# (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 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
 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円-037円]')

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 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

 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.")