Re: [libmicrohttpd] How to know MHD_OPTION_CONNECTION_LIMIT has reached?

[Christian Grothoff]

On 02/11/2014 09:42 PM, Nikhil Saraf wrote:
> Hello Folks,
> 
> I've been trying for more than a week to figure out a way to handle
> MHD_OPTION_CONNECTION_LIMIT; but no breakthrough yet.
> 
> As of now, with the latest version of microhttpd, if I configure max.no.of
> connections to, say, 3, then a 4th connection just "waits" until one of the
> earlier connection closes down. I want the 4th connection to not even get
> through. Is there a way to achieve this?
> 
> I was thinking to let the "handler" insert "Connection: close" header into
> the response; but the question is: how does handler become aware that
> MHD_OPTION_CONNECTION_LIMIT has reached?
> 
> Please advise/suggest/help.

Ok, first of all, the behavior that MHD won't even accept the 4th
connection if your
limit is 3 is totally intended by design.  Once one of the first three
is done, MHD
will move on to #4.  Now, the number of connections that will be in this
queue to be
accepted "next" is limited by the "listen" call to 32 (by default).  If
that queue
is too long for you, you can open your own listen socket with a
different queue
size and pass that to MHD.  Again, having this listen queue is part of
the design
of TCP and generally a very good idea, because you drop fewer requests
and can
achieve a higher throughput by having a request pending in the queue
while you
process other requests.


That said, if you, for whatever strange reason, really really want the
behavior
that the 4th connection is accepted "immediately" and then simply
"closed", what
you could do (again, not recommended) is set the connection limit for
MHD to say
4 (anything above 3), implement your own counting logic, and if your counter
hits 4 simply return "MHD_NO" from the main callback.  That'll cause MHD to
instantly close the connection, without handling it.  Again, I would
generally
think this is a terrible idea, but it would work and give you the
semantics you
asked for.


Happy hacking!

Christian

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