webdav: check that purged directory really exists (#2921)

Sharepoint 2016 returns status 204 to the purge request
even if the directory to purge does not really exist.
This change adds an extra check to detect this condition
and returns a proper error code.

backend/webdav/webdav.go

@@ -142,6 +142,7 @@ type Fs struct {
 	canStream          bool          // set if can stream
 	useOCMtime         bool          // set if can use X-OC-Mtime
 	retryWithZeroDepth bool          // some vendors (sharepoint) won't list files when Depth is 1 (our default)
+	checkBeforePurge   bool          // enables extra check that directory to purge really exists
 	hasMD5             bool          // set if can use owncloud style checksums for MD5
 	hasSHA1            bool          // set if can use owncloud style checksums for SHA1
 	ntlmAuthMu         sync.Mutex    // mutex to serialize NTLM auth roundtrips
@@ -540,6 +541,12 @@ func (f *Fs) setQuirks(ctx context.Context, vendor string) error {
 		// Sharepoint with NTLM authentication
 		// See comment above
 		f.retryWithZeroDepth = true
+
+		// Sharepoint 2016 returns status 204 to the purge request
+		// even if the directory to purge does not really exist
+		// so we must perform an extra check to detect this
+		// condition and return a proper error code.
+		f.checkBeforePurge = true
 	case "other":
 	default:
 		fs.Debugf(f, "Unknown vendor %q", vendor)
@@ -879,6 +886,21 @@ func (f *Fs) purgeCheck(ctx context.Context, dir string, check bool) error {
 		if notEmpty {
 			return fs.ErrorDirectoryNotEmpty
 		}
+	} else if f.checkBeforePurge {
+		// We are doing purge as the `check` argument is unset.
+		// The quirk says that we are working with Sharepoint 2016.
+		// This provider returns status 204 even if the purged directory
+		// does not really exist so we perform an extra check here.
+		// Only the existence is checked, all other errors must be
+		// ignored here to make the rclone test suite pass.
+		depth := defaultDepth
+		if f.retryWithZeroDepth {
+			depth = "0"
+		}
+		_, err := f.readMetaDataForPath(ctx, dir, depth)
+		if err == fs.ErrorObjectNotFound {
+			return fs.ErrorDirNotFound
+		}
 	}
 	opts := rest.Opts{
 		Method:     "DELETE",