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  ?0.1?

       transfer::connect object ?options...?

       object destroy

       object connect command

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DESCRIPTION

       This  package  provides objects holding enough information to enable them to either connect to a counterpart, or to be connected to by 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 node can, after establishing the connection, either transmit or receive data. Equivalently the passive node can  do  the
       same after the waiting for it partner has ended.

API

       transfer::connect object ?options...?
              This  command  creates  and  configures  a  new connection object. The fully qualified name of the object command is returned as the
              result of the command.

              The recognized options are 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.

              -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).

       object 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 parter 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.

       object 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. For an active object the connection setup is done syn-
              chronously. I.e. the object will wait until the connection is established. In that mode the method returns the empty string  as  its
              result.

              A  passive  object however operates asynchronously. The method will return immediately after a listener has been set up and the con-
              nection will be established in the background. In that mode the method returns the port number of the listening socket, for  use  by
              the caller, like transfering this information to the counterpart so that it may know where to connect to.

              This is necessary as the object might have been configured for port 0, allowing the OS 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.

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, transfer

COPYRIGHT

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

transfer                                                                0.1                                                   transfer::connect(n)