While I use .onDisconnect() I tried to then use remove() to delete a DatabaseReference, to remove the user from waiting room from database,
here is my code example:
lastOnlineRef
.onDisconnect()
.set(ServerValue.timestamp)
.then(firebaseController.removeThisRoom());
but it seems after onDisconnect() nothing can be sent to the server, do we have a better solution for this? thanks a lot!
The onDisconnect handler (set(ServerValue.timestamp)) runs when the client is no longer connected to the server, so there is no way for the server to notify the client at that point that it has completed the write operation.
Related
So I made a website to show which services on my server are running and which are offline.
The site is an Vuetify App running in a docker container. My services are monitored via UptimeRobot.
Currently I use:
created: function () {
this.interval = setInterval(() => this.getStatuses(), 1000);
},
To trigger my API request function every second to update the status of my services.
But is there some smarter possibility to only update on change and not request every second to see if something happened?
Like I send one request to get the status and then receive a message when something changed? I hope you can understand, whats my problem. It's hard to decribe.
Yes you can by firing an event. for example:
in your app.js
window.Fire = new Vue();
For example here you create a user then you want to update table after creating a new user, Follow these steps:
createUser(){
// FireUpdate is your fire name, you can give it any name you want!
// Call this after you post something to specific route.
Fire.$emit('FireUpadte');
}
Then you will load new users using this approach:
created(){
// Load new Users after created.
Fire.$on('FireUpadte', () => { this.createUser(); });
}
For more information check this video: https://www.youtube.com/watch?v=DHuTkJzH2jI&list=PLB4AdipoHpxaHDLIaMdtro1eXnQtl_UvE&index=20
What you're looking for are websockets. You establish a websocket connection and it stays open, allowing the server to notify the web app when something changes.
You can run your own socket.io server on a Node.js backend or use a service like Pusher.com (very cheap, free tier is pretty big).
I highly recommend going the Pusher.com route, they also have great tutorials ; )
https://pusher.com
I am developing a app that chooses a user and has a 15 sec. timer for that user to respond. The user app queries the db every 5 sec to see if that user is chosen. If so The mobile app begins a 15 sec. timer. The problem is that the timers will never match up because the user app can be on a different timer cycle that the backend and can query the db at a later time. I use Angular, NodeJS, and expressJS + MongoDB to develop this app.
any suggestion on how I can get the timers to be synchronized?
You don't need to have two timers running at the same time. Start a timer on the front-end, then let the back-end know when the timer on the front-end started. As long as you treat one side as the single source of truth, the other side will be able to infer whether the timer has finished or not.
Although the timers might not be synchronized, time should be the same everywhere. If the back-end knows that the front-end timer started at 12:01:00, it also knows that the timer will end at 12:01:15. In this way, it can just continue to check whether the current time is before or after 12:01:15.
This is definitely a job for websockets! Websockets unlike HTTP enable two way data flow so your server and client can talk in real-time. Socket.io is a really popular framework for enabling this type of interaction and hooks really seamlessly into node/express.
http://socket.io/
Here is a tutorial to get your started http://socket.io/get-started/chat/.
The basic flow will be
Open a socket between the user and the server.
When the user is chosen (I assume on the server-side) then do a io.emit('user chosen', { userId: '<the user id>' });. This will send a message over the socket to all attached applications.
Start the timer on the server and send info that the period is over. Something like this should work. setTimeout(() => socket.emit('user chosen end', { userId: '<the user id>' }), 15000);
In your app you will be listening for the 'user_chosen' event and can check if the logged in user has the same id as the one sent over the socket. If the user id's match enable the text input for the user to set the input. Something like this: socket.on('user chosen', function(msg){ /* Enable the input */ });
The app will also be listening for the 'user_chosen_end' event and if the ids of the user again match, disable the text input or do whatever else you need to do. Again this will look like: socket.on('user chosen end', function(msg){ /* Disable the input & do anything else */ });
Hope this helps :)
I am using Smack 4.1.1 as Gradle dependency in mine Android project.
I have successfully established connection with mine local OpenFire server.
But I have an issue while creating temporary room from Android client.
final MultiUserChat multiUserChat = userChatManager.getMultiUserChat(roomId);
try {
multiUserChat.create(connection.getUser());
LOG.debug("room created");
} catch (XMPPException.XMPPErrorException | SmackException e) {
LOG.error("create room error:{}", e);
}
try{
multiUserChat.sendConfigurationForm(new Form(DataForm.Type.submit));
} catch (SmackException.NoResponseException | XMPPException.XMPPErrorException | SmackException.NotConnectedException e) {
LOG.error("sending room configurations error:{}", e);
}
The most great thing is that I can see that room was created in OpenFire admin panel and get room information from another client.
try {
MultiUserChatManager userChatManager = MultiUserChatManager.getInstanceFor(connection);
RoomInfo info = userChatManager.getRoomInfo(roomId);
LOG.debug("room has {} occupants", info.getOccupantsCount());
joinToExistingRoom(roomId);
} catch (XMPPException.XMPPErrorException e) {
LOG.error("join room error:{}", e);
final XMPPError.Condition condition = e.getXMPPError().getCondition();
if (condition == XMPPError.Condition.item_not_found) {
LOG.error("room does not exist error:{}", e);
createRoom(roomId);
}
}
But while trying to join room from second client I receive XMPPError: recipient-unavailable - wait.
Snippet of mine joinRoom method:
final MultiUserChat multiUserChat = userChatManager.getMultiUserChat(roomId);
try {
multiUserChat.join(connection.getUser());
LOG.debug("joined to room:{}", roomId);
} catch (SmackException.NoResponseException
| XMPPException.XMPPErrorException
| SmackException.NotConnectedException e) {
LOG.error("error joining room {}", e);
}
So I am catching error joining room org.jivesoftware.smack.XMPPException$XMPPErrorException: XMPPError:recipient-unavailable - wait
So the question is what can be wrong?
I also tried creating submitForm from createAnswerForm() method. But the result is the same.
One solution I have found to make it work is to send persistantroom as true in Answer of configuration form. But this method creates persistent room, though I need this room to be destroyed after all attendees leave room.
Maybe it is a simple problem, but now I do not know how to solve this issue.
Help will be appreciated a lot.
Thanks in advance.
The create() method documentation states that:
Creates the room according to some default configuration, assign the requesting user as the room owner, and add the owner to the room but not allow anyone else to enter the room (effectively "locking" the room). The requesting user will join the room under the specified nickname as soon as the room has been created.
To create an "Instant Room", that means a room with some default configuration that is available for immediate access, the room's owner should send an empty form after creating the room.
Try to send configuration form this way:
multiUserChat.create(connection.getUser())
Form form = new Form(DataForm.Type.submit);
multiUserChat.sendConfigurationForm(form);
See also muc extension documentation
I am trying to setup some ServiceListeners, in particular two:
zeroConf.addServiceListener("100.1.168.192.in-addr.arpa.", myListener);
zeroConf.addServiceListener("_workstation._tcp.local.", myListener);
Whenever I do this, I get callbacks for myListener on serviceResolved() and serviceAdded() for all services that match "_workstation._tcp.local." However, I get no callbacks for "100.1.168.192.in-addr.arpa." ... despite the fact that jmDns sends out the queries, and a response comes back! I've attached a tcpdump of the request packets that jmdns sends out, and the response that comes back for it. However, the callbacks are not called so I never see the response in my application.
Does anyone know why this might be happening?
http://users.ece.cmu.edu/~gnychis/jmdns_nocallback.pcap
After some debugging of the actual event type that comes in, the event type resolves to "_tcp.in-addr.arpa." Adding this to my service listeners triggers the call back.
My code is for sending Emails to multiple users.User will click on send button,and rpc will be called. Now if user clicks on Cancel button .Ongoing rpc should be cancelled. . Can anyone help ?
I googled a lot, they have introduced the concept of Request Builder. But I am not getting any perfect idea.
Make your async method return a Request instead of void so you can call cancel() on it.
For the same reason, asynchronous methods do not have return types; they generally return void. Should you wish to have more control over the state of a pending request, return Request instead.
— Source: https://developers.google.com/web-toolkit/doc/latest/DevGuideServerCommunication#DevGuideCreatingServices
FYI, you can also use RequestBuilder as the return type, you'll then have to call the send() method by yourself (after possibly customizing the request, e.g. adding headers) to actually make the request to the server.
And of course, if you need to tell the server to abort the processing, you'll have to make another RPC call.
The request is asynch, so the client side can do anything it wants.
All you need to do is add a flag to indicate that the request should be cancelled, and then change the onSuccess method to check the flag and do nothing if it is set.
You should clear the requestCancelled flag each time you make a request - or else after the first request is cancelled, you won't be able to make another one...
e.g.
boolean requestCancelled = false;
void onSuccess(...)
{
if (!requestCancelled) {
// actual response handing code
}
}
If you really want to cancel the request on the server side, it is a lot more complicated. You could do this by sending a second request - one where the fuinctionality is to cancel a request.
To make this work, the "cancel request" has to set a field somewhere the "email request" can read. The "email request" needs to check if the "cancel field" has been set.
// server side Impl
void cancelRequest()
{
// You need to implement this class and ensure it really is a singleton
// and thread safe.
RequestStatusSingleton.setCancelled(true);
}
void serverSideEmailFunc()
{
while(modeEmailAddrs && ! RequestStatusSingleton.getCancelled()) {
// get next address and send email
}
}
Obviously this is a lot of work. Have you considered:
Not having a cancel button on your GUI?
Getting the server to process emails a few at a time (i.e. client sends multiple requests until server tells the client all emails are done).
I totally understand your user. No one wants to wait for 15 seconds.
There is no standard way to "kill" the request, because there is no way to know where your server/datastore is in implementing it. Unless you deal with a process that can be put in a single transaction that can be rolled back, you will have to implement your own logic. For example, if you asked the server to save an entity, you will have to tell the server to save this entity again, but this time without the changes.
Also, think again about your use case. Why a user wants to kill the request? May be he simply wants to go to another place in the app. Then there is no need to kill the request: when the response arrives, check if the user is still in the same place patiently waiting. If not, do not execute onSuccess().