Get gerrit watching thread working as expected

This watcher addition can be tested standalone
by running.

$ python nerdreviewer/watcher.py \
  "review.openstack.org" "$USER"

Change-Id: I91142dd8d6be7649894320489c4ed3083723652a

nerdreviewer/watcher.py

@@ -0,0 +1,83 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import json
+import logging
+import select
+import threading
+
+import notifier
+import paramiko
+
+LOG = logging.getLogger(__name__)
+
+
+class Watcher(threading.Thread):
+
+    GERRIT_ACTIVITY = "GERRIT_ACTIVITY"
+
+    def __init__(self, hostname, username, port=29418, keyfile=None):
+        super(Watcher, self).__init__()
+        self.dead = threading.Event()
+        self.notifier = notifier.Notifier()
+        self._keyfile = keyfile
+        self._hostname = hostname
+        self._username = username
+        self._port = port
+        self._client = None
+
+    def connect(self):
+        self._client = paramiko.SSHClient()
+        self._client.load_system_host_keys()
+        self._client.set_missing_host_key_policy(paramiko.WarningPolicy())
+        self._client.connect(self._hostname,
+                             username=self._username,
+                             port=self._port,
+                             key_filename=self._keyfile)
+
+    def run(self):
+        client = self._client
+        if not client:
+            raise RuntimeError("Connect must be called before run")
+        _stdin, stdout, _stderr = client.exec_command("gerrit stream-events")
+        poll = select.poll()
+        poll.register(stdout.channel)
+        while not self.dead.is_set():
+            for (fd, event) in poll.poll(0.1):
+                if fd == stdout.channel.fileno():
+                    if event == select.POLLIN:
+                        event_data = {"event": json.loads(stdout.readline())}
+                        self.notifier.notify(self.GERRIT_ACTIVITY, event_data)
+                    else:
+                        LOG.warn("Unknown event %s received on stdout"
+                                 " descriptor %s [%s]", event, stdout, fd)
+
+
+if __name__ == "__main__":
+    import sys
+    import time
+
+    def on_event(event_type, details):
+        print("Received event %s with details %s" % (event_type, details))
+
+    logging.basicConfig(level=logging.DEBUG)
+    w = Watcher(sys.argv[1], sys.argv[2])
+    w.connect()
+    w.notifier.register(Watcher.GERRIT_ACTIVITY, on_event)
+    w.run()
+
+    try:
+        while True:
+            time.sleep(0.5)
+    except KeyboardInterrupt:
+        w.dead.set()
+        w.join()

requirements.txt

@@ -3,8 +3,10 @@
 # process, which may cause wedges in the gate later.
 
 pbr>=1.6 # Apache-2.0
+paramiko>=1.13.0 # LGPL
 jsonschema>=2.0.0,<3.0.0,!=2.5.0 # MIT
 netaddr>=0.7.12,!=0.7.16 # BSD
+notifier>=1.0.3 # Apache-2.0
 PyYAML>=3.1.0
 sphinx>=1.1.2,!=1.2.0,!=1.3b1,<1.3 # BSD
 six>=1.9.0