webdav: support About - fixes #2937

This means that `rclone about` will work with Webdav backends and `df`
will be correct when using them in `rclone mount`.

backend/webdav/api/types.go

@@ -209,3 +209,22 @@ func (t *Time) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
 	}
 	return err
 }
+
+// Quota is used to read the bytes used and available
+//
+// <d:multistatus xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns" xmlns:oc="http://owncloud.org/ns" xmlns:nc="http://nextcloud.org/ns">
+//  <d:response>
+//   <d:href>/remote.php/webdav/</d:href>
+//   <d:propstat>
+//    <d:prop>
+//     <d:quota-available-bytes>-3</d:quota-available-bytes>
+//     <d:quota-used-bytes>376461895</d:quota-used-bytes>
+//    </d:prop>
+//    <d:status>HTTP/1.1 200 OK</d:status>
+//   </d:propstat>
+//  </d:response>
+// </d:multistatus>
+type Quota struct {
+	Available int64 `xml:"DAV: response>propstat>prop>quota-available-bytes"`
+	Used      int64 `xml:"DAV: response>propstat>prop>quota-used-bytes"`
+}

backend/webdav/webdav.go

@@ -869,6 +869,46 @@ func (f *Fs) Hashes() hash.Set {
 	return hash.Set(hash.None)
 }
 
+// About gets quota information
+func (f *Fs) About() (*fs.Usage, error) {
+	opts := rest.Opts{
+		Method: "PROPFIND",
+		Path:   "",
+		ExtraHeaders: map[string]string{
+			"Depth": "0",
+		},
+	}
+	opts.Body = bytes.NewBuffer([]byte(`<?xml version="1.0" ?>
+<D:propfind xmlns:D="DAV:">
+ <D:prop>
+  <D:quota-available-bytes/>
+  <D:quota-used-bytes/>
+ </D:prop>
+</D:propfind>
+`))
+	var q = api.Quota{
+		Available: -1,
+		Used:      -1,
+	}
+	var resp *http.Response
+	var err error
+	err = f.pacer.Call(func() (bool, error) {
+		resp, err = f.srv.CallXML(&opts, nil, &q)
+		return shouldRetry(resp, err)
+	})
+	if err != nil {
+		return nil, errors.Wrap(err, "about call failed")
+	}
+	usage := &fs.Usage{}
+	if q.Available >= 0 && q.Used >= 0 {
+		usage.Total = fs.NewUsageValue(q.Available + q.Used)
+	}
+	if q.Used >= 0 {
+		usage.Used = fs.NewUsageValue(q.Used)
+	}
+	return usage, nil
+}
+
 // ------------------------------------------------------------
 
 // Fs returns the parent Fs
@@ -1059,5 +1099,6 @@ var (
 	_ fs.Copier      = (*Fs)(nil)
 	_ fs.Mover       = (*Fs)(nil)
 	_ fs.DirMover    = (*Fs)(nil)
+	_ fs.Abouter     = (*Fs)(nil)
 	_ fs.Object      = (*Object)(nil)
 )

docs/content/overview.md

@@ -149,7 +149,7 @@ operations more efficient.
 | pCloud                       | Yes   | Yes  | Yes  | Yes     | Yes     | No    | No           | No [#2178](https://github.com/ncw/rclone/issues/2178) | Yes |
 | QingStor                     | No    | Yes  | No   | No      | No      | Yes   | No           | No [#2178](https://github.com/ncw/rclone/issues/2178) | No  |
 | SFTP                         | No    | No   | Yes  | Yes     | No      | No    | Yes          | No [#2178](https://github.com/ncw/rclone/issues/2178) | No  |
-| WebDAV                       | Yes   | Yes  | Yes  | Yes     | No      | No    | Yes ‡        | No [#2178](https://github.com/ncw/rclone/issues/2178) | No  |
+| WebDAV                       | Yes   | Yes  | Yes  | Yes     | No      | No    | Yes ‡        | No [#2178](https://github.com/ncw/rclone/issues/2178) | Yes  |
 | Yandex Disk                  | Yes   | Yes  | Yes  | Yes     | Yes     | No    | Yes          | Yes         | Yes |
 | The local filesystem         | Yes   | No   | Yes  | Yes     | No      | No    | Yes          | No          | Yes |
 
@@ -220,5 +220,7 @@ on the particular cloud provider.
 This is used to fetch quota information from the remote, like bytes
 used/free/quota and bytes used in the trash.
 
+This is also used to return the space used, available for `rclone mount`.
+
 If the server can't do `About` then `rclone about` will return an
 error.