Re: Re: Full-Duplex communication

LOL.. I like the color red BTW.

Let me explain my project more in detail.

This system is an Instant messaging system, with the backed 
running on apache / php / mysql.  The front end client is a COM 
component that communicates with the backend, and interfaces with 
an MFC app.

Now since Instant messaging requires that the server should be 
able to send asynchronous messages to the client (Presence, IM's, 
notifications, etc), and HTTP does not allow asynchronous 
communication, the only solution is to have the client poll the 
server for messages.

Now i know that apache / php is not a good solution for an instant 
messaging server, but we needed it to be ready in a months time, 
and php is so amazing that we could get it up and running so fast.  
But it meant that we have to live with latency between messages 
because of the polling.

So i was thinking if there was some way in which i could avoid the 
polling and send data asynchronously to the client (Pls refer to 
my previous posts).  Thats why i was looking at a way in which i 
could get hold of the socket to the client, so i could use it to 
send data directly.

Tx,
Vinod.

On Fri, 24 May 2002 Miguel Cruz wrote :
> Not to be argumentative, but what you're trying to do is just so 
> amazingly
> much more complicated than any of my suggestions. Maybe I 
> haven't
> communicated it well, it maybe there's some requirement to your 
> project
> that I don't understand.
>
> Why not just write a listener in PHP and redirect to it? It's 
> basically no
> work.
>
> Handcrafting packets for this purpose is like building a car out 
> of paper
> clips and cat hair because the car that's freely available to you 
> is red -
> and you don't like the color red because your old girlfriend used 
> to wear
> it a lot.
>
> miguel
>
> On 23 May 2002, Vinod  Panicker wrote:
> > What you said did make sense, and complements my knowledge 
> of
> > sockets.
> >
> > But what i'm not sure of is this - if i construct my own 
> packet
> > and send it across, presuming that i do have the ip address 
> and
> > port number of the client on which it is reading, will the 
> client
> > accept it as a legitimate packet?
> >
> > I suspect that since the packets would be having some kind 
> of
> > session identifier / sequence number.
> >
> > Getting the ip address and port number is no problem.  I 
> already
> > have that getting stored on the server.  But from what i know 
> of
> > sockets, i'm sceptical if the client will accept the packet.
> >
> > Guess the only way to go ahead is to try this out.
> >
> > Would someone pls pls pls write a PHP interface to libnet??
> >
> > Tx,
> > Vinod.
> >
> > On Thu, 23 May 2002 Evan Nemerson wrote :
> > >You're right- this is getting interesting ;)
> > >
> > >http://www.packetfactory.net/libnet/manual/4.html#s4.1.5
> > >
> > >Unless I'm mistaken, you don't need to actually hijack the
> > >socket- you merely
> > >need to write to the network. Check out section 3.1 of RFC 
> 793.
> > >There is
> > >source and destination port- that is how they are routed. 
> Okay
> > >anyone PLEASE
> > >correct me if i'm wrong...
> > >
> > >My understanding is a socket is an interface to the kernel. 
> So
> > >basically, you
> > >talk to a socket, which the kernel associates with source 
> and
> > >destination
> > >ports, and destination IP address. Thats why you can just 
> write
> > >to a socket
> > >instead of explicitly stating all the information. The 
> kernel
> > >then sends out
> > >then creates the packet and send it to the destination IP.
> > >
> > >libnet would allow you to bypass the socket phase, and 
> manually
> > >create a
> > >socket. Think of a socket as a GUI for the network, and 
> libnet is
> > >like a
> > >console ;)
> > >
> > >Hope that helps, and once again anyone PLEASE correct any
> > >inaccuracies, since
> > >I want to know.
> > >
> > >
> > >
> > >
> > >On Tuesday 21 May 2002 23:53 pm, Vinod Panicker wrote:
> > > > Thanks for the reply Miguel, but here i'm not trying to
> > >implement
> > > > my own multi-threaded server - exactly the reason why 
> i'm
> > >using
> > > > Apache / PHP.
> > > >
> > > > I could have made a listening server which is based on a
> > > > multi-threaded or multi-forked model, but the time and
> > > > complexities involved would be huge.  Thats why I chose 
> Apache
> > >/
> > > > PHP.
> > > >
> > > > Now if what i'm asking for can be done, developers can
> > >easily
> > > > leverage existing efficient server technologies (Apache) 
> to
> > >build
> > > > their own App servers.
> > > >
> > > > I know that there is no existing function in PHP that 
> would
> > >allow
> > > > it to retrieve the socket from Apache ;), all i'm asking 
> for
> > >is a
> > > > hack that would allow me to do it.
> > > >
> > > > I thought that i'd just as well post it on the mailing 
> list
> > >before
> > > > diving into the source code and trying to figure out for
> > >myself.
> > > > No point trying to re-invent the wheel, right?
> > > >
> > > > Evan, that lib will allow me to create my own packets, 
> but
> > >which
> > > > socket do i send it to?  Thats been the question all 
> along.
> > > >
> > > > I think this is getting really interesting :)
> > > >
> > > > Tx,
> > > > Vinod.
> > > >
> > > > On Wed, 22 May 2002 Miguel Cruz wrote :
> > > > >I don't think you're going to get Apache to hand you 
> the
> > > > >socket.
> > > > >
> > > > >However, you can write a program using the standalone 
> (CGI)
> > >PHP
> > > > >interpreter that will act like a server - check out
> > > > >http://php.net/socket_create_listen for more info.
> > > > >
> > > > >You could redirect from your standard web server to 
> your
> > > > >listening PHP app
> > > > >running on another port. You'll then have to implement 
> at
> > >least a
> > > > >subset
> > > > >of the HTTP protocol in order to get browsers to talk 
> to
> > >you.
> > > > >
> > > > >Unfortunately, since you can't - to the best of my 
> knowledge
> > >-
> > > > >fork a PHP
> > > > >program, you're going to have to do your own homebrew
> > >threading
> > > > >which will
> > > > >make life slightly complicated.
> > > > >
> > > > >miguel
> > > > >
> > > > >On 22 May 2002, Vinod  Panicker wrote:
> > > > > > It still seems like I havent made the problem clear
> > >enough.
> > > > > >
> > > > > > I am aware of the print(), echo() and flush() 
> functions
> > >and
> > > > >
> > > > >what
> > > > >
> > > > > > they do.  It does not fit in as a solution.  Let me
> > >explain
> > > > >
> > > > >my
> > > > >
> > > > > > problem more elaborately -
> > > > > > The client calls a PHP script, script_a.php on the
> > >Apache
> > > > >
> > > > >web
> > > > >
> > > > > > server, using a Keep-Alive connection.  The script
> > >returns
> > > > >
> > > > >some
> > > > >
> > > > > > response to the client which it uses.  Now since the
> > > > >
> > > > >connection is
> > > > >
> > > > > > a Keep-alive, apache still has it open for reading 
> and
> > > > >
> > > > >writing.
> > > > >
> > > > > > When the client wants to call other scripts, it just
> > >sends
> > > > >
> > > > >the
> > > > >
> > > > > > request over the same connection.  Now the thing is 
> that
> > >if
> > > > >
> > > > >the
> > > > >
> > > > > > server needs to send some ASYNCHRONOUS data to the
> > >client,
> > > > >
> > > > >without
> > > > >
> > > > > > the client requesting for anything, a normal PHP 
> script
> > >wont
> > > > >
> > > > >be
> > > > >
> > > > > > able to do it, since the script would get executed 
> by
> > >the
> > > > >
> > > > >web
> > > > >
> > > > > > server ONLY on a client request (coz thats the way 
> HTTP
> > > > >
> > > > >works).
> > > > >
> > > > > > Now what i was thinking was - if i could get hold of 
> the
> > > > >
> > > > >socket
> > > > >
> > > > > > that is being used by apache to send data to the 
> client,
> > >I
> > > > >
> > > > >could
> > > > >
> > > > > > effectively write() to it, from a C++ app or a PHP
> > >script
> > > > >
> > > > >(which
> > > > >
> > > > > > gets invoked from lets say another server).  
> print(),
> > >echo()
> > > > >
> > > > >etc
> > > > >
> > > > > > are functions that write to the output stream, which 
> is
> > >opened
> > > > >
> > > > >as
> > > > >
> > > > > > a result of the clients request, by the web server.
> > > > > >
> > > > > > I want the ability to write to a socket thats been
> > >created
> > > > >
> > > > >earlier
> > > > >
> > > > > > - i want to steal it from Apache, so that i can use 
> it
> > >when
> > > > >
> > > > >and
> > > > >
> > > > > > where i like.
> > > > > >
> > > > > > Functions like echo() and print() are not going to 
> work
> > >here,
> > > > >
> > > > >i
> > > > >
> > > > > > will have to use write() so that i can specify the 
> socket
> > >to
> > > > >
> > > > >which
> > > > >
> > > > > > the data has to be written!
> > > > > >
> > > > > > Hope the problem is understood now.
> > > > > >
> > > > > > Now for your question -
> > > > > > When the client wants to send data to the server, it 
> just
> > >has
> > > > >
> > > > >to
> > > > >
> > > > > > open a socket connection with the web server, and 
> issue a
> > >GET
> > > > >
> > > > >or a
> > > > >
> > > > > > POST request!  if the connection is a keep-alive
> > >connection,
> > > > >
> > > > >and
> > > > >
> > > > > > it has already been created, the client just has to do 
> a
> > >GET
> > > > >
> > > > >or a
> > > > >
> > > > > > POST without the need to connect().
> > > > > >
> > > > > > This mechanism, where the client frequently 
> connects()
> > >to
> > > > >
> > > > >the
> > > > >
> > > > > > server and checks for messages is called polling.  
> One
> > >way
> > > > >
> > > > >of
> > > > >
> > > > > > reducing the high overhead of this is to reuse the
> > >connection
> > > > >
> > > > >by
> > > > >
> > > > > > using a keep-alive connection.  A still better
> > >improvement
> > > > >
> > > > >would
> > > > >
> > > > > > be to remove the need for a poll altogether, by 
> doing
> > > > >
> > > > >something
> > > > >
> > > > > > (thats what my question is all about) on the server 
> so
> > >that it
> > > > >
> > > > >can
> > > > >
> > > > > > send data asynchronously to the server.
> > > > > >
> > > > > >
> > > > > > Tx,
> > > > > > Vinod.
> > > > > >
> > > > > > On Wed, 22 May 2002 Bogdan Stancescu wrote :
> > > > > > >For your specific problem, I think Mr. Lemos has 
> provided
> > >a
> > > > > > >viable solution (using print() or echo() and 
> flush()
> > >whenever
> > > > >
> > > > >you
> > > > >
> > > > > > >need to, instead of grabbing the socket and write() 
> to
> > >it).
> > > > >
> > > > >My
> > > > >
> > > > > > >problem however is how you envision solving the
> > >communication
> > > > >
> > > > >the
> > > > >
> > > > > > >other way around (i.e. when the CLIENT wants to send 
> data
> > >to
> > > > >
> > > > >the
> > > > >
> > > > > > >server).
> > > > > > >
> > > > > > >Bogdan
> > > > > > >
> > > > > > >Vinod Panicker wrote:
> > > > > > >>Hi,
> > > > > > >>
> > > > > > >>Tx for your very prompt reply.
> > > > > > >>
> > > > > > >>Yeah, I'll post the solution as soon as I find it
> > > > >
> > > > >someplace.
> > > > >
> > > > > > >>Let me outline the problem in more detail -
> > > > > > >>
> > > > > > >>Client (VC++) calls a PHP script on the server,
> > >specifies
> > > > >
> > > > >the
> > > > >
> > > > > > >>connection type as Keep-Alive.  The PHP script,
> > >somehow
> > > > >
> > > > >(still a
> > > > >
> > > > > > >>big question) gets the socket on which the apache
> > >server
> > > > >
> > > > >has
> > > > >
> > > > > > >>received the client request (so that it can send 
> data
> > >to
> > > > >
> > > > >the
> > > > >
> > > > > > >>client later) and stores it in a database.
> > > > > > >>
> > > > > > >>Now whenever another PHP script wants to send data
> > > > > > >>asynchronously to the client, it gets the socket 
> from
> > >the
> > > > > > >>database, and just calls a write() on it.  Since 
> the
> > > > >
> > > > >connection
> > > > >
> > > > > > >>is still open (Keep-Alive), the client receives 
> the
> > > > >
> > > > >information,
> > > > >
> > > > > > >>and doesnt have to poll the server periodically.
> > > > > > >>
> > > > > > >>The application of this is indeed destined for a
> > >messaging
> > > > > > >>product, and could benefit a lot of other areas as
> > >well.
> > > > > > >>
> > > > > > >>The only thing that is needed is the socket from
> > >apache.
> > > > > > >>
> > > > > > >>Someone somewhere knows how to get this done, i'm 
> sure
> > >:)
> > > > > > >>
> > > > > > >>Possibly a hack into the PHP module can get this 
> done,
> > >i'm
> > > > >
> > > > >open
> > > > >
> > > > > > >>to suggestions.
> > > > > > >>
> > > > > > >>Tx,
> > > > > > >>Vinod.
> > > > > > >>
> > > > > > >>On Tue, 21 May 2002 Bogdan Stancescu wrote :
> > > > > > >>>Hi!
> > > > > > >>>
> > > > > > >>>I'm looking for an answer to your questions as 
> well, so
> > >if
> > > > >
> > > > >you
> > > > >
> > > > > > >>>do find a solution on other lists, could you 
> please
> > >post
> > > > >
> > > > >it
> > > > >
> > > > > > >>>here as well?
> > > > > > >>>
> > > > > > >>>Regarding the issue, your proposal wouldn't make 
> for
> > > > > > >>>full-duplex as far as I understand since I don't 
> see
> > >how
> > > > >
> > > > >the
> > > > >
> > > > > > >>>client would be able to send any data on the same
> > > > >
> > > > >connection
> > > > >
> > > > > > >>>_after_ getting connected.
> > > > > > >>>
> > > > > > >>>What are you using on the other end of the pipe 
> (on
> > >the
> > > > > > >>>client)? Plain HTML? Flash? Java? Something else?
> > > > > > >>>
> > > > > > >>>Bogdan
> > > > > > >>>
> > > > > > >>>Vinod Panicker wrote:
> > > > > > >>>>Hi,
> > > > > > >>>>
> > > > > > >>>>We have developed a client-server application 
> where
> > >the
> > > > >
> > > > >server
> > > > >
> > > > > > >>>>needs to send asynchronous data to the client.  
> Now
> > >since
> > > > >
> > > > >we
> > > > >
> > > > > > >>>>are using Apache/PHP/MySQL, the client needs to 
> poll
> > >the
> > > > > > >>>>server periodically for information.
> > > > > > >>>>
> > > > > > >>>>I was thinking if there was some way to get 
> around
> > >this
> > > > >
> > > > >basic
> > > > >
> > > > > > >>>>problem.  I understand that this is how things 
> are
> > > > >
> > > > >supposed to
> > > > >
> > > > > > >>>>work, but it would be just great if i could PUSH 
> data
> > > from
> > > > >
> > > > >the
> > > > >
> > > > > > >>>>server to the client, using HTTP.
> > > > > > >>>>
> > > > > > >>>>Since HTTP is a request/response based protocol,
> > >Apache
> > > > >
> > > > >would
> > > > >
> > > > > > >>>>not send any data to the client asynchronously.  
> So
> > >what i
> > > > >
> > > > >was
> > > > >
> > > > > > >>>>thinking was - If i tell the server to allow
> > >Keep-Alive
> > > > > > >>>>connections, and increase the timeout value and 
> max
> > > > >
> > > > >requests,
> > > > >
> > > > > > >>>>I would effectively have a constant TCP 
> connection.
> > >Now
> > > > >
> > > > >the
> > > > >
> > > > > > >>>>only problem would be of sending asynchronous 
> data
> > >to
> > > > >
> > > > >the
> > > > >
> > > > > > >>>>client.  Solution?  Here goes - If there was some 
> way
> > >in
> > > > >
> > > > >which
> > > > >
> > > > > > >>>>i could get hold of the file descriptor(socket) 
> that
> > >is
> > > > >
> > > > >being
> > > > >
> > > > > > >>>>used by apache to write data to the client, then 
> i
> > >could,
> > > > >
> > > > > from
> > > > >
> > > > > > >>>>a PHP script also send any data to the client 
> using
> > >the
> > > > >
> > > > >socket
> > > > >
> > > > > > >>>>functions of PHP since i already have the socket
> > >with
> > > > >
> > > > >me.
> > > > >
> > > > > > >>>>This would mean that the client doesnt have to 
> poll
> > >the
> > > > >
> > > > >server
> > > > >
> > > > > > >>>>for data any more... and if the connection does 
> get
> > > > >
> > > > >closed,
> > > > >
> > > > > > >>>>the client could reconnect to the server asking 
> for
> > > > >
> > > > >another
> > > > >
> > > > > > >>>>keep-alive connection.
> > > > > > >>>>
> > > > > > >>>>Now I know that this is probably the wrong place 
> to
> > >put
> > > > >
> > > > >such a
> > > > >
> > > > > > >>>>query - maybe the apache list would have been
> > >better.
> > > > >
> > > > >But
> > > > >
> > > > > > >>>>since I'm using PHP out here, i thought i'd give 
> it
> > >a
> > > > >
> > > > >try.
> > > > >
> > > > > > >>>>Does the solution sound very outlandish?  Are 
> there
> > >any
> > > > > > >>>>pitfalls?  And finally, how do i get hold of the
> > >socket?
> >
> >
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