import struct import mapping class NotImplementedException(Exception): pass class ConnectionError(Exception): pass class Transport(object): def __init__(self, device, *args, **kwargs): self.device = device self.session_depth = 0 self._open() def _open(self): raise NotImplementedException("Not implemented") def _close(self): raise NotImplementedException("Not implemented") def _write(self, msg): raise NotImplementedException("Not implemented") def _read(self): raise NotImplementedException("Not implemented") def _session_begin(self): pass def _session_end(self): pass def ready_to_read(self): raise NotImplementedException("Not implemented") def session_begin(self): if self.session_depth == 0: self._session_begin() self.session_depth += 1 def session_end(self): self.session_depth -= 1 self.session_depth = max(0, self.session_depth) if self.session_depth == 0: self._session_end() 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): if not self.ready_to_read(): return None data = self._read() if data == None: return None return self._parse_message(data) def read_blocking(self): while True: data = self._read() if data != None: break return self._parse_message(data) def _parse_message(self, data): (msg_type, data) = data 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) i = 0 while c != '#': i += 1 if i >= 64: # timeout raise Exception("Timed out while waiting for the magic character") #print "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)