Re: SSH Global Request

[Jakub Jelen <jjelen@xxxxxxxxxx>]

On Mon, 2020-03-09 at 08:02 +0100, Michal Vaško wrote:
> 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.

Hello,
it used to be this way, before the following commit:

https://gitlab.com/libssh/libssh-mirror/commit/59ada799

I am not completely clear about the reasoning for "dropping" the return
value so better ask the author directly (in CC).

Regards,
Jakub

> 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.
> > 
> > 
>  
>  
> 
> 
-- 
Jakub Jelen
Senior Software Engineer
Security Technologies
Red Hat, Inc.