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1317
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1 import logging
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2 import traceback
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3 from rdflib import ConjunctiveGraph
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4 from rdflib.parser import StringInputSource
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5 from twisted.internet import reactor, defer
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6
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7 from patchablegraph import patchFromJson
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8 from rdfdb.patch import Patch
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9 from twisted_sse_demo.eventsource import EventSource
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10
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11 log = logging.getLogger('fetch')
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12
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13 class PatchSource(object):
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14 """wrap EventSource so it emits Patch objects and has an explicit stop method."""
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15 def __init__(self, url, agent):
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16 self.url = str(url)
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17
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18 # add callbacks to these to learn if we failed to connect
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19 # (approximately) or if the ccnnection was unexpectedly lost
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20 self.connectionFailed = defer.Deferred()
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21 self.connectionLost = defer.Deferred()
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22
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23 self._listeners = set()
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24 log.info('start read from %s', url)
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25 # note: fullGraphReceived isn't guaranteed- the stream could
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26 # start with patches
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27 self._fullGraphReceived = False
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28 self._eventSource = EventSource(url.toPython().encode('utf8'),
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29 userAgent=agent)
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30
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31 self._eventSource.addEventListener(b'fullGraph', self._onFullGraph)
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32 self._eventSource.addEventListener(b'patch', self._onPatch)
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33 self._eventSource.onerror(self._onError)
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34 self._eventSource.onConnectionLost = self._onDisconnect
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35
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36 def state(self):
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37 return {
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38 'url': self.url,
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39 'fullGraphReceived': self._fullGraphReceived,
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40 }
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41
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42 def addPatchListener(self, func):
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43 """
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44 func(patch, fullGraph=[true if the patch is the initial fullgraph])
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45 """
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46 self._listeners.add(func)
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47
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48 def stop(self):
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49 log.info('stop read from %s', self.url)
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50 try:
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51 self._eventSource.protocol.stopProducing() # needed?
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52 except AttributeError:
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53 pass
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54 self._eventSource = None
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55
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56 def _onDisconnect(self, reason):
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57 log.debug('PatchSource._onDisconnect from %s (%s)', self.url, reason)
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58 # skip this if we're doing a stop?
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59 self.connectionLost.callback(None)
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60
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61 def _onError(self, msg):
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62 log.debug('PatchSource._onError from %s %r', self.url, msg)
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63 if not self._fullGraphReceived:
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64 self.connectionFailed.callback(msg)
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65 else:
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66 self.connectionLost.callback(msg)
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67
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68 def _onFullGraph(self, message):
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69 try:
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70 g = ConjunctiveGraph()
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71 g.parse(StringInputSource(message), format='json-ld')
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72 p = Patch(addGraph=g)
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73 self._sendPatch(p, fullGraph=True)
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74 except Exception:
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75 log.error(traceback.format_exc())
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76 raise
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77 self._fullGraphReceived = True
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78
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79 def _onPatch(self, message):
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80 try:
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81 p = patchFromJson(message)
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82 self._sendPatch(p, fullGraph=False)
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83 except:
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84 log.error(traceback.format_exc())
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85 raise
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86
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87 def _sendPatch(self, p, fullGraph):
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88 log.debug('PatchSource %s received patch %s (fullGraph=%s)',
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89 self.url, p.shortSummary(), fullGraph)
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90 for lis in self._listeners:
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91 lis(p, fullGraph=fullGraph)
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92
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93 def __del__(self):
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94 if self._eventSource:
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95 raise ValueError("PatchSource wasn't stopped before del")
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96
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97 class ReconnectingPatchSource(object):
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98 """
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99 PatchSource api, but auto-reconnects internally and takes listener
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100 at init time to not miss any patches. You'll get another
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101 fullGraph=True patch if we have to reconnect.
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102
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103 todo: generate connection stmts in here
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104 """
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105 def __init__(self, url, listener, reconnectSecs=60, agent='unset'):
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106 # type: (str, Any, Any, str)
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107 self.url = url
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108 self._stopped = False
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109 self._listener = listener
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110 self.reconnectSecs = reconnectSecs
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111 self.agent = agent
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112 self._reconnect()
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113
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114 def _reconnect(self):
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115 if self._stopped:
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116 return
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117 self._ps = PatchSource(self.url, agent=self.agent)
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118 self._ps.addPatchListener(self._onPatch)
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119 self._ps.connectionFailed.addCallback(self._onConnectionFailed)
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120 self._ps.connectionLost.addCallback(self._onConnectionLost)
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121
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122 def _onPatch(self, p, fullGraph):
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123 self._listener(p, fullGraph=fullGraph)
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124
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125 def state(self):
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126 return {
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127 'reconnectedPatchSource': self._ps.state(),
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128 }
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129
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130 def stop(self):
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131 self._stopped = True
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132 self._ps.stop()
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133
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134 def _onConnectionFailed(self, arg):
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135 reactor.callLater(self.reconnectSecs, self._reconnect)
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136
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137 def _onConnectionLost(self, arg):
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138 reactor.callLater(self.reconnectSecs, self._reconnect)
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139
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