feat(sftp): support range header

drivers/base/util.go

@@ -0,0 +1,30 @@
+package base
+
+import (
+	"io"
+	"net/http"
+	"strconv"
+
+	"github.com/alist-org/alist/v3/internal/model"
+	"github.com/alist-org/alist/v3/pkg/http_range"
+	"github.com/alist-org/alist/v3/pkg/utils"
+)
+
+func HandleRange(link *model.Link, file io.ReadSeekCloser, header http.Header, size int64) {
+	if header.Get("Range") != "" {
+		r, err := http_range.ParseRange(header.Get("Range"), size)
+		if err == nil && len(r) > 0 {
+			_, err := file.Seek(r[0].Start, io.SeekStart)
+			if err == nil {
+				link.Data = utils.NewLimitReadCloser(file, func() error {
+					return file.Close()
+				}, r[0].Length)
+				link.Status = http.StatusPartialContent
+				link.Header = http.Header{
+					"Content-Range":  []string{r[0].ContentRange(size)},
+					"Content-Length": []string{strconv.FormatInt(r[0].Length, 10)},
+				}
+			}
+		}
+	}
+}