Re: [Boost-users] Monitor lost client data connections

Subject: Re: [Boost-users] Monitor lost client data connections
From: jupiter (jupiter.hce_at_[hidden])
Date: 2017-02-24 20:33:44

Thanks Gavin for the response, please see following embedded comments.

On Fri, Feb 24, 2017 at 1:04 PM, Gavin Lambert via Boost-users <
boost-users_at_[hidden]> wrote:

> On 23/02/2017 23:09, jupiter via Boost-users wrote:
>
>> I have a server socket connected by many clients using
>> boost::asio::ip::tcp::socket to set up server socket connection and to
>> use boost::asio::ip::tcp::acceptor async_accept for new client
>> connections. The client may come and go, so I need to check if the
>> connection is still valid or not before sending message to clients. How
>> can I check if a client connection is no longer valid? My server does
>> not seem get any indication when a client terminate the connection.
>>
>
> There are a few platform-specific sockopts that sometimes do the trick,
> but generally the simplest way to test whether a connection is still alive
> is to try to transmit something -- if the connection is lost it will then
> either immediately or after a timeout fail with a "connection reset"
> error.  You usually can't detect a disconnection if you're just waiting for
> a read without sending anything.
>

That is exactly I am currently doing, if I failed to run
boost::asio::async_write to a specific client, I removed the connection and
wait until a new connection from the client is established. Doesn't seem
there are other better detecting methods.

>
> Also, if clients have some means of identification or authentication
> (using the IP is possible but not really recommended due to gatewaying or
> multiple separate applications), and provided you're expecting only one
> connection per client, then you could treat a reconnection from the same
> client as a disconnection of their previous connection.  If clients
> auto-reconnect this would probably be the fastest method of identifying a
> lost connection, but it can be tricky to avoid causing problems if not
> implemented carefully.
>
> Yes, I am also writhe the client program, each client has an unique
identification and provides expecting only one connection per client. The
client will auto-reconnect to the server if it detect lost connection, the
question again, is writing to boost::asio::write the efficient way to
detect a stalled connection or  are there any better alternatives to get
feedback from the boost::asio::ip::tcp::socket lowest_layer? The problem is
the client is always waiting receiving from server, if the client cannot
detect from the oost::asio::ip::tcp::socket while waiting on
boost::asio::read, then I have to run constantly heartbeat in every second
or so which I try to avoid too much unnecessary bandwidth usage as the
client is replying on LTE transmission, network bandwidth cost needs be
considered.

Thank you.

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