Webhooks: block multiple subscriptions to the same callback URL

Will allow only one subscription to a given callback URL. If trying to
subscribe again to the same URL, will return success but with a message
saying the callback URL is duplicated, very similar to the response of
create when called multiple times.

labs/bbb-callback/config.coffee

@@ -47,6 +47,13 @@ config.api.responses.subscribeSuccess = (id) ->
    </response>"
 config.api.responses.subscribeFailure =
   config.api.responses.failure("subscribeEventError", "An error happened while storing your subscription. Check the logs.")
+config.api.responses.subscribeDuplicated = (id) ->
+  "<response> \
+     <returncode>SUCCESS</returncode> \
+     <subscriptionID>#{id}</subscriptionID> \
+     <messageKey>duplicateWarning</messageKey> \
+     <message>There is already a subscription for this callback URL.</message>
+   </response>"
 
 config.api.responses.unsubscribeSuccess =
   "<response> \

labs/bbb-callback/hook.coffee

@@ -26,11 +26,10 @@ module.exports = class Hook
   destroySync: ->
     Hook.destroySync @id
 
-  # TODO: review
-  mapFromRedis: (redisData) ->
-    @callbackURL = redisData?.callbackURL
-    @externalMeetingID = redisData?.externalMeetingID
-    @id = redisData?.subscriptionID
+  # mapFromRedis: (redisData) ->
+  #   @callbackURL = redisData?.callbackURL
+  #   @externalMeetingID = redisData?.externalMeetingID
+  #   @id = redisData?.subscriptionID
 
   # Puts a new message in the queue. Will also trigger a processing in the queue so this
   # message might be processed instantly.
@@ -60,12 +59,16 @@ module.exports = class Hook
       @_processQueue() # go to the next message
 
   @addSubscription = (callbackURL, meetingID=null, callback) ->
-    hook = new Hook()
-    hook.id = nextId++
-    hook.callbackURL = callbackURL
-    hook.externalMeetingID = meetingID
-    hook.saveSync()
-    callback?(null, hook)
+    hook = Hook.findByCallbackURLSync(callbackURL)
+    if hook?
+      callback?(new Error("There is already a subscription for this callback URL"), hook)
+    else
+      hook = new Hook()
+      hook.id = nextId++
+      hook.callbackURL = callbackURL
+      hook.externalMeetingID = meetingID
+      hook.saveSync()
+      callback?(null, hook)
 
   @removeSubscription = (subscriptionID, callback) ->
     hook = Hook.getSync(subscriptionID)
@@ -106,3 +109,8 @@ module.exports = class Hook
     for id of db
       delete db[id]
     db = {}
+
+  @findByCallbackURLSync = (callbackURL) ->
+    for id of db
+      if db[id].callbackURL is callbackURL
+        return db[id]

labs/bbb-callback/web_server.coffee

@@ -42,7 +42,9 @@ module.exports = class WebServer
       respondWithXML(res, config.api.responses.missingParamCallbackURL)
     else
       Hook.addSubscription callbackURL, meetingID, (error, hook) ->
-        if hook?
+        if error? # the only error for now is for duplicated callbackURL
+          msg = config.api.responses.subscribeDuplicated(hook.id)
+        else if hook?
           msg = config.api.responses.subscribeSuccess(hook.id)
         else
           msg = config.api.responses.subscribeFailure