http server-sent events

an attempt to get swim processes on asdi-db to work using http server-sent events

summary of WebSockets vs. Server-Sent events/EventSource https://stackoverflow.com/questions/5195452/websockets-vs-server-sent-events-eventsource

a question on stack overflow: https://stackoverflow.com/questions/35927900/how-to-setup-cherrypy-server-sent-events

possible pastebin of above code: https://pastebin.com/xCFBqAAg

description of fields: https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#Fields

an old (incorrect) blog entry from 2011: http://neokannon.blogspot.com/2011/07/cherrypy-server-sent-events-and-you.html

6-year-old git demo: https://github.com/liyanage/bottlepy-eventsource-test uses bottle (a framework on top of cherrypy?)

blog entry 2018, possible useful: https://medium.com/conectric-networks/a-look-at-server-sent-events-54a77f8d6ff7 (server-side is in Node.js)

dice demo from above, it seems that server is in python, but calls npm for processing: https://github.com/simonprickett/server-sent-events-demo

proceeding with suggestions from stackoverflow

code is from: https://stackoverflow.com/questions/35927900/how-to-setup-cherrypy-server-sent-events

for the html:

    cd ~/webapps/cherry
    vim srvsent.html
        <copy/paste html index.btml from above link>

    and comment out css:
        <!-- link rel="stylesheet" href="style.css" -->

    and edit this:
        //r sse_handler = new EventSource('http://localhost:8080/getUpdate');
        var sse_handler = new EventSource('http://here.ilikecarrots.com/getUpdate');

for the server, add this to the cherrypy site.py file:

        vim site.py

 30 #-------------------- test example of server-sent
 31 # from https://stackoverflow.com/questions/35927900/how-to-setup-cherrypy-server-sent-events
 32
 33 #import datetime
 34 from pathlib import Path
 35
 36 class TestServerSentEvent(object):
 37     @cherrypy.expose
 38     def index(self):
 39         return Path("index.html").read_text()
 40
 41     @cherrypy.expose
 42     def getUpdate(self, * pos, ** nam):
 43         cherrypy.response.headers["Content-Type"] = "text/event-stream;charset=utf-8"
 44         return 'retry: 1200\ndata: {0}\n\n'.format(self.output())
 45
 46     def output(self) :
 47         #d = datetime.datetime.now()
 48         #return f"TEST - {d}"
 49         d = datetime.now()
 50         return "TEST - %s" % d
 51
 52     getUpdate._cp_config = {'response.stream': True, 'tools.encode.encoding':'utf-8'}
 53
 54 #--------------------

then, open this: http://here.ilikecarrots.com/srvsent.html

hmm..., Console complains about

Firefox can't establish a connection to the server at http://here.ilikecarrots.com/getUpdate.

lots of edits, then: it finally works!!!

• done: make srvrsent a dns name
• done: add srvrsent.ilc to cherry domain/app
• done: separate out here from srvsent
• not sure: send 'thank you' to stackoverflow guy

moving past example

current message:

    retry: 2000
    data: TEST2 - 2019-01-17 16:37:17.042353

note: if 'retry' on there, then default is apparently 5 secs.

proposed:

struct: { 'acid' : 'N13285',
          'lat' : 38.5,
          'lng:   -84.5
          }

also separated out ss.py for these functions

• looks good

finally, have

• dict in python converted to string (json.dumps),
• sent to client
• parsed into struct (JSON.parse(xx))

ok, seems working, will proceed to mergint this with actual swim code...