EWS Pull notifications are great in fetching new mails arriving while polling for the notifications, however if I increase the intervals between polling requests, the mails arriving between each requests do not get picked up.
Am I doing something wrong, or missing something trivial?
String subscriptionID = null
do {
PullSubscription subscription = service.subscribeToPullNotifications (...subscriptionID ...)
subscriptionID = subscription.getWaterMark();
...
} while(true);
Retaining previous watermark solvEd it
Related
What is the best practice to handle seen/unseen messages in a chat room application based on Nodejs/SocketIO/React.
Consider User1 sends a message to a room. If another user has seen that message, notify all users that the state of message has been seen.
In my opinion using message brokers can be the better solution instead socket. I actually think that socket should only handle chat messages that are synchronously. but for seen/unseen status I prefer message brokers that are asynchronous. Are there any solutions or best practice in large scale applications?
It's unclear what you have currently tried, meaning that I can only advise solutions in order to achieve your aim.
To firstly identify that a message was seen, IntersectionObserver is an inbuilt API that detects when an element has entered the viewport, meaning that it is visible, therefore; obviously seen. I have added comments in the code below where you should add a function to call to the server that the message was seen, however, that's up to you to implement.
const observer = new window.IntersectionObserver(([entry]) => {
if (entry.isIntersecting) {
// Send a message to the server that the user has viewed the message.
// Eg. socket.emit('read-message', message.id)
return
}
}, {
root: null,
threshold: 0.1,
})
observer.observe(document.getElementById(message.id));
Additionally, there's no need to use message broker, as socket.io can handle simple interactions such as this.
You then need to send a message to the server that denotes the specified message ID was seen, then broadcast to every other client that the state was changed, and update it to read - if that's needed.
I am investigating using sagas in mass transit to orchestrate activities across several services. The lifetime of the saga is short - less than 2 seconds if all goes well.
For my use case, i would like to use the request/respond approach, whereby the client requests a command, the saga handles that command, goes through some state changes as messages are received and eventually responds to the first command that initiated the saga, at which point the client receives the response and can display the result of the saga.
From what i can see, by this point, the context is no longer aware of the initial request. How can I reply to a message that was received in this way? Is there something i can persist to the saga data when handling the first event, and use that to reply later on?
Thanks Alexey. I have realised that I can store the ResponseAddress and RequestId from the original message on the saga, and then construct a Send() later on.
Getting the response details from the original request
MassTransit.EntityFrameworkIntegration.Saga.EntityFramework
SagaConsumeContext<TSagaData, TMessage> payload;
if (ctx.TryGetPayload(out payload))
{
ResponseAddress = payload.ResponseAddress;
RequestId = payload.RequestId ;
}
Sending the response
var responseEndpoint = await ctx.GetSendEndpoint(responseAddress);
await responseEndpoint.Send(message, c => c.RequestId = requestId);
UPDATE: The documentation has been updated to include a more complete example.
Currently, the saga state machine can only do immediate response like this:
// client
var response = await client.Request(requestMessage);
// saga
During(SomeState,
When(RequestReceived)
.Then(...)
.Respond(c => MakeResponseMessage(c))
.TransitionTo(Whatever)
)
So you can respond when handling a request.
If you want to respond to something you received before, you will have to craft the request/response conversation yourself. I mean that you will have to have decoupled response, so you need to send a message and have a full-blown consumer for the reply message. This will be completely asynchronous business.
I'm looking to develop a chat application with Pubnub where I want to make sure all the chat messages that are send is been stored in the database and also want to send messages in chat.
I found out that I can use the Parse with pubnub to provide storage options, But I'm not sure how to setup those two in a way where the messages and images send in the chat are been stored in the database.
Anyone have done this before with pubnub and parse? Are there any other easy options available to use with pubnub instead of using parse?
Sutha,
What you are seeking is not a trivial solution unless you are talking about a limited number of end users. So I wouldn't say there are no "easy" solutions, but there are solutions.
The reason is your server would need to listen (subscribe) to every chat channel that is active and store the messages being sent into your database. Imagine your app scaling to 1 million users (doesn't even need to get that big, but that number should help you realize how this can get tricky to scale where several server instances are listening to channels in a non-overlapping manner or with overlap but using a server queue implementation and de-duping messages).
That said, yes, there are PubNub customers that have implemented such a solution - Parse not being the key to making this happen, by the way.
You have three basic options for implementing this:
Implement a solution that will allow many instances of your server to subscribe to all of the channels as they become active and store the messages as they come in. There are a lot of details to making this happen so if you are not up to this then this is not likely where you want to go.
There is a way to monitor all channels that become active or inactive with PubNub Presence webhooks (enable Presence on your keys). You would use this to keep a list of all channels that your server would use to pull history (enable Storage & Playback on your keys) from in an on-demand (not completely realtime) fashion.
For every channel that goes active or inactive, your server will receive these events via the REST call (and endpoint that you implement on your server - your Parse server in this case):
channel active: record "start chat" timetoken in your Parse db
channel inactive: record "end chat" timetoken in your Parse db
the inactive event is the kickoff for a process that uses start/end timetokens that you recorded for that channel to get history from for channel from PubNub: pubnub.history({channel: channelName, start:startTT, end:endTT})
you will need to iterate on this history call until you receive < 100 messages (100 is the max number of messages you can retrieve at a time)
as you retrieve these messages you will save them to your Parse db
New Presence Webhooks have been added:
We now have webhooks for all presence events: join, leave, timeout, state-change.
Finally, you could just save each message to Parse db on success of every pubnub.publish call. I am not a Parse expert and barely know all of its capabilities but I believe they have some sort or store local then sync to cloud db option (like StackMob when that was a product), but even if not, you will save msg to Parse cloud db directly.
The code would look something like this (not complete, likely errors, figure it out or ask PubNub support for details) in your JavaScript client (on the browser).
var pubnub = PUBNUB({
publish_key : your_pub_key,
subscribe_key : your_sub_key
});
var msg = ... // get the message form your UI text box or whatever
pubnub.publish({
// this is some variable you set up when you enter a chat room
channel: chat_channel,
message: msg
callback: function(event){
// DISCLAIMER: code pulled from [Parse example][4]
// but there are some object creation details
// left out here and msg object is not
// fully fleshed out in this sample code
var ChatMessage = Parse.Object.extend("ChatMessage");
var chatMsg = new ChatMessage();
chatMsg.set("message", msg);
chatMsg.set("user", uuid);
chatMsg.set("channel", chat_channel);
chatMsg.set("timetoken", event[2]);
// this ChatMessage object can be
// whatever you want it to be
chatMsg.save();
}
error: function (error) {
// Handle error here, like retry until success, for example
console.log(JSON.stringify(error));
}
});
You might even just store the entire set of publishes (on both ends of the conversation) based on time interval, number of publishes or size of total data but be careful because either user could exit the chat and the browser without notice and you will fail to save. So the per publish save is probably best practice if a bit noisy.
I hope you find one of these techniques as a means to get started in the right direction. There are details left out so I expect you will have follow up questions.
Just some other links that might be helpful:
http://blog.parse.com/learn/building-a-killer-webrtc-video-chat-app-using-pubnub-parse/
http://www.pubnub.com/blog/realtime-collaboration-sync-parse-api-pubnub/
https://www.pubnub.com/knowledge-base/discussion/293/how-do-i-publish-a-message-from-parse
And we have a PubNub Parse SDK, too. :)
I've created a real time game for Google Play Game Services. It's in the later alpha stages right now. I have a question about sendReliableMessage. I've noticed certain cases where the other peer doesn't receive the message. I am aware that there is a callback onRealTimeMessageSent and I have some code in my MainActivity:
#Override
public void onRealTimeMessageSent(int i, int i2, String s) {
if(i== GamesStatusCodes.STATUS_OK)
{
}
else
{
lastMessageStatus=i;
sendToast("lastMessageStatus:"+Integer.toString(lastMessageStatus));
}
}
My games render loop is checking every iteration the value of lastMessageStatus and if there was something other than STATUS_OK I'm painting a T-Rex right now.
My question is is checking the sent status really enough? I also could create source code where the sender has to wait for an Acknowledged message. Each message would be stamped with a UUID and if ack is not received within a timeout then the sender would send the message again? Is an ACK based system necessary to create a persistent connection?
I've noticed certain cases where there is some lag before the opposite peer received the reliable message and I was wondering is there a timeout on the sendReliable message? Google Play Services documentation doesn't seem to indicate in the documentation that there is a timeout at all.
Thank you
Reliable messages are just that, reliable. There are not a lot of use cases for the onRealTimeMessageSent callback for reliable messages because, as you said, it does not guarantee that the recipient has processed the message yet. Only that it was sent.
It may seem annoying, but an ACK-based system is the best way to know for sure that your user has received the message. A UUID is one good way to do this. I have done this myself and found it to work great (although now you have round-trip latency).
As far as timeout, that is not implemented in the RealTime Messaging API. I have personally found round trip latency (send message, receive ACK in callback) to be about 200ms, and I have never found a way to make a message fail to deliver eventually even when purposefully using bad network conditions.
So I have request/response queues that I am putting messages on and reading messages off from.
The problem is that I have multiple local instances that are reading/feeding off the same queues, and what happens sometimes is that one instance can read some other instance's reply message.
So is there a way I can configure my JMS, using spring that actually makes the instances read the messages that are only requested by them and not read other instance's messages.
I have very little knowledge about JMS and related stuff. So if the above question needs more info then I can dig around and provide it.
Thanks
It's easy!
A JMS message have two properties you can use - JMSMessageID and JMSCorrelationID.
A JMSMessageId is supposed to be unique for each message, so you could do something like this:
Let the client send a request, then start to listen for responses where the correlation id = the sent message id. The server side is then responsible for copying the message id of the request to the correlation id of the response. Something like: responseMsg.setJMSCorrelationID(requestMsg.getJMSMessageID());
Example client side code:
Session session = getSession();
Message msg = createRequest();
MessageProducer mp = session.createProducer(session.createQueue("REQUEST.QUEUE"));
mp.send(msg,DeliveryMode.NON_PERSISTENT,0,TIMEOUT);
// If session is transactional - commit now.
String msgID = msg.getJMSMessageID();
MessageConsumer mc = session.createConsumer(session.createQueue("REPLY.QUEUE"),
"JMSCorrelationID='" + msgId + "'");
Message response = mc.receive(TIMEOUT);
A more performant solution would be to use dedicated reply queues per destination. Simply set message.setJMSReplyTo(session.createQueue("REPLY.QUEUE."+getInstanceId())); and make sure the server side sends response to requestMsg.getJMSReplyTo() and not to a hard coded value.