Newbie questions

[Bozo Juretic]

Christian Migowski wrote:
> Hi,
>
> On Tue, Aug 11, 2009 at 10:13 AM, Bozo Juretic<bjuretic at inet.hr> wrote:
>   
>> Hi all,
>>
>> I have two newbie questions; I couldn't find examples dealing with those
>> two, so perhaps someone can give me a hand here.
>>
>> 1. What is the best way to implement reconnecting mechanism for TCP
>> client in which the connection with the server should be up at all
>> times. I need to send periodic "ping status" messages to the server as
>> well. At the start of app I need to connect to host (and retry if host
>> is not available), and if the connection goes down I need to reconnect
>> up with the server in some smart way (perhaps you have reconnecting
>> strategies implemented somewhere in netty code?).
>>     
>
> As far as I know, there is not (yet) automatic reconnection in Netty -
> ie. you need to implement it by yourself. Pass a reference of the
> ClientBootStrap to the handler where you want to handle the reconnect
> and then use it in channelClosed()
>
> for example (don't use it as-it-is!):
>
> while(ch.isConnected()) {
> ChannelFuture f = bootstrap.connect(new InetSocketAddress(host, port));
> f.awaitUninterruptibly();
> ch = f.getChannel();
> }
>
> The "ping" mechanism can be implemented very well using a
> IdleChannelHandler in your pipeline - there are examples within Netty
> for this (package timeout).
>   
I've done it, and it works, although I had to replace await() with a
listener or netty complained.

Another thing related to IdleStateHandler.. it works for all data
sent/received.

What's the best way to check if the single request message got response
or not in specified time? I guess there should be a separate thread that
would browse some kind of a queue (filled by handler with all incoming
messages), read messages from it and see if some expired (all of this
outside of netty handler)? I'm not sure how useful IdleStateHandler is
here since it may as well happen that a lot of traffic goes over the
wire, but none of it is the required response message, so
IdleStateHandler would never send me an event I need. Is there a netty
component that can send a MessageTimeoutedEvent for a specific message
request, where a message would be registered with this component before
channel.write(), and then it would work similar to an IdleStateHandler -
you could catch the exception and place your business logic there (i.e.
send error to the original requestor).

Thank you for your kind answers,

Bozo