diff -ur v5/sock_ut.py v6/sock_ut.py
--- v5/sock_ut.py	2021-06-30 04:15:08.000000000 +0900
+++ v6/sock_ut.py	2021-07-02 21:40:11.000000000 +0900
@@ -26,8 +26,7 @@
 		return False
 	return True
 
-def recv_bt( sc ):
-	bufmax = 16 * 1024
+def recv_bt( sc, bufmax=16*1024 ):
 	bt = sc.recv( bufmax )
 	return bt
 
@@ -44,8 +43,8 @@
 	bt = s.encode( 'utf-8' )
 	return send_bt( sc, bt )
 
-def recv_str( sc ):
-	bt = recv_bt( sc )
+def recv_str( sc, bufmax=16*1024 ):
+	bt = recv_bt( sc, bufmax )
 	return bt.decode( 'utf-8' )
 
 def recv_str_all( sc ):
@@ -228,7 +227,7 @@
 	if not send_str( cs, s ):
 		cs.close()
 		return None
-	s = recv_str( cs )
+	s = recv_str( cs, bufmax=2 )
 	if s != 'ok':
 		cs.close()
 		return None
@@ -273,7 +272,7 @@
 		cs.close()
 		return None
 
-	s = recv_str( cs )
+	s = recv_str( cs, bufmax=2 )
 	if s != 'ok':
 		cs.close()
 		return None