Re: SSH Global Request

[Jakub Jelen <jjelen@xxxxxxxxxx>]

On Fri, 2020-03-06 at 12:01 +0100, Michal Vaško wrote:
> Hi Jakub,
> right, I have not noticed the function before, thanks. However, I am
> not sure the API is suitable. What is the general behavior, meaning
> what happens if a reply is not sent back?

Hi,
see the discussion in, where we tried to understand this functionality
in libssh (I did not implement that so I am not much better suited to
hint here):

https://bugs.libssh.org/T212

> Is the connection automatically disconnected?

The above function handles only the sending of the request. The answer
is IGNORE message, which is handled with other packets. AFAIK if the
TCP socket gets disconnected, your application can check using
ssh_is_connected().

> Is it possible to use custom max probes (how many keep-alive packets
> are sent unsuccessfully before a connection is considered dead) and
> probe interval (the interval between keep-alive packets) or some
> specific values are always used?

This is up to the application. The above API does just what it says in
the name -- sends the keepalive packet to avoid disconnecting on TCP
level. If you want to count how many times it was send and when. There
is no simple way for libssh to handle this magically in background.

> There is no documentation, that is why I am asking. Thanks for
> providing these details.

The server API is generally poorly documented so if you will learn more
how does it work in real environment, contributions are welcomed.

Regards,
Jakub

> Regards,
> Michal
> 
> On Friday, March 6, 2020 11:29 CET, Jakub Jelen <jjelen@xxxxxxxxxx>
> wrote: 
>  
> > On Fri, 2020-03-06 at 09:11 +0100, Michal Vaško wrote:
> > > Hello,
> > > I was wondering if the authors of libssh would have anything
> > > against
> > > making ssh_global_request() function from channels.h public. It
> > > would
> > > enable implementing NETCONF Call Home SSH keep-alive [1]. Thanks.
> > 
> > Hello,
> > in server side, there is already API for sending keepalive
> > messages:
> > https://gitlab.com/libssh/libssh-mirror/-/blob/master/include/libssh/server.h#L368
> > 
> > In the connection, only one of the peers needs to send the
> > keepalive
> > messages to keep a connection alive.
> > 
> > If you need the similar functionality in the client, I would rather
> > see
> > it implemented by creating a new API function than exposing this
> > internal function.
> > 
> > Regards,
> > -- 
> > Jakub Jelen
> > Senior Software Engineer
> > Security Technologies
> > Red Hat, Inc.
> > 
> > 
>  
>  
> 
> 
-- 
Jakub Jelen
Senior Software Engineer
Security Technologies
Red Hat, Inc.