transfer::connect -
Connection setup
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
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 established.
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.
-
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
namespace otherwise.
The fully qualified name of the object command is returned as the
result of the 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
specifications.
-
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.
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
compatible 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, without
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).
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 ...
...
This document, and the package it describes, will undoubtedly contain
bugs and other problems.
Please report such in the category
transfer of the
http://sourceforge.net/tracker/?group_id=12883.
Please also report any ideas for enhancements you may have for either
package and/or documentation.
transfer, channel, connection, passive, active, ssl, tls, secure