From: Marco Vidonis <31407403+marcovidonis@users.noreply.github.com>
Date: Thu, 23 Jun 2022 12:44:06 +0000 (+0100)
Subject: optimise torrent piece length (#758)
X-Git-Tag: v1.46.0~2
X-Git-Url: http://www.git.stargrave.org/?a=commitdiff_plain;h=8f711b633fbaaff3d4e41cc831496853663ff55a;p=btrtrc.git

optimise torrent piece length (#758)
---

diff --git a/cmd/torrent/piece-length.go b/cmd/torrent/piece-length.go
new file mode 100644
index 00000000..b6574fd3
--- /dev/null
+++ b/cmd/torrent/piece-length.go
@@ -0,0 +1,53 @@
+// From https://github.com/jackpal/Taipei-Torrent
+
+// Copyright (c) 2010 Jack Palevich. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (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
+
+// 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
+
+// Target piece count should be < TargetPieceCountMax
+const TargetPieceCountMax = TargetPieceCountMin << 1
+
+// Choose a good piecelength.
+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
+	pieces := totalLength / pieceLength
+	for pieces >= TargetPieceCountMax {
+		pieceLength <<= 1
+		pieces >>= 1
+	}
+	return
+}
diff --git a/cmd/torrent/serve.go b/cmd/torrent/serve.go
index a6a47aae..7915ddd9 100644
--- a/cmd/torrent/serve.go
+++ b/cmd/torrent/serve.go
@@ -27,8 +27,13 @@ func serve(ctx args.SubCmdCtx) error {
 		http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
 			cl.WriteStatus(w)
 		})
+		totalLength, err := totalLength(filePath)
+		if err != nil {
+			return fmt.Errorf("calculating total length of %q: %v", filePath, err)
+		}
+		pieceLength := choosePieceLength(totalLength)
 		info := metainfo.Info{
-			PieceLength: 1 << 18,
+			PieceLength: pieceLength,
 		}
 		err = info.BuildFromFilePath(filePath)
 		if err != nil {
diff --git a/cmd/torrent/total-length.go b/cmd/torrent/total-length.go
new file mode 100644
index 00000000..52888eef
--- /dev/null
+++ b/cmd/torrent/total-length.go
@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+func totalLength(path string) (totalLength int64, err error) {
+	err = filepath.Walk(path, func(path string, info os.FileInfo, err error) error {
+		if info.IsDir() {
+			return nil
+		}
+		totalLength += info.Size()
+		return nil
+	})
+	if err != nil {
+		return 0, fmt.Errorf("walking path, %w", err)
+	}
+	return totalLength, nil
+}