added Seek() function to FileReader

Adds a new function to the FileReader implementation of the
Reader interface for seeking within a file. It additionally
adds a new Status code to represent that a request to use
the Seek() function has failed, which will happen when the
file is stdin or something similar.

Change-Id: Iae299a3b36a8440da941b182c8865429ee3515d4

AUTHORS.TXT

@@ -2,3 +2,4 @@
 # Name or Organization <email address>
 
 Google Inc.
+Elijah Cirioli <[email protected]>

webm_parser/include/webm/file_reader.h

@@ -67,6 +67,19 @@ class FileReader : public Reader {
  Status Skip(std::uint64_t num_to_skip,
  std::uint64_t* num_actually_skipped) override;
 
+ /**
+ Moves the reader to a new absolute byte position in the file.
+
+ It is required to call DidSeek() on the parser after successfully seeking.
+ Seeking will only work on actual files, not stdin or pipes.
+
+ \param seek_position The new absolute byte position in the file.
+ \return `Status::kOkCompleted` if reader position is now `seek_position`.
+ `Status::kSeekFailed` if the reader was unable to seek to `seek_position`
+ such as when the file is stdin.
+ */
+ Status Seek(std::uint64_t seek_position);
+
  std::uint64_t Position() const override;
 
  private:

webm_parser/include/webm/status.h

@@ -56,6 +56,11 @@ struct Status {
  */
  kEndOfFile = -3,
 
+ /**
+ The reader was unable to seek to the requested location.
+ */
+ kSeekFailed = -4,
+
  // Parsing errors. Range: -1025 to -2048.
  /**
  An element's ID is malformed.

webm_parser/src/file_reader.cc

@@ -16,6 +16,19 @@
 
 #include "webm/status.h"
 
+#ifdef _MSC_VER
+#define FSEEK_(stream, offset, whence) _fseeki64(stream, offset, whence)
+#elif defined(_WIN32)
+#define FSEEK_(stream, offset, whence) \
+ fseeko64(stream, static_cast<off_t>(offset), whence)
+#elif _POSIX_C_SOURCE >= 200112L
+#define FSEEK_(stream, offset, whence) \
+ fseeko(stream, static_cast<off_t>(offset), whence)
+#else
+#define FSEEK_(stream, offset, whence) \
+ std::fseek(stream, static_cast<long>(offset), whence)
+#endif
+
 namespace webm {
 
 FileReader::FileReader(FILE* file) : file_(file) { assert(file); }
@@ -77,8 +90,7 @@ Status FileReader::Skip(std::uint64_t num_to_skip,
  if (num_to_skip < static_cast<unsigned long>(seek_offset)) { // NOLINT
  seek_offset = static_cast<long>(num_to_skip); // NOLINT
  }
- // TODO(mjbshaw): Use fseeko64/_fseeki64 if available.
- if (!std::fseek(file_.get(), seek_offset, SEEK_CUR)) {
+ if (!FSEEK_(file_.get(), seek_offset, SEEK_CUR)) {
  *num_actually_skipped = static_cast<std::uint64_t>(seek_offset);
  position_ += static_cast<std::uint64_t>(seek_offset);
  if (static_cast<unsigned long>(seek_offset) == num_to_skip) { // NOLINT
@@ -117,6 +129,14 @@ Status FileReader::Skip(std::uint64_t num_to_skip,
  }
 }
 
+Status FileReader::Seek(std::uint64_t seek_position) {
+ if (FSEEK_(file_.get(), seek_position, SEEK_SET)) {
+ return Status(Status::kSeekFailed);
+ }
+ position_ = seek_position;
+ return Status(Status::kOkCompleted);
+}
+
 std::uint64_t FileReader::Position() const { return position_; }
 
 } // namespace webm