Trying to find buffering deadlock

primary.py

@@ -122,6 +122,7 @@ class Server:
                     pos = buf.find(b'\x00')
                     if pos == -1:
                         tmp = f.read(4096)
+                        print('Got:', len(tmp), file=sys.stderr)
                         if len(tmp) == 0:
                             if len(buf) == 0:
                                 return