Hello,

In a socket based program,is it possible to know, when returning from
listening to whom we will be connected before issueing the accept

s= socket(xxx)
bind(xxx)
listen(xxxx)

Can we know here to whom we will be connected (ip address of peer)

accept(xxx)


Thank you

Aron

awahl@yahoo.com writes:
> In a socket based program,is it possible to know, when returning from
> listening to whom we will be connected before issueing the accept
>
> s= socket(xxx)
> bind(xxx)
> listen(xxxx)
>
> Can we know here to whom we will be connected (ip address of peer)
>
> accept(xxx)

No.

It sounds like what you _might_ want is something that's sometimes
called "lazy accept" -- the ability to look at inbound TCP SYN
messages and decide which ones you want to reply to, rather than
having the stack itself manage SYN-ACK. I don't know of any modern OS
that does this, and unless your application is in the kernel (and in
fact part of TCP itself), there's a serious denial-of-service risk
associated with it.

If what you're looking for is actually just a "peek" mode on accept,
what would you do if you had this? (Is this an inetd "nowait" service
but with libwrap?)

--
James Carlson, KISS Network <james.d.carlson@sun.com>
Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

On Tue, 21 Nov 2006 11:33:01 -0500, James Carlson wrote:

> awahl@yahoo.com writes:
>> In a socket based program,is it possible to know, when returning from
>> listening to whom we will be connected before issueing the accept
>>
>> s= socket(xxx)
>> bind(xxx)
>> listen(xxxx)
>>
>> Can we know here to whom we will be connected (ip address of peer)
>>
>> accept(xxx)
>
> No.
>
> It sounds like what you _might_ want is something that's sometimes
> called "lazy accept" -- the ability to look at inbound TCP SYN
> messages and decide which ones you want to reply to, rather than
> having the stack itself manage SYN-ACK. I don't know of any modern OS
> that does this, and unless your application is in the kernel (and in
> fact part of TCP itself), there's a serious denial-of-service risk
> associated with it.

On Linux you can write it using netfilter queues. Not that I advocate
that, but if you really need that functionality.

Or just use tcpwrappers, it may be exactly what the OP wants.

M4
--
Redundancy is a great way to introduce more single points of failure.

awahl@yahoo.com wrote:

> In a socket based program,is it possible to know, when returning from
> listening to whom we will be connected before issueing the accept
>
> s= socket(xxx)
> bind(xxx)
> listen(xxxx)
>
> Can we know here to whom we will be connected (ip address of peer)
>
> accept(xxx)

On most TCP/IP stacks, you may be already connected. So the question
doesn't make sense.

DS

Ok thanks to all,

The only think I wanted to know if it was possible to do it within the
socket framework. Apparently it is not.

Too bad.

Aron
David Schwartz wrote:
> awahl@yahoo.com wrote:
>
> > In a socket based program,is it possible to know, when returning from
> > listening to whom we will be connected before issueing the accept
> >
> > s= socket(xxx)
> > bind(xxx)
> > listen(xxxx)
> >
> > Can we know here to whom we will be connected (ip address of peer)
> >
> > accept(xxx)
>
> On most TCP/IP stacks, you may be already connected. So the question
> doesn't make sense.
>
> DS