import struct import bitkey_pb2 as proto import mapping class Transport(object): def __init__(self, device, *args, **kwargs): self.device = device self._open() def _open(self): raise NotImplemented def _close(self): raise NotImplemented def _write(self, msg): raise NotImplemented def _read(self): raise NotImplemented def ready_to_read(self): raise NotImplemented def close(self): self._close() def write(self, msg): ser = msg.SerializeToString() header = struct.pack(">HL", mapping.get_type(msg), len(ser)) self._write("##%s%s" % (header, ser)) def read(self): (msg_type, data) = self._read() inst = mapping.get_class(msg_type)() inst.ParseFromString(data) return inst def _read_headers(self, read_f): # Try to read headers until some sane value are detected is_ok = False while not is_ok: # Align cursor to the beginning of the header ("##") c = read_f.read(1) while c != '#': if c == '': # timeout raise Exception("Timed out while waiting for the magic character") print "Warning: Aligning to magic characters" c = read_f.read(1) if read_f.read(1) != "#": # Second character must be # to be valid header raise Exception("Second magic character is broken") # Now we're most likely on the beginning of the header try: headerlen = struct.calcsize(">HL") (msg_type, datalen) = struct.unpack(">HL", read_f.read(headerlen)) break except: raise Exception("Cannot parse header length") return (msg_type, datalen)