media/formats/mp4/box_reader.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_FORMATS_MP4_BOX_READER_H_
   6 #define MEDIA_FORMATS_MP4_BOX_READER_H_
   7
   8 #include <map>
   9 #include <vector>
  10
  11 #include "base/compiler_specific.h"
  12 #include "base/logging.h"
  13 #include "media/base/media_export.h"
  14 #include "media/base/media_log.h"
  15 #include "media/formats/mp4/fourccs.h"
  16 #include "media/formats/mp4/rcheck.h"
  17
  18 namespace media {
  19 namespace mp4 {
  20
  21 class BoxReader;
  22
  23 struct MEDIA_EXPORT Box {
  24   virtual ~Box();
  25   virtual bool Parse(BoxReader* reader) = 0;
  26   virtual FourCC BoxType() const = 0;
  27 };
  28
  29 class MEDIA_EXPORT BufferReader {
  30  public:
  31   BufferReader(const uint8* buf, const int size)
  32       : buf_(buf), size_(size), pos_(0) {
  33     CHECK(buf);
  34     CHECK_GE(size, 0);
  35   }
  36
  37   bool HasBytes(int count) { return (pos() + count <= size()); }
  38
  39   // Read a value from the stream, perfoming endian correction, and advance the
  40   // stream pointer.
  41   bool Read1(uint8* v)  WARN_UNUSED_RESULT;
  42   bool Read2(uint16* v) WARN_UNUSED_RESULT;
  43   bool Read2s(int16* v) WARN_UNUSED_RESULT;
  44   bool Read4(uint32* v) WARN_UNUSED_RESULT;
  45   bool Read4s(int32* v) WARN_UNUSED_RESULT;
  46   bool Read8(uint64* v) WARN_UNUSED_RESULT;
  47   bool Read8s(int64* v) WARN_UNUSED_RESULT;
  48
  49   bool ReadFourCC(FourCC* v) WARN_UNUSED_RESULT;
  50
  51   bool ReadVec(std::vector<uint8>* t, int count) WARN_UNUSED_RESULT;
  52
  53   // These variants read a 4-byte integer of the corresponding signedness and
  54   // store it in the 8-byte return type.
  55   bool Read4Into8(uint64* v) WARN_UNUSED_RESULT;
  56   bool Read4sInto8s(int64* v) WARN_UNUSED_RESULT;
  57
  58   // Advance the stream by this many bytes.
  59   bool SkipBytes(int nbytes) WARN_UNUSED_RESULT;
  60
  61   const uint8* data() const { return buf_; }
  62   int size() const { return size_; }
  63   int pos() const { return pos_; }
  64
  65  protected:
  66   const uint8* buf_;
  67   int size_;
  68   int pos_;
  69
  70   template<typename T> bool Read(T* t) WARN_UNUSED_RESULT;
  71 };
  72
  73 class MEDIA_EXPORT BoxReader : public BufferReader {
  74  public:
  75   ~BoxReader();
  76
  77   // Create a BoxReader from a buffer. Note that this function may return NULL
  78   // if an intact, complete box was not available in the buffer. If |*err| is
  79   // set, there was a stream-level error when creating the box; otherwise, NULL
  80   // values are only expected when insufficient data is available.
  81   //
  82   // |buf| is retained but not owned, and must outlive the BoxReader instance.
  83   static BoxReader* ReadTopLevelBox(const uint8* buf,
  84                                     const int buf_size,
  85                                     const LogCB& log_cb,
  86                                     bool* err);
  87
  88   // Read the box header from the current buffer. This function returns true if
  89   // there is enough data to read the header and the header is sane; that is, it
  90   // does not check to ensure the entire box is in the buffer before returning
  91   // true. The semantics of |*err| are the same as above.
  92   //
  93   // |buf| is not retained.
  94   static bool StartTopLevelBox(const uint8* buf,
  95                                const int buf_size,
  96                                const LogCB& log_cb,
  97                                FourCC* type,
  98                                int* box_size,
  99                                bool* err) WARN_UNUSED_RESULT;
 100
 101   // Returns true if |type| is recognized to be a top-level box, false
 102   // otherwise. This returns true for some boxes which we do not parse.
 103   // Helpful in debugging misaligned appends.
 104   static bool IsValidTopLevelBox(const FourCC& type,
 105                                  const LogCB& log_cb);
 106
 107   // Scan through all boxes within the current box, starting at the current
 108   // buffer position. Must be called before any of the *Child functions work.
 109   bool ScanChildren() WARN_UNUSED_RESULT;
 110
 111   // Return true if child with type |child.BoxType()| exists.
 112   bool HasChild(Box* child) WARN_UNUSED_RESULT;
 113
 114   // Read exactly one child box from the set of children. The type of the child
 115   // will be determined by the BoxType() method of |child|.
 116   bool ReadChild(Box* child) WARN_UNUSED_RESULT;
 117
 118   // Read one child if available. Returns false on error, true on successful
 119   // read or on child absent.
 120   bool MaybeReadChild(Box* child) WARN_UNUSED_RESULT;
 121
 122   // Read at least one child. False means error or no such child present.
 123   template<typename T> bool ReadChildren(
 124       std::vector<T>* children) WARN_UNUSED_RESULT;
 125
 126   // Read any number of children. False means error.
 127   template<typename T> bool MaybeReadChildren(
 128       std::vector<T>* children) WARN_UNUSED_RESULT;
 129
 130   // Read all children, regardless of FourCC. This is used from exactly one box,
 131   // corresponding to a rather significant inconsistency in the BMFF spec.
 132   // Note that this method is mutually exclusive with ScanChildren().
 133   template<typename T> bool ReadAllChildren(
 134       std::vector<T>* children) WARN_UNUSED_RESULT;
 135
 136   // Populate the values of 'version()' and 'flags()' from a full box header.
 137   // Many boxes, but not all, use these values. This call should happen after
 138   // the box has been initialized, and does not re-read the main box header.
 139   bool ReadFullBoxHeader() WARN_UNUSED_RESULT;
 140
 141   FourCC type() const   { return type_; }
 142   uint8 version() const { return version_; }
 143   uint32 flags() const  { return flags_; }
 144
 145   const LogCB& log_cb() const { return log_cb_; }
 146
 147  private:
 148   BoxReader(const uint8* buf, const int size, const LogCB& log_cb);
 149
 150   // Must be called immediately after init. If the return is false, this
 151   // indicates that the box header and its contents were not available in the
 152   // stream or were nonsensical, and that the box must not be used further. In
 153   // this case, if |*err| is false, the problem was simply a lack of data, and
 154   // should only be an error condition if some higher-level component knows that
 155   // no more data is coming (i.e. EOS or end of containing box). If |*err| is
 156   // true, the error is unrecoverable and the stream should be aborted.
 157   bool ReadHeader(bool* err);
 158
 159   LogCB log_cb_;
 160   FourCC type_;
 161   uint8 version_;
 162   uint32 flags_;
 163
 164   typedef std::multimap<FourCC, BoxReader> ChildMap;
 165
 166   // The set of child box FourCCs and their corresponding buffer readers. Only
 167   // valid if scanned_ is true.
 168   ChildMap children_;
 169   bool scanned_;
 170 };
 171
 172 // Template definitions
 173 template<typename T> bool BoxReader::ReadChildren(std::vector<T>* children) {
 174   RCHECK(MaybeReadChildren(children) && !children->empty());
 175   return true;
 176 }
 177
 178 template<typename T>
 179 bool BoxReader::MaybeReadChildren(std::vector<T>* children) {
 180   DCHECK(scanned_);
 181   DCHECK(children->empty());
 182
 183   children->resize(1);
 184   FourCC child_type = (*children)[0].BoxType();
 185
 186   ChildMap::iterator start_itr = children_.lower_bound(child_type);
 187   ChildMap::iterator end_itr = children_.upper_bound(child_type);
 188   children->resize(std::distance(start_itr, end_itr));
 189   typename std::vector<T>::iterator child_itr = children->begin();
 190   for (ChildMap::iterator itr = start_itr; itr != end_itr; ++itr) {
 191     RCHECK(child_itr->Parse(&itr->second));
 192     ++child_itr;
 193   }
 194   children_.erase(start_itr, end_itr);
 195
 196   DVLOG(2) << "Found " << children->size() << " "
 197            << FourCCToString(child_type) << " boxes.";
 198   return true;
 199 }
 200
 201 template<typename T>
 202 bool BoxReader::ReadAllChildren(std::vector<T>* children) {
 203   DCHECK(!scanned_);
 204   scanned_ = true;
 205
 206   bool err = false;
 207   while (pos() < size()) {
 208     BoxReader child_reader(&buf_[pos_], size_ - pos_, log_cb_);
 209     if (!child_reader.ReadHeader(&err)) break;
 210     T child;
 211     RCHECK(child.Parse(&child_reader));
 212     children->push_back(child);
 213     pos_ += child_reader.size();
 214   }
 215
 216   return !err;
 217 }
 218
 219 }  // namespace mp4
 220 }  // namespace media
 221
 222 #endif  // MEDIA_FORMATS_MP4_BOX_READER_H_