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# (c) 2005 Ian Bicking and contributors; written for Paste (
# Licensed under the MIT license:
# Also licenced under the Apache License, 2.0:
# Licensed to PSF under a Contributor Agreement
Middleware to check for obedience to the WSGI specification.
Some of the things this checks:
* Signature of the application and start_response (including that
keyword arguments are not used).
* Environment checks:
- Environment is a dictionary (and not a subclass).
- That all the required keys are in the environment: REQUEST_METHOD,
SERVER_NAME, SERVER_PORT, wsgi.version, wsgi.input, wsgi.errors,
wsgi.multithread, wsgi.multiprocess, wsgi.run_once
environment (these headers should appear as CONTENT_LENGTH and
- Warns if QUERY_STRING is missing, as the cgi module acts
unpredictably in that case.
- That CGI-style variables (that don't contain a .) have
(non-unicode) string values
- That wsgi.version is a tuple
- That wsgi.url_scheme is 'http' or 'https' (@@: is this too
- Warns if the REQUEST_METHOD is not known (@@: probably too
- That SCRIPT_NAME and PATH_INFO are empty or start with /
- That at least one of SCRIPT_NAME or PATH_INFO are set.
- That CONTENT_LENGTH is a positive integer.
- That SCRIPT_NAME is not '/' (it should be '', and PATH_INFO should
be '/').
- That wsgi.input has the methods read, readline, readlines, and
- That wsgi.errors has the methods flush, write, writelines
* The status is a string, contains a space, starts with an integer,
and that integer is in range (> 100).
* That the headers is a list (not a subclass, not another kind of
* That the items of the headers are tuples of strings.
* That there is no 'status' header (that is used in CGI, but not in
* That the headers don't contain newlines or colons, end in _ or -, or
contain characters codes below 037.
* That Content-Type is given if there is content (CGI often has a
default content type, but WSGI does not).
* That no Content-Type is given when there is no content (@@: is this
too restrictive?)
* That the exc_info argument to start_response is a tuple or None.
* That all calls to the writer are with strings, and no other methods
on the writer are accessed.
* That wsgi.input is used properly:
- .read() is called with zero or one argument
- That it returns a string
- That readline, readlines, and __iter__ return strings
- That .close() is not called
- No other methods are provided
* That wsgi.errors is used properly:
- .write() and .writelines() is called with a string
- That .close() is not called, and no other methods are provided.
* The response iterator:
- That it is not a string (it should be a list of a single string; a
string will work, but perform horribly).
- That .next() returns a string
- That the iterator is not iterated over until start_response has
been called (that can signal either a server or application
- That .close() is called (doesn't raise exception, only prints to
sys.stderr, because we only know it isn't called when the object
is garbage collected).
__all__ = ['validator']
import re
import sys
from types import DictType, StringType, TupleType, ListType
import warnings
header_re = re.compile(r'^[a-zA-Z][a-zA-Z0-9\-_]*$')
bad_header_value_re = re.compile(r'[\000-\037]')
class WSGIWarning(Warning):
Raised in response to WSGI-spec-related warnings
def assert_(cond, *args):
if not cond:
raise AssertionError(*args)
def validator(application):
When applied between a WSGI server and a WSGI application, this
middleware will check for WSGI compliancy on a number of levels.
This middleware does not modify the request or response in any
way, but will raise an AssertionError if anything seems off
(except for a failure to close the application iterator, which
will be printed to stderr -- there's no way to raise an exception
at that point).
def lint_app(*args, **kw):
assert_(len(args) == 2, "Two arguments required")
assert_(not kw, "No keyword arguments allowed")
environ, start_response = args
# We use this to check if the application returns without
# calling start_response:
start_response_started = []
def start_response_wrapper(*args, **kw):
assert_(len(args) == 2 or len(args) == 3, (
"Invalid number of arguments: %s" % (args,)))
assert_(not kw, "No keyword arguments allowed")
status = args[0]
headers = args[1]
if len(args) == 3:
exc_info = args[2]
exc_info = None
check_content_type(status, headers)
return WriteWrapper(start_response(*args))
environ['wsgi.input'] = InputWrapper(environ['wsgi.input'])
environ['wsgi.errors'] = ErrorWrapper(environ['wsgi.errors'])
iterator = application(environ, start_response_wrapper)
assert_(iterator is not None and iterator != False,
"The application must return an iterator, if only an empty list")
return IteratorWrapper(iterator, start_response_started)
return lint_app
class InputWrapper:
def __init__(self, wsgi_input):
self.input = wsgi_input
def read(self, *args):
assert_(len(args) <= 1)
v =*args)
assert_(type(v) is type(""))
return v
def readline(self):
v = self.input.readline()
assert_(type(v) is type(""))
return v
def readlines(self, *args):
assert_(len(args) <= 1)
lines = self.input.readlines(*args)
assert_(type(lines) is type([]))
for line in lines:
assert_(type(line) is type(""))
return lines
def __iter__(self):
while 1:
line = self.readline()
if not line:
yield line
def close(self):
assert_(0, "input.close() must not be called")
class ErrorWrapper:
def __init__(self, wsgi_errors):
self.errors = wsgi_errors
def write(self, s):
assert_(type(s) is type(""))
def flush(self):
def writelines(self, seq):
for line in seq:
def close(self):
assert_(0, "errors.close() must not be called")
class WriteWrapper:
def __init__(self, wsgi_writer):
self.writer = wsgi_writer
def __call__(self, s):
assert_(type(s) is type(""))
class PartialIteratorWrapper:
def __init__(self, wsgi_iterator):
self.iterator = wsgi_iterator
def __iter__(self):
# We want to make sure __iter__ is called
return IteratorWrapper(self.iterator, None)
class IteratorWrapper:
def __init__(self, wsgi_iterator, check_start_response):
self.original_iterator = wsgi_iterator
self.iterator = iter(wsgi_iterator)
self.closed = False
self.check_start_response = check_start_response
def __iter__(self):
return self
def next(self):
assert_(not self.closed,
"Iterator read after closed")
v =
if self.check_start_response is not None:
"The application returns and we started iterating over its body, but start_response has not yet been called")
self.check_start_response = None
return v
def close(self):
self.closed = True
if hasattr(self.original_iterator, 'close'):
def __del__(self):
if not self.closed:
"Iterator garbage collected without being closed")
"Iterator garbage collected without being closed")
def check_environ(environ):
assert_(type(environ) is DictType,
"Environment is not of the right type: %r (environment: %r)"
% (type(environ), environ))
'wsgi.version', 'wsgi.input', 'wsgi.errors',
'wsgi.multithread', 'wsgi.multiprocess',
assert_(key in environ,
"Environment missing required key: %r" % (key,))
assert_(key not in environ,
"Environment should not have the key: %s "
"(use %s instead)" % (key, key[5:]))
if 'QUERY_STRING' not in environ:
'QUERY_STRING is not in the WSGI environment; the cgi '
'module will use sys.argv when this variable is missing, '
'so application errors are more likely',
for key in environ.keys():
if '.' in key:
# Extension, we don't care about its type
assert_(type(environ[key]) is StringType,
"Environmental variable %s is not a string: %r (value: %r)"
% (key, type(environ[key]), environ[key]))
assert_(type(environ['wsgi.version']) is TupleType,
"wsgi.version should be a tuple (%r)" % (environ['wsgi.version'],))
assert_(environ['wsgi.url_scheme'] in ('http', 'https'),
"wsgi.url_scheme unknown: %r" % environ['wsgi.url_scheme'])
# @@: these need filling out:
if environ['REQUEST_METHOD'] not in (
"Unknown REQUEST_METHOD: %r" % environ['REQUEST_METHOD'],
assert_(not environ.get('SCRIPT_NAME')
or environ['SCRIPT_NAME'].startswith('/'),
"SCRIPT_NAME doesn't start with /: %r" % environ['SCRIPT_NAME'])
assert_(not environ.get('PATH_INFO')
or environ['PATH_INFO'].startswith('/'),
"PATH_INFO doesn't start with /: %r" % environ['PATH_INFO'])
if environ.get('CONTENT_LENGTH'):
assert_(int(environ['CONTENT_LENGTH']) >= 0,
"Invalid CONTENT_LENGTH: %r" % environ['CONTENT_LENGTH'])
if not environ.get('SCRIPT_NAME'):
assert_('PATH_INFO' in environ,
"One of SCRIPT_NAME or PATH_INFO are required (PATH_INFO "
"should at least be '/' if SCRIPT_NAME is empty)")
assert_(environ.get('SCRIPT_NAME') != '/',
"SCRIPT_NAME cannot be '/'; it should instead be '', and "
"PATH_INFO should be '/'")
def check_input(wsgi_input):
for attr in ['read', 'readline', 'readlines', '__iter__']:
assert_(hasattr(wsgi_input, attr),
"wsgi.input (%r) doesn't have the attribute %s"
% (wsgi_input, attr))
def check_errors(wsgi_errors):
for attr in ['flush', 'write', 'writelines']:
assert_(hasattr(wsgi_errors, attr),
"wsgi.errors (%r) doesn't have the attribute %s"
% (wsgi_errors, attr))
def check_status(status):
assert_(type(status) is StringType,
"Status must be a string (not %r)" % status)
# Implicitly check that we can turn it into an integer:
status_code = status.split(None, 1)[0]
assert_(len(status_code) == 3,
"Status codes must be three characters: %r" % status_code)
status_int = int(status_code)
assert_(status_int >= 100, "Status code is invalid: %r" % status_int)
if len(status) < 4 or status[3] != ' ':
"The status string (%r) should be a three-digit integer "
"followed by a single space and a status explanation"
% status, WSGIWarning)
def check_headers(headers):
assert_(type(headers) is ListType,
"Headers (%r) must be of type list: %r"
% (headers, type(headers)))
header_names = {}
for item in headers:
assert_(type(item) is TupleType,
"Individual headers (%r) must be of type tuple: %r"
% (item, type(item)))
assert_(len(item) == 2)
name, value = item
assert_(name.lower() != 'status',
"The Status header cannot be used; it conflicts with CGI "
"script, and HTTP status is not given through headers "
"(value: %r)." % value)
header_names[name.lower()] = None
assert_('\n' not in name and ':' not in name,
"Header names may not contain ':' or '\\n': %r" % name)
assert_(, "Bad header name: %r" % name)
assert_(not name.endswith('-') and not name.endswith('_'),
"Names may not end in '-' or '_': %r" % name)
assert_(0, "Bad header value: %r (bad char: %r)"
% (value,
def check_content_type(status, headers):
code = int(status.split(None, 1)[0])
# @@: need one more person to verify this interpretation of RFC 2616
NO_MESSAGE_BODY = (204, 304)
for name, value in headers:
if name.lower() == 'content-type':
if code not in NO_MESSAGE_BODY:
assert_(0, ("Content-Type header found in a %s response, "
"which must not return content.") % code)
if code not in NO_MESSAGE_BODY:
assert_(0, "No Content-Type header found in headers (%s)" % headers)
def check_exc_info(exc_info):
assert_(exc_info is None or type(exc_info) is type(()),
"exc_info (%r) is not a tuple: %r" % (exc_info, type(exc_info)))
# More exc_info checks?
def check_iterator(iterator):
# Technically a string is legal, which is why it's a really bad
# idea, because it may cause the response to be returned
# character-by-character
assert_(not isinstance(iterator, str),
"You should not return a string as your application iterator, "
"instead return a single-item list containing that string.")