From 45a2e309b068e165a3a8d806eaedfad7d2b17e1d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tam=C3=A1s=20Gul=C3=A1csi?= <tamas@gulacsi.eu>
Date: Sun, 27 Apr 2025 11:04:12 +0200
Subject: [PATCH 1/2] Use mmap in ReadAll if possible

---
 excelize.go       |  2 +-
 lib.go            |  2 +-
 lib_nonwindows.go | 35 +++++++++++++++++++++++++++++++++++
 lib_windows.go    | 16 ++++++++++++++++
 4 files changed, 53 insertions(+), 2 deletions(-)
 create mode 100644 lib_nonwindows.go
 create mode 100644 lib_windows.go

diff --git a/excelize.go b/excelize.go
index 61bb6d3489..71d721a3fe 100644
--- a/excelize.go
+++ b/excelize.go
@@ -176,7 +176,7 @@ func (f *File) checkOpenReaderOptions() error {
 // OpenReader read data stream from io.Reader and return a populated
 // spreadsheet file.
 func OpenReader(r io.Reader, opts ...Options) (*File, error) {
-	b, err := io.ReadAll(r)
+	b, err := readAll(r)
 	if err != nil {
 		return nil, err
 	}
diff --git a/lib.go b/lib.go
index 113d574fbf..01588a869f 100644
--- a/lib.go
+++ b/lib.go
@@ -118,7 +118,7 @@ func (f *File) readBytes(name string) []byte {
 	if err != nil {
 		return content
 	}
-	content, _ = io.ReadAll(file)
+	content, _ = readAll(file)
 	f.Pkg.Store(name, content)
 	_ = file.Close()
 	return content
diff --git a/lib_nonwindows.go b/lib_nonwindows.go
new file mode 100644
index 0000000000..7dbcadc79b
--- /dev/null
+++ b/lib_nonwindows.go
@@ -0,0 +1,35 @@
+//go:build !windows
+
+// Copyright 2025 The excelize Authors. All rights reserved. Use of
+// this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package excelize
+
+import (
+	"io"
+	"os"
+	"runtime"
+	"syscall"
+)
+
+// readAll is like io.ReadAll, but uses mmap if possible.
+func readAll(r io.Reader) ([]byte, error) {
+	if fder, ok := r.(interface {
+		Fd() int
+		Stat() (os.FileInfo, error)
+	}); ok {
+		if fi, err := fder.Stat(); err == nil {
+			if b, err := syscall.Mmap(fder.Fd(), 0, int(fi.Size()),
+				syscall.PROT_READ,
+				syscall.MAP_PRIVATE|syscall.MAP_POPULATE,
+			); err == nil {
+				runtime.SetFinalizer(&b, func(_ any) error {
+					return syscall.Munmap(b)
+				})
+				return b, nil
+			}
+		}
+	}
+	return io.ReadAll(r)
+}
diff --git a/lib_windows.go b/lib_windows.go
new file mode 100644
index 0000000000..aca1bdefb0
--- /dev/null
+++ b/lib_windows.go
@@ -0,0 +1,16 @@
+//go:build windows
+
+// Copyright 2025 The excelize Authors. All rights reserved. Use of
+// this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package excelize
+
+import (
+	"io"
+)
+
+// readAll is like io.ReadAll, but uses mmap if possible.
+func readAll(r io.Reader) ([]byte, error) {
+	return io.ReadAll(r)
+}

From 3da8b58f5fb466da55189064a478aa6e0563f7e2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tam=C3=A1s=20Gul=C3=A1csi?= <tamas@gulacsi.eu>
Date: Tue, 29 Apr 2025 17:24:22 +0200
Subject: [PATCH 2/2] Fd() uintptr

os.File.Fd() never returned int...
---
 lib_nonwindows.go | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib_nonwindows.go b/lib_nonwindows.go
index 7dbcadc79b..35a2b54de0 100644
--- a/lib_nonwindows.go
+++ b/lib_nonwindows.go
@@ -16,11 +16,13 @@ import (
 // readAll is like io.ReadAll, but uses mmap if possible.
 func readAll(r io.Reader) ([]byte, error) {
 	if fder, ok := r.(interface {
-		Fd() int
+		Fd() uintptr
 		Stat() (os.FileInfo, error)
 	}); ok {
 		if fi, err := fder.Stat(); err == nil {
-			if b, err := syscall.Mmap(fder.Fd(), 0, int(fi.Size()),
+			if b, err := syscall.Mmap(
+				int(fder.Fd()),
+				0, int(fi.Size()),
 				syscall.PROT_READ,
 				syscall.MAP_PRIVATE|syscall.MAP_POPULATE,
 			); err == nil {