annotate web/settings.py @ 256:6d06795aefbb

merge
author Matt Johnston <matt@ucc.asn.au>
date Mon, 08 Jun 2015 22:33:04 +0800
parents 0a1b642e3086
children 03e540c3ec24
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1 import gevent
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2 import fcntl
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3 import hashlib
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4
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5 class Settings(object):
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6 RAND_SIZE = 15 # 120 bits
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7
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8 """ Handles state updates from both the web UI and from the fridge client.
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9 The fridge client is canonical. It provides the epoch (apart from 'startepoch'), that
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10 is changed any time the fridge reloads its local config. The fridge only accepts
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11 updates that have the same epoch.
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12
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13 When the web UI changes it keeps the same epoch but generates a new tag. The fridge sends
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14 its current known tag and waits for it to change.
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15
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16 content is opaque, presently a dictionary of decoded json
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17 """
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18
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19 def __init__(self):
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20 self.event = gevent.event.Event()
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21 self.contents = None
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22 self.epoch = None
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23 self.tag = None
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24
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25 self.update(self, None, 'startepoch')
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26
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27 def wait(self, epoch_tag = None, timeout = None):
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28 """ returns false if the timeout was hit """
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29 if self.epoch_tag() != epoch_tag:
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30 # has alredy changed
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31 return True
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32 return self.event.wait(timeout)
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33
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34 def epoch_tag(self):
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35 return '%s-%s' % (self.epoch, self.tag)
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36
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37 def random(self):
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38 return binascii.hexlify(os.urandom(self.RAND_SIZE))
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39
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40 def update(self, contents, epoch = None):
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41 """ replaces settings contents and updates waiters if changed """
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42 if epoch:
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43 if self.epoch == epoch:
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44 return
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45 else:
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46 self.epoch = epoch
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47
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48 self.tag = self.random()
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49 self.contents = contents
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50
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51 self.event.set()
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52 self.event.clear()
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53
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54 def get(self):
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55 """ Returns (contents, epoch-tag) """
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56 return self.contents, self.epoch_tag()
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