1 # (c) 2005 Ian Bicking and contributors; written for Paste (http://pythonpaste.org)
2 # Licensed under the MIT license: https://opensource.org/licenses/mit-license.php
3 # Also licenced under the Apache License, 2.0: https://opensource.org/licenses/apache2.0.php
4 # Licensed to PSF under a Contributor Agreement
5 """
6 Middleware to check for obedience to the WSGI specification.
7
8 Some of the things this checks:
9
10 * Signature of the application and start_response (including that
11 keyword arguments are not used).
12
13 * Environment checks:
14
15 - Environment is a dictionary (and not a subclass).
16
17 - That all the required keys are in the environment: REQUEST_METHOD,
18 SERVER_NAME, SERVER_PORT, wsgi.version, wsgi.input, wsgi.errors,
19 wsgi.multithread, wsgi.multiprocess, wsgi.run_once
20
21 - That HTTP_CONTENT_TYPE and HTTP_CONTENT_LENGTH are not in the
22 environment (these headers should appear as CONTENT_LENGTH and
23 CONTENT_TYPE).
24
25 - Warns if QUERY_STRING is missing, as the cgi module acts
26 unpredictably in that case.
27
28 - That CGI-style variables (that don't contain a .) have
29 (non-unicode) string values
30
31 - That wsgi.version is a tuple
32
33 - That wsgi.url_scheme is 'http' or 'https' (@@: is this too
34 restrictive?)
35
36 - Warns if the REQUEST_METHOD is not known (@@: probably too
37 restrictive).
38
39 - That SCRIPT_NAME and PATH_INFO are empty or start with /
40
41 - That at least one of SCRIPT_NAME or PATH_INFO are set.
42
43 - That CONTENT_LENGTH is a positive integer.
44
45 - That SCRIPT_NAME is not '/' (it should be '', and PATH_INFO should
46 be '/').
47
48 - That wsgi.input has the methods read, readline, readlines, and
49 __iter__
50
51 - That wsgi.errors has the methods flush, write, writelines
52
53 * The status is a string, contains a space, starts with an integer,
54 and that integer is in range (> 100).
55
56 * That the headers is a list (not a subclass, not another kind of
57 sequence).
58
59 * That the items of the headers are tuples of strings.
60
61 * That there is no 'status' header (that is used in CGI, but not in
62 WSGI).
63
64 * That the headers don't contain newlines or colons, end in _ or -, or
65 contain characters codes below 037.
66
67 * That Content-Type is given if there is content (CGI often has a
68 default content type, but WSGI does not).
69
70 * That no Content-Type is given when there is no content (@@: is this
71 too restrictive?)
72
73 * That the exc_info argument to start_response is a tuple or None.
74
75 * That all calls to the writer are with strings, and no other methods
76 on the writer are accessed.
77
78 * That wsgi.input is used properly:
79
80 - .read() is called with exactly one argument
81
82 - That it returns a string
83
84 - That readline, readlines, and __iter__ return strings
85
86 - That .close() is not called
87
88 - No other methods are provided
89
90 * That wsgi.errors is used properly:
91
92 - .write() and .writelines() is called with a string
93
94 - That .close() is not called, and no other methods are provided.
95
96 * The response iterator:
97
98 - That it is not a string (it should be a list of a single string; a
99 string will work, but perform horribly).
100
101 - That .__next__() returns a string
102
103 - That the iterator is not iterated over until start_response has
104 been called (that can signal either a server or application
105 error).
106
107 - That .close() is called (doesn't raise exception, only prints to
108 sys.stderr, because we only know it isn't called when the object
109 is garbage collected).
110 """
111 __all__ = ['validator']
112
113
114 import re
115 import sys
116 import warnings
117
118 header_re = re.compile(r'^[a-zA-Z][a-zA-Z0-9\-_]*$')
119 bad_header_value_re = re.compile(r'[\000-\037]')
120
121 class ESC[4;38;5;81mWSGIWarning(ESC[4;38;5;149mWarning):
122 """
123 Raised in response to WSGI-spec-related warnings
124 """
125
126 def assert_(cond, *args):
127 if not cond:
128 raise AssertionError(*args)
129
130 def check_string_type(value, title):
131 if type (value) is str:
132 return value
133 raise AssertionError(
134 "{0} must be of type str (got {1})".format(title, repr(value)))
135
136 def validator(application):
137
138 """
139 When applied between a WSGI server and a WSGI application, this
140 middleware will check for WSGI compliance on a number of levels.
141 This middleware does not modify the request or response in any
142 way, but will raise an AssertionError if anything seems off
143 (except for a failure to close the application iterator, which
144 will be printed to stderr -- there's no way to raise an exception
145 at that point).
146 """
147
148 def lint_app(*args, **kw):
149 assert_(len(args) == 2, "Two arguments required")
150 assert_(not kw, "No keyword arguments allowed")
151 environ, start_response = args
152
153 check_environ(environ)
154
155 # We use this to check if the application returns without
156 # calling start_response:
157 start_response_started = []
158
159 def start_response_wrapper(*args, **kw):
160 assert_(len(args) == 2 or len(args) == 3, (
161 "Invalid number of arguments: %s" % (args,)))
162 assert_(not kw, "No keyword arguments allowed")
163 status = args[0]
164 headers = args[1]
165 if len(args) == 3:
166 exc_info = args[2]
167 else:
168 exc_info = None
169
170 check_status(status)
171 check_headers(headers)
172 check_content_type(status, headers)
173 check_exc_info(exc_info)
174
175 start_response_started.append(None)
176 return WriteWrapper(start_response(*args))
177
178 environ['wsgi.input'] = InputWrapper(environ['wsgi.input'])
179 environ['wsgi.errors'] = ErrorWrapper(environ['wsgi.errors'])
180
181 iterator = application(environ, start_response_wrapper)
182 assert_(iterator is not None and iterator != False,
183 "The application must return an iterator, if only an empty list")
184
185 check_iterator(iterator)
186
187 return IteratorWrapper(iterator, start_response_started)
188
189 return lint_app
190
191 class ESC[4;38;5;81mInputWrapper:
192
193 def __init__(self, wsgi_input):
194 self.input = wsgi_input
195
196 def read(self, *args):
197 assert_(len(args) == 1)
198 v = self.input.read(*args)
199 assert_(type(v) is bytes)
200 return v
201
202 def readline(self, *args):
203 assert_(len(args) <= 1)
204 v = self.input.readline(*args)
205 assert_(type(v) is bytes)
206 return v
207
208 def readlines(self, *args):
209 assert_(len(args) <= 1)
210 lines = self.input.readlines(*args)
211 assert_(type(lines) is list)
212 for line in lines:
213 assert_(type(line) is bytes)
214 return lines
215
216 def __iter__(self):
217 while line := self.readline():
218 yield line
219
220 def close(self):
221 assert_(0, "input.close() must not be called")
222
223 class ESC[4;38;5;81mErrorWrapper:
224
225 def __init__(self, wsgi_errors):
226 self.errors = wsgi_errors
227
228 def write(self, s):
229 assert_(type(s) is str)
230 self.errors.write(s)
231
232 def flush(self):
233 self.errors.flush()
234
235 def writelines(self, seq):
236 for line in seq:
237 self.write(line)
238
239 def close(self):
240 assert_(0, "errors.close() must not be called")
241
242 class ESC[4;38;5;81mWriteWrapper:
243
244 def __init__(self, wsgi_writer):
245 self.writer = wsgi_writer
246
247 def __call__(self, s):
248 assert_(type(s) is bytes)
249 self.writer(s)
250
251 class ESC[4;38;5;81mPartialIteratorWrapper:
252
253 def __init__(self, wsgi_iterator):
254 self.iterator = wsgi_iterator
255
256 def __iter__(self):
257 # We want to make sure __iter__ is called
258 return IteratorWrapper(self.iterator, None)
259
260 class ESC[4;38;5;81mIteratorWrapper:
261
262 def __init__(self, wsgi_iterator, check_start_response):
263 self.original_iterator = wsgi_iterator
264 self.iterator = iter(wsgi_iterator)
265 self.closed = False
266 self.check_start_response = check_start_response
267
268 def __iter__(self):
269 return self
270
271 def __next__(self):
272 assert_(not self.closed,
273 "Iterator read after closed")
274 v = next(self.iterator)
275 if type(v) is not bytes:
276 assert_(False, "Iterator yielded non-bytestring (%r)" % (v,))
277 if self.check_start_response is not None:
278 assert_(self.check_start_response,
279 "The application returns and we started iterating over its body, but start_response has not yet been called")
280 self.check_start_response = None
281 return v
282
283 def close(self):
284 self.closed = True
285 if hasattr(self.original_iterator, 'close'):
286 self.original_iterator.close()
287
288 def __del__(self):
289 if not self.closed:
290 sys.stderr.write(
291 "Iterator garbage collected without being closed")
292 assert_(self.closed,
293 "Iterator garbage collected without being closed")
294
295 def check_environ(environ):
296 assert_(type(environ) is dict,
297 "Environment is not of the right type: %r (environment: %r)"
298 % (type(environ), environ))
299
300 for key in ['REQUEST_METHOD', 'SERVER_NAME', 'SERVER_PORT',
301 'wsgi.version', 'wsgi.input', 'wsgi.errors',
302 'wsgi.multithread', 'wsgi.multiprocess',
303 'wsgi.run_once']:
304 assert_(key in environ,
305 "Environment missing required key: %r" % (key,))
306
307 for key in ['HTTP_CONTENT_TYPE', 'HTTP_CONTENT_LENGTH']:
308 assert_(key not in environ,
309 "Environment should not have the key: %s "
310 "(use %s instead)" % (key, key[5:]))
311
312 if 'QUERY_STRING' not in environ:
313 warnings.warn(
314 'QUERY_STRING is not in the WSGI environment; the cgi '
315 'module will use sys.argv when this variable is missing, '
316 'so application errors are more likely',
317 WSGIWarning)
318
319 for key in environ.keys():
320 if '.' in key:
321 # Extension, we don't care about its type
322 continue
323 assert_(type(environ[key]) is str,
324 "Environmental variable %s is not a string: %r (value: %r)"
325 % (key, type(environ[key]), environ[key]))
326
327 assert_(type(environ['wsgi.version']) is tuple,
328 "wsgi.version should be a tuple (%r)" % (environ['wsgi.version'],))
329 assert_(environ['wsgi.url_scheme'] in ('http', 'https'),
330 "wsgi.url_scheme unknown: %r" % environ['wsgi.url_scheme'])
331
332 check_input(environ['wsgi.input'])
333 check_errors(environ['wsgi.errors'])
334
335 # @@: these need filling out:
336 if environ['REQUEST_METHOD'] not in (
337 'GET', 'HEAD', 'POST', 'OPTIONS', 'PATCH', 'PUT', 'DELETE', 'TRACE'):
338 warnings.warn(
339 "Unknown REQUEST_METHOD: %r" % environ['REQUEST_METHOD'],
340 WSGIWarning)
341
342 assert_(not environ.get('SCRIPT_NAME')
343 or environ['SCRIPT_NAME'].startswith('/'),
344 "SCRIPT_NAME doesn't start with /: %r" % environ['SCRIPT_NAME'])
345 assert_(not environ.get('PATH_INFO')
346 or environ['PATH_INFO'].startswith('/'),
347 "PATH_INFO doesn't start with /: %r" % environ['PATH_INFO'])
348 if environ.get('CONTENT_LENGTH'):
349 assert_(int(environ['CONTENT_LENGTH']) >= 0,
350 "Invalid CONTENT_LENGTH: %r" % environ['CONTENT_LENGTH'])
351
352 if not environ.get('SCRIPT_NAME'):
353 assert_('PATH_INFO' in environ,
354 "One of SCRIPT_NAME or PATH_INFO are required (PATH_INFO "
355 "should at least be '/' if SCRIPT_NAME is empty)")
356 assert_(environ.get('SCRIPT_NAME') != '/',
357 "SCRIPT_NAME cannot be '/'; it should instead be '', and "
358 "PATH_INFO should be '/'")
359
360 def check_input(wsgi_input):
361 for attr in ['read', 'readline', 'readlines', '__iter__']:
362 assert_(hasattr(wsgi_input, attr),
363 "wsgi.input (%r) doesn't have the attribute %s"
364 % (wsgi_input, attr))
365
366 def check_errors(wsgi_errors):
367 for attr in ['flush', 'write', 'writelines']:
368 assert_(hasattr(wsgi_errors, attr),
369 "wsgi.errors (%r) doesn't have the attribute %s"
370 % (wsgi_errors, attr))
371
372 def check_status(status):
373 status = check_string_type(status, "Status")
374 # Implicitly check that we can turn it into an integer:
375 status_code = status.split(None, 1)[0]
376 assert_(len(status_code) == 3,
377 "Status codes must be three characters: %r" % status_code)
378 status_int = int(status_code)
379 assert_(status_int >= 100, "Status code is invalid: %r" % status_int)
380 if len(status) < 4 or status[3] != ' ':
381 warnings.warn(
382 "The status string (%r) should be a three-digit integer "
383 "followed by a single space and a status explanation"
384 % status, WSGIWarning)
385
386 def check_headers(headers):
387 assert_(type(headers) is list,
388 "Headers (%r) must be of type list: %r"
389 % (headers, type(headers)))
390 for item in headers:
391 assert_(type(item) is tuple,
392 "Individual headers (%r) must be of type tuple: %r"
393 % (item, type(item)))
394 assert_(len(item) == 2)
395 name, value = item
396 name = check_string_type(name, "Header name")
397 value = check_string_type(value, "Header value")
398 assert_(name.lower() != 'status',
399 "The Status header cannot be used; it conflicts with CGI "
400 "script, and HTTP status is not given through headers "
401 "(value: %r)." % value)
402 assert_('\n' not in name and ':' not in name,
403 "Header names may not contain ':' or '\\n': %r" % name)
404 assert_(header_re.search(name), "Bad header name: %r" % name)
405 assert_(not name.endswith('-') and not name.endswith('_'),
406 "Names may not end in '-' or '_': %r" % name)
407 if bad_header_value_re.search(value):
408 assert_(0, "Bad header value: %r (bad char: %r)"
409 % (value, bad_header_value_re.search(value).group(0)))
410
411 def check_content_type(status, headers):
412 status = check_string_type(status, "Status")
413 code = int(status.split(None, 1)[0])
414 # @@: need one more person to verify this interpretation of RFC 2616
415 # http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
416 NO_MESSAGE_BODY = (204, 304)
417 for name, value in headers:
418 name = check_string_type(name, "Header name")
419 if name.lower() == 'content-type':
420 if code not in NO_MESSAGE_BODY:
421 return
422 assert_(0, ("Content-Type header found in a %s response, "
423 "which must not return content.") % code)
424 if code not in NO_MESSAGE_BODY:
425 assert_(0, "No Content-Type header found in headers (%s)" % headers)
426
427 def check_exc_info(exc_info):
428 assert_(exc_info is None or type(exc_info) is tuple,
429 "exc_info (%r) is not a tuple: %r" % (exc_info, type(exc_info)))
430 # More exc_info checks?
431
432 def check_iterator(iterator):
433 # Technically a bytestring is legal, which is why it's a really bad
434 # idea, because it may cause the response to be returned
435 # character-by-character
436 assert_(not isinstance(iterator, (str, bytes)),
437 "You should not return a string as your application iterator, "
438 "instead return a single-item list containing a bytestring.")