Re: Server API: How to communicate connection failures to client

[Andreas Schneider <asn@xxxxxxxxxxxxxx>]

On Monday, February 11, 2019 8:56:49 AM CET g4-lisz@xxxxxxxxxxxx wrote:
> On 06.02.19 17:41, g4-lisz@xxxxxxxxxxxx wrote:
> > Hi there,
> > 
> > My server implementation accepts direct-tcpip requests.
> > 
> > In the message CB function, after receiving a message of type
> > SSH_REQUEST_CHANNEL_OPEN, subtype SSH_CHANNEL_DIRECT_TCPIP, we try to
> > open a local socket. If this is successful, a new channel with
> > ssh_message_channel_request_open_reply_accept(message) is attached.
> > 
> > But if opening of the local socket fails, how should the message be
> > treated? Is there a way to signalize to the client that the connection
> > failed, without opening a new channel?
> > 
> > Or do I have to accept the request and open a channel in any case? And
> > then close the channel again when the local socket operation failed?
> > 
> > Right now I'm reading the OpenSSH server code to find out. But maybe
> > someone could give me the answer and tell me what libssh functions
> > should be used?
> 
> No one?
> 
> Maybe my mail had too much text ;-))
> 
> Short version: When writing a server, how do should it signal to the
> client when the destination for the direct-tcpip request can not be
> reached (or resolved)?
> 
> - The API only let me send a channel EOF or close
> - Should it accept the request at all (i.e. open a new channel) _before_
> the local (server side) connection could been made?
> - Does it make sense (if it opened the channel) to send something on the
> channel stderr?

Any words in the RFC about it?

-- 
Andreas Schneider                 asn@xxxxxxxxxxxxxx
GPG-ID:     8DFF53E18F2ABC8D8F3C92237EE0FC4DCC014E3D