transfer::connect(n)					     Data transfer facilities					      transfer::connect(n)

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NAME

       transfer::connect - Connection setup

SYNOPSIS

       package require Tcl  8.4

       package require snit  ?1.0?

       package require transfer::connect  ?0.2?

       transfer::connect objectName ?options...?

       objectName method ?arg arg ...?

       objectName destroy

       objectName connect command

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DESCRIPTION

       This  package  provides objects holding enough information to enable them to either actively connect to a counterpart, or to passively wait
       for a connection from said counterpart.	I.e. any object created by this packages is always in  one  of	two  complementary  modes,  called
       active (the object initiates the connection) and passive (the object receives the connection).

       Of the two objects in a connecting pair one has to be configured for active mode, and the other then has to be configured for passive mode.
       This establishes which of the two partners connects to whom (the active to the other), or, who is waiting  on  whom  (the  passive  on  the
       other).	 Note  that this is completely independent of the direction of any data transmission using the connection after it has been estab-
       lished.	An active object can, after establishing the connection, either transmit or receive data. Equivalently the passive object  can	do
       the same after the waiting for its partner has ended.

API

   PACKAGE COMMANDS
       transfer::connect objectName ?options...?
	      This  command  creates  a  new  connection  object  with an associated Tcl command whose name is objectName.  This object command is
	      explained in full detail in the sections Object command and Object methods. The set of supported options	is  explained  in  section
	      Options.

	      The object command will be created under the current namespace if the objectName is not fully qualified, and in the specified names-
	      pace otherwise.  The fully qualified name of the object command is returned as the result of the command.

   OBJECT COMMAND
       All objects created by the ::transfer::connect command have the following general form:

       objectName method ?arg arg ...?
	      The method method and its arg'uments determine the exact behavior of the command.  See section Object methods for the detailed spec-
	      ifications.

   OBJECT METHODS
       objectName destroy
	      This  method  destroys  the  object.   This is safe to do for an active object when a connection has been started, as the completion
	      callback is synchronous.	For a passive object currently waiting for its partner to establish the connection  however  this  is  not
	      safe  and will cause errors later on, when the connection setup completes and tries to access the now missing data structures of the
	      destroyed object.

       objectName connect command
	      This method starts the connection setup per the configuration of the object. When the connection is established the callback command
	      will be invoked with one additional argument, the channel handle of the socket over which data can be transfered.

	      The detailed behaviour of the method depends on the configured mode.

	      active The  connection  setup  is  done  synchronously. The object waits until the connection is established. The method returns the
		     empty string as its result.

	      passive
		     The connection setup is done asynchronously. The method returns immediately after a listening socket has  been  set  up.  The
		     connection will be established in the background.	The method returns the port number of the listening socket, for use by the
		     caller. One important use is the transfer of this information to the counterpart so that it knows where it has to connect to.

		     This is necessary as the object might have been configured for port 0, allowing the operating system  to  choose  the  actual
		     port it will listen on.

		     The  listening port is closed immediately when the connection was established by the partner, to keep the time interval small
		     within which a third party can connect to the port too.  Even so it is recommended to use additional measures in the protocol
		     outside  of the connect and transfer object to ensure that a connection is not used with an unidentified/unauthorized partner
		     One possibility for this is the use of SSL/TLS.  See the option -socketcmd and section Secure connections for information	on
		     how to do this.

   OPTIONS
       Connection objects support the set of options listed below.

       -mode mode
	      This option specifies the mode the object is in. It is optional and defaults to active mode. The two possible modes are:

	      active In this mode the two options -host and -port are relevant and specify the host and TCP port the object has to connect to. The
		     host is given by either name or IP address.

	      passive
		     In this mode the option -host has no relevance and is ignored should it be configured.  The only option the object  needs	is
		     -port, and it specifies the TCP port on which the listening socket is opened to await the connection from the partner.

       -host hostname-or-ipaddr
	      This  option  specifies  the  host to connect to in active mode, either by name or ip-address. An object configured for passive mode
	      ignores this option.

       -port int
	      For active mode this option specifies the port the object is expected to connect to. For passive mode however it is the  port  where
	      the object creates the listening socket waiting for a connection. It defaults to 0, which allows the OS to choose the actual port to
	      listen on.

       -socketcmd command
	      This option allows the user to specify which command to use to open a socket. The default is to use the builtin ::socket.  Any  com-
	      patible with that command is allowed.

	      The envisioned main use is the specfication of tls::socket. I.e.	this option allows the creation of secure transfer channels, with-
	      out making this package explicitly dependent on the tls package.

	      See also section Secure connections.

       -encoding encodingname

       -eofchar eofspec

       -translation transspec
	      These options are the same as are recognized by the builtin command fconfigure. They provide the configuration to  be  set  for  the
	      channel between the two partners after it has been established, but before the callback is invoked (See method connect).

SECURE CONNECTIONS

       One  way  to  secure  connections made by objects of this package is to require the package tls and then configure the option -socketcmd to
       force the use of command tls::socket to open the socket.

	   # Load and initialize tls
	   package require tls
	   tls::init -cafile /path/to/ca/cert -keyfile ...

	   # Create a connector with secure socket setup,
	   transfer::connect C -socketcmd tls::socket ...
	   ...

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain bugs and other problems.  Please report such in the category transfer
       of the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883].  Please also report any ideas for enhancements you may have for
       either package and/or documentation.

KEYWORDS

       active, channel, connection, passive, secure, ssl, tls, transfer

CATEGORY

       Transfer module

COPYRIGHT

       Copyright (c) 2006-2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>

transfer								0.2						      transfer::connect(n)