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protocols.py
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protocols.py
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import struct
from collections import deque
import mint
from mint import Protocol, Host, utils, wait
from mint.utils import put
class StopAndWait(Protocol):
HEADER_SIZE = 3
TAIL_SIZE = 0
SEQ_SIZE = 2
ACK = 0x01
NOT_ACK = 0x00
def __init__(self, master, servant,
resend_timeout=100):
super(StopAndWait, self).__init__(master, servant)
self.timer = mint.timer(resend_timeout, self.resend)
self.acked = True
self.sending_seq = 0
self.expecting_seq = 0
@mint.outputer
def sender(self):
while True:
if self.acked:
payload = self.master.pull()
header = self.build(
acking=False,
ack=0, # meaningless
seq=self.sending_seq)
self.frame = self.compose(header, payload)
self.servant.send(self.frame)
self.timer.start()
self.acked = False
else:
mint.wait(0)
@mint.inputer
def recver(self):
while True:
frame = self.servant.recv()
header, payload, _ = self.decompose(frame)
header = self.unbuild(header)
if header.acking:
# sending frame ACKed
if header.ack == self.sending_seq:
self.acked = True
self.sending_seq = (self.sending_seq + 1) % self.SEQ_SIZE
self.timer.stop()
if payload:
# is the expecting frame
if header.seq == self.expecting_seq:
self.master.push(payload)
self.expecting_seq = (self.expecting_seq + 1) % self.SEQ_SIZE
else:
utils.put(self.host, 'drop',
struct.unpack('!B', payload)[0], 'at', mint.now())
# send ACK
header = self.build(
acking=True,
ack=header.seq, # ack the recved frame
seq=0) # meaningless
frame = self.compose(header) # no payload
self.servant.send(frame)
def resend(self):
self.servant.send(self.frame)
self.timer.start()
def build(self, acking, seq, ack):
info = self.ACK if acking else self.NOT_ACK
return struct.pack('!3B', info, seq, ack)
def unbuild(self, header):
info, seq, ack = struct.unpack('!3B', header)
return utils.Bunch(
acking=info & self.ACK,
seq=seq,
ack=ack)