Geofiles: Implement mmap in filesystem to reduce ram usage (#5480)

For https://github.com/XTLS/Xray-core/issues/4422

common/platform/filesystem/file.go

@@ -1,9 +1,12 @@
+//go:build !windows && !wasm
+
 package filesystem
 
 import (
 	"io"
 	"os"
 	"path/filepath"
+	"syscall"
 
 	"github.com/xtls/xray-core/common/buf"
 	"github.com/xtls/xray-core/common/platform"
@@ -16,6 +19,29 @@ var NewFileReader FileReaderFunc = func(path string) (io.ReadCloser, error) {
 }
 
 func ReadFile(path string) ([]byte, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	stat, err := file.Stat()
+	if err != nil {
+		return nil, err
+	}
+
+	size := stat.Size()
+	if size == 0 {
+		return []byte{}, nil
+	}
+
+	// use mmap to save RAM
+	bs, err := syscall.Mmap(int(file.Fd()), 0, int(size), syscall.PROT_READ, syscall.MAP_SHARED)
+	if err == nil {
+		return bs, nil
+	}
+
+	// fallback
 	reader, err := NewFileReader(path)
 	if err != nil {
 		return nil, err

common/platform/filesystem/file_other.go

@@ -0,0 +1,54 @@
+//go:build windows || wasm
+
+package filesystem
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+
+	"github.com/xtls/xray-core/common/buf"
+	"github.com/xtls/xray-core/common/platform"
+)
+
+type FileReaderFunc func(path string) (io.ReadCloser, error)
+
+var NewFileReader FileReaderFunc = func(path string) (io.ReadCloser, error) {
+	return os.Open(path)
+}
+
+func ReadFile(path string) ([]byte, error) {
+	reader, err := NewFileReader(path)
+	if err != nil {
+		return nil, err
+	}
+	defer reader.Close()
+
+	return buf.ReadAllToBytes(reader)
+}
+
+func ReadAsset(file string) ([]byte, error) {
+	return ReadFile(platform.GetAssetLocation(file))
+}
+
+func ReadCert(file string) ([]byte, error) {
+	if filepath.IsAbs(file) {
+		return ReadFile(file)
+	}
+	return ReadFile(platform.GetCertLocation(file))
+}
+
+func CopyFile(dst string, src string) error {
+	bytes, err := ReadFile(src)
+	if err != nil {
+		return err
+	}
+	f, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY, 0o644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	_, err = f.Write(bytes)
+	return err
+}