From ae2e4bf7e7af32a432a1c500f95ed32377276890 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Mon, 27 Jun 2022 19:25:38 +1000
Subject: [PATCH] Use metainfo.ChoosePieceLength from more locations

---
 cmd/torrent/serve.go                      |  2 +-
 metainfo/info.go                          |  3 +++
 metainfo/metainfo.go                      |  2 --
 {cmd/torrent => metainfo}/piece-length.go | 18 +++++++++---------
 4 files changed, 13 insertions(+), 12 deletions(-)
 rename {cmd/torrent => metainfo}/piece-length.go (83%)

diff --git a/cmd/torrent/serve.go b/cmd/torrent/serve.go
index 7915ddd9..b32f245b 100644
--- a/cmd/torrent/serve.go
+++ b/cmd/torrent/serve.go
@@ -31,7 +31,7 @@ func serve(ctx args.SubCmdCtx) error {
 		if err != nil {
 			return fmt.Errorf("calculating total length of %q: %v", filePath, err)
 		}
-		pieceLength := choosePieceLength(totalLength)
+		pieceLength := metainfo.ChoosePieceLength(totalLength)
 		info := metainfo.Info{
 			PieceLength: pieceLength,
 		}
diff --git a/metainfo/info.go b/metainfo/info.go
index 1b794473..bab08af9 100644
--- a/metainfo/info.go
+++ b/metainfo/info.go
@@ -74,6 +74,9 @@ func (info *Info) BuildFromFilePath(root string) (err error) {
 	slices.Sort(info.Files, func(l, r FileInfo) bool {
 		return strings.Join(l.Path, "/") < strings.Join(r.Path, "/")
 	})
+	if info.PieceLength == 0 {
+		info.PieceLength = ChoosePieceLength(info.TotalLength())
+	}
 	err = info.GeneratePieces(func(fi FileInfo) (io.ReadCloser, error) {
 		return os.Open(filepath.Join(root, strings.Join(fi.Path, string(filepath.Separator))))
 	})
diff --git a/metainfo/metainfo.go b/metainfo/metainfo.go
index 7ffa6d5b..cd787260 100644
--- a/metainfo/metainfo.go
+++ b/metainfo/metainfo.go
@@ -62,10 +62,8 @@ func (mi MetaInfo) Write(w io.Writer) error {
 
 // Set good default values in preparation for creating a new MetaInfo file.
 func (mi *MetaInfo) SetDefaults() {
-	mi.Comment = ""
 	mi.CreatedBy = "github.com/anacrolix/torrent"
 	mi.CreationDate = time.Now().Unix()
-	// mi.Info.PieceLength = 256 * 1024
 }
 
 // Creates a Magnet from a MetaInfo. Optional infohash and parsed info can be provided.
diff --git a/cmd/torrent/piece-length.go b/metainfo/piece-length.go
similarity index 83%
rename from cmd/torrent/piece-length.go
rename to metainfo/piece-length.go
index b6574fd3..9835dc5b 100644
--- a/cmd/torrent/piece-length.go
+++ b/metainfo/piece-length.go
@@ -28,24 +28,24 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-package main
+package metainfo
 
 // For more context on why these numbers, see http://wiki.vuze.com/w/Torrent_Piece_Size
-const MinimumPieceLength = 16 * 1024
-const TargetPieceCountLog2 = 10
-const TargetPieceCountMin = 1 << TargetPieceCountLog2
+const minimumPieceLength = 16 * 1024
+const targetPieceCountLog2 = 10
+const targetPieceCountMin = 1 << targetPieceCountLog2
 
-// Target piece count should be < TargetPieceCountMax
-const TargetPieceCountMax = TargetPieceCountMin << 1
+// Target piece count should be < targetPieceCountMax
+const targetPieceCountMax = targetPieceCountMin << 1
 
 // Choose a good piecelength.
-func choosePieceLength(totalLength int64) (pieceLength int64) {
+func ChoosePieceLength(totalLength int64) (pieceLength int64) {
 	// Must be a power of 2.
 	// Must be a multiple of 16KB
 	// Prefer to provide around 1024..2048 pieces.
-	pieceLength = MinimumPieceLength
+	pieceLength = minimumPieceLength
 	pieces := totalLength / pieceLength
-	for pieces >= TargetPieceCountMax {
+	for pieces >= targetPieceCountMax {
 		pieceLength <<= 1
 		pieces >>= 1
 	}
-- 
2.48.1