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Subject: Re: libssh2_session_free changes nonblock state of already unused fd

Re: libssh2_session_free changes nonblock state of already unused fd

From: Pavel Strashkin <pavel.strashkin_at_gmail.com>
Date: Fri, 28 Oct 2011 01:11:04 -0700

You're correct, but as i said we have the deal with a Perl, Python,
whatever else that has GC which doesn't guarantee anything to you. An
object can be destroyed at an time. In this world you should you take
care of it too (in case if it happens). My point here (no hacks, no
workarounds) is that you shouldn't change IO from blocking to async.
You have the stream (socket) and the only thing which you should have
to do is just send and recv. How it happens - async or blocking - is
not up to library. I mean you have to support both cases as you do
already, but you don't have to change the mode. Leave it to library's
user. This small change will make life easier i believe. Right now, to
cheat against Perl's GC, i create a new session before close a
previous one. I don't like it. Just recv or send. Will it block or not
- doesn't matter. User decides.

2011/10/28 Daniel Stenberg <daniel_at_haxx.se>:
> On Thu, 27 Oct 2011, Pavel Strashkin wrote:
>
>> What happened to me is that i had one session (socket fd = 3) which was
>> closed by server side so i handled it and closed everything on my side
>> (sockets, ...). Net::SSH2 wrapper around the session had not been deleted
>> yet so libssh2_session_free had not been called either.
>
> Right, and here's the problem. You handed over the control of the socket to
> libssh2, and then you closed it behind its back...
>
>> I think libssh2 should never touch nonblock state or, at least, should set
>> it to TRUE and forget about it till the end (i.e. nothing should happen
>> inside libssh2_session_free).
>
> The basic principles:
>
> 1. the socket is handed over to libssh2 to handle when doing SSH operations
>
> 2. libssh2 owns the socket as long as you haven't told it properly that
> you're
>   done and want control back
>
> 3. when libssh2 stops controlling the socket, it restores the original
>   blocking state of the socket so that to the application that passed in the
>   socket in step (1) it won't be any surprise
>
> I don't think just skipping the restoring of the blocking state in step 3 is
> going to save you. When you fiddle with the socket before libssh2 has been
> told to give it up, you're out on very thin ice. We can't guarantee that
> libssh2 won't have to do some other little thing on the socket before it
> returns out and you as a user of libssh2 must not assume otherwise.
>
> Or am I wrong?
>
> --
>
>  / daniel.haxx.se
> _______________________________________________
> libssh2-devel http://cool.haxx.se/cgi-bin/mailman/listinfo/libssh2-devel
>

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Received on 2011-10-28

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