ddest man page

transfer::data::destination — Data destination


package require Tcl  8.4

package require snit  ?1.0?

package require transfer::data::destination  ?0.2?

transfer::data::destination objectName ?options...?

objectName method ?arg arg ...?

objectName destroy

objectName put chunk

objectName done

objectName valid msgvar

objectName receive channel done


This package provides objects mainly describing the destination of a data transfer. They are also able to initiate the reception of information from a channel into the described destination.


transfer::data::destination objectName ?options...?

This command creates a new data destination 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.

Object Command

All objects created by the ::transfer::data::destination 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.

Object Methods

objectName destroy

This method destroys the object. Doing so while the object is busy with the reception of information from a channel will cause errors later on, when the reception completes and tries to access the now missing data structures of the destroyed object.

objectName put chunk

The main receptor method. Saves the received chunk of data into the configured destination. It has to be called for each piece of data received.

objectName done

The secondary receptor method. Finalizes the receiver. It has to be called when the receiving channel signals EOF. Afterward neither itself nor method put can be called anymore.

objectName valid msgvar

This method checks the configuration of the object for validity. It returns a boolean flag as result, whose value is True if the object is valid, and False otherwise. In the latter case the variable whose name is stored in msgvar is set to an error message describing the problem found with the configuration. Otherwise this variable is not touched.

objectName receive channel done

This method initiates the reception of data from the specified channel. The received data will be stored into the configured destination, via calls to the methods put and done. When the reception completes the command prefix done is invoked, with the number of received characters appended to it as the sole additional argument.


All data destinations support the options listed below. It should be noted that all are semi-exclusive, each specifying a different type of destination and associated information. If these options are specified more than once then the last option specified is used to actually configure the object.

-channel handle

This option specifies that the destination of the data is a channel, and its associated argument is the handle of the channel to write the received data to.

-file path

This option specifies that the destination of the data is a file, and its associated argument is the path of the file to write the received data to.

-variable varname

This option specifies that the destination of the data is a variable, and its associated argument contains the name of the variable to write the received data to. The variable is assumed to be global or namespaced, anchored at the global namespace.

-progress command

This option, if specified, defines a command to be invoked for each chunk of bytes received, allowing the user to monitor the progress of the reception of the data. The callback is always invoked with one additional argument, the number of bytes received so far.

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 Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also report any ideas for enhancements you may have for either package and/or documentation.


channel, copy, data destination, transfer


Transfer module


0.2 tcllib Data transfer facilities