Don't write control file if content is not changed from previous one

This is desirable so that we don't have to wake up disk if control
file is not changed, and it is not have to be written again.  We use
the same method (SHA1 hash) to check the content is the same.  The
limitation is the hash is stored in memory, so we have to write the
first time in each session.

See GH-382

1 files changed, 7 insertions, 0 deletions

diff --git a/src/DefaultBtProgressInfoFile.h b/src/DefaultBtProgressInfoFile.h
index 28175e47..33a28044 100644
--- a/src/DefaultBtProgressInfoFile.h
+++ b/src/DefaultBtProgressInfoFile.h
@@ -46,6 +46,7 @@ class PieceStorage;
 class PeerStorage;
 class BtRuntime;
 class Option;
+class IOFile;
 
 class DefaultBtProgressInfoFile : public BtProgressInfoFile {
 private:
@@ -57,8 +58,14 @@ private:
 #endif // ENABLE_BITTORRENT
   const Option* option_;
   std::string filename_;
+  // Last SHA1 digest value of the content written.  Initially, this
+  // is empty string.  This is used to avoid to write same content
+  // repeatedly, which could wake up disk that may be sleeping.
+  std::string lastDigest_;
 
   bool isTorrentDownload();
+  void save(IOFile& fp);
+
 public:
   DefaultBtProgressInfoFile(const std::shared_ptr<DownloadContext>& btContext,
                             const std::shared_ptr<PieceStorage>& pieceStorage,