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

4 files changed, 41 insertions, 2 deletions

diff --git a/AUTHORS.TXT b/AUTHORS.TXT
index 9686ac1..59b648c 100644
--- a/AUTHORS.TXT
+++ b/AUTHORS.TXT
@@ -2,3 +2,4 @@
 # Name or Organization <email address>
 
 Google Inc.
+Elijah Cirioli <eli.cirioli@gmail.com>
diff --git a/webm_parser/include/webm/file_reader.h b/webm_parser/include/webm/file_reader.h
index 6ccdc4d..69bec76 100644
--- a/webm_parser/include/webm/file_reader.h
+++ b/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:
diff --git a/webm_parser/include/webm/status.h b/webm_parser/include/webm/status.h
index ff3f0c6..9577ef4 100644
--- a/webm_parser/include/webm/status.h
+++ b/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.
diff --git a/webm_parser/src/file_reader.cc b/webm_parser/src/file_reader.cc
index 0921abe..a2a397b 100644
--- a/webm_parser/src/file_reader.cc
+++ b/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