Re: which LibSSH API notifies Client if Server gets Disconnected.

[Jakub Jelen <jjelen@xxxxxxxxxx>]

On 2/17/20 2:43 PM, V Sidnal, Nagraju wrote:
> Dear Team,
>
> We are using below logic to execute command on SSH Server.
>
>  Â  int rc = ssh_connect(my_ssh_session);
>
>  Â Â rc = ssh_pki_import_privkey_file("id_rsa", NULL, NULL, NULL, &pkey);
>
>  Â  rc = ssh_userauth_publickey(my_ssh_session, NULL, pkey);
>
>  Â  channel = ssh_channel_new(my_ssh_session);
>
>  Â Â rc = ssh_channel_open_session(channel);
>
>  Â  rc = ssh_channel_request_exec(channel, "lscommand");
>
> //after this we reading the result & closing the channel.
>
> We are keeping session saved in our class for next command 
> execution/call iteration, so that we don’t need to create connection again.
>
> However For next call, every time we are creating new channel for 
> executing the command, as we cannot use same channel.
>
> We are running some logic internally, which keeps checking 
>  Â ssh_is_connected() , to keep track of connection status with Server.
>
> However this logic looks heavy.
>
> Could you please help me with the API of libssh – callback API’s of 
> libssh, using which I don’t need to check ssh_is_connected().
>
> I’m unable to figure out a Call back Api , using which Client will get 
> notified whenever server gets disconnected.

Hello,
There is no straight-forward callback API to notify you about disconnect 
asynchronously as this disconnect can happen for various reason from 
software failure, software disconnect, network failure, timeouts and so on.

Generally, you don't know if the remote is connected before you try to 
write anything to the channel, either directly the channel request or 
using (periodic) keekapive message (this was recently discussed on this 
mailing list.

Regards,
--
Jakub Jelen
Senior Software Engineer
Crypto Team, Security Engineering
Red Hat, Inc.