From: Matt Joiner <anacrolix@gmail.com>
Date: Tue, 19 Aug 2025 07:44:37 +0000 (+1000)
Subject: Specialize the limited write for hashing in file storage
X-Git-Url: http://www.git.stargrave.org/?a=commitdiff_plain;h=eb0897c01dcbdd211ae5142e3306969bf18bae97;p=btrtrc.git

Specialize the limited write for hashing in file storage
---

diff --git a/storage/file-io-classic.go b/storage/file-io-classic.go
index 5c5ea7a6..56c5e9e1 100644
--- a/storage/file-io-classic.go
+++ b/storage/file-io-classic.go
@@ -28,6 +28,14 @@ type classicFileReader struct {
 	*os.File
 }
 
+func (c classicFileReader) writeToN(w io.Writer, n int64) (written int64, err error) {
+	lw := limitWriter{
+		rem: n,
+		w:   w,
+	}
+	return c.File.WriteTo(&lw)
+}
+
 func (c classicFileReader) seekDataOrEof(offset int64) (ret int64, err error) {
 	ret, err = seekData(c.File, offset)
 	if err == io.EOF {
diff --git a/storage/file-io-mmap.go b/storage/file-io-mmap.go
index 3e1d1277..ec060712 100644
--- a/storage/file-io-mmap.go
+++ b/storage/file-io-mmap.go
@@ -210,6 +210,19 @@ func (me *mmapFileHandle) WriteTo(w io.Writer) (n int64, err error) {
 	return
 }
 
+func (me *mmapFileHandle) writeToN(w io.Writer, n int64) (written int64, err error) {
+	b := me.shared.f.m
+	if me.pos >= int64(len(b)) {
+		return
+	}
+	b = b[me.pos:]
+	b = b[:min(int64(len(b)), n)]
+	i, err := w.Write(b)
+	written = int64(i)
+	me.pos += written
+	return
+}
+
 func (me *mmapFileHandle) Close() error {
 	return me.shared.Close()
 }
diff --git a/storage/file-io.go b/storage/file-io.go
index 0f86f0f6..437ccc95 100644
--- a/storage/file-io.go
+++ b/storage/file-io.go
@@ -12,7 +12,7 @@ type fileWriter interface {
 type fileReader interface {
 	// Seeks to the next data in the file. If there is no more data, seeks to the end of the file.
 	seekDataOrEof(offset int64) (ret int64, err error)
-	io.WriterTo
+	writeToN(w io.Writer, n int64) (written int64, err error)
 	io.ReadCloser
 }
 
diff --git a/storage/file-piece.go b/storage/file-piece.go
index 5173bb79..f9b73c25 100644
--- a/storage/file-piece.go
+++ b/storage/file-piece.go
@@ -376,19 +376,7 @@ func (me *filePieceImpl) writeFileTo(w io.Writer, fileIndex int, extent segments
 		panicif.NotEq(n1, n)
 		extentRemaining -= n1
 	}
-	var n1 int64
-	if true {
-		n1, err = f.WriteTo(&limitWriter{
-			rem: extentRemaining,
-			w:   w,
-		})
-		// limitWriter will block f from writing too much.
-		if n1 == extentRemaining {
-			err = nil
-		}
-	} else {
-		n1, err = io.CopyN(w, f, extentRemaining)
-	}
+	n1, err := f.writeToN(w, extentRemaining)
 	packageExpvarMap.Add("bytesReadNotSkipped", n1)
 	written += n1
 	return