse a delta file on disk. It will
+// copy the metadata into memory, but not the file data. This class can
+// also be used to copy file data out to disk.
+
+// The DeltaDiffParserIterator class is used to iterate through the
+// metadata of a delta file. It will return directories before their
+// children.
+
+namespace chromeos_update_engine {
+
+class DeltaDiffParser;
+
+class DeltaDiffParserIterator {
+  friend class DeltaDiffParser;
+ public:
+  void Increment();
+
+  // Returns the full path for the current file, e.g. "/bin/bash".
+  // Returns empty string for root.
+  const std::string& path() const {
+    return path_;
+  }
+
+  // Returns the basename for the current file. If path() returns
+  // "/bin/bash", then GetName() returns "bash".
+  // Returns empty string for root
+  const std::string GetName() const;
+
+  const DeltaArchiveManifest_File& GetFile() const;
+  bool operator==(const DeltaDiffParserIterator& that) const {
+    return path_indices_ == that.path_indices_ &&
+        child_indices_ == that.child_indices_ &&
+        path_ == that.path_ &&
+        archive_ == that.archive_;
+  }
+  bool operator!=(const DeltaDiffParserIterator& that) const {
+    return !(*this == that);
+  }
+ private:
+  // Container of all the File messages. Each File message has an index
+  // in archive_. The root directory is always stored at index 0.
+  const DeltaArchiveManifest* archive_;
+  
+  // These variables are used to implement the common recursive depth-first
+  // search algorithm (which we can't use here, since we need to walk the
+  // tree incrementally).
+  
+  // Indices into 'archive_' of the current path components.  For example, if
+  // the current path is "/bin/bash", 'path_stack_' will contain the archive
+  // indices for "/", "/bin", and "/bin/bash", in that order.  This is
+  // analogous to the call stack of the recursive algorithm.
+  std::vector<int> path_indices_;
+
+  // For each component in 'path_stack_', the currently-selected child in its
+  // child vector.  In the previous example, if "/" has "abc" and "bin"
+  // subdirectories and "/bin" contains only "bash", this will contain
+  // [0, 1, 0], since we are using the 0th child at the root directory level
+  // (there's only one child there), the first of the root dir's children
+  // ("bin"), and the 0th child of /bin ("bash").  This is analogous to the
+  // state of each function (in terms of which child it's currently
+  // handling) in the call stack of the recursive algorithm.
+  std::vector<int> child_indices_;
+
+  std::string path_;
+  // Instantiated by friend class DeltaDiffParser
+  explicit DeltaDiffParserIterator(const DeltaArchiveManifest* archive)
+      : archive_(archive) {}
+  DeltaDiffParserIterator() {
+    CHECK(false);  // Should never be called.
+  }
+};
+
+class DeltaDiffParser {
+ public:
+  DeltaDiffParser(const std::string& delta_file);
+  ~DeltaDiffParser();
+  bool valid() const { return valid_; }
+  bool ContainsPath(const std::string& path) const;
+  const DeltaArchiveManifest_File& GetFileAtPath(const std::string& path) const;
+
+  // Reads length bytes at offset of the delta file into the out string
+  // or vector. Be careful not to call this with large length values,
+  // since that much memory will have to be allocated to store the output.
+  // Returns true on success.
+  bool ReadDataVector(off_t offset, off_t length, std::vector<char>* out) const;
+
+  // Copies length bytes of data from offset into a new file at path specified.
+  // If should_decompress is true, will gzip decompress while writing to the
+  // file. Returns true on success.
+  bool CopyDataToFile(off_t offset, off_t length, bool should_decompress,
+                      const std::string& path) const;
+
+  typedef DeltaDiffParserIterator Iterator;
+  const Iterator Begin();
+  const Iterator End();
+
+  // The identifier we expect at the beginning of a delta file.
+  static const char* const kFileMagic;
+
+ private:
+  // (Binary) Searches the children of 'file' for one named child_name.
+  // If found, returns the index into the archive. If not found, returns -1.
+  int GetIndexOfFileChild(const DeltaArchiveManifest_File& file,
+                            const std::string& child_name) const;
+
+  // Returns -1 if not found, 0 for root
+  int GetIndexForPath(const std::string& path) const;
+
+  // We keep a filedescriptor open to the delta file.
+  int fd_;
+
+  DeltaArchiveManifest archive_;
+  bool valid_;
+  DISALLOW_COPY_AND_ASSIGN(DeltaDiffParser);
+};
+
+};  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_DELTA_DIFF_PARSER_H__