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# Copyright 2015 Google Inc.
#
# 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.
"""Helper functions for commonly used utilities."""
import base64
import calendar
import datetime
import six
from six.moves import urllib
CLOCK_SKEW_SECS = 10 # 10 seconds
CLOCK_SKEW = datetime.timedelta(seconds=CLOCK_SKEW_SECS)
def copy_docstring(source_class):
"""Decorator that copies a method's docstring from another class.
Args:
source_class (type): The class that has the documented method.
Returns:
Callable: A decorator that will copy the docstring of the same
named method in the source class to the decorated method.
"""
def decorator(method):
"""Decorator implementation.
Args:
method (Callable): The method to copy the docstring to.
Returns:
Callable: the same method passed in with an updated docstring.
Raises:
ValueError: if the method already has a docstring.
"""
if method.__doc__:
raise ValueError("Method already has a docstring.")
source_method = getattr(source_class, method.__name__)
method.__doc__ = source_method.__doc__
return method
return decorator
def utcnow():
"""Returns the current UTC datetime.
Returns:
datetime: The current time in UTC.
"""
return datetime.datetime.utcnow()
def datetime_to_secs(value):
"""Convert a datetime object to the number of seconds since the UNIX epoch.
Args:
value (datetime): The datetime to convert.
Returns:
int: The number of seconds since the UNIX epoch.
"""
return calendar.timegm(value.utctimetuple())
def to_bytes(value, encoding="utf-8"):
"""Converts a string value to bytes, if necessary.
Unfortunately, ``six.b`` is insufficient for this task since in
Python 2 because it does not modify ``unicode`` objects.
Args:
value (Union[str, bytes]): The value to be converted.
encoding (str): The encoding to use to convert unicode to bytes.
Defaults to "utf-8".
Returns:
bytes: The original value converted to bytes (if unicode) or as
passed in if it started out as bytes.
Raises:
ValueError: If the value could not be converted to bytes.
"""
result = value.encode(encoding) if isinstance(value, six.text_type) else value
if isinstance(result, six.binary_type):
return result
else:
raise ValueError("{0!r} could not be converted to bytes".format(value))
def from_bytes(value):
"""Converts bytes to a string value, if necessary.
Args:
value (Union[str, bytes]): The value to be converted.
Returns:
str: The original value converted to unicode (if bytes) or as passed in
if it started out as unicode.
Raises:
ValueError: If the value could not be converted to unicode.
"""
result = value.decode("utf-8") if isinstance(value, six.binary_type) else value
if isinstance(result, six.text_type):
return result
else:
raise ValueError("{0!r} could not be converted to unicode".format(value))
def update_query(url, params, remove=None):
"""Updates a URL's query parameters.
Replaces any current values if they are already present in the URL.
Args:
url (str): The URL to update.
params (Mapping[str, str]): A mapping of query parameter
keys to values.
remove (Sequence[str]): Parameters to remove from the query string.
Returns:
str: The URL with updated query parameters.
Examples:
>>> url = 'http://example.com?a=1'
>>> update_query(url, {'a': '2'})
http://example.com?a=2
>>> update_query(url, {'b': '3'})
http://example.com?a=1&b=3
>> update_query(url, {'b': '3'}, remove=['a'])
http://example.com?b=3
"""
if remove is None:
remove = []
# Split the URL into parts.
parts = urllib.parse.urlparse(url)
# Parse the query string.
query_params = urllib.parse.parse_qs(parts.query)
# Update the query parameters with the new parameters.
query_params.update(params)
# Remove any values specified in remove.
query_params = {
key: value for key, value in six.iteritems(query_params) if key not in remove
}
# Re-encoded the query string.
new_query = urllib.parse.urlencode(query_params, doseq=True)
# Unsplit the url.
new_parts = parts._replace(query=new_query)
return urllib.parse.urlunparse(new_parts)
def scopes_to_string(scopes):
"""Converts scope value to a string suitable for sending to OAuth 2.0
authorization servers.
Args:
scopes (Sequence[str]): The sequence of scopes to convert.
Returns:
str: The scopes formatted as a single string.
"""
return " ".join(scopes)
def string_to_scopes(scopes):
"""Converts stringifed scopes value to a list.
Args:
scopes (Union[Sequence, str]): The string of space-separated scopes
to convert.
Returns:
Sequence(str): The separated scopes.
"""
if not scopes:
return []
return scopes.split(" ")
def padded_urlsafe_b64decode(value):
"""Decodes base64 strings lacking padding characters.
Google infrastructure tends to omit the base64 padding characters.
Args:
value (Union[str, bytes]): The encoded value.
Returns:
bytes: The decoded value
"""
b64string = to_bytes(value)
padded = b64string + b"=" * (-len(b64string) % 4)
return base64.urlsafe_b64decode(padded)
def unpadded_urlsafe_b64encode(value):
"""Encodes base64 strings removing any padding characters.
`rfc 7515`_ defines Base64url to NOT include any padding
characters, but the stdlib doesn't do that by default.
_rfc7515: https://tools.ietf.org/html/rfc7515#page-6
Args:
value (Union[str|bytes]): The bytes-like value to encode
Returns:
Union[str|bytes]: The encoded value
"""
return base64.urlsafe_b64encode(value).rstrip(b"=")
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