media/mp4/box_reader.h

   1 // Copyright (c) 2012 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_MP4_BOX_READER_H_
   6 #define MEDIA_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/mp4/fourccs.h"
  16 #include "media/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
  34   bool HasBytes(int count) { return (pos() + count <= size()); }
  35
  36   // Read a value from the stream, perfoming endian correction, and advance the
  37   // stream pointer.
  38   bool Read1(uint8* v)  WARN_UNUSED_RESULT;
  39   bool Read2(uint16* v) WARN_UNUSED_RESULT;
  40   bool Read2s(int16* v) WARN_UNUSED_RESULT;
  41   bool Read4(uint32* v) WARN_UNUSED_RESULT;
  42   bool Read4s(int32* v) WARN_UNUSED_RESULT;
  43   bool Read8(uint64* v) WARN_UNUSED_RESULT;
  44   bool Read8s(int64* v) WARN_UNUSED_RESULT;
  45
  46   bool ReadFourCC(FourCC* v) WARN_UNUSED_RESULT;
  47
  48   bool ReadVec(std::vector<uint8>* t, int count) WARN_UNUSED_RESULT;
  49
  50   // These variants read a 4-byte integer of the corresponding signedness and
  51   // store it in the 8-byte return type.
  52   bool Read4Into8(uint64* v) WARN_UNUSED_RESULT;
  53   bool Read4sInto8s(int64* v) WARN_UNUSED_RESULT;
  54
  55   // Advance the stream by this many bytes.
  56   bool SkipBytes(int nbytes) WARN_UNUSED_RESULT;
  57
  58   const uint8* data() const { return buf_; }
  59   int size() const { return size_; }
  60   int pos() const { return pos_; }
  61
  62  protected:
  63   const uint8* buf_;
  64   int size_;
  65   int pos_;
  66
  67   template<typename T> bool Read(T* t) WARN_UNUSED_RESULT;
  68 };
  69
  70 class MEDIA_EXPORT BoxReader : public BufferReader {
  71  public:
  72   ~BoxReader();
  73
  74   // Create a BoxReader from a buffer. Note that this function may return NULL
  75   // if an intact, complete box was not available in the buffer. If |*err| is
  76   // set, there was a stream-level error when creating the box; otherwise, NULL
  77   // values are only expected when insufficient data is available.
  78   //
  79   // |buf| is retained but not owned, and must outlive the BoxReader instance.
  80   static BoxReader* ReadTopLevelBox(const uint8* buf,
  81                                     const int buf_size,
  82                                     const LogCB& log_cb,
  83                                     bool* err);
  84
  85   // Read the box header from the current buffer. This function returns true if
  86   // there is enough data to read the header and the header is sane; that is, it
  87   // does not check to ensure the entire box is in the buffer before returning
  88   // true. The semantics of |*err| are the same as above.
  89   //
  90   // |buf| is not retained.
  91   static bool StartTopLevelBox(const uint8* buf,
  92                                const int buf_size,
  93                                const LogCB& log_cb,
  94                                FourCC* type,
  95                                int* box_size,
  96                                bool* err) WARN_UNUSED_RESULT;
  97
  98   // Returns true if |type| is recognized to be a top-level box, false
  99   // otherwise. This returns true for some boxes which we do not parse.
 100   // Helpful in debugging misaligned appends.
 101   static bool IsValidTopLevelBox(const FourCC& type,
 102                                  const LogCB& log_cb);
 103
 104   // Scan through all boxes within the current box, starting at the current
 105   // buffer position. Must be called before any of the *Child functions work.
 106   bool ScanChildren() WARN_UNUSED_RESULT;
 107
 108   // Read exactly one child box from the set of children. The type of the child
 109   // will be determined by the BoxType() method of |child|.
 110   bool ReadChild(Box* child) WARN_UNUSED_RESULT;
 111
 112   // Read one child if available. Returns false on error, true on successful
 113   // read or on child absent.
 114   bool MaybeReadChild(Box* child) WARN_UNUSED_RESULT;
 115
 116   // Read at least one child. False means error or no such child present.
 117   template<typename T> bool ReadChildren(
 118       std::vector<T>* children) WARN_UNUSED_RESULT;
 119
 120   // Read any number of children. False means error.
 121   template<typename T> bool MaybeReadChildren(
 122       std::vector<T>* children) WARN_UNUSED_RESULT;
 123
 124   // Read all children, regardless of FourCC. This is used from exactly one box,
 125   // corresponding to a rather significant inconsistency in the BMFF spec.
 126   // Note that this method is mutually exclusive with ScanChildren().
 127   template<typename T> bool ReadAllChildren(
 128       std::vector<T>* children) WARN_UNUSED_RESULT;
 129
 130   // Populate the values of 'version()' and 'flags()' from a full box header.
 131   // Many boxes, but not all, use these values. This call should happen after
 132   // the box has been initialized, and does not re-read the main box header.
 133   bool ReadFullBoxHeader() WARN_UNUSED_RESULT;
 134
 135   FourCC type() const   { return type_; }
 136   uint8 version() const { return version_; }
 137   uint32 flags() const  { return flags_; }
 138
 139  private:
 140   BoxReader(const uint8* buf, const int size, const LogCB& log_cb);
 141
 142   // Must be called immediately after init. If the return is false, this
 143   // indicates that the box header and its contents were not available in the
 144   // stream or were nonsensical, and that the box must not be used further. In
 145   // this case, if |*err| is false, the problem was simply a lack of data, and
 146   // should only be an error condition if some higher-level component knows that
 147   // no more data is coming (i.e. EOS or end of containing box). If |*err| is
 148   // true, the error is unrecoverable and the stream should be aborted.
 149   bool ReadHeader(bool* err);
 150
 151   LogCB log_cb_;
 152   FourCC type_;
 153   uint8 version_;
 154   uint32 flags_;
 155
 156   typedef std::multimap<FourCC, BoxReader> ChildMap;
 157
 158   // The set of child box FourCCs and their corresponding buffer readers. Only
 159   // valid if scanned_ is true.
 160   ChildMap children_;
 161   bool scanned_;
 162 };
 163
 164 // Template definitions
 165 template<typename T> bool BoxReader::ReadChildren(std::vector<T>* children) {
 166   RCHECK(MaybeReadChildren(children) && !children->empty());
 167   return true;
 168 }
 169
 170 template<typename T>
 171 bool BoxReader::MaybeReadChildren(std::vector<T>* children) {
 172   DCHECK(scanned_);
 173   DCHECK(children->empty());
 174
 175   children->resize(1);
 176   FourCC child_type = (*children)[0].BoxType();
 177
 178   ChildMap::iterator start_itr = children_.lower_bound(child_type);
 179   ChildMap::iterator end_itr = children_.upper_bound(child_type);
 180   children->resize(std::distance(start_itr, end_itr));
 181   typename std::vector<T>::iterator child_itr = children->begin();
 182   for (ChildMap::iterator itr = start_itr; itr != end_itr; ++itr) {
 183     RCHECK(child_itr->Parse(&itr->second));
 184     ++child_itr;
 185   }
 186   children_.erase(start_itr, end_itr);
 187
 188   DVLOG(2) << "Found " << children->size() << " "
 189            << FourCCToString(child_type) << " boxes.";
 190   return true;
 191 }
 192
 193 template<typename T>
 194 bool BoxReader::ReadAllChildren(std::vector<T>* children) {
 195   DCHECK(!scanned_);
 196   scanned_ = true;
 197
 198   bool err = false;
 199   while (pos() < size()) {
 200     BoxReader child_reader(&buf_[pos_], size_ - pos_, log_cb_);
 201     if (!child_reader.ReadHeader(&err)) break;
 202     T child;
 203     RCHECK(child.Parse(&child_reader));
 204     children->push_back(child);
 205     pos_ += child_reader.size();
 206   }
 207
 208   return !err;
 209 }
 210
 211 }  // namespace mp4
 212 }  // namespace media
 213
 214 #endif  // MEDIA_MP4_BOX_READER_H_