From 29af44518270efb3b625bcae44166583c014e10e Mon Sep 17 00:00:00 2001
From: Sergey Matveev <stargrave@stargrave.org>
Date: Tue, 29 Nov 2022 14:21:35 +0300
Subject: [PATCH] Shortened long filenames

---
 cmd/btrtrc/README    |  1 +
 cmd/btrtrc/fifos.go  |  3 ++-
 storage/file.go      | 11 ++++++-----
 storage/shortener.go | 30 ++++++++++++++++++++++++++++++
 4 files changed, 39 insertions(+), 6 deletions(-)
 create mode 100644 storage/shortener.go

diff --git a/cmd/btrtrc/README b/cmd/btrtrc/README
index d485409d..8e7b15c2 100644
--- a/cmd/btrtrc/README
+++ b/cmd/btrtrc/README
@@ -9,6 +9,7 @@ the file to delete. But what advantages does it have?
 * Optimized file-based storage:
   * linearized I/O operations prevent creation of huge quantity of threads
   * cached file descriptors save a lot of syscalls
+* Shortened long filenames in file-based storage
 * Ability to specify both IPv4 and IPv6 addresses to announce
 * Ability to specify DHT bootstrap nodes
 * Dynamic addition and removing of the torrents
diff --git a/cmd/btrtrc/fifos.go b/cmd/btrtrc/fifos.go
index f9aa0117..508f6c09 100644
--- a/cmd/btrtrc/fifos.go
+++ b/cmd/btrtrc/fifos.go
@@ -18,6 +18,7 @@ import (
 	"github.com/anacrolix/dht/v2"
 	"github.com/anacrolix/torrent"
 	"github.com/anacrolix/torrent/metainfo"
+	"github.com/anacrolix/torrent/storage"
 	"github.com/anacrolix/torrent/types/infohash"
 	"github.com/dustin/go-humanize"
 )
@@ -304,7 +305,7 @@ func readLinesFromFIFO(pth string) []string {
 }
 
 func saveTorrent(t *torrent.Torrent) error {
-	pth := t.Name() + TorrentExt
+	pth := storage.PathShortener(t.Name()) + TorrentExt
 	if _, err := os.Stat(pth); err == nil {
 		return nil
 	}
diff --git a/storage/file.go b/storage/file.go
index aa67df15..6871cad3 100644
--- a/storage/file.go
+++ b/storage/file.go
@@ -115,7 +115,7 @@ func (fs fileClientImpl) OpenTorrent(info *metainfo.Info, infoHash metainfo.Hash
 			length: fileInfo.Length,
 		}
 		if f.length == 0 {
-			err = CreateNativeZeroLengthFile(f.path)
+			err = CreateNativeZeroLengthFile(PathShortener(f.path))
 			if err != nil {
 				err = fmt.Errorf("creating zero length file: %w", err)
 				return
@@ -185,10 +185,11 @@ type fileTorrentImplIO struct {
 // Returns EOF on short or missing file.
 func (fst *fileTorrentImplIO) readFileAt(file file, b []byte, off int64) (n int, err error) {
 	fdRCacheM.Lock()
-	centry := fdRCache[file.path]
+	pth := PathShortener(file.path)
+	centry := fdRCache[pth]
 	if centry == nil {
 		var fd *os.File
-		fd, err = os.Open(file.path)
+		fd, err = os.Open(pth)
 		if os.IsNotExist(err) {
 			// File missing is treated the same as a short file.
 			err = io.EOF
@@ -198,7 +199,7 @@ func (fst *fileTorrentImplIO) readFileAt(file file, b []byte, off int64) (n int,
 			return
 		}
 		centry = &fdCacheEntry{fd: fd}
-		fdRCache[file.path] = centry
+		fdRCache[pth] = centry
 	}
 	fdRCacheM.Unlock()
 	// Limit the read to within the expected bounds of this file.
@@ -229,7 +230,7 @@ func (fst fileTorrentImplIO) ReadAt(b []byte, off int64) (n int, err error) {
 
 func (fst fileTorrentImplIO) WriteAt(p []byte, off int64) (n int, err error) {
 	fst.fts.segmentLocater.Locate(segments.Extent{off, int64(len(p))}, func(i int, e segments.Extent) bool {
-		name := fst.fts.files[i].path
+		name := PathShortener(fst.fts.files[i].path)
 		_, ok := fdMkdirAllCache[filepath.Dir(name)]
 		if !ok {
 			os.MkdirAll(filepath.Dir(name), 0o777)
diff --git a/storage/shortener.go b/storage/shortener.go
new file mode 100644
index 00000000..e3ed5df9
--- /dev/null
+++ b/storage/shortener.go
@@ -0,0 +1,30 @@
+package storage
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"path"
+	"strings"
+	"unicode/utf8"
+)
+
+const MaxFilenameLen = 200
+
+func PathShortener(pth string) string {
+	parts := strings.Split(pth, "/")
+	for i, part := range parts {
+		if len(part) <= MaxFilenameLen {
+			continue
+		}
+		n := 0
+		var short []rune
+		for (n < len(part)) && (len(string(short)) <= MaxFilenameLen) {
+			r, w := utf8.DecodeRuneInString(part[n:])
+			n += w
+			short = append(short, r)
+		}
+		h := sha1.Sum([]byte(part))
+		parts[i] = string(short[:len(short)-1]) + "-" + hex.EncodeToString(h[:])
+	}
+	return path.Join(parts...)
+}
-- 
2.44.0