_metadata.py

# Copyright 2016 Google Inc. All rights reserved.
#
# 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.

"""Provides helper methods for talking to the Compute Engine metadata server.

See https://cloud.google.com/compute/docs/metadata for more details.
"""

import datetime
import json
import os

from six.moves import http_client
from six.moves.urllib import parse as urlparse

from google.auth import _helpers
from google.auth import exceptions

_METADATA_ROOT = 'http://metadata.google.internal/computeMetadata/v1/'

# This is used to ping the metadata server, it avoids the cost of a DNS
# lookup.
_METADATA_IP_ROOT = 'http://169.254.169.254'
_METADATA_HEADERS = {'Metadata-Flavor': 'Google'}

# Timeout in seconds to wait for the GCE metadata server when detecting the
# GCE environment.
try:
    _METADATA_DEFAULT_TIMEOUT = int(os.getenv('GCE_METADATA_TIMEOUT', 3))
except ValueError:  # pragma: NO COVER
    _METADATA_DEFAULT_TIMEOUT = 3


def ping(request, timeout=_METADATA_DEFAULT_TIMEOUT):
    """Checks to see if the metadata server is available.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        timeout (int): How long to wait for the metadata server to respond.

    Returns:
        bool: True if the metadata server is reachable, False otherwise.
    """
    # NOTE: The explicit ``timeout`` is a workaround. The underlying
    #       issue is that resolving an unknown host on some networks will take
    #       20-30 seconds; making this timeout short fixes the issue, but
    #       could lead to false negatives in the event that we are on GCE, but
    #       the metadata resolution was particularly slow. The latter case is
    #       "unlikely".
    try:
        response = request(
            'GET', _METADATA_IP_ROOT, headers=_METADATA_HEADERS,
            timeout=timeout, retries=False)
        return response.status == http_client.OK

    # TODO: Remove bare except when transport has a unified exception.
    # pylint: disable=bare-except
    except:  # socket.timeout or socket.error(64, 'Host is down')
        # logger.info('Timeout attempting to reach GCE metadata service.')
        return False


def get(request, path, root=_METADATA_ROOT, recursive=None):
    """Fetch a resource from the metadata server.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        path (str): The resource to retrieve. For example,
            ``'instance/service-accounts/defualt'``.
        root (str): The full path to the metadata server root.
        recursive (bool): Whether to do a recursive query of metadata. See
            https://cloud.google.com/compute/docs/metadata#aggcontents for more
            details.

    Returns:
        Union[Mapping, str]: If the metadata server returns JSON, a mapping of
            the decoded JSON is return. Otherwise, the response content is
            returned as a string.

    Raises:
        google.auth.exceptions.TransportError: if an error occurred while
            retrieving metadata.
    """
    url = urlparse.urljoin(root, path)
    url = _helpers.update_query(url, {'recursive': recursive})

    response = request('GET', url, headers=_METADATA_HEADERS)

    if response.status == http_client.OK:
        content = _helpers.from_bytes(response.data)
        if response.headers['content-type'] == 'application/json':
            return json.loads(content)
        else:
            return content
    else:
        raise exceptions.TransportError(
            'Failed to retrieve {} from the Google Compute Engine'
            'metadata service. Status: {} Response:\n{}'.format(
                url, response.status, response.data), response)


def get_service_account_info(request, service_account='default'):
    """Get information about a service account from the metadata server.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        service_account (str): The string 'default' or a service account email
            address. The determines which service account for which to acquire
            information.

    Returns:
        Mapping: The service account's information, for example::

            {
                'email': '...',
                'scopes': ['scope', ...],
                'aliases': ['default', '...']
            }

    Raises:
        google.auth.exceptions.TransportError: if an error occurred while
            retrieving metadata.
    """
    return get(
        request,
        'instance/service-accounts/{0}/'.format(service_account),
        recursive=True)


def get_service_account_token(request, service_account='default'):
    """Get the OAuth 2.0 access token for a service account.

    Args:
        request (google.auth.transport.Request): A callable used to make
            HTTP requests.
        service_account (str): The string 'default' or a service account email
            address. The determines which service account for which to acquire
            an access token.

    Returns:
        Union[str, datetime]: The access token and its expiration.

    Raises:
        google.auth.exceptions.TransportError: if an error occurred while
            retrieving metadata.
    """
    token_json = get(
        request,
        'instance/service-accounts/{0}/token'.format(service_account))
    token_expiry = _helpers.now() + datetime.timedelta(
        seconds=token_json['expires_in'])
    return token_json['access_token'], token_expiry