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validate.py
# (c) 2005 Ian Bicking and contributors; written for Paste (http://pythonpaste.org) # Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php # Also licenced under the Apache License, 2.0: http://opensource.org/licenses/apache2.0.php # 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 - That HTTP_CONTENT_TYPE and HTTP_CONTENT_LENGTH are not in the environment (these headers should appear as CONTENT_LENGTH and CONTENT_TYPE). - 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 restrictive?) - Warns if the REQUEST_METHOD is not known (@@: probably too restrictive). - 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 __iter__ - 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 sequence). * That the items of the headers are tuples of strings. * That there is no 'status' header (that is used in CGI, but not in WSGI). * 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 exactly 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 error). - 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 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 check_string_type(value, title): if type (value) is str: return value raise AssertionError( "{0} must be of type str (got {1})".format(title, repr(value))) def validator(application): """ When applied between a WSGI server and a WSGI application, this middleware will check for WSGI compliance 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 check_environ(environ) # 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] else: exc_info = None check_status(status) check_headers(headers) check_content_type(status, headers) check_exc_info(exc_info) start_response_started.append(None) 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") check_iterator(iterator) 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 = self.input.read(*args) assert_(type(v) is bytes) return v def readline(self, *args): assert_(len(args) <= 1) v = self.input.readline(*args) assert_(type(v) is bytes) return v def readlines(self, *args): assert_(len(args) <= 1) lines = self.input.readlines(*args) assert_(type(lines) is list) for line in lines: assert_(type(line) is bytes) return lines def __iter__(self): while 1: line = self.readline() if not line: return 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 str) self.errors.write(s) def flush(self): self.errors.flush() def writelines(self, seq): for line in seq: self.write(line) 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 bytes) self.writer(s) 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 = next(self.iterator) if type(v) is not bytes: assert_(False, "Iterator yielded non-bytestring (%r)" % (v,)) if self.check_start_response is not None: assert_(self.check_start_response, "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'): self.original_iterator.close() def __del__(self): if not self.closed: sys.stderr.write( "Iterator garbage collected without being closed") assert_(self.closed, "Iterator garbage collected without being closed") def check_environ(environ): assert_(type(environ) is dict, "Environment is not of the right type: %r (environment: %r)" % (type(environ), environ)) for key in ['REQUEST_METHOD', 'SERVER_NAME', 'SERVER_PORT', 'wsgi.version', 'wsgi.input', 'wsgi.errors', 'wsgi.multithread', 'wsgi.multiprocess', 'wsgi.run_once']: assert_(key in environ, "Environment missing required key: %r" % (key,)) for key in ['HTTP_CONTENT_TYPE', 'HTTP_CONTENT_LENGTH']: assert_(key not in environ, "Environment should not have the key: %s " "(use %s instead)" % (key, key[5:])) if 'QUERY_STRING' not in environ: warnings.warn( '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', WSGIWarning) for key in environ.keys(): if '.' in key: # Extension, we don't care about its type continue assert_(type(environ[key]) is str, "Environmental variable %s is not a string: %r (value: %r)" % (key, type(environ[key]), environ[key])) assert_(type(environ['wsgi.version']) is tuple, "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']) check_input(environ['wsgi.input']) check_errors(environ['wsgi.errors']) # @@: these need filling out: if environ['REQUEST_METHOD'] not in ( 'GET', 'HEAD', 'POST', 'OPTIONS', 'PATCH', 'PUT', 'DELETE', 'TRACE'): warnings.warn( "Unknown REQUEST_METHOD: %r" % environ['REQUEST_METHOD'], WSGIWarning) 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): status = check_string_type(status, "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] != ' ': warnings.warn( "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 list, "Headers (%r) must be of type list: %r" % (headers, type(headers))) for item in headers: assert_(type(item) is tuple, "Individual headers (%r) must be of type tuple: %r" % (item, type(item))) assert_(len(item) == 2) name, value = item name = check_string_type(name, "Header name") value = check_string_type(value, "Header value") 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) assert_('\n' not in name and ':' not in name, "Header names may not contain ':' or '\\n': %r" % name) assert_(header_re.search(name), "Bad header name: %r" % name) assert_(not name.endswith('-') and not name.endswith('_'), "Names may not end in '-' or '_': %r" % name) if bad_header_value_re.search(value): assert_(0, "Bad header value: %r (bad char: %r)" % (value, bad_header_value_re.search(value).group(0))) def check_content_type(status, headers): status = check_string_type(status, "Status") code = int(status.split(None, 1)[0]) # @@: need one more person to verify this interpretation of RFC 2616 # http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html NO_MESSAGE_BODY = (204, 304) for name, value in headers: name = check_string_type(name, "Header name") if name.lower() == 'content-type': if code not in NO_MESSAGE_BODY: return 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 tuple, "exc_info (%r) is not a tuple: %r" % (exc_info, type(exc_info))) # More exc_info checks? def check_iterator(iterator): # Technically a bytestring 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, bytes)), "You should not return a string as your application iterator, " "instead return a single-item list containing a bytestring.")
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