Cloning a socket connection, using other port numbers Post: 302149766

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Top Forums Programming Cloning a socket connection, using other port numbers Post 302149766 by jonas.gabriel on Friday 7th of December 2007 09:13:03 AM

12-07-2007

Registered User

Cloning a socket connection, using other port numbers

Hello everybody,

I've coded a multi-client server based on internet sockets using the scheme
listen on port X-accept-fork, exactly like beej's guide

At some point I would like to establish a secondary connection between a client and the server-child serving him.

I was considering the server-child bind() a socket to port X+1 listen() to it and then accept() a connect()ion by the client.But that can't be done, because if 2 server-children do that simultaneously, one would get "address already in use" error.

So then I've considered the client listen()ing on the Y+1 port (Y is the port assigned to the client's socket automatically by the primary connect() ).But my problem here is how can I find this port ? getpeername() on client's socket gives me the server's address & port.Is there any function giving the local address & port ?

I know that some problems remain. I am not guaranteed that port Y+1 is available.

A possible solution is that the client could send a free port number to the server through the primary connection and then the server-child connect()s to that port.

Or another one: The server-child knows the client's Y port when server-parent accepted() the connection.So server-child could send it back to the client.

But these aren't elegant solutions.Have you any ideas or suggestions?

Thank you

jonas.gabriel

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LEARN ABOUT HPUX

listen

listen(2)							System Calls Manual							 listen(2)

NAME

       listen - listen for connections on a socket

SYNOPSIS

DESCRIPTION

       To  accept  connections,  a  socket  is	first  created	using a queue for incoming connections is activated using and then connections are
       accepted using applies only to unconnected sockets of type SOCK_STREAM.	Except for AF_VME_LINK, if the socket has  not	been  bound  to  a
       local  port  before is invoked, the system automatically binds a local port for the socket to listen on (see inet(7F)).	For sockets in the
       address family AF_CCITT and AF_VME_LINK, the socket be bound to an address by using before connection establishment can continue, otherwise
       an error is returned.

       A listen queue is established for the socket specified by the s parameter, which is a socket descriptor.

       backlog defines the desirable queue length for pending connections.  The actual queue length may be greater than the specified backlog.	If
       a connection request arrives when the queue is full, the client will receive an error.

       backlog is limited to the range of 0 to which is defined in is currently set to 4096.  If any other value is specified, the system automat-
       ically  assigns	the  closest  value  within the range.	Note that for a backlog of 0 specifies only 1 pending connection is allowed at any
       given time.  For a backlog of 0 specifies no further connection is allowed.

   X/Open Sockets Compilation Environment
       See xopen_networking(7).

DEPENDENCIES

   AF_CCITT
       Call-acceptance can be controlled by the call described in Upon successful completion, returns 0; otherwise, it	returns  -1  and  sets	to
       indicate the error.

ERRORS

       fails if any of the following conditions are encountered:

	      s 		  is not a valid file descriptor.

	      The socket	  s has not been bound to an address by using

	      s 		  is a valid file descriptor but it is not a socket.

	      The socket referenced by
				  s does not support

	      The socket has been shut down or is already connected.

WARNINGS

       Linking	binary	objects  compiled to specification and binary objects compiled to specification to the same executable may result in unex-
       pected behavior, including application abnormal termination and unexpected socket errors.  See xopen_networking(7) for details and remedy.

FUTURE DIRECTION

       Currently, the default behavior is the however, it might be changed to in a future release.  At that time, any behavior that is	incompati-
       ble  with  might be obsoleted.  Applications that conform to the X/Open specification now will avoid migration problems (see xopen_network-
       ing(7)).

AUTHOR

       was developed by HP and the University of California, Berkeley.

SEE ALSO

       accept(2), connect(2), socket(2), thread_safety(5), xopen_networking(7), inet(7F).

STANDARDS CONFORMANCE

																	 listen(2)

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