Re: SSH Global Request

[Michal Vaško <mvasko@xxxxxxxxx>]

Hi Jakub,
thanks for the response. I was aware of the bug report but there was some information that I have missed. Hopefully understanding it better now I have one last request. I believe ssh_global_request() with reply set to 1 should block until a response is received, which is fine. But in case a non-blocking socket is used, it returns immediately. Could the function ssh_send_keepalive() simply return the value of ssh_global_request() instead of ignoring it? That way it could be checked for SSH_AGAIN. I am fine with returning SSH_OK irrespective of whether the client accepts or denies the request.

Regards,
Michal

On Friday, March 6, 2020 16:54 CET, Jakub Jelen <jjelen@xxxxxxxxxx> wrote:

> 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.
>
>