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# (c) 2005 Ian Bicking and contributors; written for Paste (http://pythonpaste.org)
# Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php
"""
Cascades through several applications, so long as applications
return ``404 Not Found``.
"""
import httpexceptions
from paste.deploy import converters
__all__ = ['Cascade']
def make_cascade(loader, global_conf, catch='404', **local_conf):
"""
Expects configuration like:
[composit:cascade]
use = egg:Paste#cascade
# all start with 'app' and are sorted alphabetically
app1 = foo
app2 = bar
...
catch = 404 500 ...
"""
catch = map(int, converters.aslist(catch))
apps = []
for name, value in local_conf.items():
if not name.startswith('app'):
raise ValueError(
"Bad configuration key %r (=%r); all configuration keys "
"must start with 'app'"
% (name, value))
app = loader.get_app(value, global_conf=global_conf)
apps.append((name, app))
apps.sort()
apps = [app for name, app in apps]
return Cascade(apps, catch=catch)
class Cascade(object):
"""
Passed a list of applications, ``Cascade`` will try each of them
in turn. If one returns a status code listed in ``catch`` (by
default just ``404 Not Found``) then the next application is
tried.
If all applications fail, then the last application's failure
response is used.
"""
def __init__(self, applications, catch=(404,)):
self.apps = applications
self.catch_codes = {}
self.catch_exceptions = []
for error in catch:
if isinstance(error, str):
error = int(error.split(None, 1)[0])
if isinstance(error, httpexceptions.HTTPException):
exc = error
code = error.code
else:
exc = httpexceptions.get_exception(error)
code = error
self.catch_codes[code] = exc
self.catch_exceptions.append(exc)
self.catch_exceptions = tuple(self.catch_exceptions)
def __call__(self, environ, start_response):
def repl_start_response(status, headers, exc_info=None):
code = int(status.split(None, 1)[0])
if code in self.catch_codes:
raise self.catch_codes[code]
return start_response(status, headers, exc_info)
for app in self.apps[:-1]:
environ_copy = environ.copy()
try:
return app(environ_copy, repl_start_response)
except self.catch_exceptions:
pass
return self.apps[-1](environ, start_response)
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