File: session.py

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import base64
import binascii
import hashlib
import hmac
import os
import time

from zope.deprecation import deprecated
from zope.interface import implementer

from webob.cookies import SignedSerializer

from pyramid.compat import (
    pickle,
    PY3,
    text_,
    bytes_,
    native_,
    )

from pyramid.exceptions import BadCSRFToken
from pyramid.interfaces import ISession
from pyramid.util import strings_differ

def manage_accessed(wrapped):
    """ Decorator which causes a cookie to be renewed when an accessor
    method is called."""
    def accessed(session, *arg, **kw):
        session.accessed = now = int(time.time())
        if session._reissue_time is not None:
            if now - session.renewed > session._reissue_time:
                session.changed()
        return wrapped(session, *arg, **kw)
    accessed.__doc__ = wrapped.__doc__
    return accessed

def manage_changed(wrapped):
    """ Decorator which causes a cookie to be set when a setter method
    is called."""
    def changed(session, *arg, **kw):
        session.accessed = int(time.time())
        session.changed()
        return wrapped(session, *arg, **kw)
    changed.__doc__ = wrapped.__doc__
    return changed

def signed_serialize(data, secret):
    """ Serialize any pickleable structure (``data``) and sign it
    using the ``secret`` (must be a string).  Return the
    serialization, which includes the signature as its first 40 bytes.
    The ``signed_deserialize`` method will deserialize such a value.

    This function is useful for creating signed cookies.  For example:

    .. code-block:: python

       cookieval = signed_serialize({'a':1}, 'secret')
       response.set_cookie('signed_cookie', cookieval)
    """
    pickled = pickle.dumps(data, pickle.HIGHEST_PROTOCOL)
    try:
        # bw-compat with pyramid <= 1.5b1 where latin1 is the default
        secret = bytes_(secret)
    except UnicodeEncodeError:
        secret = bytes_(secret, 'utf-8')
    sig = hmac.new(secret, pickled, hashlib.sha1).hexdigest()
    return sig + native_(base64.b64encode(pickled))

def signed_deserialize(serialized, secret, hmac=hmac):
    """ Deserialize the value returned from ``signed_serialize``.  If
    the value cannot be deserialized for any reason, a
    :exc:`ValueError` exception will be raised.

    This function is useful for deserializing a signed cookie value
    created by ``signed_serialize``.  For example:

    .. code-block:: python

       cookieval = request.cookies['signed_cookie']
       data = signed_deserialize(cookieval, 'secret')
    """
    # hmac parameterized only for unit tests
    try:
        input_sig, pickled = (bytes_(serialized[:40]),
                              base64.b64decode(bytes_(serialized[40:])))
    except (binascii.Error, TypeError) as e:
        # Badly formed data can make base64 die
        raise ValueError('Badly formed base64 data: %s' % e)

    try:
        # bw-compat with pyramid <= 1.5b1 where latin1 is the default
        secret = bytes_(secret)
    except UnicodeEncodeError:
        secret = bytes_(secret, 'utf-8')
    sig = bytes_(hmac.new(secret, pickled, hashlib.sha1).hexdigest())

    # Avoid timing attacks (see
    # http://seb.dbzteam.org/crypto/python-oauth-timing-hmac.pdf)
    if strings_differ(sig, input_sig):
        raise ValueError('Invalid signature')

    return pickle.loads(pickled)

def check_csrf_token(request,
                     token='csrf_token',
                     header='X-CSRF-Token',
                     raises=True):
    """ Check the CSRF token in the request's session against the value in
    ``request.params.get(token)`` or ``request.headers.get(header)``.
    If a ``token`` keyword is not supplied to this function, the string
    ``csrf_token`` will be used to look up the token in ``request.params``.
    If a ``header`` keyword is not supplied to this function, the string
    ``X-CSRF-Token`` will be used to look up the token in ``request.headers``.

    If the value supplied by param or by header doesn't match the value
    supplied by ``request.session.get_csrf_token()``, and ``raises`` is
    ``True``, this function will raise an
    :exc:`pyramid.exceptions.BadCSRFToken` exception.
    If the check does succeed and ``raises`` is ``False``, this
    function will return ``False``.  If the CSRF check is successful, this
    function will return ``True`` unconditionally.

    Note that using this function requires that a :term:`session factory` is
    configured.

    .. versionadded:: 1.4a2
    """
    supplied_token = request.params.get(token, request.headers.get(header, ""))
    if strings_differ(request.session.get_csrf_token(), supplied_token):
        if raises:
            raise BadCSRFToken('check_csrf_token(): Invalid token')
        return False
    return True

class PickleSerializer(object):
    """ A serializer that uses the pickle protocol to dump Python
    data to bytes.

    This is the default serializer used by Pyramid.

    ``protocol`` may be specified to control the version of pickle used.
    Defaults to :attr:`pickle.HIGHEST_PROTOCOL`.

    """
    def __init__(self, protocol=pickle.HIGHEST_PROTOCOL):
        self.protocol = protocol

    def loads(self, bstruct):
        """Accept bytes and return a Python object."""
        return pickle.loads(bstruct)

    def dumps(self, appstruct):
        """Accept a Python object and return bytes."""
        return pickle.dumps(appstruct, self.protocol)

def BaseCookieSessionFactory(
    serializer,
    cookie_name='session',
    max_age=None,
    path='/',
    domain=None,
    secure=False,
    httponly=False,
    timeout=1200,
    reissue_time=0,
    set_on_exception=True,
    ):
    """
    .. versionadded:: 1.5
    
    Configure a :term:`session factory` which will provide cookie-based
    sessions.  The return value of this function is a :term:`session factory`,
    which may be provided as the ``session_factory`` argument of a
    :class:`pyramid.config.Configurator` constructor, or used as the
    ``session_factory`` argument of the
    :meth:`pyramid.config.Configurator.set_session_factory` method.

    The session factory returned by this function will create sessions
    which are limited to storing fewer than 4000 bytes of data (as the
    payload must fit into a single cookie).

    .. warning:

       This class provides no protection from tampering and is only intended
       to be used by framework authors to create their own cookie-based
       session factories.

    Parameters:

    ``serializer``
      An object with two methods: ``loads`` and ``dumps``.  The ``loads``
      method should accept bytes and return a Python object.  The ``dumps``
      method should accept a Python object and return bytes.  A ``ValueError``
      should be raised for malformed inputs.

    ``cookie_name``
      The name of the cookie used for sessioning. Default: ``'session'``.

    ``max_age``
      The maximum age of the cookie used for sessioning (in seconds).
      Default: ``None`` (browser scope).

    ``path``
      The path used for the session cookie. Default: ``'/'``.

    ``domain``
      The domain used for the session cookie.  Default: ``None`` (no domain).

    ``secure``
      The 'secure' flag of the session cookie. Default: ``False``.

    ``httponly``
      Hide the cookie from Javascript by setting the 'HttpOnly' flag of the
      session cookie. Default: ``False``.

    ``timeout``
      A number of seconds of inactivity before a session times out. If
      ``None`` then the cookie never expires. This lifetime only applies
      to the *value* within the cookie. Meaning that if the cookie expires
      due to a lower ``max_age``, then this setting has no effect.
      Default: ``1200``.

    ``reissue_time``
      The number of seconds that must pass before the cookie is automatically
      reissued as the result of a request which accesses the session. The
      duration is measured as the number of seconds since the last session
      cookie was issued and 'now'.  If this value is ``0``, a new cookie
      will be reissued on every request accessing the session. If ``None``
      then the cookie's lifetime will never be extended.

      A good rule of thumb: if you want auto-expired cookies based on
      inactivity: set the ``timeout`` value to 1200 (20 mins) and set the
      ``reissue_time`` value to perhaps a tenth of the ``timeout`` value
      (120 or 2 mins).  It's nonsensical to set the ``timeout`` value lower
      than the ``reissue_time`` value, as the ticket will never be reissued.
      However, such a configuration is not explicitly prevented.

      Default: ``0``.

    ``set_on_exception``
      If ``True``, set a session cookie even if an exception occurs
      while rendering a view. Default: ``True``.

    .. versionadded: 1.5a3
    """

    @implementer(ISession)
    class CookieSession(dict):
        """ Dictionary-like session object """

        # configuration parameters
        _cookie_name = cookie_name
        _cookie_max_age = max_age if max_age is None else int(max_age)
        _cookie_path = path
        _cookie_domain = domain
        _cookie_secure = secure
        _cookie_httponly = httponly
        _cookie_on_exception = set_on_exception
        _timeout = timeout if timeout is None else int(timeout)
        _reissue_time = reissue_time if reissue_time is None else int(reissue_time)

        # dirty flag
        _dirty = False

        def __init__(self, request):
            self.request = request
            now = time.time()
            created = renewed = now
            new = True
            value = None
            state = {}
            cookieval = request.cookies.get(self._cookie_name)
            if cookieval is not None:
                try:
                    value = serializer.loads(bytes_(cookieval))
                except ValueError:
                    # the cookie failed to deserialize, dropped
                    value = None

            if value is not None:
                try:
                    # since the value is not necessarily signed, we have
                    # to unpack it a little carefully
                    rval, cval, sval = value
                    renewed = float(rval)
                    created = float(cval)
                    state = sval
                    new = False
                except (TypeError, ValueError):
                    # value failed to unpack properly or renewed was not
                    # a numeric type so we'll fail deserialization here
                    state = {}

            if self._timeout is not None:
                if now - renewed > self._timeout:
                    # expire the session because it was not renewed
                    # before the timeout threshold
                    state = {}

            self.created = created
            self.accessed = renewed
            self.renewed = renewed
            self.new = new
            dict.__init__(self, state)

        # ISession methods
        def changed(self):
            if not self._dirty:
                self._dirty = True
                def set_cookie_callback(request, response):
                    self._set_cookie(response)
                    self.request = None # explicitly break cycle for gc
                self.request.add_response_callback(set_cookie_callback)

        def invalidate(self):
            self.clear() # XXX probably needs to unset cookie

        # non-modifying dictionary methods
        get = manage_accessed(dict.get)
        __getitem__ = manage_accessed(dict.__getitem__)
        items = manage_accessed(dict.items)
        values = manage_accessed(dict.values)
        keys = manage_accessed(dict.keys)
        __contains__ = manage_accessed(dict.__contains__)
        __len__ = manage_accessed(dict.__len__)
        __iter__ = manage_accessed(dict.__iter__)

        if not PY3:
            iteritems = manage_accessed(dict.iteritems)
            itervalues = manage_accessed(dict.itervalues)
            iterkeys = manage_accessed(dict.iterkeys)
            has_key = manage_accessed(dict.has_key)

        # modifying dictionary methods
        clear = manage_changed(dict.clear)
        update = manage_changed(dict.update)
        setdefault = manage_changed(dict.setdefault)
        pop = manage_changed(dict.pop)
        popitem = manage_changed(dict.popitem)
        __setitem__ = manage_changed(dict.__setitem__)
        __delitem__ = manage_changed(dict.__delitem__)

        # flash API methods
        @manage_changed
        def flash(self, msg, queue='', allow_duplicate=True):
            storage = self.setdefault('_f_' + queue, [])
            if allow_duplicate or (msg not in storage):
                storage.append(msg)

        @manage_changed
        def pop_flash(self, queue=''):
            storage = self.pop('_f_' + queue, [])
            return storage

        @manage_accessed
        def peek_flash(self, queue=''):
            storage = self.get('_f_' + queue, [])
            return storage

        # CSRF API methods
        @manage_changed
        def new_csrf_token(self):
            token = text_(binascii.hexlify(os.urandom(20)))
            self['_csrft_'] = token
            return token

        @manage_accessed
        def get_csrf_token(self):
            token = self.get('_csrft_', None)
            if token is None:
                token = self.new_csrf_token()
            return token

        # non-API methods
        def _set_cookie(self, response):
            if not self._cookie_on_exception:
                exception = getattr(self.request, 'exception', None)
                if exception is not None: # dont set a cookie during exceptions
                    return False
            cookieval = native_(serializer.dumps(
                (self.accessed, self.created, dict(self))
                ))
            if len(cookieval) > 4064:
                raise ValueError(
                    'Cookie value is too long to store (%s bytes)' %
                    len(cookieval)
                    )
            response.set_cookie(
                self._cookie_name,
                value=cookieval,
                max_age=self._cookie_max_age,
                path=self._cookie_path,
                domain=self._cookie_domain,
                secure=self._cookie_secure,
                httponly=self._cookie_httponly,
                )
            return True

    return CookieSession


def UnencryptedCookieSessionFactoryConfig(
    secret,
    timeout=1200,
    cookie_name='session',
    cookie_max_age=None,
    cookie_path='/',
    cookie_domain=None,
    cookie_secure=False,
    cookie_httponly=False,
    cookie_on_exception=True,
    signed_serialize=signed_serialize,
    signed_deserialize=signed_deserialize,
    ):
    """
    .. deprecated:: 1.5
        Use :func:`pyramid.session.SignedCookieSessionFactory` instead.
        Caveat: Cookies generated using ``SignedCookieSessionFactory`` are not
        compatible with cookies generated using
        ``UnencryptedCookieSessionFactory``, so existing user session data
        will be destroyed if you switch to it.
    
    Configure a :term:`session factory` which will provide unencrypted
    (but signed) cookie-based sessions.  The return value of this
    function is a :term:`session factory`, which may be provided as
    the ``session_factory`` argument of a
    :class:`pyramid.config.Configurator` constructor, or used
    as the ``session_factory`` argument of the
    :meth:`pyramid.config.Configurator.set_session_factory`
    method.

    The session factory returned by this function will create sessions
    which are limited to storing fewer than 4000 bytes of data (as the
    payload must fit into a single cookie).

    Parameters:

    ``secret``
      A string which is used to sign the cookie.

    ``timeout``
      A number of seconds of inactivity before a session times out.

    ``cookie_name``
      The name of the cookie used for sessioning.

    ``cookie_max_age``
      The maximum age of the cookie used for sessioning (in seconds).
      Default: ``None`` (browser scope).

    ``cookie_path``
      The path used for the session cookie.

    ``cookie_domain``
      The domain used for the session cookie.  Default: ``None`` (no domain).

    ``cookie_secure``
      The 'secure' flag of the session cookie.

    ``cookie_httponly``
      The 'httpOnly' flag of the session cookie.

    ``cookie_on_exception``
      If ``True``, set a session cookie even if an exception occurs
      while rendering a view.

    ``signed_serialize``
      A callable which takes more or less arbitrary Python data structure and
      a secret and returns a signed serialization in bytes.
      Default: ``signed_serialize`` (using pickle).

    ``signed_deserialize``
      A callable which takes a signed and serialized data structure in bytes
      and a secret and returns the original data structure if the signature
      is valid. Default: ``signed_deserialize`` (using pickle).
    """

    class SerializerWrapper(object):
        def __init__(self, secret):
            self.secret = secret
            
        def loads(self, bstruct):
            return signed_deserialize(bstruct, secret)

        def dumps(self, appstruct):
            return signed_serialize(appstruct, secret)

    serializer = SerializerWrapper(secret)

    return BaseCookieSessionFactory(
        serializer,
        cookie_name=cookie_name,
        max_age=cookie_max_age,
        path=cookie_path,
        domain=cookie_domain,
        secure=cookie_secure,
        httponly=cookie_httponly,
        timeout=timeout,
        reissue_time=0, # to keep session.accessed == session.renewed
        set_on_exception=cookie_on_exception,
    )

deprecated(
    'UnencryptedCookieSessionFactoryConfig',
    'The UnencryptedCookieSessionFactoryConfig callable is deprecated as of '
    'Pyramid 1.5.  Use ``pyramid.session.SignedCookieSessionFactory`` instead.'
    ' Caveat: Cookies generated using SignedCookieSessionFactory are not '
    'compatible with cookies generated using UnencryptedCookieSessionFactory, '
    'so existing user session data will be destroyed if you switch to it.'
    )

def SignedCookieSessionFactory(
    secret,
    cookie_name='session',
    max_age=None,
    path='/',
    domain=None,
    secure=False,
    httponly=False,
    set_on_exception=True,
    timeout=1200,
    reissue_time=0,
    hashalg='sha512',
    salt='pyramid.session.',
    serializer=None,
    ):
    """
    .. versionadded:: 1.5
    
    Configure a :term:`session factory` which will provide signed
    cookie-based sessions.  The return value of this
    function is a :term:`session factory`, which may be provided as
    the ``session_factory`` argument of a
    :class:`pyramid.config.Configurator` constructor, or used
    as the ``session_factory`` argument of the
    :meth:`pyramid.config.Configurator.set_session_factory`
    method.

    The session factory returned by this function will create sessions
    which are limited to storing fewer than 4000 bytes of data (as the
    payload must fit into a single cookie).

    Parameters:

    ``secret``
      A string which is used to sign the cookie. The secret should be at
      least as long as the block size of the selected hash algorithm. For
      ``sha512`` this would mean a 128 bit (64 character) secret.  It should
      be unique within the set of secret values provided to Pyramid for
      its various subsystems (see :ref:`admonishment_against_secret_sharing`).

    ``hashalg``
      The HMAC digest algorithm to use for signing. The algorithm must be
      supported by the :mod:`hashlib` library. Default: ``'sha512'``.

    ``salt``
      A namespace to avoid collisions between different uses of a shared
      secret. Reusing a secret for different parts of an application is
      strongly discouraged (see :ref:`admonishment_against_secret_sharing`).
      Default: ``'pyramid.session.'``.

    ``cookie_name``
      The name of the cookie used for sessioning. Default: ``'session'``.

    ``max_age``
      The maximum age of the cookie used for sessioning (in seconds).
      Default: ``None`` (browser scope).

    ``path``
      The path used for the session cookie. Default: ``'/'``.

    ``domain``
      The domain used for the session cookie.  Default: ``None`` (no domain).

    ``secure``
      The 'secure' flag of the session cookie. Default: ``False``.

    ``httponly``
      Hide the cookie from Javascript by setting the 'HttpOnly' flag of the
      session cookie. Default: ``False``.

    ``timeout``
      A number of seconds of inactivity before a session times out. If
      ``None`` then the cookie never expires. This lifetime only applies
      to the *value* within the cookie. Meaning that if the cookie expires
      due to a lower ``max_age``, then this setting has no effect.
      Default: ``1200``.

    ``reissue_time``
      The number of seconds that must pass before the cookie is automatically
      reissued as the result of accessing the session. The
      duration is measured as the number of seconds since the last session
      cookie was issued and 'now'.  If this value is ``0``, a new cookie
      will be reissued on every request accessing the session. If ``None``
      then the cookie's lifetime will never be extended.

      A good rule of thumb: if you want auto-expired cookies based on
      inactivity: set the ``timeout`` value to 1200 (20 mins) and set the
      ``reissue_time`` value to perhaps a tenth of the ``timeout`` value
      (120 or 2 mins).  It's nonsensical to set the ``timeout`` value lower
      than the ``reissue_time`` value, as the ticket will never be reissued.
      However, such a configuration is not explicitly prevented.

      Default: ``0``.

    ``set_on_exception``
      If ``True``, set a session cookie even if an exception occurs
      while rendering a view. Default: ``True``.

    ``serializer``
      An object with two methods: ``loads`` and ``dumps``.  The ``loads``
      method should accept bytes and return a Python object.  The ``dumps``
      method should accept a Python object and return bytes.  A ``ValueError``
      should be raised for malformed inputs.  If a serializer is not passed,
      the :class:`pyramid.session.PickleSerializer` serializer will be used.

    .. versionadded: 1.5a3
    """
    if serializer is None:
        serializer = PickleSerializer()

    signed_serializer = SignedSerializer(
        secret,
        salt,
        hashalg,
        serializer=serializer,
        )

    return BaseCookieSessionFactory(
        signed_serializer,
        cookie_name=cookie_name,
        max_age=max_age,
        path=path,
        domain=domain,
        secure=secure,
        httponly=httponly,
        timeout=timeout,
        reissue_time=reissue_time,
        set_on_exception=set_on_exception,
    )