dropbox: Retry link without expiry

Dropbox only allows public links with expiry for certain account types.
Rather than erroring for other accounts, retry without expiry.

backend/dropbox/dropbox.go

@@ -1333,6 +1333,16 @@ func (f *Fs) PublicLink(ctx context.Context, remote string, expire fs.Duration,
 		return shouldRetry(ctx, err)
 	})
 
+	if err != nil && createArg.Settings.Expires != nil && strings.Contains(err.Error(), sharing.SharedLinkSettingsErrorNotAuthorized) {
+		// Some plans can't create links with expiry
+		fs.Debugf(absPath, "can't create link with expiry, trying without")
+		createArg.Settings.Expires = nil
+		err = f.pacer.Call(func() (bool, error) {
+			linkRes, err = f.sharing.CreateSharedLinkWithSettings(&createArg)
+			return shouldRetry(ctx, err)
+		})
+	}
+
 	if err != nil && strings.Contains(err.Error(),
 		sharing.CreateSharedLinkWithSettingsErrorSharedLinkAlreadyExists) {
 		fs.Debugf(absPath, "has a public link already, attempting to retrieve it")

fstest/test_all/config.yaml

@@ -144,10 +144,6 @@ backends:
  - backend:  "dropbox"
    remote:   "TestDropbox:"
    fastlist: false
-   ignore:
-     # This test doesn't work on a standard dropbox account because it
-     # tries to set the expiry of the link
-     - TestIntegration/FsMkdir/FsPutFiles/PublicLink
  # - backend:  "filefabric"
  #   remote:   "TestFileFabric:"
  #   fastlist: false