Add Message and MessageSet HEADER_SIZE bytes

kafka/protocol/message.py

@@ -20,6 +20,7 @@ class Message(Struct):
     CODEC_MASK = 0x03
     CODEC_GZIP = 0x01
     CODEC_SNAPPY = 0x02
+    HEADER_SIZE = 14 # crc(4), magic(1), attributes(1), key+value size(4*2)
 
     def __init__(self, value, key=None, magic=0, attributes=0, crc=0):
         assert value is None or isinstance(value, bytes), 'value must be bytes'
@@ -83,6 +84,7 @@ class MessageSet(AbstractType):
         ('message_size', Int32),
         ('message', Message.SCHEMA)
     )
+    HEADER_SIZE = 12 # offset + message_size
 
     @classmethod
     def encode(cls, items, size=True, recalc_message_size=True):