1 # (c) 2005 Ian Bicking and contributors; written for Paste (http://pythonpaste.org)

     2 # Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php

     3 # Also licenced under the Apache License, 2.0: http://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 zero or 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 from types import DictType, StringType, TupleType, ListType

   117 import warnings

   118 

   119 header_re = re.compile(r'^[a-zA-Z][a-zA-Z0-9\-_]*$')

   120 bad_header_value_re = re.compile(r'[\000-\037]')

   121 

   122 class WSGIWarning(Warning):

   123     """

   124     Raised in response to WSGI-spec-related warnings

   125     """

   126 

   127 def assert_(cond, *args):

   128     if not cond:

   129         raise AssertionError(*args)

   130 

   131 def validator(application):

   132 

   133     """

   134     When applied between a WSGI server and a WSGI application, this

   135     middleware will check for WSGI compliancy on a number of levels.

   136     This middleware does not modify the request or response in any

   137     way, but will throw an AssertionError if anything seems off

   138     (except for a failure to close the application iterator, which

   139     will be printed to stderr -- there's no way to throw an exception

   140     at that point).

   141     """

   142 

   143     def lint_app(*args, **kw):

   144         assert_(len(args) == 2, "Two arguments required")

   145         assert_(not kw, "No keyword arguments allowed")

   146         environ, start_response = args

   147 

   148         check_environ(environ)

   149 

   150         # We use this to check if the application returns without

   151         # calling start_response:

   152         start_response_started = []

   153 

   154         def start_response_wrapper(*args, **kw):

   155             assert_(len(args) == 2 or len(args) == 3, (

   156                 "Invalid number of arguments: %s" % (args,)))

   157             assert_(not kw, "No keyword arguments allowed")

   158             status = args[0]

   159             headers = args[1]

   160             if len(args) == 3:

   161                 exc_info = args[2]

   162             else:

   163                 exc_info = None

   164 

   165             check_status(status)

   166             check_headers(headers)

   167             check_content_type(status, headers)

   168             check_exc_info(exc_info)

   169 

   170             start_response_started.append(None)

   171             return WriteWrapper(start_response(*args))

   172 

   173         environ['wsgi.input'] = InputWrapper(environ['wsgi.input'])

   174         environ['wsgi.errors'] = ErrorWrapper(environ['wsgi.errors'])

   175 

   176         iterator = application(environ, start_response_wrapper)

   177         assert_(iterator is not None and iterator != False,

   178             "The application must return an iterator, if only an empty list")

   179 

   180         check_iterator(iterator)

   181 

   182         return IteratorWrapper(iterator, start_response_started)

   183 

   184     return lint_app

   185 

   186 class InputWrapper:

   187 

   188     def __init__(self, wsgi_input):

   189         self.input = wsgi_input

   190 

   191     def read(self, *args):

   192         assert_(len(args) <= 1)

   193         v = self.input.read(*args)

   194         assert_(type(v) is type(""))

   195         return v

   196 

   197     def readline(self):

   198         v = self.input.readline()

   199         assert_(type(v) is type(""))

   200         return v

   201 

   202     def readlines(self, *args):

   203         assert_(len(args) <= 1)

   204         lines = self.input.readlines(*args)

   205         assert_(type(lines) is type([]))

   206         for line in lines:

   207             assert_(type(line) is type(""))

   208         return lines

   209 

   210     def __iter__(self):

   211         while 1:

   212             line = self.readline()

   213             if not line:

   214                 return

   215             yield line

   216 

   217     def close(self):

   218         assert_(0, "input.close() must not be called")

   219 

   220 class ErrorWrapper:

   221 

   222     def __init__(self, wsgi_errors):

   223         self.errors = wsgi_errors

   224 

   225     def write(self, s):

   226         assert_(type(s) is type(""))

   227         self.errors.write(s)

   228 

   229     def flush(self):

   230         self.errors.flush()

   231 

   232     def writelines(self, seq):

   233         for line in seq:

   234             self.write(line)

   235 

   236     def close(self):

   237         assert_(0, "errors.close() must not be called")

   238 

   239 class WriteWrapper:

   240 

   241     def __init__(self, wsgi_writer):

   242         self.writer = wsgi_writer

   243 

   244     def __call__(self, s):

   245         assert_(type(s) is type(""))

   246         self.writer(s)

   247 

   248 class PartialIteratorWrapper:

   249 

   250     def __init__(self, wsgi_iterator):

   251         self.iterator = wsgi_iterator

   252 

   253     def __iter__(self):

   254         # We want to make sure __iter__ is called

   255         return IteratorWrapper(self.iterator, None)

   256 

   257 class IteratorWrapper:

   258 

   259     def __init__(self, wsgi_iterator, check_start_response):

   260         self.original_iterator = wsgi_iterator

   261         self.iterator = iter(wsgi_iterator)

   262         self.closed = False

   263         self.check_start_response = check_start_response

   264 

   265     def __iter__(self):

   266         return self

   267 

   268     def next(self):

   269         assert_(not self.closed,

   270             "Iterator read after closed")

   271         v = self.iterator.next()

   272         if self.check_start_response is not None:

   273             assert_(self.check_start_response,

   274                 "The application returns and we started iterating over its body, but start_response has not yet been called")

   275             self.check_start_response = None

   276         return v

   277 

   278     def close(self):

   279         self.closed = True

   280         if hasattr(self.original_iterator, 'close'):

   281             self.original_iterator.close()

   282 

   283     def __del__(self):

   284         if not self.closed:

   285             sys.stderr.write(

   286                 "Iterator garbage collected without being closed")

   287         assert_(self.closed,

   288             "Iterator garbage collected without being closed")

   289 

   290 def check_environ(environ):

   291     assert_(type(environ) is DictType,

   292         "Environment is not of the right type: %r (environment: %r)"

   293         % (type(environ), environ))

   294 

   295     for key in ['REQUEST_METHOD', 'SERVER_NAME', 'SERVER_PORT',

   296                 'wsgi.version', 'wsgi.input', 'wsgi.errors',

   297                 'wsgi.multithread', 'wsgi.multiprocess',

   298                 'wsgi.run_once']:

   299         assert_(key in environ,

   300             "Environment missing required key: %r" % (key,))

   301 

   302     for key in ['HTTP_CONTENT_TYPE', 'HTTP_CONTENT_LENGTH']:

   303         assert_(key not in environ,

   304             "Environment should not have the key: %s "

   305             "(use %s instead)" % (key, key[5:]))

   306 

   307     if 'QUERY_STRING' not in environ:

   308         warnings.warn(

   309             'QUERY_STRING is not in the WSGI environment; the cgi '

   310             'module will use sys.argv when this variable is missing, '

   311             'so application errors are more likely',

   312             WSGIWarning)

   313 

   314     for key in environ.keys():

   315         if '.' in key:

   316             # Extension, we don't care about its type

   317             continue

   318         assert_(type(environ[key]) is StringType,

   319             "Environmental variable %s is not a string: %r (value: %r)"

   320             % (key, type(environ[key]), environ[key]))

   321 

   322     assert_(type(environ['wsgi.version']) is TupleType,

   323         "wsgi.version should be a tuple (%r)" % (environ['wsgi.version'],))

   324     assert_(environ['wsgi.url_scheme'] in ('http', 'https'),

   325         "wsgi.url_scheme unknown: %r" % environ['wsgi.url_scheme'])

   326 

   327     check_input(environ['wsgi.input'])

   328     check_errors(environ['wsgi.errors'])

   329 

   330     # @@: these need filling out:

   331     if environ['REQUEST_METHOD'] not in (

   332         'GET', 'HEAD', 'POST', 'OPTIONS','PUT','DELETE','TRACE'):

   333         warnings.warn(

   334             "Unknown REQUEST_METHOD: %r" % environ['REQUEST_METHOD'],

   335             WSGIWarning)

   336 

   337     assert_(not environ.get('SCRIPT_NAME')

   338             or environ['SCRIPT_NAME'].startswith('/'),

   339         "SCRIPT_NAME doesn't start with /: %r" % environ['SCRIPT_NAME'])

   340     assert_(not environ.get('PATH_INFO')

   341             or environ['PATH_INFO'].startswith('/'),

   342         "PATH_INFO doesn't start with /: %r" % environ['PATH_INFO'])

   343     if environ.get('CONTENT_LENGTH'):

   344         assert_(int(environ['CONTENT_LENGTH']) >= 0,

   345             "Invalid CONTENT_LENGTH: %r" % environ['CONTENT_LENGTH'])

   346 

   347     if not environ.get('SCRIPT_NAME'):

   348         assert_(environ.has_key('PATH_INFO'),

   349             "One of SCRIPT_NAME or PATH_INFO are required (PATH_INFO "

   350             "should at least be '/' if SCRIPT_NAME is empty)")

   351     assert_(environ.get('SCRIPT_NAME') != '/',

   352         "SCRIPT_NAME cannot be '/'; it should instead be '', and "

   353         "PATH_INFO should be '/'")

   354 

   355 def check_input(wsgi_input):

   356     for attr in ['read', 'readline', 'readlines', '__iter__']:

   357         assert_(hasattr(wsgi_input, attr),

   358             "wsgi.input (%r) doesn't have the attribute %s"

   359             % (wsgi_input, attr))

   360 

   361 def check_errors(wsgi_errors):

   362     for attr in ['flush', 'write', 'writelines']:

   363         assert_(hasattr(wsgi_errors, attr),

   364             "wsgi.errors (%r) doesn't have the attribute %s"

   365             % (wsgi_errors, attr))

   366 

   367 def check_status(status):

   368     assert_(type(status) is StringType,

   369         "Status must be a string (not %r)" % status)

   370     # Implicitly check that we can turn it into an integer:

   371     status_code = status.split(None, 1)[0]

   372     assert_(len(status_code) == 3,

   373         "Status codes must be three characters: %r" % status_code)

   374     status_int = int(status_code)

   375     assert_(status_int >= 100, "Status code is invalid: %r" % status_int)

   376     if len(status) < 4 or status[3] != ' ':

   377         warnings.warn(

   378             "The status string (%r) should be a three-digit integer "

   379             "followed by a single space and a status explanation"

   380             % status, WSGIWarning)

   381 

   382 def check_headers(headers):

   383     assert_(type(headers) is ListType,

   384         "Headers (%r) must be of type list: %r"

   385         % (headers, type(headers)))

   386     header_names = {}

   387     for item in headers:

   388         assert_(type(item) is TupleType,

   389             "Individual headers (%r) must be of type tuple: %r"

   390             % (item, type(item)))

   391         assert_(len(item) == 2)

   392         name, value = item

   393         assert_(name.lower() != 'status',

   394             "The Status header cannot be used; it conflicts with CGI "

   395             "script, and HTTP status is not given through headers "

   396             "(value: %r)." % value)

   397         header_names[name.lower()] = None

   398         assert_('\n' not in name and ':' not in name,

   399             "Header names may not contain ':' or '\\n': %r" % name)

   400         assert_(header_re.search(name), "Bad header name: %r" % name)

   401         assert_(not name.endswith('-') and not name.endswith('_'),

   402             "Names may not end in '-' or '_': %r" % name)

   403         if bad_header_value_re.search(value):

   404             assert_(0, "Bad header value: %r (bad char: %r)"

   405             % (value, bad_header_value_re.search(value).group(0)))

   406 

   407 def check_content_type(status, headers):

   408     code = int(status.split(None, 1)[0])

   409     # @@: need one more person to verify this interpretation of RFC 2616

   410     #     http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

   411     NO_MESSAGE_BODY = (204, 304)

   412     for name, value in headers:

   413         if name.lower() == 'content-type':

   414             if code not in NO_MESSAGE_BODY:

   415                 return

   416             assert_(0, ("Content-Type header found in a %s response, "

   417                         "which must not return content.") % code)

   418     if code not in NO_MESSAGE_BODY:

   419         assert_(0, "No Content-Type header found in headers (%s)" % headers)

   420 

   421 def check_exc_info(exc_info):

   422     assert_(exc_info is None or type(exc_info) is type(()),

   423         "exc_info (%r) is not a tuple: %r" % (exc_info, type(exc_info)))

   424     # More exc_info checks?

   425 

   426 def check_iterator(iterator):

   427     # Technically a string is legal, which is why it's a really bad

   428     # idea, because it may cause the response to be returned

   429     # character-by-character

   430     assert_(not isinstance(iterator, str),

   431         "You should not return a string as your application iterator, "

   432         "instead return a single-item list containing that string.")