Pylons
Latest Version: 0.9.6.2
0001# (c) 2005 Ian Bicking and contributors; written for Paste (http://pythonpaste.org)
0002# Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php
0003
0004"""
0005Cascades through several applications, so long as applications
0006return ``404 Not Found``.
0007"""
0008from paste import httpexceptions
0009from paste.util import converters
0010
0011__all__ = ['Cascade']
0012
0013def make_cascade(loader, global_conf, catch='404', **local_conf):
0014 """
0015 Expects configuration like:
0016
0017 [composit:cascade]
0018 use = egg:Paste#cascade
0019 # all start with 'app' and are sorted alphabetically
0020 app1 = foo
0021 app2 = bar
0022 ...
0023 catch = 404 500 ...
0024 """
0025 catch = map(int, converters.aslist(catch))
0026 apps = []
0027 for name, value in local_conf.items():
0028 if not name.startswith('app'):
0029 raise ValueError(
0030 "Bad configuration key %r (=%r); all configuration keys "
0031 "must start with 'app'"
0032 % (name, value))
0033 app = loader.get_app(value, global_conf=global_conf)
0034 apps.append((name, app))
0035 apps.sort()
0036 apps = [app for name, app in apps]
0037 return Cascade(apps, catch=catch)
0038
0039class Cascade(object):
0040
0041 """
0042 Passed a list of applications, ``Cascade`` will try each of them
0043 in turn. If one returns a status code listed in ``catch`` (by
0044 default just ``404 Not Found``) then the next application is
0045 tried.
0046
0047 If all applications fail, then the last application's failure
0048 response is used.
0049 """
0050
0051 def __init__(self, applications, catch=(404,)):
0052 self.apps = applications
0053 self.catch_codes = {}
0054 self.catch_exceptions = []
0055 for error in catch:
0056 if isinstance(error, str):
0057 error = int(error.split(None, 1)[0])
0058 if isinstance(error, httpexceptions.HTTPException):
0059 exc = error
0060 code = error.code
0061 else:
0062 exc = httpexceptions.get_exception(error)
0063 code = error
0064 self.catch_codes[code] = exc
0065 self.catch_exceptions.append(exc)
0066 self.catch_exceptions = tuple(self.catch_exceptions)
0067
0068 def __call__(self, environ, start_response):
0069 failed = []
0070 def repl_start_response(status, headers, exc_info=None):
0071 code = int(status.split(None, 1)[0])
0072 if code in self.catch_codes:
0073 failed.append(None)
0074 return _consuming_writer
0075 return start_response(status, headers, exc_info)
0076
0077 for app in self.apps[:-1]:
0078 environ_copy = environ.copy()
0079 failed = []
0080 try:
0081 v = app(environ_copy, repl_start_response)
0082 if not failed:
0083 return v
0084 else:
0085 if hasattr(v, 'close'):
0086 # Exhaust the iterator first:
0087 list(v)
0088 # then close:
0089 v.close()
0090 except self.catch_exceptions, e:
0091 pass
0092 return self.apps[-1](environ, start_response)
0093
0094def _consuming_writer(s):
0095 pass