_helpers.py

# Copyright 2014 Google LLC
#
# 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 Cloud Storage utility classes.

These are *not* part of the API.
"""

import base64
from hashlib import md5
import os
from urllib.parse import urlsplit

from google import resumable_media
from google.cloud.storage.constants import _DEFAULT_TIMEOUT
from google.cloud.storage.retry import DEFAULT_RETRY
from google.cloud.storage.retry import DEFAULT_RETRY_IF_METAGENERATION_SPECIFIED


STORAGE_EMULATOR_ENV_VAR = "STORAGE_EMULATOR_HOST"
"""Environment variable defining host for Storage emulator."""

_DEFAULT_STORAGE_HOST = u"https://storage.googleapis.com"

# etag match parameters in snake case and equivalent header
_ETAG_MATCH_PARAMETERS = (
    ("if_etag_match", "If-Match"),
    ("if_etag_not_match", "If-None-Match"),
)

# generation match parameters in camel and snake cases
_GENERATION_MATCH_PARAMETERS = (
    ("if_generation_match", "ifGenerationMatch"),
    ("if_generation_not_match", "ifGenerationNotMatch"),
    ("if_metageneration_match", "ifMetagenerationMatch"),
    ("if_metageneration_not_match", "ifMetagenerationNotMatch"),
    ("if_source_generation_match", "ifSourceGenerationMatch"),
    ("if_source_generation_not_match", "ifSourceGenerationNotMatch"),
    ("if_source_metageneration_match", "ifSourceMetagenerationMatch"),
    ("if_source_metageneration_not_match", "ifSourceMetagenerationNotMatch"),
)

_NUM_RETRIES_MESSAGE = (
    "`num_retries` has been deprecated and will be removed in a future "
    "release. Use the `retry` argument with a Retry or ConditionalRetryPolicy "
    "object, or None, instead."
)


def _get_storage_host():
    return os.environ.get(STORAGE_EMULATOR_ENV_VAR, _DEFAULT_STORAGE_HOST)


def _validate_name(name):
    """Pre-flight ``Bucket`` name validation.

    :type name: str or :data:`NoneType`
    :param name: Proposed bucket name.

    :rtype: str or :data:`NoneType`
    :returns: ``name`` if valid.
    """
    if name is None:
        return

    # The first and last characters must be alphanumeric.
    if not all([name[0].isalnum(), name[-1].isalnum()]):
        raise ValueError("Bucket names must start and end with a number or letter.")
    return name


class _PropertyMixin(object):
    """Abstract mixin for cloud storage classes with associated properties.

    Non-abstract subclasses should implement:
      - path
      - client
      - user_project

    :type name: str
    :param name: The name of the object. Bucket names must start and end with a
                 number or letter.
    """

    def __init__(self, name=None):
        self.name = name
        self._properties = {}
        self._changes = set()

    @property
    def path(self):
        """Abstract getter for the object path."""
        raise NotImplementedError

    @property
    def client(self):
        """Abstract getter for the object client."""
        raise NotImplementedError

    @property
    def user_project(self):
        """Abstract getter for the object user_project."""
        raise NotImplementedError

    def _require_client(self, client):
        """Check client or verify over-ride.

        :type client: :class:`~google.cloud.storage.client.Client` or
                      ``NoneType``
        :param client: the client to use.  If not passed, falls back to the
                       ``client`` stored on the current object.

        :rtype: :class:`google.cloud.storage.client.Client`
        :returns: The client passed in or the currently bound client.
        """
        if client is None:
            client = self.client
        return client

    def _encryption_headers(self):
        """Return any encryption headers needed to fetch the object.

        .. note::
           Defined here because :meth:`reload` calls it, but this method is
           really only relevant for :class:`~google.cloud.storage.blob.Blob`.

        :rtype: dict
        :returns: a mapping of encryption-related headers.
        """
        return {}

    @property
    def _query_params(self):
        """Default query parameters."""
        params = {}
        if self.user_project is not None:
            params["userProject"] = self.user_project
        return params

    def reload(
        self,
        client=None,
        projection="noAcl",
        if_etag_match=None,
        if_etag_not_match=None,
        if_generation_match=None,
        if_generation_not_match=None,
        if_metageneration_match=None,
        if_metageneration_not_match=None,
        timeout=_DEFAULT_TIMEOUT,
        retry=DEFAULT_RETRY,
    ):
        """Reload properties from Cloud Storage.

        If :attr:`user_project` is set, bills the API request to that project.

        :type client: :class:`~google.cloud.storage.client.Client` or
                      ``NoneType``
        :param client: the client to use. If not passed, falls back to the
                       ``client`` stored on the current object.

        :type projection: str
        :param projection: (Optional) If used, must be 'full' or 'noAcl'.
                           Defaults to ``'noAcl'``. Specifies the set of
                           properties to return.

        :type if_etag_match: Union[str, Set[str]]
        :param if_etag_match: (Optional) See :ref:`using-if-etag-match`

        :type if_etag_not_match: Union[str, Set[str]])
        :param if_etag_not_match: (Optional) See :ref:`using-if-etag-not-match`

        :type if_generation_match: long
        :param if_generation_match:
            (Optional) See :ref:`using-if-generation-match`

        :type if_generation_not_match: long
        :param if_generation_not_match:
            (Optional) See :ref:`using-if-generation-not-match`

        :type if_metageneration_match: long
        :param if_metageneration_match:
            (Optional) See :ref:`using-if-metageneration-match`

        :type if_metageneration_not_match: long
        :param if_metageneration_not_match:
            (Optional) See :ref:`using-if-metageneration-not-match`

        :type timeout: float or tuple
        :param timeout:
            (Optional) The amount of time, in seconds, to wait
            for the server response.  See: :ref:`configuring_timeouts`

        :type retry: google.api_core.retry.Retry or google.cloud.storage.retry.ConditionalRetryPolicy
        :param retry:
            (Optional) How to retry the RPC. See: :ref:`configuring_retries`
        """
        client = self._require_client(client)
        query_params = self._query_params
        # Pass only '?projection=noAcl' here because 'acl' and related
        # are handled via custom endpoints.
        query_params["projection"] = projection
        _add_generation_match_parameters(
            query_params,
            if_generation_match=if_generation_match,
            if_generation_not_match=if_generation_not_match,
            if_metageneration_match=if_metageneration_match,
            if_metageneration_not_match=if_metageneration_not_match,
        )
        headers = self._encryption_headers()
        _add_etag_match_headers(
            headers, if_etag_match=if_etag_match, if_etag_not_match=if_etag_not_match
        )
        api_response = client._get_resource(
            self.path,
            query_params=query_params,
            headers=headers,
            timeout=timeout,
            retry=retry,
            _target_object=self,
        )
        self._set_properties(api_response)

    def _patch_property(self, name, value):
        """Update field of this object's properties.

        This method will only update the field provided and will not
        touch the other fields.

        It **will not** reload the properties from the server. The behavior is
        local only and syncing occurs via :meth:`patch`.

        :type name: str
        :param name: The field name to update.

        :type value: object
        :param value: The value being updated.
        """
        self._changes.add(name)
        self._properties[name] = value

    def _set_properties(self, value):
        """Set the properties for the current object.

        :type value: dict or :class:`google.cloud.storage.batch._FutureDict`
        :param value: The properties to be set.
        """
        self._properties = value
        # If the values are reset, the changes must as well.
        self._changes = set()

    def patch(
        self,
        client=None,
        if_generation_match=None,
        if_generation_not_match=None,
        if_metageneration_match=None,
        if_metageneration_not_match=None,
        timeout=_DEFAULT_TIMEOUT,
        retry=DEFAULT_RETRY_IF_METAGENERATION_SPECIFIED,
    ):
        """Sends all changed properties in a PATCH request.

        Updates the ``_properties`` with the response from the backend.

        If :attr:`user_project` is set, bills the API request to that project.

        :type client: :class:`~google.cloud.storage.client.Client` or
                      ``NoneType``
        :param client: the client to use. If not passed, falls back to the
                       ``client`` stored on the current object.

        :type if_generation_match: long
        :param if_generation_match:
            (Optional) See :ref:`using-if-generation-match`

        :type if_generation_not_match: long
        :param if_generation_not_match:
            (Optional) See :ref:`using-if-generation-not-match`

        :type if_metageneration_match: long
        :param if_metageneration_match:
            (Optional) See :ref:`using-if-metageneration-match`

        :type if_metageneration_not_match: long
        :param if_metageneration_not_match:
            (Optional) See :ref:`using-if-metageneration-not-match`

        :type timeout: float or tuple
        :param timeout:
            (Optional) The amount of time, in seconds, to wait
            for the server response.  See: :ref:`configuring_timeouts`

        :type retry: google.api_core.retry.Retry or google.cloud.storage.retry.ConditionalRetryPolicy
        :param retry:
            (Optional) How to retry the RPC. See: :ref:`configuring_retries`
        """
        client = self._require_client(client)
        query_params = self._query_params
        # Pass '?projection=full' here because 'PATCH' documented not
        # to work properly w/ 'noAcl'.
        query_params["projection"] = "full"
        _add_generation_match_parameters(
            query_params,
            if_generation_match=if_generation_match,
            if_generation_not_match=if_generation_not_match,
            if_metageneration_match=if_metageneration_match,
            if_metageneration_not_match=if_metageneration_not_match,
        )
        update_properties = {key: self._properties[key] for key in self._changes}

        # Make the API call.
        api_response = client._patch_resource(
            self.path,
            update_properties,
            query_params=query_params,
            _target_object=self,
            timeout=timeout,
            retry=retry,
        )
        self._set_properties(api_response)

    def update(
        self,
        client=None,
        if_generation_match=None,
        if_generation_not_match=None,
        if_metageneration_match=None,
        if_metageneration_not_match=None,
        timeout=_DEFAULT_TIMEOUT,
        retry=DEFAULT_RETRY_IF_METAGENERATION_SPECIFIED,
    ):
        """Sends all properties in a PUT request.

        Updates the ``_properties`` with the response from the backend.

        If :attr:`user_project` is set, bills the API request to that project.

        :type client: :class:`~google.cloud.storage.client.Client` or
                      ``NoneType``
        :param client: the client to use. If not passed, falls back to the
                       ``client`` stored on the current object.

        :type if_generation_match: long
        :param if_generation_match:
            (Optional) See :ref:`using-if-generation-match`

        :type if_generation_not_match: long
        :param if_generation_not_match:
            (Optional) See :ref:`using-if-generation-not-match`

        :type if_metageneration_match: long
        :param if_metageneration_match:
            (Optional) See :ref:`using-if-metageneration-match`

        :type if_metageneration_not_match: long
        :param if_metageneration_not_match:
            (Optional) See :ref:`using-if-metageneration-not-match`

        :type timeout: float or tuple
        :param timeout:
            (Optional) The amount of time, in seconds, to wait
            for the server response.  See: :ref:`configuring_timeouts`

        :type retry: google.api_core.retry.Retry or google.cloud.storage.retry.ConditionalRetryPolicy
        :param retry:
            (Optional) How to retry the RPC. See: :ref:`configuring_retries`
        """
        client = self._require_client(client)

        query_params = self._query_params
        query_params["projection"] = "full"
        _add_generation_match_parameters(
            query_params,
            if_generation_match=if_generation_match,
            if_generation_not_match=if_generation_not_match,
            if_metageneration_match=if_metageneration_match,
            if_metageneration_not_match=if_metageneration_not_match,
        )

        api_response = client._put_resource(
            self.path,
            self._properties,
            query_params=query_params,
            timeout=timeout,
            retry=retry,
            _target_object=self,
        )
        self._set_properties(api_response)


def _scalar_property(fieldname):
    """Create a property descriptor around the :class:`_PropertyMixin` helpers."""

    def _getter(self):
        """Scalar property getter."""
        return self._properties.get(fieldname)

    def _setter(self, value):
        """Scalar property setter."""
        self._patch_property(fieldname, value)

    return property(_getter, _setter)


def _write_buffer_to_hash(buffer_object, hash_obj, digest_block_size=8192):
    """Read blocks from a buffer and update a hash with them.

    :type buffer_object: bytes buffer
    :param buffer_object: Buffer containing bytes used to update a hash object.

    :type hash_obj: object that implements update
    :param hash_obj: A hash object (MD5 or CRC32-C).

    :type digest_block_size: int
    :param digest_block_size: The block size to write to the hash.
                              Defaults to 8192.
    """
    block = buffer_object.read(digest_block_size)

    while len(block) > 0:
        hash_obj.update(block)
        # Update the block for the next iteration.
        block = buffer_object.read(digest_block_size)


def _base64_md5hash(buffer_object):
    """Get MD5 hash of bytes (as base64).

    :type buffer_object: bytes buffer
    :param buffer_object: Buffer containing bytes used to compute an MD5
                          hash (as base64).

    :rtype: str
    :returns: A base64 encoded digest of the MD5 hash.
    """
    hash_obj = md5()
    _write_buffer_to_hash(buffer_object, hash_obj)
    digest_bytes = hash_obj.digest()
    return base64.b64encode(digest_bytes)


def _add_etag_match_headers(headers, **match_parameters):
    """Add generation match parameters into the given parameters list.

    :type headers: dict
    :param headers: Headers dict.

    :type match_parameters: dict
    :param match_parameters: if*etag*match parameters to add.
    """
    for snakecase_name, header_name in _ETAG_MATCH_PARAMETERS:
        value = match_parameters.get(snakecase_name)

        if value is not None:
            if isinstance(value, str):
                value = [value]
            headers[header_name] = ", ".join(value)


def _add_generation_match_parameters(parameters, **match_parameters):
    """Add generation match parameters into the given parameters list.

    :type parameters: list or dict
    :param parameters: Parameters list or dict.

    :type match_parameters: dict
    :param match_parameters: if*generation*match parameters to add.

    :raises: :exc:`ValueError` if ``parameters`` is not a ``list()``
             or a ``dict()``.
    """
    for snakecase_name, camelcase_name in _GENERATION_MATCH_PARAMETERS:
        value = match_parameters.get(snakecase_name)

        if value is not None:
            if isinstance(parameters, list):
                parameters.append((camelcase_name, value))

            elif isinstance(parameters, dict):
                parameters[camelcase_name] = value

            else:
                raise ValueError(
                    "`parameters` argument should be a dict() or a list()."
                )


def _raise_if_more_than_one_set(**kwargs):
    """Raise ``ValueError`` exception if more than one parameter was set.

    :type error: :exc:`ValueError`
    :param error: Description of which fields were set

    :raises: :class:`~ValueError` containing the fields that were set
    """
    if sum(arg is not None for arg in kwargs.values()) > 1:
        escaped_keys = ["'%s'" % name for name in kwargs.keys()]

        keys_but_last = ", ".join(escaped_keys[:-1])
        last_key = escaped_keys[-1]

        msg = "Pass at most one of {keys_but_last} and {last_key}".format(
            keys_but_last=keys_but_last, last_key=last_key
        )

        raise ValueError(msg)


def _bucket_bound_hostname_url(host, scheme=None):
    """Helper to build bucket bound hostname URL.

    :type host: str
    :param host: Host name.

    :type scheme: str
    :param scheme: (Optional) Web scheme. If passed, use it
                   as a scheme in the result URL.

    :rtype: str
    :returns: A bucket bound hostname URL.
    """
    url_parts = urlsplit(host)
    if url_parts.scheme and url_parts.netloc:
        return host

    return "{scheme}://{host}/".format(scheme=scheme, host=host)


def _api_core_retry_to_resumable_media_retry(retry, num_retries=None):
    """Convert google.api.core.Retry to google.resumable_media.RetryStrategy.

    Custom predicates are not translated.

    :type retry: google.api_core.Retry
    :param retry: (Optional) The google.api_core.Retry object to translate.

    :type num_retries: int
    :param num_retries: (Optional) The number of retries desired. This is
        supported for backwards compatibility and is mutually exclusive with
        `retry`.

    :rtype: google.resumable_media.RetryStrategy
    :returns: A RetryStrategy with all applicable attributes copied from input,
              or a RetryStrategy with max_retries set to 0 if None was input.
    """

    if retry is not None and num_retries is not None:
        raise ValueError("num_retries and retry arguments are mutually exclusive")

    elif retry is not None:
        return resumable_media.RetryStrategy(
            max_sleep=retry._maximum,
            max_cumulative_retry=retry._deadline,
            initial_delay=retry._initial,
            multiplier=retry._multiplier,
        )
    elif num_retries is not None:
        return resumable_media.RetryStrategy(max_retries=num_retries)
    else:
        return resumable_media.RetryStrategy(max_retries=0)