watcha-synapse/synapse/util/stringutils.py

# -*- coding: utf-8 -*-
# Copyright 2014-2016 OpenMarket Ltd
# Copyright 2020 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import itertools
import random
import re
import string
from collections import Iterable

import six
from six import PY2, PY3
from six.moves import range

from synapse.api.errors import Codes, SynapseError

_string_with_symbols = string.digits + string.ascii_letters + ".,;:^&*-_+=#~@"

# https://matrix.org/docs/spec/client_server/r0.6.0#post-matrix-client-r0-register-email-requesttoken
# Note: The : character is allowed here for older clients, but will be removed in a
# future release. Context: https://github.com/matrix-org/synapse/issues/6766
client_secret_regex = re.compile(r"^[0-9a-zA-Z\.\=\_\-\:]+$")

# random_string and random_string_with_symbols are used for a range of things,
# some cryptographically important, some less so. We use SystemRandom to make sure
# we get cryptographically-secure randoms.
rand = random.SystemRandom()


def random_string(length):
    return "".join(rand.choice(string.ascii_letters) for _ in range(length))


def random_string_with_symbols(length):
    return "".join(rand.choice(_string_with_symbols) for _ in range(length))


def is_ascii(s):

    if PY3:
        if isinstance(s, bytes):
            try:
                s.decode("ascii").encode("ascii")
            except UnicodeDecodeError:
                return False
            except UnicodeEncodeError:
                return False
            return True

    try:
        s.encode("ascii")
    except UnicodeEncodeError:
        return False
    except UnicodeDecodeError:
        return False
    else:
        return True


def to_ascii(s):
    """Converts a string to ascii if it is ascii, otherwise leave it alone.

    If given None then will return None.
    """
    if PY3:
        return s

    if s is None:
        return None

    try:
        return s.encode("ascii")
    except UnicodeEncodeError:
        return s


def exception_to_unicode(e):
    """Helper function to extract the text of an exception as a unicode string

    Args:
        e (Exception): exception to be stringified

    Returns:
        unicode
    """
    # urgh, this is a mess. The basic problem here is that psycopg2 constructs its
    # exceptions with PyErr_SetString, with a (possibly non-ascii) argument. str() will
    # then produce the raw byte sequence. Under Python 2, this will then cause another
    # error if it gets mixed with a `unicode` object, as per
    # https://github.com/matrix-org/synapse/issues/4252

    # First of all, if we're under python3, everything is fine because it will sort this
    # nonsense out for us.
    if not PY2:
        return str(e)

    # otherwise let's have a stab at decoding the exception message. We'll circumvent
    # Exception.__str__(), which would explode if someone raised Exception(u'non-ascii')
    # and instead look at what is in the args member.

    if len(e.args) == 0:
        return ""
    elif len(e.args) > 1:
        return six.text_type(repr(e.args))

    msg = e.args[0]
    if isinstance(msg, bytes):
        return msg.decode("utf-8", errors="replace")
    else:
        return msg


def assert_valid_client_secret(client_secret):
    """Validate that a given string matches the client_secret regex defined by the spec"""
    if client_secret_regex.match(client_secret) is None:
        raise SynapseError(
            400, "Invalid client_secret parameter", errcode=Codes.INVALID_PARAM
        )


def shortstr(iterable: Iterable, maxitems: int = 5) -> str:
    """If iterable has maxitems or fewer, return the stringification of a list
    containing those items.

    Otherwise, return the stringification of a a list with the first maxitems items,
    followed by "...".

    Args:
        iterable: iterable to truncate
        maxitems: number of items to return before truncating
    """

    items = list(itertools.islice(iterable, maxitems + 1))
    if len(items) <= maxitems:
        return str(items)
    return "[" + ", ".join(repr(r) for r in items[:maxitems]) + ", ...]"