The design of my current stomp client process is as follows:
Open stomp connection (sending CONNECT frame)
Subscribe to a feed (send a SUBSCRIBE frame)
Do a loop to continually receive feed:
while (true) {
connection.begin("txt1");
StompFrame message = connection.receive();
System.out.println("message get header"+message.toString());
LOG.info(message.getBody());
connection.ack(message, "txt1");
connection.commit("txt1");
}
My problem with this process is that I get
java.net.SocketTimeoutException: Read timed out
at java.net.SocketInputStream.socketRead0(Native Method)...
and I think the cause of this is mostly because the feed I am subscribed to gives information slower on certain times (as I normally get this error when the weekend comes, holidays or evenings).
I have been reading up on this here and I think this would help with my problem. However, I'm not so sure how to incorporate it with the current layout of my stomp client. Would I have to send a CONNECT header within Step 3?
I am currently using activemq to create my stomp client if that helps.
In the stomp spec we have:
Regarding the heart-beats themselves, any new data received over the
network connection is an indication that the remote end is alive. In a
given direction, if heart-beats are expected every milliseconds:
the sender MUST send new data over the network connection at least every milliseconds
if the sender has no real STOMP frame to send, it MUST send a single newline byte (0x0A)
if, inside a time window of at least milliseconds, the receiver did not receive any new data, it CAN consider the
connection as dead
because of timing inaccuracies, the receiver SHOULD be tolerant and take into account an error margin
Would that mean my client would need to send a newline bye every n seconds?
The stomp server you are connected to has timed out your connection due to innactivity.
Providing the server supports Stomp version 1.1 or newer, the easiest solution for your client is to include a heart-beat instruction in the header of your CONNECT, such as "0,10000". This tells the server that you cannot send heart-beats, but you want it to send one every 10 seconds. This way you don't need to implement them, and the server will keep the connection active by sending them to you.
Of course the server will have its own requirements of the client. In your comment it responds to your request with "1000,0". This indicates that it will send a heart-beat every 1000 millisecs, and it expects you to send one every 0 millisecs, 0 indicating none at all. So your job will be minimal.
Related
I have a controller in spring which getting a POST request which is handling as asynchronous(using DeferredResult object as a return value).
The response for this request is writing bytes to the HTTP stream directly (HttpServletResponse.getWriter().print()) and when it's done writing it sets result on the DeferredResult object for close the connection.
I'm writing my response in stream chunks.
I have an issue in this request handling because the client is closing the connection if I'm not writing to it for 1 minute. (I can write some chunks and then stop writing for 1 minute - therefore the connection will be closed in the middle of my procedure).
I want to control the closing connection procedure - I want to send keep alive when I'm not writing any data to the stream so that the connection won't be closed until I decided to close it from the server-side.
I didn't find out how should I get control of the connection from the controller in the server.
Please assist.
Thanks.
There is no such thing as a "keep alive" during an ongoing request or response in HTTP which can help with idle timeouts when receiving a request or response.
HTTP keep alive is only about keeping the TCP connection open after a response in order to process more requests on the same connection. TCP keep alive is instead used to detect connection loss without TCP shutdown and can also be used to prevent idle timeouts in stateful packet filters (as used in firewalls or NAT routers) in between client and server. It does not prevent idle timeouts at the application level though since it does not transport any data visible to the application level.
Note that the way you want to use HTTP is contrary to how HTTP was designed originally. It was designed for a client sending a full request and the server sending a full response immediately and not for the server sending some parts of the response, idling some time and then send some more. The proper way to implement such behavior would be by using WebSockets. With WebSockets both client and server can send new messages at any time (i.e. no request-response schema) and it also supports keep-alive messages. If WebSockets are not an option you can instead implement a polling client which regularly polls for new data from the server with a new request.
I ran into similar need just recently. The server code executes a long running operation that can take as long as 30 minutes to return, and the client times out long before that. The solution was to have the long running operation send periodic "keep alive" packets of data to the client via a "callback" argument provided by the request handler method. The callback is nothing more than a function (think of Lambda in Java) that takes as parameter the "keep alive" data packet to send to client, and then writes that data packet to the client via the java.io.PrintWriter reference that you can get off of javax.servlet.http.HttpServletResponse. Below code is the handler method that does this. I had to refactor the code in the call hierarchy to accept this new "callback" parameter until the "callback" can reach the method that is performing the long running operation, and inside that code I invoke the "callback" every so often, for example every time 10 records are processed. Not that below is Groovy code (scripting code on top of Java that runs on the JVM) and the server-side framework is Spring,
...
#Autowired
DataImporter dataImporter
#PostMapping("/my/endpoint")
void importData(#RequestBody MyDto myDto, HttpServletResponse response) {
// Callback to allow servant code deep in the call hierarchy to report back to client any arbitrary message
Closure<Void> callback = { String str ->
response.writer.print str
response.writer.flush()
}
// This leads to the code that is performing a long running operation. Using
// this "hook" that code has a direct connection to the client whereby
// it can send packets of data to keep the connection from timing out.
dataImporter.importData(myDto, callback)
}
}
I have a distributed system application that uses JBoss as an application server. I have a client application that serves as a simulation engine. When client is up, it sends an registration message(JMS message) to Server, then some field is set in the database. When Server is up, it sends a message ( a topic) to all clients to check that they are alive. If clients are alive, they can read message and send a response to server (queue) that it is alive.
If user close client normally, client send a message to server that I will unregister. Then server unregisters it. This is done in database side.
If user close client abnormally(kill) , then client can not send a message to server for unregistration. Then server does not know this client is not alive anymore. This causes inconsistency in my application. So I need a way to understand that client subscribed a topic is not subscribed anymore.
Server sends a message to topic to check that clients are alive.
#Schedule(hour = "*", minute = "*", second = "30", persistent = false)
public void sendNodeStatusRequest() {
Message msg = MessageFactory.createStatusRequestMessage();
publishNodeMessage(msg);
}
After a time, Server show following logs. Could I catch this warning from Java?
07:17:00,698 WARN [org.hornetq.core.protocol.core.impl.RemotingConnectionImpl] Connection failure
has been detected: Did not receive ping from /127.0.0.1:61888. It is likely
the client has exited or crashed without closing its connection, or the
network between the server and client has failed. The connection will now be closed. [code=3]
07:17:00,698 WARN [org.hornetq.core.server.impl.ServerSessionImpl] Client
connection failed, clearing up resources for session 4e4e9dc6-153e-11e7-
80fa-742b62812c29
To me the whole point of messaging system is decoupled communication. The sender (server in your case) send its stuff to the topic without actually knowing who will get the message. The clients come and go, and they should be able to read the message whenever it (still) resides in the topic.
Now from your question I understand that the server keeps track of all the connected clients by means of receiving the message back to the dedicated queue.
So I'm asking myself - maybe its something wrong with the design here.
Let me propose slightly different way of implementation.
The server should not be aware of any client, at most (because your system seems to work this way) it should know that client A, B and C are alive now only because these clients passed to the server this knowledge.
Why just don't make clients sending the "keep-alive" message every, say 1 minute (or less, depending on your needs) to the server queue without prior message from the server.
The message can include some client identifier and probably time if its not added by the infrastructure or something)
So the server will just get this message and it will keep track in memory the list of available clients along with the last time they've sent something.
So if some client disconnects "gracefully" - it can send a special message to the server like "I'm client A and consider me disconnected". Otherwise (abnormal termination/network outage/whatever) - it just won't send anything, the server will have a special process that will check whether there are stale clients on the list and if it finds them - it knows that something went wrong.
If you still want to stick with JMS way of doing, then you can try to send the message synchronously, meaning the producer will wait until it hears from the consumer. More information here : http://docs.oracle.com/javaee/6/tutorial/doc/bncfa.html
I am sending TCP packets just few bits each (one line of text or so). I am sending them to remote server via HTTP proxy however for some reason when the connection with the proxy is slow or interrupted to the server arrives just a fragment of the packet and not entire packet and it causes exceptions on the server side, how it that posible ? Is there any way on the client side how to prevent sending fragment of the packet instead of entire packet ?
Example: I am trying to send this packet:
packetHead: id (1-99)
integer: 1
short: 0
byte: 4
And in my case sometimes happens that to the server arrives just packetHead and integer and the rest of the packet is lost somewhere when the connection with the proxy is bad.
I have no access to modify server source code so I need to fix it on the client side.
Thanks for any tips.
Please show how you send your data. Every time I had a similar problem it was my fault for not flushing the stream. Especially if the stream is compressed you need to call close/complete on the GZIP or similar object to actually send out everything.
I'm trying to make a port of a chat program a friend of mine made with lacewing and multimedia fusion 2 for android device.
I've managed to create a socket connecting to the listening socket of the server successfully, but I cannot seem to be able to send data to login and enter the chat. The login for now just requires a name, but even if I send a String of data, the server doesn't seem to reply or accept that data to get me over the channel.
I know I could easily port this with other way like using the NDK of the multimedia fusion 2 exporter, but I just want to figure out how this works
PS: I'm using Java and libgdx for the development
You need to read the liblacewing relay protocol:
https://github.com/udp/lacewing/blob/0.2.x/relay/current_spec.txt
On initial connection, you have to send byte 0 to identify that you are not an HTTP client. After this, you can exchange normal protocol messages.
The first message you need to send is the connection request (which may be denied by the server with a deny message). This would be:
byte 0 (2.1.0 request)
(1.2 size)
byte 0 (2.1.0.0 connection request)
string "revision 3" (2.1.0.0 connection request -> version)
When the server responds with response 0 (2.2.0.0 Connect), you then have to set a name before you may join any channels. This is done with message 2.1.0.1 SetName, which is the same structure as above but instead of 2.1.0.0's byte 0, it is 2.1.0.1's byte 1, followed by the name as a string instead of the protocol version.
The server should then respond with 2.2.0.1 SetName, assuming it accepted your name change request. You should process this message in case the server gave you a different name than you requested. Finally, once you have a name, you can join a channel with 2.1.0.2 JoinChannel. The flags you specify here will be used if the channel doesn't exist yet (e.g. nobody is in the chat yet) - these should match the ones in the MMF2 project file. The name should also match.
After all that, you're still not done! You have to process more messages, etc. it's almost like writing the RelayClient class yourself. It's a tough task, but with the protocol specification in hand you should be able to work it all out.
I am trying to create a client socket connection, when a new request is created a connection is established & data transfer takes place. Is there any way that once the Connection is created it will be open for all time ? If yes then how can create it & also how can I identify what request is sent & got the response for the same request?
Looking forward for your response.
You can create a connection for all time, by not closing it. However the trick is detecting when a connection has failed. e.g. the client/server has restarted.
If you want to match requests to responses you can use a request id, but a much simpler approach is to only send one request at a time per socket, that way the response you get is for the request you just sent. You can use more than one socket in a thread if this is required.