.

wcfs/wcfs.go

@@ -1306,7 +1306,8 @@ func (wlink *WatchLink) setupWatch(ctx context.Context, foid zodb.Oid, at zodb.T
 
 	// XXX locking
 
-	if f.δtail.Tail() < at {
+	if at < f.δtail.Tail() {
+		// XXX err += head.at?
 		return fmt.Errorf("at is too far away back from head/at")
 	}
 
@@ -1317,6 +1318,8 @@ func (wlink *WatchLink) setupWatch(ctx context.Context, foid zodb.Oid, at zodb.T
 	//
 	// FIXME (!!!) since f.δtail does not have all changes to f, here we
 	// can be missing some pins we should be sending. (see wcfs_test.py for details)
+	//
+	// XXX at can be > f.δtail.Head due to ^^^ (and then SliceByRev panics)
 	for _, δ := range f.δtail.SliceByRev(at, f.δtail.Head()) {
 		for _, blk := range δ.Changev {
 			_, already := toPin[blk]
@@ -1423,12 +1426,11 @@ func (wlink *WatchLink) _serveRX() (err error) {
 
 		fmt.Printf("S: watch: AAA\n")
 
-		if false {
 		err = wlink.setupWatch(ctx, foid, at)
 		if err != nil {
+			fmt.Printf("S: watch: QQQ: %s\n", err)
 			return fmt.Errorf("%d: %s", stream, err)
 		}
-	}
 
 		fmt.Printf("S: watch: BBB\n")