[3] | 1 | # (c) 2005 Ian Bicking and contributors; written for Paste (http://pythonpaste.org) |
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| 2 | # Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php |
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| 3 | |
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| 4 | """ |
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| 5 | Cascades through several applications, so long as applications |
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| 6 | return ``404 Not Found``. |
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| 7 | """ |
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| 8 | from paste import httpexceptions |
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| 9 | from paste.util import converters |
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| 10 | import tempfile |
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| 11 | from cStringIO import StringIO |
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| 12 | |
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| 13 | __all__ = ['Cascade'] |
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| 14 | |
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| 15 | def make_cascade(loader, global_conf, catch='404', **local_conf): |
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| 16 | """ |
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| 17 | Expects configuration like: |
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| 18 | |
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| 19 | [composit:cascade] |
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| 20 | use = egg:Paste#cascade |
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| 21 | # all start with 'app' and are sorted alphabetically |
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| 22 | app1 = foo |
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| 23 | app2 = bar |
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| 24 | ... |
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| 25 | catch = 404 500 ... |
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| 26 | """ |
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| 27 | catch = map(int, converters.aslist(catch)) |
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| 28 | apps = [] |
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| 29 | for name, value in local_conf.items(): |
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| 30 | if not name.startswith('app'): |
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| 31 | raise ValueError( |
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| 32 | "Bad configuration key %r (=%r); all configuration keys " |
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| 33 | "must start with 'app'" |
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| 34 | % (name, value)) |
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| 35 | app = loader.get_app(value, global_conf=global_conf) |
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| 36 | apps.append((name, app)) |
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| 37 | apps.sort() |
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| 38 | apps = [app for name, app in apps] |
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| 39 | return Cascade(apps, catch=catch) |
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| 40 | |
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| 41 | class Cascade(object): |
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| 42 | |
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| 43 | """ |
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| 44 | Passed a list of applications, ``Cascade`` will try each of them |
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| 45 | in turn. If one returns a status code listed in ``catch`` (by |
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| 46 | default just ``404 Not Found``) then the next application is |
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| 47 | tried. |
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| 48 | |
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| 49 | If all applications fail, then the last application's failure |
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| 50 | response is used. |
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| 51 | """ |
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| 52 | |
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| 53 | def __init__(self, applications, catch=(404,)): |
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| 54 | self.apps = applications |
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| 55 | self.catch_codes = {} |
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| 56 | self.catch_exceptions = [] |
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| 57 | for error in catch: |
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| 58 | if isinstance(error, str): |
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| 59 | error = int(error.split(None, 1)[0]) |
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| 60 | if isinstance(error, httpexceptions.HTTPException): |
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| 61 | exc = error |
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| 62 | code = error.code |
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| 63 | else: |
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| 64 | exc = httpexceptions.get_exception(error) |
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| 65 | code = error |
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| 66 | self.catch_codes[code] = exc |
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| 67 | self.catch_exceptions.append(exc) |
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| 68 | self.catch_exceptions = tuple(self.catch_exceptions) |
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| 69 | |
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| 70 | def __call__(self, environ, start_response): |
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| 71 | failed = [] |
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| 72 | def repl_start_response(status, headers, exc_info=None): |
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| 73 | code = int(status.split(None, 1)[0]) |
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| 74 | if code in self.catch_codes: |
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| 75 | failed.append(None) |
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| 76 | return _consuming_writer |
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| 77 | return start_response(status, headers, exc_info) |
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| 78 | |
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| 79 | try: |
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| 80 | length = int(environ.get('CONTENT_LENGTH', 0) or 0) |
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| 81 | except ValueError: |
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| 82 | length = 0 |
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| 83 | if length > 0: |
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| 84 | # We have to copy wsgi.input |
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| 85 | copy_wsgi_input = True |
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| 86 | if length > 4096 or length < 0: |
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| 87 | f = tempfile.TemporaryFile() |
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| 88 | if length < 0: |
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| 89 | f.write(environ['wsgi.input'].read()) |
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| 90 | else: |
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| 91 | copy_len = length |
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| 92 | while copy_len > 0: |
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| 93 | chunk = environ['wsgi.input'].read(min(copy_len, 4096)) |
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| 94 | f.write(chunk) |
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| 95 | copy_len -= len(chunk) |
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| 96 | f.seek(0) |
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| 97 | else: |
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| 98 | f = StringIO(environ['wsgi.input'].read(length)) |
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| 99 | environ['wsgi.input'] = f |
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| 100 | else: |
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| 101 | copy_wsgi_input = False |
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| 102 | for app in self.apps[:-1]: |
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| 103 | environ_copy = environ.copy() |
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| 104 | if copy_wsgi_input: |
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| 105 | environ_copy['wsgi.input'].seek(0) |
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| 106 | failed = [] |
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| 107 | try: |
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| 108 | v = app(environ_copy, repl_start_response) |
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| 109 | if not failed: |
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| 110 | return v |
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| 111 | else: |
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| 112 | if hasattr(v, 'close'): |
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| 113 | # Exhaust the iterator first: |
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| 114 | list(v) |
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| 115 | # then close: |
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| 116 | v.close() |
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| 117 | except self.catch_exceptions, e: |
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| 118 | pass |
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| 119 | if copy_wsgi_input: |
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| 120 | environ['wsgi.input'].seek(0) |
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| 121 | return self.apps[-1](environ, start_response) |
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| 122 | |
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| 123 | def _consuming_writer(s): |
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| 124 | pass |
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