webdav: don't delete files on error - fixes #3263

Previous to this change rclone deleted a file if the upload failed
half way through.

After this change we only delete the upload if the
--webdav-delete-on-error flag is set.

We set this in the serve webdav tests to make them pass.

backend/webdav/webdav.go

@@ -86,6 +86,15 @@ func init() {
 			Name:     "bearer_token_command",
 			Help:     "Command to run to get a bearer token",
 			Advanced: true,
+		}, {
+			Name:    "delete_on_error",
+			Default: false,
+			Help: `Delete a partially uploaded file on upload failure.
+
+Some webdav backends (eg rclone serve webdav) leave behind half
+written files on error.  This flag causes them to be deleted if the
+upload fails part of the way through.`,
+			Advanced: true,
 		}},
 	})
 }
@@ -98,6 +107,7 @@ type Options struct {
 	Pass               string `config:"pass"`
 	BearerToken        string `config:"bearer_token"`
 	BearerTokenCommand string `config:"bearer_token_command"`
+	DeleteOnError bool   `config:"delete_on_error"`
 }
 
 // Fs represents a remote webdav
@@ -1193,6 +1203,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 		return o.fs.shouldRetry(resp, err)
 	})
 	if err != nil {
+		if o.fs.opt.DeleteOnError {
 			// Give the WebDAV server a chance to get its internal state in order after the
 			// error.  The error may have been local in which case we closed the connection.
 			// The server may still be dealing with it for a moment. A sleep isn't ideal but I
@@ -1201,6 +1212,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 			time.Sleep(1 * time.Second)
 			// Remove failed upload
 			_ = o.Remove(ctx)
+		}
 		return err
 	}
 	// read metadata from remote

cmd/serve/webdav/webdav_test.go

@@ -67,6 +67,7 @@ func TestWebDav(t *testing.T) {
 			"url":             w.Server.URL(),
 			"user":            testUser,
 			"pass":            obscure.MustObscure(testPass),
+			"delete_on_error": "true",
 		}
 
 		return config, func() {