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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 coun-terpart, counterpart,
terpart, 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 established. 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 con-figured. configured.
figured. 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. ipaddress.
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 connec-tion connection
tion 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 synchronously. 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 connection 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://source-
forge.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)
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