admin: Implement sychronization backends

We are now able, depending on configuration, to retrieve files from either WebDAV or local file system.

admin/sync/importer_localfs.go

@@ -0,0 +1,49 @@
+package sync
+
+import (
+	"bufio"
+	"io/ioutil"
+	"os"
+	"path"
+)
+
+type LocalImporter struct {
+	Base string
+}
+
+func (i LocalImporter) Kind() string {
+	return "local file importer: " + i.Base
+}
+
+func (i LocalImporter) exists(filename string) bool {
+	_, err := os.Stat(path.Join(i.Base, filename))
+	return !os.IsNotExist(err)
+}
+
+func (i LocalImporter) toURL(filename string) string {
+	return path.Join(i.Base, filename)
+}
+
+func (i LocalImporter) getFile(filename string, writer *bufio.Writer) error {
+	if fd, err := os.Open(path.Join(i.Base, filename)); err != nil {
+		return err
+	} else {
+		defer fd.Close()
+		reader := bufio.NewReader(fd)
+		reader.WriteTo(writer)
+		writer.Flush()
+		return nil
+	}
+}
+
+func (i LocalImporter) listDir(filename string) ([]string, error) {
+	if files, err := ioutil.ReadDir(path.Join(i.Base, filename)); err != nil {
+		return nil, err
+	} else {
+		res := make([]string, 0)
+		for _, file := range files {
+			res = append(res, file.Name())
+		}
+		return res, nil
+	}
+}