I have a netty web socket server running to which various native javascript clients connect. Now what I want to do is to get requests for data from the clients and pass back data according to what each client requested. There is a class A that actually needs to send continuous data asynchronously(ie: not a simple request reply model)to the client according to the request.
The question is - at class A , I have all the data that I need to send but how to figure out which data has to be sent to which client(has to be according to the client requests) , ie: how do I map the client requests , data to be sent from class A and the channel over which the data needs to be sent from class A. (I store all the channels in a shared ChannelGroup).
You might want to try this.
Instance a DefaultChannelGroup: DefaultChannelGroup myChannels = new DefaultChannelGroup("myChannels")
When a web socket connect is established, add it to the channel group: myChannels.add()
Add the channel id and your request id to a hashmap
When you have data to write, I assume that you have the request id. Use it to look up your channel id in the hashmap
Then get the channel from the channel group: myCahnnels.find(channelId)
Lastly, write the data to the channel.
Hope this helps.
Related
I have a doubt, in a group chat system that has a database with a rest API, who should issue the event of a new message?
The client or the endpoint to create the new message?
For example: X user sends a message to group Y, then uses the api endpoint api.com/message-create and that endpoint emits the message-create event through websocket
Example 2: X user sends a message to group Y, then uses the api api.com/message-create endpoint and the endpoint does not emit the message-create event, but was emitted when the user pressed the send message button
I still don't quite understand if it would occupy more websocket channels to achieve that, if a global one is enough, etc.
The server should be responsible for communication logic. So your first example is better.
But: why do you use two communication channels for sending an creating messages?
If you use websocket, you don't need create a message from a client by using additional rest endpoint.
This approach is prone to errors. For example if the client will loose network connection after sending message through websocket and before executing call to the REST endpoint?
The message will not be stored in a database.
Your flow should looks as follows:
User clicks the send button.
Message is send through the websocket.
Message is stored in the database asynchronously (you can do it directly from communication server, or use rest endpoint)
Emit "new message" event to the group.
I have a http route /checkout which initiates a workflow process in Zeebe. The checkout route will return 200 response straight-away to calling client. Now, workflow will run for a while. So to push the response back to client after completion, I have a /sse separate route for server-sent events. Here, I will store all the client connection in a global map.
My doubt is how do I find the exact client to send the response back through sse once?
Example: Client A listening to /sse and calls /checkout endpoint which will return 200. The /sse has to return the response to client A after completion.
Currently, I thought of using cookie to identify the client. Is there a better way?
If you are already using cookies in your app than that's the way to go since the very purpose of cookies is identifying the client, so if you already have that, you should use it.
But if you rely on another authentication mechanism (like JWT), what you could do is using the url as a query.
So in the client instead of
let eventSource = new EventSource("/sse");
Do
let eventSource = new EventSource("/sse?authorization=jwt_token");
In the backend, you would validate that token, extract the Client ID and hit that global map with it to retrieve the corresponding connection.
(PS: instead of a global map, you should use a proper store, like redis, or an embedded key/value store like bbolt)
I have an application which uses IBM MQ to send out the request in a queue manager to a particular system B.
The response corresponding to that request is then received back from system B by the application in a sync call and then further business processing happens.
Since we are working on the offshore region, we do not actually send out the request to system B but rather capture it ourselves using the MQJExplorer tool and send back the response, which kind of simulates the prod. behaviour.
The problem here is, or i would say, the overhead is that we have to manually open the mqjexplorer tool, check the request, take a particular attribute from the request(lets say ID), and send back ID+1 so that the application recognizes the response is for ID-1 request.
I would like to know if this particular thing can be automated, with some other tool, where i can define like whenever any such kind of request is received in for eg: MQ001 queue manager and its REQ queue, just extract the ID attribute, do a ID+1 and send back the response in RESP queue of same qm.
There are a pair of IBM supplied samples that come with IBM MQ:-
amqsreq0.c - Sample C program that puts request messages to a message queue and shows the replies (example using REPLY queue)
amqsecha.c - Sample C program - echo messages to reply to queue
They are supplied to allow you to try out a request/reply application.
You already have the equivalent app to do the job that amqsreq0.c does, and you could adapt amqsecha.c to extract your ID attribute, increment it, and then the sample already has the code to send the reply back.
It can be automated by running as a triggered application too.
If 'C' language is not your thing and prefer Java then have a read of a blog posting I did in 2017. It is a complete request/reply scenario with 2 applications: BEServer01.java and RQClient01.java
You can modify BEServer01.java to your liking (and remove the SQL code). BEServer01.java contains all of the code for getting a request message and sending a reply message. Simply replace the variable 'replyText' contents with the reply message that you want.
If you are not a programmer then there is another option but it does not modify the message contents. MQ Visual Edit has a component called: SIM Server. Its purpose is to simulate a server-side component. You configure what 'request' queue to get the messages from and what the reply message text will be. When a messages lands on the request queue, the SIM Server will retrieve it and send the reply message to the queue & queue manager specified in the MQMD's ReplyToQueueName and ReplyToQueueManagerName fields.
I am trying to connect to an API that uses websockets. I need to do the following:
Connect to the websocket using a given URI
Send a login request
Send a request for the required data stream(s)
Store the returned streamed data in an array for immediate processing (the array will be continually updated while data is streamed)
When finished collecting data, send a logout request
I have a general understanding of websockets, but have never tried to connect to a websocket. I have read through the “documentation” for packages HTTP (which I have used before), WebSockets, and DandelionWebSockets. Each has left me scratching my head trying to understand how to implement the above tasks.
Would someone please help by showing me, line-by-line, how to set up the above tasks and also explain why each line or function is used? (Assume I have the correct URI, login, data, and logout request formats.)
I'm building a Grails app which queries several API's across the Web. The problem is that this queries are very time consuming and it is really annoying for the user to click one button and wait so much time without nothing changes in the page.
The basic architecture of my app is, when the user clicks the button, the client side performs an Ajax request with Prototype library to the server side. The server side, then, connects to the Last.fm API and retrieve a list of events. When the server side is finished populating the list with events it sends a JSON response to the client side which allows the client side to create markers for each event on a Google map.
What I want to achieve is, instead of waiting for all the events being retrieved from the API to send the JSON response, the server side sends a JSON response as soon as it retrieve one event, allowing the client side to populate the map while other events are yet being retrieved.
Any ideas how can I implement this? I read about the concept of Ajax Push but I'm not sure if it is what I need.
Thanks for the help!
There is no way to open a listening connection on the client that your server might connect to. Instead, what you need is a connection to the server that is kept alive and can be used to receive events. This way, you could directly return the "action" request and inform the client through your persistent event connection once the last.fm request was completed.
That said, the way I would implement is using ajax keep alive.
Take a look at cometd plugin.