1
2
3
4
5 """ Helper package for handling fragmentation of messages """
6
7 from __future__ import generators
8
9 from .utils.codec import Parser
10
12
13 """
14 Class for demultiplexing TLS messages.
15
16 Since the messages can be interleaved and fragmented between each other
17 we need to cache not complete ones and return in order of urgency.
18
19 Supports messages with given size (like Alerts) or with a length header
20 in specific place (like Handshake messages).
21
22 @ivar priorities: order in which messages from given types should be
23 returned.
24 @ivar buffers: data buffers for message types
25 @ivar decoders: functions which check buffers if a message of given type
26 is complete
27 """
28
30 """Set up empty defregmenter"""
31 self.priorities = []
32 self.buffers = {}
33 self.decoders = {}
34
36 """Add a message type which all messages are of same length"""
37 if msgType in self.priorities:
38 raise ValueError("Message type already defined")
39 if size < 1:
40 raise ValueError("Message size must be positive integer")
41
42 self.priorities += [msgType]
43
44 self.buffers[msgType] = bytearray(0)
45 def sizeHandler(data):
46 """
47 Size of message in parameter
48
49 If complete message is present in parameter returns its size,
50 None otherwise.
51 """
52 if len(data) < size:
53 return None
54 else:
55 return size
56 self.decoders[msgType] = sizeHandler
57
59 """Add a message type which has a dynamic size set in a header"""
60 if msgType in self.priorities:
61 raise ValueError("Message type already defined")
62 if sizeOfSize < 1:
63 raise ValueError("Size of size must be positive integer")
64 if sizeOffset < 0:
65 raise ValueError("Offset can't be negative")
66
67 self.priorities += [msgType]
68 self.buffers[msgType] = bytearray(0)
69
70 def sizeHandler(data):
71 """
72 Size of message in parameter
73
74 If complete message is present in parameter returns its size,
75 None otherwise.
76 """
77 if len(data) < sizeOffset+sizeOfSize:
78 return None
79 else:
80 parser = Parser(data)
81
82 parser.getFixBytes(sizeOffset)
83
84 payloadLength = parser.get(sizeOfSize)
85 if parser.getRemainingLength() < payloadLength:
86
87 return None
88 return sizeOffset + sizeOfSize + payloadLength
89
90 self.decoders[msgType] = sizeHandler
91
93 """Adds data to buffers"""
94 if msgType not in self.priorities:
95 raise ValueError("Message type not defined")
96
97 self.buffers[msgType] += data
98
100 """Extract the highest priority complete message from buffer"""
101 for msgType in self.priorities:
102 length = self.decoders[msgType](self.buffers[msgType])
103 if length is None:
104 continue
105
106
107 data = self.buffers[msgType][:length]
108
109 self.buffers[msgType] = self.buffers[msgType][length:]
110 return (msgType, data)
111 return None
112
114 """Remove all data from buffers"""
115 for key in self.buffers.keys():
116 self.buffers[key] = bytearray(0)
117