--- a/lib/twisted_sse_demo/eventsource.py	Fri Apr 19 01:08:01 2019 -0700
+++ b/lib/twisted_sse_demo/eventsource.py	Fri Apr 19 04:18:44 2019 -0700
@@ -3,16 +3,18 @@
 from twisted.web.client import Agent
 from twisted.web.http_headers import Headers
 
-from sse_client import EventSourceProtocol
+from .sse_client import EventSourceProtocol
 
 
 class EventSource(object):
     """
     The main EventSource class
     """
-    def __init__(self, url):
+    def __init__(self, url, userAgent):
+        # type: (str, bytes)
         self.url = url
-        self.protocol = EventSourceProtocol()
+        self.userAgent = userAgent
+        self.protocol = EventSourceProtocol(self.onConnectionLost)
         self.errorHandler = None
         self.stashedError = None
         self.connect()
@@ -21,34 +23,36 @@
         """
         Connect to the event source URL
         """
-        agent = Agent(reactor)
+        agent = Agent(reactor, connectTimeout=5)
+        self.agent = agent
         d = agent.request(
-            'GET',
+            b'GET',
             self.url,
             Headers({
-                'User-Agent': ['Twisted SSE Client'],
-                'Cache-Control': ['no-cache'],
-                'Accept': ['text/event-stream; charset=utf-8'],
+                b'User-Agent': [self.userAgent],
+                b'Cache-Control': [b'no-cache'],
+                b'Accept': [b'text/event-stream; charset=utf-8'],
             }),
             None)
-        d.addErrback(self.connectError)
-        d.addCallback(self.cbRequest)
+        d.addCallbacks(self.cbRequest, self.connectError)
 
     def cbRequest(self, response):
         if response is None:
+            # seems out of spec, according to https://twistedmatrix.com/documents/current/api/twisted.web.iweb.IAgent.html
             raise ValueError('no response for url %r' % self.url)
         elif response.code != 200:
             self.callErrorHandler("non 200 response received: %d" %
                                   response.code)
         else:
-            finished = Deferred()
-            self.protocol.setFinishedDeferred(finished)
             response.deliverBody(self.protocol)
-            return finished
 
     def connectError(self, ignored):
         self.callErrorHandler("error connecting to endpoint: %s" % self.url)
 
+    def onConnectionLost(self, reason):
+        # overridden
+        reason.printDetailedTraceback()
+        
     def callErrorHandler(self, msg):
         if self.errorHandler:
             func, callInThread = self.errorHandler
@@ -68,6 +72,7 @@
         self.addEventListener('message', func, callInThread)
 
     def addEventListener(self, event, func, callInThread=False):
+        assert isinstance(event, bytes), event
         callback = func
         if callInThread:
             callback = lambda data: reactor.callInThread(func, data)