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module Koala
module Facebook
class RealtimeUpdates
# Manage realtime callbacks for changes to users' information.
# See
# @note: to subscribe to real-time updates, you must have an application access token
# or provide the app secret when initializing your RealtimeUpdates object.
attr_reader :app_id, :app_access_token, :secret
# Create a new RealtimeUpdates instance.
# If you don't have your app's access token, provide the app's secret and
# Koala will make a request to Facebook for the appropriate token.
# @param options initialization options.
# @option options :app_id the application's ID.
# @option options :app_access_token an application access token, if known.
# @option options :secret the application's secret.
# @raise ArgumentError if the application ID and one of the app access token or the secret are not provided.
def initialize(options = {})
@app_id = options[:app_id] || Koala.config.app_id
@app_access_token = options[:app_access_token] || Koala.config.app_access_token
@secret = options[:secret] || Koala.config.app_secret
unless @app_id && (@app_access_token || @secret) # make sure we have what we need
raise ArgumentError, "Initialize must receive a hash with :app_id and either :app_access_token or :secret! (received #{options.inspect})"
# The app access token, either provided on initialization or fetched from Facebook using the
# app_id and secret.
def app_access_token
# If a token isn't provided but we need it, fetch it
@app_access_token ||=, @secret).get_app_access_token
# The application API interface used to communicate with Facebook.
# @return [Koala::Facebook::API]
def api
# Only instantiate the API if needed. validate_update doesn't require it, so we shouldn't
# make an unnecessary request to get the app_access_token.
@api ||=
# Subscribe to realtime updates for certain fields on a given object (user, page, etc.).
# See { the realtime updates documentation}
# for more information on what objects and fields you can register for.
# @note Your callback_url must be set up to handle the verification request or the subscription will not be set up.
# @param object a Facebook ID (name or number)
# @param fields the fields you want your app to be updated about
# @param callback_url the URL Facebook should ping when an update is available
# @param verify_token a token included in the verification request, allowing you to ensure the call is genuine
# (see the docs for more information)
# @param options (see Koala::HTTPService.make_request)
# @raise A subclass of Koala::Facebook::APIError if the subscription request failed.
def subscribe(object, fields, callback_url, verify_token, options = {})
args = {
:object => object,
:fields => fields,
:callback_url => callback_url,
}.merge(verify_token ? {:verify_token => verify_token} : {})
# a subscription is a success if Facebook returns a 200 (after hitting your server for verification)
api.graph_call(subscription_path, args, 'post', options)
# Unsubscribe from updates for a particular object or from updates.
# @param object the object whose subscriptions to delete.
# If no object is provided, all subscriptions will be removed.
# @param options (see Koala::HTTPService.make_request)
# @raise A subclass of Koala::Facebook::APIError if the subscription request failed.
def unsubscribe(object = nil, options = {})
api.graph_call(subscription_path, object ? {:object => object} : {}, "delete", options)
# List all active subscriptions for this application.
# @param options (see Koala::HTTPService.make_request)
# @return [Array] a list of active subscriptions
def list_subscriptions(options = {})
api.graph_call(subscription_path, {}, "get", options)
# As a security measure (to prevent DDoS attacks), Facebook sends a verification request to your server
# after you request a subscription.
# This method parses the challenge params and makes sure the call is legitimate.
# @param params the request parameters sent by Facebook. (You can pass in a Rails params hash.)
# @param verify_token the verify token sent in the {#subscribe subscription request}, if you provided one
# @yield verify_token if you need to compute the verification token
# (for instance, if your callback URL includes a record ID, which you look up
# and use to calculate a hash), you can pass meet_challenge a block, which
# will receive the verify_token received back from Facebook.
# @return the challenge string to be sent back to Facebook, or false if the request is invalid.
def self.meet_challenge(params, verify_token = nil, &verification_block)
if params["hub.mode"] == "subscribe" &&
# you can make sure this is legitimate through two ways
# if your store the token across the calls, you can pass in the token value
# and we'll make sure it matches
((verify_token && params["hub.verify_token"] == verify_token) ||
# alternately, if you sent a specially-constructed value (such as a hash of various secret values)
# you can pass in a block, which we'll call with the verify_token sent by Facebook
# if it's legit, return anything that evaluates to true; otherwise, return nil or false
(verification_block && yield(params["hub.verify_token"])))
# Public: As a security measure, all updates from facebook are signed using
# X-Hub-Signature: sha1=XXXX where XXX is the sha1 of the json payload
# using your application secret as the key.
# Example:
# # in Rails controller
# # @oauth being a previously defined Koala::Facebook::OAuth instance
# def receive_update
# if @oauth.validate_update(request.body, headers)
# ...
# end
# end
def validate_update(body, headers)
unless @secret
raise AppSecretNotDefinedError, "You must init RealtimeUpdates with your app secret in order to validate updates"
request_signature = headers['X-Hub-Signature'] || headers['HTTP_X_HUB_SIGNATURE']
return unless request_signature
signature_parts = request_signature.split("sha1=")
request_signature = signature_parts[1]
calculated_signature = OpenSSL::HMAC.hexdigest('sha1', @secret, body)
calculated_signature == request_signature
# The Facebook subscription management URL for your application.
def subscription_path
@subscription_path ||= "#{@app_id}/subscriptions"