shaka-packager/media/mp4/box_reader.h

// Copyright (c) 2012 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 MEDIA_MP4_BOX_READER_H_
#define MEDIA_MP4_BOX_READER_H_

#include <map>
#include <vector>

#include "base/compiler_specific.h"
#include "base/logging.h"
#include "media/base/buffer_reader.h"
#include "media/mp4/fourccs.h"
#include "media/mp4/rcheck.h"

namespace media {
namespace mp4 {

class Box;

class BoxReader : public BufferReader {
 public:
  ~BoxReader();

  // Create a BoxReader from a buffer. Note that this function may return NULL
  // if an intact, complete box was not available in the buffer. If |*err| is
  // set, there was a stream-level error when creating the box; otherwise, NULL
  // values are only expected when insufficient data is available.
  //
  // |buf| is retained but not owned, and must outlive the BoxReader instance.
  static BoxReader* ReadTopLevelBox(const uint8* buf,
                                    const int buf_size,
                                    bool* err);

  // Read the box header from the current buffer. This function returns true if
  // there is enough data to read the header and the header is sane; that is, it
  // does not check to ensure the entire box is in the buffer before returning
  // true. The semantics of |*err| are the same as above.
  //
  // |buf| is not retained.
  static bool StartTopLevelBox(const uint8* buf,
                               const int buf_size,
                               FourCC* type,
                               int* box_size,
                               bool* err) WARN_UNUSED_RESULT;

  // Returns true if |type| is recognized to be a top-level box, false
  // otherwise. This returns true for some boxes which we do not parse.
  // Helpful in debugging misaligned appends.
  static bool IsValidTopLevelBox(const FourCC& type);

  // Scan through all boxes within the current box, starting at the current
  // buffer position. Must be called before any of the *Child functions work.
  bool ScanChildren() WARN_UNUSED_RESULT;

  // Return true if child with type |child.BoxType()| exists.
  bool ChildExist(Box* child) WARN_UNUSED_RESULT;

  // Read exactly one child box from the set of children. The type of the child
  // will be determined by the BoxType() method of |child|.
  bool ReadChild(Box* child) WARN_UNUSED_RESULT;

  // Read one child if available. Returns false on error, true on successful
  // read or on child absent.
  bool TryReadChild(Box* child) WARN_UNUSED_RESULT;

  // Read at least one child. False means error or no such child present.
  template <typename T>
  bool ReadChildren(std::vector<T>* children) WARN_UNUSED_RESULT;

  // Read any number of children. False means error.
  template <typename T>
  bool TryReadChildren(std::vector<T>* children) WARN_UNUSED_RESULT;

  // Read all children, regardless of FourCC. This is used from exactly one box,
  // corresponding to a rather significant inconsistency in the BMFF spec.
  // Note that this method is mutually exclusive with ScanChildren().
  template <typename T>
  bool ReadAllChildren(std::vector<T>* children) WARN_UNUSED_RESULT;

  bool ReadFourCC(FourCC* fourcc) {
    uint32 val;
    if (!Read4(&val))
      return false;
    *fourcc = static_cast<FourCC>(val);
    return true;
  }

  FourCC type() const { return type_; }

 private:
  BoxReader(const uint8* buf, size_t size);

  // Must be called immediately after init. If the return is false, this
  // indicates that the box header and its contents were not available in the
  // stream or were nonsensical, and that the box must not be used further. In
  // this case, if |*err| is false, the problem was simply a lack of data, and
  // should only be an error condition if some higher-level component knows that
  // no more data is coming (i.e. EOS or end of containing box). If |*err| is
  // true, the error is unrecoverable and the stream should be aborted.
  bool ReadHeader(bool* err);

  FourCC type_;

  typedef std::multimap<FourCC, BoxReader*> ChildMap;

  // The set of child box FourCCs and their corresponding buffer readers. Only
  // valid if scanned_ is true.
  ChildMap children_;
  bool scanned_;

  DISALLOW_COPY_AND_ASSIGN(BoxReader);
};

// Template definitions.
template <typename T>
bool BoxReader::ReadChildren(std::vector<T>* children) {
  RCHECK(TryReadChildren(children) && !children->empty());
  return true;
}

template <typename T>
bool BoxReader::TryReadChildren(std::vector<T>* children) {
  DCHECK(scanned_);
  DCHECK(children->empty());

  children->resize(1);
  FourCC child_type = (*children)[0].BoxType();

  ChildMap::iterator start_itr = children_.lower_bound(child_type);
  ChildMap::iterator end_itr = children_.upper_bound(child_type);
  children->resize(std::distance(start_itr, end_itr));
  typename std::vector<T>::iterator child_itr = children->begin();
  for (ChildMap::iterator itr = start_itr; itr != end_itr; ++itr) {
    RCHECK(child_itr->Parse(itr->second));
    delete itr->second;
    ++child_itr;
  }
  children_.erase(start_itr, end_itr);

  DVLOG(2) << "Found " << children->size() << " " << FourCCToString(child_type)
           << " boxes.";
  return true;
}

template <typename T>
bool BoxReader::ReadAllChildren(std::vector<T>* children) {
  DCHECK(!scanned_);
  scanned_ = true;

  while (pos() < size()) {
    BoxReader child_reader(&data()[pos()], size() - pos());
    bool err;
    if (!child_reader.ReadHeader(&err))
      return false;

    T child;
    RCHECK(child.Parse(&child_reader));
    children->push_back(child);
    RCHECK(SkipBytes(child_reader.size()));
  }

  return true;
}

}  // namespace mp4
}  // namespace media

#endif  // MEDIA_MP4_BOX_READER_H_