Do message reassembly
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Dan Williams
parent
e4516c6d81
commit
0f7dc51ac0
@ -15,90 +15,126 @@ _HEADER_LEN = 30
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_MAGIC = 0xbaea4304
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_TTL = 120 # 2 minutes
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def _stringify_sha(sha):
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print_sha = ""
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for char in sha:
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print_sha = print_sha + binascii.b2a_hex(char)
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return print_sha
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def _sha_data(data):
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sha_hash = sha.new()
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sha_hash.update(data)
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return sha_hash.digest()
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class MessageSegment(object):
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# 4: magic (0xbaea4304)
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# 2: segment number
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# 2: total segments
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# 2: data size
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#20: total message sha1
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# 2: message sequence number
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#20: total data sha1
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_HEADER_TEMPLATE = "! IHHH20s"
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def _new_from_parts(self, num, all, data, master_sha):
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def _new_from_parts(self, msg_seq_num, segno, total_segs, data, master_sha):
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"""Construct a new message segment from individual attributes."""
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if not data:
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raise ValueError("Must have valid data.")
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if num > 65535:
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if segno > 65535:
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raise ValueError("Segment number cannot be more than 65535.")
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if num < 1:
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if segno < 1:
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raise ValueError("Segment number must be greater than zero.")
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if all > 65535:
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if total_segs > 65535:
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raise ValueError("Message cannot have more than 65535 segments.")
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if all < 1:
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if total_segs < 1:
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raise ValueError("Message must have at least one segment.")
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if msg_seq_num < 1:
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raise ValueError("Message sequence number must be greater than 0.")
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self._stime = time.time()
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self._data = data
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self._data_len = len(data)
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self._master_sha = master_sha
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self._num = num
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self._all = all
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self._segno = segno
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self._total_segs = total_segs
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self._msg_seq_num = msg_seq_num
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self._addr = None
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self._header = struct.pack(self._HEADER_TEMPLATE, _MAGIC, self._num,
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self._all, self._data_len, self._master_sha)
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# Make the header
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self._header = struct.pack(self._HEADER_TEMPLATE, _MAGIC, self._segno,
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self._total_segs, self._msg_seq_num, self._master_sha)
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def _new_from_data(self, data):
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def _new_from_data(self, addr, data):
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"""Verify and construct a new message segment from network data."""
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if len(data) < _HEADER_LEN + 1:
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raise ValueError("Message is less then minimum required length")
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stream = StringIO.StringIO(data)
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self._stime = None
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(magic, num, all, data_len, master_sha) = struct.unpack(self._HEADER_TEMPLATE,
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stream.read(struct.calcsize(self._HEADER_TEMPLATE)))
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self._addr = addr
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# Format checking
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# Determine and verify the length of included data
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stream.seek(0, 2)
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header_size = struct.calcsize(self._HEADER_TEMPLATE)
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self._data_len = stream.tell() - header_size
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if self._data_len < 1:
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raise ValueError("Message must have some data.")
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if self._data_len > _MTU:
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raise ValueError("Data length must not be larger than the MTU (%s)." % _MTU)
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stream.seek(0)
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# Read the header attributes
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(magic, segno, total_segs, msg_seq_num, master_sha) = struct.unpack(self._HEADER_TEMPLATE,
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stream.read(header_size))
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# Sanity checks on the message attributes
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if magic != _MAGIC:
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raise ValueError("Message does not have the correct magic.")
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if not num:
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if segno < 1:
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raise ValueError("Segment number must be greater than 0.")
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if not all:
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if segno > total_segs:
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raise ValueError("Segment number cannot be larger than message segment total.")
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if total_segs < 1:
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raise ValueError("Message must have at least one segment.")
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if not data_len:
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raise ValueError("Message must have some data.")
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if data_len > _MTU:
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raise ValueError("Data length must not be larger than the MTU (%s)." % _MTU)
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if msg_seq_num < 1:
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raise ValueError("Message sequence number must be greater than 0.")
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self._num = num
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self._all = all
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self._data_len = data_len
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self._segno = segno
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self._total_segs = total_segs
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self._msg_seq_num = msg_seq_num
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self._master_sha = master_sha
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# Read data
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self._data = struct.unpack("! %ds" % self._data_len, stream.read(self._data_len))
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# Reconstruct the data
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self._data = struct.unpack("! %ds" % self._data_len, stream.read(self._data_len))[0]
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def new_from_parts(num, all, data, master_sha):
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def new_from_parts(msg_seq_num, segno, total_segs, data, master_sha):
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"""Static constructor for creation from individual attributes."""
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segment = MessageSegment()
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segment._new_from_parts(num, all, data, master_sha)
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segment._new_from_parts(msg_seq_num, segno, total_segs, data, master_sha)
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return segment
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new_from_parts = staticmethod(new_from_parts)
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def new_from_data(data):
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def new_from_data(addr, data):
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"""Static constructor for creation from a packed data stream."""
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segment = MessageSegment()
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segment._new_from_data(data)
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segment._new_from_data(addr, data)
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return segment
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new_from_data = staticmethod(new_from_data)
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def stime(self):
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return self._stime
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def num(self):
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return self._num
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def addr(self):
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return self._addr
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def all(self):
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return self._all
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def segment_number(self):
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return self._segno
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def total_segments(self):
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return self._total_segs
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def message_sequence_number(self):
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return self._msg_seq_num
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def data(self):
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return self._data
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def header(self):
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return self._header
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def master_sha(self):
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return self._master_sha
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@ -117,19 +153,25 @@ class MostlyReliablePipe(object):
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self._data_cb = data_cb
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self._user_data = user_data
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self._started = False
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self._worker = 0
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self._seq_counter = 0
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self._outgoing = []
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self._sent = []
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self._worker = 0
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self._incoming = {} # (message sha, # of segments) -> [segment1, segment2, ...]
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self._setup_listener()
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self._setup_sender()
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def _setup_sender(self):
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"""Setup the send socket for multicast."""
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self._send_sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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# Make the socket multicast-aware, and set TTL.
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self._send_sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 20) # Change TTL (=20) to suit
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def _setup_listener(self):
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"""Set up the listener socket for multicast traffic."""
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# Listener socket
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self._listen_sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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@ -139,6 +181,7 @@ class MostlyReliablePipe(object):
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self._listen_sock.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_LOOP, 1)
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def start(self):
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"""Let the listener socket start listening for network data."""
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# Set some more multicast options
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self._listen_sock.bind((self._local_addr, self._port)) # Bind to all interfaces
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self._listen_sock.settimeout(2)
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@ -155,31 +198,84 @@ class MostlyReliablePipe(object):
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self._started = True
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def _segment_ttl_worker(self):
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"""Cull already-sent message segments that are past their TTL."""
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now = time.time()
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for segment in self._sent[:]:
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if segment.stime() < now - _MSG_TTL:
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self._sent.remove(segment)
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return True
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def _dispatch_message(self, addr, message):
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"""Send complete message data to the owner's data callback."""
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self._data_cb(addr, message, self._user_data)
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def _process_incoming(self, segment):
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"""Handle a new message segment. First checks if there is only one
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segment to the message, and if the checksum from the header matches
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that computed from the data, dispatches it. Otherwise, it adds the
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new segment to the list of other segments for that message, and
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checks to see if the message is complete. If all segments are present,
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the message is reassembled and dispatched."""
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string_sha = _stringify_sha(segment.master_sha())
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nsegs = segment.total_segments()
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addr = segment.addr()
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segno = segment.segment_number()
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# Short-circuit single-segment messages
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if segno == 1 and nsegs == 1:
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# Ensure the header's master sha actually equals the data's sha
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if string_sha == _stringify_sha(_sha_data(segment.data())):
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self._dispatch_message(addr, segment.data())
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return
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# Otherwise, track the new segment
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msg_seq_num = segment.message_sequence_number()
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msg_key = (addr[0], msg_seq_num, string_sha, nsegs)
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if not self._incoming.has_key(msg_key):
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self._incoming[msg_key] = {}
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# Look for a dupe, and if so, drop the new segment
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if self._incoming[msg_key].has_key(segno):
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return
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self._incoming[msg_key][segno] = segment
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# Dispatch the message if all segments are present and the sha is correct
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if len(self._incoming[msg_key]) == nsegs:
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all_data = ''
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for i in range(1, nsegs + 1):
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all_data = all_data + self._incoming[msg_key][i].data()
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if string_sha == _stringify_sha(_sha_data(all_data)):
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self._dispatch_message(addr, all_data)
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del self._incoming[msg_key]
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def _handle_incoming_data(self, source, condition):
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"""Handle incoming network data by making a message segment out of it
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sending it off to the processing function."""
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if not (condition & gobject.IO_IN):
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return True
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msg = {}
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data, addr = source.recvfrom(_MTU + _HEADER_LEN)
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if self._data_cb:
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self._data_cb(addr, data, self._user_data)
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try:
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segment = MessageSegment.new_from_data(addr, data)
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self._process_incoming(segment)
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except ValueError, exc:
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pass
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return True
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def send(self, data):
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"""Break data up into chunks and queue for later transmission."""
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if not self._started:
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raise Exception("Can't send anything until started!")
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self._seq_counter = self._seq_counter + 1
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if self._seq_counter > 65535:
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self._seq_counter = 1
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# Pack the data into network byte order
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template = "! %ds" % len(data)
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data = struct.pack(template, data)
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sha_hash = sha.new()
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sha_hash.update(data)
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master_sha = sha_hash.digest()
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master_sha = _sha_data(data)
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# Split up the data into segments
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left = length = len(data)
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@ -188,7 +284,8 @@ class MostlyReliablePipe(object):
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nmessages = nmessages + 1
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msg_num = 1
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while left > 0:
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msg = MessageSegment.new_from_parts(msg_num, nmessages, data[:_MTU], master_sha)
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msg = MessageSegment.new_from_parts(self._seq_counter, msg_num,
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nmessages, data[:_MTU], master_sha)
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self._outgoing.append(msg)
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msg_num = msg_num + 1
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data = data[_MTU:]
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@ -197,6 +294,7 @@ class MostlyReliablePipe(object):
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self._worker = gobject.idle_add(self._send_worker)
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def _send_worker(self):
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"""Send all queued segments that have yet to be transmitted."""
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self._worker = 0
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for segment in self._outgoing:
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data = segment.segment()
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@ -207,14 +305,7 @@ class MostlyReliablePipe(object):
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def got_data(addr, data, user_data=None):
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segment = MessageSegment.new_from_data(data)
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print "Segment (%d/%d)" % (segment.num(), segment.all())
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print_sha = ""
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for char in segment.master_sha():
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print_sha = print_sha + binascii.b2a_hex(char)
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print " Master SHA: %s" % print_sha
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print " Data: '%s'" % segment.data()
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print ""
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print "Data (%s): %s" % (addr, data)
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def main():
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pipe = MostlyReliablePipe('', '224.0.0.222', 2293, got_data)
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