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# -*- coding: utf-8 -*-
.. versionadded:: 0.5
This module provides a middleware that performs sanity checks of the WSGI
application. It checks that :pep:`333` is properly implemented and warns
on some common HTTP errors such as non-empty responses for 304 status
This module provides a middleware, the :class:`LintMiddleware`. Wrap your
application with it and it will warn about common problems with WSGI and
HTTP while your application is running.
It's strongly recommended to use it during development.
:copyright: (c) 2014 by the Werkzeug Team, see AUTHORS for more details.
:license: BSD, see LICENSE for more details.
from urlparse import urlparse
from warnings import warn
from werkzeug.datastructures import Headers
from werkzeug.http import is_entity_header
from werkzeug.wsgi import FileWrapper
from werkzeug._compat import string_types
class WSGIWarning(Warning):
"""Warning class for WSGI warnings."""
class HTTPWarning(Warning):
"""Warning class for HTTP warnings."""
def check_string(context, obj, stacklevel=3):
if type(obj) is not str:
warn(WSGIWarning('%s requires bytestrings, got %s' %
(context, obj.__class__.__name__)))
class InputStream(object):
def __init__(self, stream):
self._stream = stream
def read(self, *args):
if len(args) == 0:
warn(WSGIWarning('wsgi does not guarantee an EOF marker on the '
'input stream, thus making calls to '
' unsafe. Conforming servers '
'may never return from this call.'),
elif len(args) != 1:
warn(WSGIWarning('too many parameters passed to'),
def readline(self, *args):
if len(args) == 0:
warn(WSGIWarning('Calls to wsgi.input.readline() without arguments'
' are unsafe. Use instead.'),
elif len(args) == 1:
warn(WSGIWarning('wsgi.input.readline() was called with a size hint. '
'WSGI does not support this, although it\'s available '
'on all major servers.'),
raise TypeError('too many arguments passed to wsgi.input.readline()')
return self._stream.readline(*args)
def __iter__(self):
return iter(self._stream)
except TypeError:
warn(WSGIWarning('wsgi.input is not iterable.'), stacklevel=2)
return iter(())
def close(self):
warn(WSGIWarning('application closed the input stream!'),
class ErrorStream(object):
def __init__(self, stream):
self._stream = stream
def write(self, s):
check_string('wsgi.error.write()', s)
def flush(self):
def writelines(self, seq):
for line in seq:
def close(self):
warn(WSGIWarning('application closed the error stream!'),
class GuardedWrite(object):
def __init__(self, write, chunks):
self._write = write
self._chunks = chunks
def __call__(self, s):
check_string('write()', s)
class GuardedIterator(object):
def __init__(self, iterator, headers_set, chunks):
self._iterator = iterator
self._next = iter(iterator).next
self.closed = False
self.headers_set = headers_set
self.chunks = chunks
def __iter__(self):
return self
def next(self):
if self.closed:
warn(WSGIWarning('iterated over closed app_iter'),
rv = self._next()
if not self.headers_set:
warn(WSGIWarning('Application returned before it '
'started the response'), stacklevel=2)
check_string('application iterator items', rv)
return rv
def close(self):
self.closed = True
if hasattr(self._iterator, 'close'):
if self.headers_set:
status_code, headers = self.headers_set
bytes_sent = sum(self.chunks)
content_length = headers.get('content-length', type=int)
if status_code == 304:
for key, value in headers:
key = key.lower()
if key not in ('expires', 'content-location') and \
warn(HTTPWarning('entity header %r found in 304 '
'response' % key))
if bytes_sent:
warn(HTTPWarning('304 responses must not have a body'))
elif 100 <= status_code < 200 or status_code == 204:
if content_length != 0:
warn(HTTPWarning('%r responses must have an empty '
'content length') % status_code)
if bytes_sent:
warn(HTTPWarning('%r responses must not have a body' %
elif content_length is not None and content_length != bytes_sent:
warn(WSGIWarning('Content-Length and the number of bytes '
'sent to the client do not match.'))
def __del__(self):
if not self.closed:
warn(WSGIWarning('Iterator was garbage collected before '
'it was closed.'))
except Exception:
class LintMiddleware(object):
"""This middleware wraps an application and warns on common errors.
Among other thing it currently checks for the following problems:
- invalid status codes
- non-bytestrings sent to the WSGI server
- strings returned from the WSGI application
- non-empty conditional responses
- unquoted etags
- relative URLs in the Location header
- unsafe calls to wsgi.input
- unclosed iterators
Detected errors are emitted using the standard Python :mod:`warnings`
system and usually end up on :data:`stderr`.
from werkzeug.contrib.lint import LintMiddleware
app = LintMiddleware(app)
:param app: the application to wrap
def __init__(self, app): = app
def check_environ(self, environ):
if type(environ) is not dict:
warn(WSGIWarning('WSGI environment is not a standard python dict.'),
'wsgi.version', 'wsgi.input', 'wsgi.errors',
'wsgi.multithread', 'wsgi.multiprocess',
if key not in environ:
warn(WSGIWarning('required environment key %r not found'
% key), stacklevel=3)
if environ['wsgi.version'] != (1, 0):
warn(WSGIWarning('environ is not a WSGI 1.0 environ'),
script_name = environ.get('SCRIPT_NAME', '')
if script_name and script_name[:1] != '/':
warn(WSGIWarning('SCRIPT_NAME does not start with a slash: %r'
% script_name), stacklevel=3)
path_info = environ.get('PATH_INFO', '')
if path_info[:1] != '/':
warn(WSGIWarning('PATH_INFO does not start with a slash: %r'
% path_info), stacklevel=3)
def check_start_response(self, status, headers, exc_info):
check_string('status', status)
status_code = status.split(None, 1)[0]
if len(status_code) != 3 or not status_code.isdigit():
warn(WSGIWarning('Status code must be three digits'), stacklevel=3)
if len(status) < 4 or status[3] != ' ':
warn(WSGIWarning('Invalid value for status %r. Valid '
'status strings are three digits, a space '
'and a status explanation'), stacklevel=3)
status_code = int(status_code)
if status_code < 100:
warn(WSGIWarning('status code < 100 detected'), stacklevel=3)
if type(headers) is not list:
warn(WSGIWarning('header list is not a list'), stacklevel=3)
for item in headers:
if type(item) is not tuple or len(item) != 2:
warn(WSGIWarning('Headers must tuple 2-item tuples'),
name, value = item
if type(name) is not str or type(value) is not str:
warn(WSGIWarning('header items must be strings'),
if name.lower() == 'status':
warn(WSGIWarning('The status header is not supported due to '
'conflicts with the CGI spec.'),
if exc_info is not None and not isinstance(exc_info, tuple):
warn(WSGIWarning('invalid value for exc_info'), stacklevel=3)
headers = Headers(headers)
return status_code, headers
def check_headers(self, headers):
etag = headers.get('etag')
if etag is not None:
if etag.startswith(('W/', 'w/')):
if etag.startswith('w/'):
warn(HTTPWarning('weak etag indicator should be upcase.'),
etag = etag[2:]
if not (etag[:1] == etag[-1:] == '"'):
warn(HTTPWarning('unquoted etag emitted.'), stacklevel=4)
location = headers.get('location')
if location is not None:
if not urlparse(location).netloc:
warn(HTTPWarning('absolute URLs required for location header'),
def check_iterator(self, app_iter):
if isinstance(app_iter, string_types):
warn(WSGIWarning('application returned string. Response will '
'send character for character to the client '
'which will kill the performance. Return a '
'list or iterable instead.'), stacklevel=3)
def __call__(self, *args, **kwargs):
if len(args) != 2:
warn(WSGIWarning('Two arguments to WSGI app required'), stacklevel=2)
if kwargs:
warn(WSGIWarning('No keyword arguments to WSGI app allowed'),
environ, start_response = args
environ['wsgi.input'] = InputStream(environ['wsgi.input'])
environ['wsgi.errors'] = ErrorStream(environ['wsgi.errors'])
# hook our own file wrapper in so that applications will always
# iterate to the end and we can check the content length
environ['wsgi.file_wrapper'] = FileWrapper
headers_set = []
chunks = []
def checking_start_response(*args, **kwargs):
if len(args) not in (2, 3):
warn(WSGIWarning('Invalid number of arguments: %s, expected '
'2 or 3' % len(args), stacklevel=2))
if kwargs:
warn(WSGIWarning('no keyword arguments allowed.'))
status, headers = args[:2]
if len(args) == 3:
exc_info = args[2]
exc_info = None
headers_set[:] = self.check_start_response(status, headers,
return GuardedWrite(start_response(status, headers, exc_info),
app_iter =, checking_start_response)
return GuardedIterator(app_iter, headers_set, chunks)
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