When using AdvancedBus for EasyNetQ, if the connection is broken up for any reason, how can I reconnect? Does it try to reconnect by itself?
I know IBus reconnects itself, but AdvancedBus does not seem to do that. For example, if I manually force close the connection using the web management console then the connection is gone forever. And if I recreate the IAdvancedBus again I see two new connections.
Related
We have an IOS application which only listens on a INADDR_ANY socket connection for inbound connection using CFSocketCreate/CFSocketGetNative/CFSocketCreateRunLoopSource/CFStreamCreatePairWithSocket etc (to display debug information via HTTP).
(So it falls into the category "Listening for and accepting incoming TCP connections").
If the first incoming socket connection happens on a new installed app we run into the error mentioned above. As we do neither use Bonjour nor getpeername() I wonder where the problem is. Obviously it doesn't matter how the dialog is closed, our program works. But it is of course annoying for us (QA is harder) and our customers.
Any idea what could be the problem ?
I looked into all the questions related here, but I think we are not using one of the 'banned' APIs triggering the dialog
If I set a breakpoint to the stream:handleEvent: function of the NSStreamDelegate the popup appears before NSStreamEventOpenCompleted, so it appears some internals of the NSStream processing cause this.
on the debug console this appears btw:
[connection] nw_connection_copy_connected_path [C1] Client called nw_connection_copy_connected_path on unconnected nw_connection 2022-04-06 17:28:55.811551+0200 GenMob[35630:3181485] [] tcp_connection_is_cellular No connected path
I did fiddle together a small demo app downloadable from https://github.com/leopatras/cfsocket.
For the record, we ended up rewriting our code to use plain Berkeley sockets together with the GCD dispatch_source machinery ... there is a working socket server sample not triggering the local network prompt at https://github.com/leopatras/GCDSimpleSocketServer/
The dispatch_source_zzz functions allow a similar event driven approach like the CFStreamCreatePairWithSocket function. In comparison to https://github.com/leopatras/cfsocket it needs even less code. If the local network prompt is always triggered is questionable, it may depend from other parameters such as the used dev certificate/provisioning profile.
I had an intensive exchange with the Apple support about this topic,
(they weren't able to reproduce our problem initially, but after retrying on several devices they got it too) : they did recommend using the new Network framework functions instead of Berkeley sockets (See https://developer.apple.com/documentation/network?language=objc) and I tried hard to use them however I failed to create a simple reliable working echo server with those functions in obj-C (didn't try the Swift route).
I have a server application which runs on a Linux machine. I can connect this application from Windows/Linux machines and can send/recieve data. After a few hours, something occurs and I get following error on the client side.
On Windows: An existing connection was forcibly closed by the remote host
On Linux: Connection timed out
I have made a search on the web and found some posts which suggest to increase/decrease OS's keep alive time. However, it didin't work for me.
Can I found a soultion to this problem or should I simply try to reconnect to the server when the connection is forcibly closed?
EDIT: I have tracked the situation. I sent a data to the remote node and sent another data after waiting 5 hours. Sending side sent the first data, but whet the sender sent the second data it didn't response. TCP/IP stack of the sender repeated this 5 times by incrementing the times between retries. Finally, sender reset the connection. I can't be sure why this is happening (Maybe because of a firewall or NAT - see Section 2.4) but I applied two different approach to solve this problem:
Use TCP/IP keep alive using setsockopt (Section 4.2)
Make an application level keep alive. This is more reliable since the first approach is OS related.
It depends on what your application is supposed to do. A little more information and perhaps the code you use for listening and handling connections could be of help.
Regardless, technically a longer keep alive time, should prevent the OS from cutting you off. So perhaps it is something else causing the trouble.
Such a thing could be router malfunction or traffic causing your keep-alive packet to get lost.
If you aren't already testing it on a LAN (without heavy trafic) I suggest doing so.
It might also be due to how your socket is handled (which I can't determine from your question)
This article might help.
Non blocking socket with timeout
I'm not used to how connections are handled on Linux, but I expect the OS won't cut off a connection unnecessary.
You can re-establish connection as a recovery, but you need to take into account that not all disconnects are gentle, and therefore you could end up making recovery on a connection you actually wish to be closed.
Since it is TCP, it will do its best to make a gentle disconnect, but you can send a custom message telling the server or client not to re-establish the connection right before disconnecting. That way you be absolutely sure, despite that it should be unnecessary to do so.
I have a Datasnap application(Delphi 7) which uses TSocketConnectiom to connect to application server. If my application stays idle for a long time after opening a clientdataset, most of the times when i want to refresh the clientdataset the application freezes without raising any exceptions.It seems that the connection is dropped and the Socketconnection is not aware of that.I am experiencing this problem very often and I am not sure where can I find the solution. Could it be a bug in TSocketconnection?
Best Regards
Firewalls sometimes drop inactive TCP connections after some time to keep their cache usage low. In this case it helps to call some server method (maybe every five minutes).
If the "setup and teardown" code for the server side DataSnap session is not to resource-consuming, you can also disconnect and reconnect the DataSnap client between all actions. This will initiate a fresh TCP connection, execute, and close it.
I am using TClientSocket and TServerSocket to comunicate with a server the problem is that sometimes connection is lost either by the server issuing me the following exceptions : Error on WsaSend, acess violation etc or by the Client : Asychronious socket error.
Witch is the best method to recover from these errors and keep the connection open no mather what ?
There is no such thing as "keeping the connection open no matter what". What if the cable gets cut? The best you can do is to send a heartbeat on some interval to let intermediate routers know you are still interested in using that connection, and to carefully handle all errors, and, if necessary, re-establish the connection.
Great question... what you're receiving is WSAECONNABORTED (Asynchronous Socket Error 10053).
How did i prevent it from happening in MY code ? well, there's something called Keepalive, if you look carefully into the name, Keep-Alive, it meant to keep the connection alive, just send Null data to the connection (Can be One-way), that's all...
i made a Timer (named it TmrKeepAlive) and set its interval to 5000ms (5 seconds), More info on KeepAlive.
Edit: Also, if you don't want to write your own KeepAlive mechanism, check this out
I'm looking to detect local connection loss. Is there a mean to do that, as with the events on the Corelabs components ?
Thanks
EDIT:
Sorry, I'm going to try to be more specific:
I'm currently designing a prototype using datasnap 2009. So I've got a thin client, a stateless server app and a database server.
What I would be able to do is to detect and handle connection loss (internet connectivity) between the client and the server app to handle it appropriately, ie: Display an informative error message to the user or to detect a server shutdown to silently redirect on another app server.
In 2-tier I used to manage that with ODAC components, the TOraSession have some events to handle this issues.
Normally there is no event fired when a connection is broken, unless a statement is fired against the database. This is because there is no way of knowing a connection loss unless there is some sort of is-alive pinging going on.
Many frameworks check if a connection is still valid by doing a very small query against the server. Could be getting the time from a server. Especially in a connection pooling environment.
You can implement a connection checking function in your application in some of the database events (beforeexecute?). Or make a timer that checks every 10 seconds.
Spawn a thread on the client which periodically sends some RPC 'Ping' or 'Heartbeat' commands to the server.
if this fails, the client knows that something happened to the connection
if the server does not hear the client anymore for some time period (for example, two times the heartbeat interval), he can conclude that the client disconnected, however this requires a stateful server (and your design is stateless so it would require event processing in a secondary system, which could be fed through a message queue)