path: root/wsgitools/middlewares.py

__all__ = []

import time
import sys
import cgitb
from filters import CloseableList, CloseableIterator
try:
    import cStringIO as StringIO
except ImportError:
    import StringIO

__all__.append("SubdirMiddleware")
class SubdirMiddleware:
    """Middleware choosing wsgi applications based on a dict."""
    def __init__(self, default, mapping={}):
        self.default = default
        self.mapping = mapping
    def __call__(self, environ, start_response):
        """wsgi interface"""
        assert isinstance(environ, dict)
        app = None
        script = environ["PATH_INFO"]
        path_info = ""
        while '/' in script:
            if script in self.mapping:
                app = self.mapping[script]
                break
            script, tail = script.rsplit('/', 1)
            path_info = "/%s%s" % (tail, path_info)
        if app is None:
            app = self.mapping.get(script, None)
            if app is None:
                app = self.default
        environ["SCRIPT_NAME"] += script
        environ["PATH_INFO"] = path_info
        return app(environ, start_response)

__all__.append("NoWriteCallableMiddleware")
class NoWriteCallableMiddleware:
    """This middleware wraps a wsgi application that needs the return value of
    start_response function to a wsgi application that doesn't need one by
    writing the data to a StringIO and then making it be the first result
    element."""
    def __init__(self, app):
        """Wraps wsgi application app."""
        self.app = app
    def __call__(self, environ, start_response):
        """wsgi interface"""
        assert isinstance(environ, dict)
        todo = []
        def modified_start_response(status, headers, exc_info=None):
            assert isinstance(status, str)
            assert isinstance(headers, list)
            if exc_info is not None:
                todo.append(None)
                return start_response(status, headers, exc_info)
            else:
                sio = StringIO.StringIO()
                todo.append((status, headers, sio))
                return sio.write

        ret = self.app(environ, modified_start_response)
        assert hasattr(ret, "__iter__")

        if todo and todo[0] is None:
            return ret

        if isinstance(ret, list):
            status, headers, data = todo[0]
            data = data.getvalue()
            if data:
                ret.insert(0, data)
            start_response(status, headers)
            return ret

        ret = iter(ret)
        stopped = False
        try:
            first = ret.next()
        except StopIteration:
            stopped = True

        status, headers, data = todo[0]
        data = data.getvalue()
        start_response(status, headers)

        if stopped:
            return CloseableList(getattr(ret, "close", None), (data,))

        return CloseableIterator(getattr(ret, "close", None),
                                 (data, first), ret)

__all__.append("ContentLengthMiddleware")
class ContentLengthMiddleware:
    """Guesses the content length header if possible.
    Note: The application used must not use the write callable returned by
          start_response."""
    def __init__(self, app, maxstore=0):
        """Wraps wsgi application app. It can also store the first result bytes
        to possibly return a list of strings which will make guessing the size
        of iterators possible. At most maxstore bytes will be accumulated.
        Please note that a value larger than 0 will violate the wsgi standard.
        The magical value () will make it always gather all data.
        """
        self.app = app
        self.maxstore = maxstore
    def __call__(self, environ, start_response):
        """wsgi interface"""
        assert isinstance(environ, dict)
        todo = []
        def modified_start_response(status, headers, exc_info=None):
            assert isinstance(status, str)
            assert isinstance(headers, list)
            if (exc_info is not None or
                 [v for h, v in headers if h.lower() == "content-length"]):
                todo[:] = (None,)
                return start_response(status, headers, exc_info)
            else:
                todo[:] = ((status, headers),)
                def raise_not_imp(*args):
                    raise NotImplementedError
                return raise_not_imp

        ret = self.app(environ, modified_start_response)
        assert hasattr(ret, "__iter__")

        if todo and todo[0] is None: # nothing to do
            #print "content-length: nothing"
            return ret

        if isinstance(ret, list):
            #print "content-length: simple"
            status, headers = todo[0]
            length = sum(map(len, ret))
            headers.append(("Content-length", str(length)))
            start_response(status, headers)
            return ret

        ret = iter(ret)
        stopped = False
        data = CloseableList(getattr(ret, "close", None))
        length = 0
        try:
            data.append(ret.next()) # fills todo
            length += len(data[-1])
        except StopIteration:
            stopped = True

        status, headers = todo[0]

        while (not stopped) and length < self.maxstore:
            try:
                data.append(ret.next())
                length += len(data[-1])
            except StopIteration:
                stopped = True

        if stopped:
            #print "content-length: gathered"
            headers.append(("Content-length", str(length)))
            start_response(status, headers)
            return data

        #print "content-length: passthrough"
        start_response(status, headers)

        return CloseableIterator(getattr(ret, "close", None), data, ret)

def storable(environ):
    if environ["REQUEST_METHOD"] != "GET":
        return False
    return True

def cacheable(environ):
    if environ.get("HTTP_CACHE_CONTROL", "") == "max-age=0":
        return False
    return True

__all__.append("CachingMiddleware")
class CachingMiddleware:
    """Caches reponses to requests based on SCRIPT_NAME, PATH_INFO and
    QUERY_STRING."""
    def __init__(self, app, maxage=60, storable=storable, cacheable=cacheable):
        """app is a wsgi application to be cached.
        maxage is the number of seconds a reponse may be cached.
        storable is a predicated that determines whether the response may be
                 cached at all based on the environ dict.
        cacheable is a predicate that determines whether this request
                  invalidates the cache."""
        self.app = app
        self.maxage = maxage
        self.storable = storable
        self.cacheable = cacheable
        self.cache = {}
    def __call__(self, environ, start_response):
        """wsgi interface"""
        assert isinstance(environ, dict)
        if not self.storable(environ):
            return self.app(environ, start_response)
        path = environ.get("SCRIPT_NAME", "/")
        path += environ.get("PATH_INFO", '')
        path += "?" + environ.get("QUERY_STRING", "")
        if self.cacheable(environ) and path in self.cache:
            if self.cache[path][0] + self.maxage >= time.time():
                start_response(self.cache[path][1], self.cache[path][2])
                return self.cache[path][3]
            else:
                del self.cache[path]
        cache_object = [time.time(), "", [], []]
        def modified_start_respesponse(status, headers, exc_info):
            assert isinstance(status, str)
            assert isinstance(headers, list)
            if exc_info is not None:
                return self.app(status, headers, exc_info)
            cache_object[1] = status
            cache_object[2] = headers
            write = start_response(status, headers)
            def modified_write(data):
                cache_object[3].append(data)
                write(data)
            return modified_write

        ret = self.app(environ, modified_start_respesponse)
        assert hasattr(ret, "__iter__")

        if isinstance(ret, list):
            cache_object[3].extend(ret)
            self.cache[path] = cache_object
            return ret
        def pass_through():
            for data in ret:
                cache_object[3].append(data)
                yield data
            self.cache[path] = cache_object
        return CloseableIterator(getattr(ret, "close", None), pass_through())

__all__.append("DictAuthChecker")
class DictAuthChecker:
    """Verifies usernames and passwords by looking them up in a dict."""
    def __init__(self, users):
        """users is a dict mapping usernames to password."""
        self.users = users
    def __call__(self, username, password):
        """check_function interface taking username and password and resulting
        in a bool."""
        return username in self.users and self.users[username] == password

__all__.append("BasicAuthMiddleware")
class BasicAuthMiddleware:
    """Middleware implementing HTTP Basic Auth."""
    def __init__(self, app, check_function, realm='www'):
        """app is a WSGI application.
        check_function is a function taking two arguments username and password
                       returning a bool indicating whether the request may is
                       allowed."""
        self.app = app
        self.check_function = check_function
        self.realm = realm

    def __call__(self, environ, start_response):
        """wsgi interface"""
        assert isinstance(environ, dict)
        auth = environ.get("HTTP_AUTHORIZATION")
        if not auth or ' ' not in auth:
            return self.authorization_required(environ, start_response)
        auth_type, enc_auth_info = auth.split(None, 1)
        try:
            auth_info = enc_auth_info.decode("base64")
        except Exception: # It throws something from binascii.
            return self.authorization_required(environ, start_response)
        if auth_type.lower() != "basic" or ':' not in auth_info:
            return self.authorization_required(environ, start_response)
        username, password = auth_info.split(':', 1)
        if self.check_function(username, password):
            environ["REMOTE_USER"] = username
            return self.app(environ, start_response)
        return self.authorization_required(environ, start_response)

    def authorization_required(self, environ, start_response):
        """wsgi application for indicating authorization is required."""
        status = "401 Authorization required"
        html = "<html><head><title>Authorization required</title></head>" + \
               "<body><h1>Authorization required</h1></body></html>\n"
        headers = [('Content-type', 'text/html'),
                   ('WWW-Authenticate', 'Basic realm="%s"' % self.realm),
                   ("Content-length", str(len(html)))]
        start_response(status, headers)
        if environ["REQUEST_METHOD"].upper() == "HEAD":
            return []
        return [html]

__all__.append("TracebackMiddleware")
class TracebackMiddleware:
    """In case the application throws an exception this middleware will show an
    html-formatted traceback using cgitb."""
    def __init__(self, app):
        """app is the wsgi application to proxy."""
        self.app = app
    def __call__(self, environ, start_response):
        """wsgi interface"""
        try:
            assert isinstance(environ, dict)
            ret = self.app(environ, start_response)
            assert hasattr(ret, "__iter__")

            if isinstance(ret, list):
                return ret
            # Take the first element of the iterator and possibly catch an
            # exception there.
            ret = iter(ret)
            try:
                first = ret.next()
            except StopIteration:
                return CloseableList(getattr(ret, "close", None), [])
            return CloseableIterator(getattr(ret, "close", None), [first], ret)
        except:
            exc_info = sys.exc_info()
            data = cgitb.html(exc_info)
            start_response("200 OK", [("Content-type", "text/html"),
                                      ("Content-length", str(len(data)))])
            if environ["REQUEST_METHOD"].upper() == "HEAD":
                return []
            return [data]