"""A WSGI middleware that run the application in a green thread.
THIS SOFTWARE IS UNDER MIT LICENSE.
Copyright (c) 2010 Manlio Perillo (manlio.perillo@gmail.com)
"""
import sys
from greenlet import getcurrent, greenlet
from mako.template import Template
class GState(tuple):
pass
GCONTINUE = 0
GSUSPEND = 1
class middleware(object):
"""A middleware that use greenlet to provide non linear control flow.
"""
def __init__(self, application):
self.app = application
def __call__(self, environ, start_response):
def _start_response(status, headers):
start_response(status, headers)
return self.write
# Initialize greenlet and state
gp = greenlet(self.app)
self.in_app_iter = False
r = gp.switch(environ, _start_response)
while isinstance(r, GState):
buf, status = r
if status == GSUSPEND:
# TODO: async WSGI extension
# environ['wsgiorg.suspend']()
# TODO: store environ as a per green thread state
# gp.environ = environ
pass
yield buf
r = gp.switch()
# The application returned the app_iter object
self.in_app_iter = True
for buf in r:
yield buf
def write(self, buf):
"""WSGI "safe" write callable.
"""
gp = getcurrent()
if self.in_app_iter:
exc = ValueError(
'write callable called from application iterator')
gp.throw(exc)
else:
gp.parent.switch(GState((buf, GCONTINUE)))
def flush(ctx):
"""A Mako function that flush the current buffer and return data
to the caller thread.
"""
gp = getcurrent()
body = ctx._buffer_stack[0].getvalue()
# TODO: get encoding to use from WSGI environ, stored in green
# thread instance
buf = body.encode('us-ascii')
# XXX assume FastEncodingBuffer is used
ctx._buffer_stack[0].data[:] = []
gp.parent.switch(GState((buf, GCONTINUE)))
return ''
@middleware
def application(environ, start_response):
"""A sample WSGI application that use Mako.
"""
headers = [('Content-Type', 'text/html')]
write = start_response('200 OK', headers)
write('some data from write callable\n')
buf = tmpl.render_unicode(body='Body')
return [buf]
tmpl = Template("""
<%namespace name="greenlet" module="__main__" />
Mako example
Header
${greenlet.flush()}
## TODO: async subrequest
${body}
${greenlet.flush()}
Footer
""")
if __name__ == '__main__':
def start_response(status, headers):
def write(buf):
raise NotImplementedError
print 'status:', status
print 'headers', headers
return write
environ = {}
r = application(environ, start_response)
for i, buf in enumerate(r):
print 'chunk #%d' % i
sys.stdout.write(buf)