1a5e30e432
API which has a much simpler interface. Look in the module doc string for how this API would be used. Reviewed in https://codereview.appspot.com/9885043/.
286 lines
9.6 KiB
Python
286 lines
9.6 KiB
Python
"""Channel notifications support.
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Classes and functions to support channel subscriptions and notifications
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on those channels.
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Notes:
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- This code is based on experimental APIs and is subject to change.
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- Notification does not do deduplication of notification ids, that's up to
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the receiver.
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- Storing the Channel between calls is up to the caller.
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Example setting up a channel:
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# Create a new channel that gets notifications via webhook.
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channel = new_webhook_channel("https://example.com/my_web_hook")
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# Store the channel, keyed by 'channel.id'. Store it before calling the
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# watch method because notifications may start arriving before the watch
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# method returns.
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...
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resp = service.objects().watchAll(
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bucket="some_bucket_id", body=channel.body()).execute()
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channel.update(resp)
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# Store the channel, keyed by 'channel.id'. Store it after being updated
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# since the resource_id value will now be correct, and that's needed to
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# stop a subscription.
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...
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An example Webhook implementation using webapp2. Note that webapp2 puts
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headers in a case insensitive dictionary, as headers aren't guaranteed to
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always be upper case.
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id = self.request.headers[X_GOOG_CHANNEL_ID]
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# Retrieve the channel by id.
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channel = ...
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# Parse notification from the headers, including validating the id.
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n = notification_from_headers(channel, self.request.headers)
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# Do app specific stuff with the notification here.
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if n.resource_state == 'sync':
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# Code to handle sync state.
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elif n.resource_state == 'exists':
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# Code to handle the exists state.
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elif n.resource_state == 'not_exists':
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# Code to handle the not exists state.
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Example of unsubscribing.
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service.channels().stop(channel.body())
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"""
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import datetime
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import uuid
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from apiclient import errors
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from oauth2client import util
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# The unix time epoch starts at midnight 1970.
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EPOCH = datetime.datetime.utcfromtimestamp(0)
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# Map the names of the parameters in the JSON channel description to
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# the parameter names we use in the Channel class.
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CHANNEL_PARAMS = {
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'address': 'address',
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'id': 'id',
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'expiration': 'expiration',
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'params': 'params',
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'resourceId': 'resource_id',
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'resourceUri': 'resource_uri',
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'type': 'type',
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'token': 'token',
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}
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X_GOOG_CHANNEL_ID = 'X-GOOG-CHANNEL-ID'
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X_GOOG_MESSAGE_NUMBER = 'X-GOOG-MESSAGE-NUMBER'
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X_GOOG_RESOURCE_STATE = 'X-GOOG-RESOURCE-STATE'
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X_GOOG_RESOURCE_URI = 'X-GOOG-RESOURCE-URI'
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X_GOOG_RESOURCE_ID = 'X-GOOG-RESOURCE-ID'
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def _upper_header_keys(headers):
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new_headers = {}
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for k, v in headers.iteritems():
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new_headers[k.upper()] = v
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return new_headers
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class Notification(object):
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"""A Notification from a Channel.
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Notifications are not usually constructed directly, but are returned
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from functions like notification_from_headers().
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Attributes:
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message_number: int, The unique id number of this notification.
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state: str, The state of the resource being monitored.
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uri: str, The address of the resource being monitored.
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resource_id: str, The unique identifier of the version of the resource at
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this event.
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"""
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@util.positional(5)
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def __init__(self, message_number, state, resource_uri, resource_id):
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"""Notification constructor.
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Args:
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message_number: int, The unique id number of this notification.
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state: str, The state of the resource being monitored. Can be one
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of "exists", "not_exists", or "sync".
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resource_uri: str, The address of the resource being monitored.
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resource_id: str, The identifier of the watched resource.
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"""
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self.message_number = message_number
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self.state = state
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self.resource_uri = resource_uri
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self.resource_id = resource_id
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class Channel(object):
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"""A Channel for notifications.
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Usually not constructed directly, instead it is returned from helper
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functions like new_webhook_channel().
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Attributes:
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type: str, The type of delivery mechanism used by this channel. For
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example, 'web_hook'.
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id: str, A UUID for the channel.
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token: str, An arbitrary string associated with the channel that
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is delivered to the target address with each event delivered
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over this channel.
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address: str, The address of the receiving entity where events are
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delivered. Specific to the channel type.
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expiration: int, The time, in milliseconds from the epoch, when this
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channel will expire.
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params: dict, A dictionary of string to string, with additional parameters
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controlling delivery channel behavior.
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resource_id: str, An opaque id that identifies the resource that is
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being watched. Stable across different API versions.
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resource_uri: str, The canonicalized ID of the watched resource.
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"""
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@util.positional(5)
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def __init__(self, type, id, token, address, expiration=None,
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params=None, resource_id="", resource_uri=""):
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"""Create a new Channel.
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In user code, this Channel constructor will not typically be called
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manually since there are functions for creating channels for each specific
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type with a more customized set of arguments to pass.
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Args:
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type: str, The type of delivery mechanism used by this channel. For
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example, 'web_hook'.
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id: str, A UUID for the channel.
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token: str, An arbitrary string associated with the channel that
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is delivered to the target address with each event delivered
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over this channel.
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address: str, The address of the receiving entity where events are
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delivered. Specific to the channel type.
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expiration: int, The time, in milliseconds from the epoch, when this
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channel will expire.
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params: dict, A dictionary of string to string, with additional parameters
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controlling delivery channel behavior.
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resource_id: str, An opaque id that identifies the resource that is
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being watched. Stable across different API versions.
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resource_uri: str, The canonicalized ID of the watched resource.
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"""
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self.type = type
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self.id = id
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self.token = token
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self.address = address
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self.expiration = expiration
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self.params = params
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self.resource_id = resource_id
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self.resource_uri = resource_uri
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def body(self):
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"""Build a body from the Channel.
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Constructs a dictionary that's appropriate for passing into watch()
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methods as the value of body argument.
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Returns:
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A dictionary representation of the channel.
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"""
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result = {
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'id': self.id,
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'token': self.token,
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'type': self.type,
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'address': self.address
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}
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if self.params:
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result['params'] = self.params
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if self.resource_id:
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result['resourceId'] = self.resource_id
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if self.resource_uri:
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result['resourceUri'] = self.resource_uri
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if self.expiration:
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result['expiration'] = self.expiration
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return result
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def update(self, resp):
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"""Update a channel with information from the response of watch().
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When a request is sent to watch() a resource, the response returned
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from the watch() request is a dictionary with updated channel information,
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such as the resource_id, which is needed when stopping a subscription.
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Args:
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resp: dict, The response from a watch() method.
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"""
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for json_name, param_name in CHANNEL_PARAMS.iteritems():
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value = resp.get(json_name)
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if value is not None:
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setattr(self, param_name, value)
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def notification_from_headers(channel, headers):
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"""Parse a notification from the webhook request headers, validate
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the notification, and return a Notification object.
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Args:
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channel: Channel, The channel that the notification is associated with.
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headers: dict, A dictionary like object that contains the request headers
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from the webhook HTTP request.
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Returns:
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A Notification object.
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Raises:
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errors.InvalidNotificationError if the notification is invalid.
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ValueError if the X-GOOG-MESSAGE-NUMBER can't be converted to an int.
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"""
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headers = _upper_header_keys(headers)
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channel_id = headers[X_GOOG_CHANNEL_ID]
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if channel.id != channel_id:
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raise errors.InvalidNotificationError(
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'Channel id mismatch: %s != %s' % (channel.id, channel_id))
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else:
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message_number = int(headers[X_GOOG_MESSAGE_NUMBER])
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state = headers[X_GOOG_RESOURCE_STATE]
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resource_uri = headers[X_GOOG_RESOURCE_URI]
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resource_id = headers[X_GOOG_RESOURCE_ID]
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return Notification(message_number, state, resource_uri, resource_id)
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@util.positional(2)
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def new_webhook_channel(url, token=None, expiration=None, params=None):
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"""Create a new webhook Channel.
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Args:
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url: str, URL to post notifications to.
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token: str, An arbitrary string associated with the channel that
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is delivered to the target address with each notification delivered
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over this channel.
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expiration: datetime.datetime, A time in the future when the channel
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should expire. Can also be None if the subscription should use the
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default expiration. Note that different services may have different
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limits on how long a subscription lasts. Check the response from the
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watch() method to see the value the service has set for an expiration
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time.
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params: dict, Extra parameters to pass on channel creation. Currently
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not used for webhook channels.
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"""
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expiration_ms = 0
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if expiration:
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delta = expiration - EPOCH
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expiration_ms = delta.microseconds/1000 + (
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delta.seconds + delta.days*24*3600)*1000
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if expiration_ms < 0:
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expiration_ms = 0
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return Channel('web_hook', str(uuid.uuid4()),
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token, url, expiration=expiration_ms,
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params=params)
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