add: remotefs/download support file download

remotefs/download.go

@@ -0,0 +1,47 @@
+package remotefs
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"fmt"
+	"io"
+	"os"
+)
+
+// Download a file from the remote host.
+func Download(fs FS, src, dst string) error {
+	remote, err := fs.Open(src)
+	if err != nil {
+		return fmt.Errorf("open remote file for download: %w", err)
+	}
+	defer remote.Close()
+
+	remoteStat, err := remote.Stat()
+	if err != nil {
+		return fmt.Errorf("stat remote file for download: %w", err)
+	}
+
+	remoteSum := sha256.New()
+	localSum := sha256.New()
+
+	local, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, remoteStat.Mode())
+	if err != nil {
+		return fmt.Errorf("open local file for download: %w", err)
+	}
+	defer local.Close()
+
+	remoteReader := io.TeeReader(remote, remoteSum)
+	if _, err := io.Copy(io.MultiWriter(local, localSum), remoteReader); err != nil {
+		_ = local.Close()
+		return fmt.Errorf("copy file from remote host: %w", err)
+	}
+	if err := local.Close(); err != nil {
+		return fmt.Errorf("close local file after download: %w", err)
+	}
+
+	if !bytes.Equal(localSum.Sum(nil), remoteSum.Sum(nil)) {
+		return fmt.Errorf("downloading %s failed: %w", src, ErrChecksumMismatch)
+	}
+
+	return nil
+}

remotefs/downloaddirectory.go

@@ -0,0 +1,43 @@
+package remotefs
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+)
+
+// DownloadDirectory downloads all files and directories recursively from the remote system to local directory.
+func DownloadDirectory(fsys FS, src, dst string) error {
+	walkErr := fs.WalkDir(fsys, src, func(path string, dir fs.DirEntry, err error) error {
+		if err != nil {
+			return fmt.Errorf("walk remote directory: %w", err)
+		}
+
+		relPath, err := filepath.Rel(src, path)
+		if err != nil {
+			return fmt.Errorf("calculate relative path: %w", err)
+		}
+		targetPath := filepath.Join(dst, relPath)
+
+		if dir.IsDir() {
+			dirInfo, err := dir.Info()
+			if err != nil {
+				return fmt.Errorf("get dir info: %w", err)
+			}
+			if err := os.MkdirAll(targetPath, dirInfo.Mode()&os.ModePerm); err != nil {
+				return fmt.Errorf("create local directory: %w", err)
+			}
+		} else {
+			if err := Download(fsys, path, targetPath); err != nil {
+				return fmt.Errorf("download directory: %w", err)
+			}
+		}
+		return nil
+	})
+
+	if walkErr != nil {
+		return fmt.Errorf("walk remote directory tree: %w", walkErr)
+	}
+	return nil
+}

remotefs/uploaddirectory.go

@@ -0,0 +1,43 @@
+package remotefs
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+)
+
+// UploadDirectory uploads all files and directories recursively to the remote system.
+func UploadDirectory(fsys FS, src, dst string) error {
+	walkErr := filepath.WalkDir(src, func(path string, dir fs.DirEntry, err error) error {
+		if err != nil {
+			return fmt.Errorf("walk local directory: %w", err)
+		}
+
+		relPath, err := filepath.Rel(src, path)
+		if err != nil {
+			return fmt.Errorf("calculate relative path: %w", err)
+		}
+		targetPath := filepath.Join(dst, relPath)
+
+		if dir.IsDir() {
+			dirInfo, err := dir.Info()
+			if err != nil {
+				return fmt.Errorf("get dir info: %w", err)
+			}
+			if err := fsys.MkdirAll(targetPath, dirInfo.Mode()&os.ModePerm); err != nil {
+				return fmt.Errorf("create remote directory: %w", err)
+			}
+		} else {
+			if err := Upload(fsys, path, targetPath); err != nil {
+				return fmt.Errorf("upload directory: %w", err)
+			}
+		}
+		return nil
+	})
+
+	if walkErr != nil {
+		return fmt.Errorf("walk remote directory tree: %w", walkErr)
+	}
+	return nil
+}