Re: [libmicrohttpd] MHD_connection_close API

[Robert Groenenberg]

Hi Christian,

Well, dropping a connection may not be very clean, but that was only to 
avoid waiting for a request only close it at that point. It's certainly 
not intended to be a 'hackish' implementation.
As MHD_connection_close() is not really thread safe, I'll go for adding 
the 'Close' header at least when there is a request pending. For now 
I'll reject new incoming request by returning MHD_NO.

Thanks for your input!

Cheers,
Robert

On 12/01/2015 04:07 PM, Christian Grothoff wrote:
> Hi Robert,
>
> I see. The issue is that there is no good way to do this safely (in all
> threading modes).  MHD may internally be trying to close the connection
> (i.e. timeout, client close), so especially if you're multi-threaded,
> there is no 'safe' way for you to just call MHD_connection_close().
>
> If you're in single-threaded mode, you could be sure that MHD doesn't
> currently try the same thing, but that's a very specific case.  For that
> case, I have a slightly hackish but reasonable alternative: just call
> MHD_get_connection_info() to get the *socket* of the connection and call
> 'shutdown()' (for reading at least) on that socket. This will unblock
> the socket on select() and cause future read attempts by MHD to fail,
> forcing MHD to shutdown the connection as intended.
>
> Given that you're doing something a bit outside of the HTTP
> specification here (in the sense of being really impolite and tearing
> down a running connection, possibly dropping data in transmission from
> the HTTP client), I think this hackish method matches the level of hack
> you desire here ;-).
>
> Note that in multi-threaded modes, doing this effectively means that you
> risk calling shutdown() on a totally unrelated socket, so you may want
> to abstain from this hack in such a setting...
>
> I hope this helps!
>
>
> Happy hacking!
>
> Christian
>
>
>
> On 12/01/2015 02:31 PM, Robert Groenenberg wrote:
> > Hi Christian,
> >
> > Let me first clarify the scenario a bit more: the goal is to close the
> > connection from a client in case the configuration in the application
> > wrt this client has changed.
> >
> > I do agree that for a request being processed it would be best to add a
> > "Connection: Close" header and I probably should do that :)
> > However, this still leaves the cases where the response has already been
> > handed to MHD before the need to close the connection arises. The next
> > opportunity to do so is then when the response is sent (NOTIFY_COMPLETED).
> > When there are no requests in progress, I'd like to be able to drop the
> > connection without waiting for it to send a request and then close the
> > connection.
> >
> > Cheers,
> > Robert