WSGI passes its request context into Flask. How do I access it?
Eg, to write to the webserver error log from Flask app that isn't using WSGI, I write to stderr:
sys.stderr.write(str(msg) + "\n")
For this type of logging output, WSGI for Python requires that I use the WSGI request context environ['wsgi.errors'] See the WSGI debugging docs.
How do I do this?
If using mod_wsgi you can just use print(). It will capture and send it to the Apache error logs. If you use a new enough mod_wsgi version and it is done inside of the context of a request, then it will even be associated with logging at Apache level for the request, which means you can tag it in Apache logs, by setting Apache log format, with Apache request ID if necessary so can associate it with any Apache logging for same request.
In general all WSGI servers will capture print() output and send it to the logs. The only exceptions tend to be for WSGI over CGI/FASTCGI/SCGI. So use of wsgi.errors is not specifically needed and it is actually rare for code to even use it.
Access the WSGI request context via request.environ
Logging to the webserver error log for both WSGI and non-WSGI configs:
def log(msg):
out_stream = sys.stderr
# See http://modwsgi.readthedocs.io/en/develop/user-guides/debugging-techniques.html
if 'wsgi.errors' in request.environ: out_stream = request.environ['wsgi.errors']
out_stream.write(str(msg) + "\n")
Related
I've uwsgi 2.0.19 on Linux running with the python plugin. I serve http(s) traffic with different applications each for a specific record of my managed domain using such kind of configuration to register them to the front uwsgi servers.
subscribe2 = server=x.x.x.x:4443,key=domain.com,sni_key=/etc/ssl/private/domain.com.key,sni_cert=/etc/ssl/certs/domain.com.crt
subscribe2 = server=x.x.x.x:4443,key=domain.com:443,sni_key=/etc/ssl/private/domain.com.key,sni_cert=/etc/ssl/certs/domain.com.crt
subscribe2 = server=y.y.y.y:4443,key=domain.com,sni_key=/etc/ssl/private/domain.com.key,sni_cert=/etc/ssl/certs/domain.com.crt
subscribe2 = server=y.y.y.y:4443,key=domain.com:443,sni_key=/etc/ssl/private/domain.com.key,sni_cert=/etc/ssl/certs/domain.com.crt
Now when I reach one of the front servers to access a not-existing host, I received such error (the TCP connexion is closed I assume)
curl: (52) Empty reply from server
I would like to be able to have a default/catchall key for such case, that permits to return an HTTP status 404 as I would do in Apache using the _default_ vhost. is it possible.
In order to implement this, you need to define a fallback application using the http-subscription-fallback-key on the front uwsgi server
http-subscription-fallback-key=default
default is a standard application registered on the frontal uwsgi like any other application
subscribe2 = server=x.x.x.x:4443,key=default
subscribe2 = server=x.x.x.x:4443,key=default:80
The API for Python's wsgiref module precludes hop-by-hop headers (as defined in RFC 2616).
I'm unclear on how to get the server to terminate a connection after a response (since there doesn't seem to be a way to add Connection: close).
This problem comes up in testing small WSGI apps and Bottle micro-services. Calls from curl get blocked by open connections from a browser. I have to click a browser refresh to terminate the connection so that the pending curl request can be answers.
Obviously, this should be a server side decision (terminate connection after a response) rather than client-side. I'm unclear how to implement this.
This is really predicated on your WSGI server you are hosting your framework via. The best solution with bottle is to run it through gevent.
botapp = bottle.app()
for Route in (mainappRoute,): #handle multiple files containing routes
botapp.merge(Route)
botapp = SessionMiddleware(botapp, beakerconfig) #in case you are using beaker sessions
botapp = WhiteNoise(botapp) #in case you want whitenoise to handle static files
botapp.add_files(staticfolder, prefix='static/') #add static route to whitenoise
server = WSGIServer(("0.0.0.0", int(80)), botapp) #gevent async web server
def shutdown():
print('Shutting down ...')
server.stop(timeout=60)
exit(signal.SIGTERM)
gevent.signal(signal.SIGTERM, shutdown)
gevent.signal(signal.SIGINT, shutdown) #CTRL C
server.serve_forever() #spawn the server
You can purge the whitenoise and bottle configs if they aren't necessary, I kept them there as an example, and a suggestion that you use them if this is outward facing.
This is purely asynchronous on every connection.
I'm working on a scientific experiment where about two dozen test persons play a turn-based game with/against each other. Right now, it's a Python web app with a WSGI interface. I'd like to augment the usability with websockets: When all players have finished their turns, I'd like to notify all clients to update their status. Right now, everyone has to either wait for the turn timeout, or continually reload and wait for the "turn is still in progress" error message not to appear again (busy waiting, effectively).
I read through multiple websocket libraries' documentation and I understand how websockets work, but I'm not sure about the architecture for mixing WSGI and websockets: Can I have a websockets and a WSGI server in the same process (and if so, how, using really any websockets library) and just call my_websocket.send_message() from a WSGI handler, or should I have a separate websockets server and do some IPC? Or should I not mix them at all?
edit, 6 months later: I ended up starting a separate websockets server process (using Autobahn), instead of integrating it with the WSGI server. The reason was that it's much easier and cleaner to separate the two of them, and talking to the websockets server from the WSGI process (server to server communication) was straight forward and worked on the first attempt using websocket-client.
Here is an example that does what you want:
https://github.com/tavendo/AutobahnPython/tree/master/examples/twisted/websocket/echo_wsgi
It runs a WSGI web app (Flask-based in this case, but can be anything WSGI conforming) plus a WebSocket server under 1 server and 1 port.
You can send WS messages from within Web handlers. Autobahn also provides PubSub on top of WebSocket, which greatly simplifies the sending of notifications (via WampServerProtocol.dispatch) like in your case.
http://autobahn.ws/python
Disclosure: I am author of Autobahn and work for Tavendo.
but I'm not sure about the architecture for mixing WSGI and websockets
I made it
use WSocket
Simple WSGI HTTP + Websocket Server, Framework, Middleware And App.
Includes
Server(WSGI) included - works with any WSGI framework
Middleware - adds Websocket support for any WSGI framework
Framework - simple Websocket WSGI web application framework
App - Event based app for Websocket communication
When external server used, some clients like Firefox requires http 1.1 Server. for Middleware, Framework, App
Handler - adds Websocket support to wsgiref(python builtin WSGI server)
Client -Coming soon...
Common Features
only single file less than 1000 lines
websocket sub protocol supported
websocket message compression supported (works if client asks)
receive and send pong and ping messages(with automatic pong sender)
receive and send binary or text messages
works for messages with or without mask
closing messages supported
auto and manual close
example using bottle web framework and WSocket middleware
from bottle import request, Bottle
from wsocket import WSocketApp, WebSocketError, logger, run
from time import sleep
logger.setLevel(10) # for debugging
bottle = Bottle()
app = WSocketApp(bottle)
# app = WSocketApp(bottle, "WAMP")
#bottle.route("/")
def handle_websocket():
wsock = request.environ.get("wsgi.websocket")
if not wsock:
return "Hello World!"
while True:
try:
message = wsock.receive()
if message != None:
print("participator : " + message)
wsock.send("you : "+message)
sleep(2)
wsock.send("you : "+message)
except WebSocketError:
break
run(app)
I have a python script that is looging to syslog without an issue. On the same box I have a python script running via apache and WSGI and I can not get it to log to syslog. The logging configuration is almost identical and here is the section from the WSGI program.
formatter=logging.Formatter('%(levelname)s:%(message)s')
logger = logging.getLogger('my_log')
logger.setLevel(logging.DEBUG)
handler = logging.handlers.SysLogHandler(address='/dev/log',facility=logging.handlers.SysLogHandler.LOG_LOCAL1)
handler.setLevel(logging.DEBUG)
handler.setFormatter(formatter)
logger.addHandler(handler)
logging.log(level,"%s" % (msg))
Any idea why it wouldn't work from WSGI or how to get this to work properly? Thanks.
Does Apache user have access to '/dev/log'?
Why not send it through to Apache error log and then configure Apache to send output to syslog?
I want a simple python web server for the following use case:
I want to write a simple server that will accept HTTP requests from my application running on Google App Engine.
The server will accept HTTP requests, and then send iphone notifications. (Basically, I need this extra server to account for the lack of socket support in google app engine).
I guess I need the server to be able to maintain this persistent connection with Apple's Push Notification Service. So I'll need to have some sort of thread always open for this. So I need some sort of web server that can accept the request pass it off to the other thread with the persistent connection to APNS.
Maybe multiple processes and one of pythons queuing tools to communicate between them? Accept the HTTP request, then enqueue a message to the other process?
I was wondering what someone with a bit of experience would suggest. I'm starting to think that maybe even writing my own simple server is a good option (http://fragments.turtlemeat.com/pythonwebserver.php).
One option would be the (appropriately named) SimpleHTTPServer, which is part of the Python standard library. Another, more flexible but more complicated option would be to write your server in Twisted.
I've been writing simple http servers using gevent and bottle -- an example:
#!/usr/bin/env python
import gevent.monkey
gevent.monkey.patch_all()
import bottle
bottle.debug(True)
import gevent.wsgi
from bottle import route, run, request, response, static_file, abort
#route('/echo')
def echo():
s = request.GET.get('s', 'o hai')
return '<html><head><title>echo server</title></head><body>%s</body></html>\r\n' % (s)
#route('/static/:filename')
def send_static(filename):
root = os.getcwd() + '/static'
return static_file(filename, root=root)
if __name__ == '__main__':
app = bottle.app()
wsgi_server = gevent.wsgi.WSGIServer(('0.0.0.0', 8000), app)
print 'Starting wsgi search on port 8000'
wsgi_server.serve_forever()
So you could write a simple server that sticks a job into a Queue (see gevent.queue) and have another worker greenlet that handles reading requests from the queue and processing them...