modpython.py

"""Use as a mod_python handler in apache.

Apache configuration example:

<Location "/mdsplusEvents/">
   SetHandler python-program
   PythonHandler MDSplus.modpython
   PythonPath "['/usr/local/myeventhandlers'] + sys.path"
   PythonDebug On

   PythonOption UDP_EVENTS yes
or
   PythonOption EVENT_SERVER host[:port]

</Location>

This configuration will handle requests such as:

http://mywebserver-host/mdsplusEvents/event-name
http://mywebserver-host/mdsplusEvents/event-name?timeout=5
http://mywebserver-host/mdsplusEvents/event-name?timeout=50&handler=myhandler

If no handler is used in the url then the default handler will be used.

The default handler does the following:

  If the event occurs before the timeout (default timeout is 60 seconds):
    returns a page of xml which looks like:
       <event><name>event-name</name><time>time-of-event</time></event> or
       <event><name>event-name</name><time>time-of-event</time><data>
              <data_bytes>[byte1,byte2,byte3,....,byte4]</data_bytes>
              <data_text>text_bytes</data_text></data>
       </event>
  If the event times out then returns an empty page with status of NO_RESPONSE(204)
  If there is an error during processing the event it returns a page of xml which
    looks like:
      <exception>text-of-exception</exception> and a status of BAD_REQUEST

If a handler is specified, a module of the name of handler specified will be
imported and the function called "handler" in that module will be called with
two arguments, the req and the MDSplus event instance in that order. The handler can use the req
object to write the response and the event object to get the event data. The
event-instance.exception will = None if no problem occurred during the event processing or
the exception string if an error occurred. The handler should return a valid
HTTP status if it handles the event otherwise it can return None to resume the
default processing. The following is a handler used on the C-Mod experiment
for monitoring the shot cycle state machine. Information about the state and
shot number is encoded in an event called CMOD_COUNTDOWN_EVENT.

from mod_python import apache
import time
import numpy
import sys,os
states=["starting", "standby", "cooldown", "test", "recool", "init", "check", "pulse", "abort"]
lastData=None
lastTime=time.time()

def handler(req,e):
    if e.exception is None:
        req.content_type="text/xml"
        data=e.getRaw().data()
        shot=int(data[range(4,8)].view(numpy.uint32).item())
        toState=states[int(data[1])]
        fromState=states[int(data[0])]
        req.write('<?xml version="1.0" encoding="ISO-8859-1" ?>')
        req.write("<cmodState><shot>%d</shot><toState>%s</toState><fromState>%s</fromState></cmodState>" % (shot,toState,fromState))
        return apache.OK

"""


from MDSplus import Event
import time
import os
from mod_python import apache
from cgi import parse_qs

class myevent(Event):
    def run(self):
        self.cancel()

def handler(req):
  try:
    opts=req.get_options()
    if "UDP_EVENTS" in opts:
      value=opts["UDP_EVENTS"].upper()
      if value=="YES":
          os.putenv('UDP_EVENTS','yes')
    if "EVENT_SERVER" in opts:
      os.putenv("mds_event_server",opts['EVENT_SERVER'])
  except:
    pass
  os.putenv('UDP_EVENTS','yes')
  event=req.path_info.rsplit('/')[-1]
  args=parse_qs(str(req.args))
  timeout=60
  try:
      timeout=int(args['timeout'][-1])
  except:
      pass
  try:
      event=args['event'][-1]
  except:
      pass
  if 'handler' in args:
      specialHandler=__import__(args['handler'][-1])
      if hasattr(specialHandler,'handler'):
        specialHandler=specialHandler.handler
      else:
        raise Exception(str(dir(specialHandler)))
  else:
      specialHandler=None
  e=myevent(event,timeout)
  e.join()
  req.headers_out['Cache-Control']='no-store, no-cache, must-revalidate'
  req.headers_out['Pragma']='no-cache'
  req.content_type="text/xml"
  if specialHandler is not None:
      result = specialHandler(req,e)
      if result is not None:
          return result
  if e.exception is None:
      data=e.getRaw()
      t=time.ctime(e.time)
      req.write('<?xml version="1.0" encoding="ISO-8859-1" ?>'+"<event><name>%s</name><time>%s</time>" % (event,t))
      if data is not None:
          dtext=""
          for c in data:
              dtext = dtext+chr(int(c))
          req.write("<data><bytes>%s</bytes><text>%s</text></data>" % (data.tolist(),dtext))
      req.write("</event>")
      return apache.OK
  else:
      if 'Timeout' in str(e.exception):
          req.content_type="text/plain"
          return apache.HTTP_NO_CONTENT
      else:
          req.exception=True
          req.write('<?xml version="1.0" encoding="ISO-8859-1" ?>'+"\n<exception>%s</exception>" % (e.exception,))
          return apache.HTTP_BAD_REQUEST