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# transfer::data::source(n) 0.2 tcllib "Data transfer facilities"

## Name

transfer::data::source - Data source

## Synopsis

- package require Tcl 8.4
- package require snit ?1.0?
- package require transfer::copy ?0.2?
- package require transfer::data::source ?0.2?

- transfer::data::source objectName ?options...?
- objectName method ?arg arg ...?
- objectName destroy
- objectName type
- objectName data
- objectName size
- objectName valid msgvar
- objectName transmit channel blocksize done

## Description

This package provides objects mainly describing the origin of some data to transfer. They are also able to initiate transfers of the described information to a channel using the foundation package transfer::copy.

## API

### Package commands

transfer::data::source objectName ?options...?

  This command creates a new data source 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::source 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 a transfer initiated by the object is active is safe as all data required for the transfer itself was copied, and the completion of the transfer will not try to access the initiating object anymore. i.e. the transfer is completely separate from the source object itself.

objectName type

  This method returns a string describing the type of the data the object is refering to. The possible values and their meanings are:

  undefined

    No data was specified at all, or it was specified incompletely. The object does not know the type.

  string

    The data to transfer is contained in a string.

  channel

    The data to transfer is contained in a channel.

objectName data

  This method returns a value depending on the type of the data the object refers to, through which the data can be accessed. The method throws an error if the type is undefined. For type string the returned result is the data itself, whereas for type channel the returned result is the handle of the channel containing the data.

objectName size

  This method returns a value depending on the type of the data the object refers to, the size of the data. The method throws an error if the type is undefined. Return of a negative value signals that the object is unable to determine an absolute size upfront (like for data in a channel).

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 transmit channel blocksize done

  This method initiates a transfer of the referenced data to the specified channel. When the transfer completes the command prefix done is invoked, per the rules for the option -command of command transfer::copy::do in the package transfer::copy. The blocksize specifies the size of the chunks to transfer in one go. See the option -blocksize of command transfer::copy::do in the package transfer::copy.

### Options

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

-string text

  This option specifies that the source of the data is an immediate string, and its associated argument contains the string in question.

-channel handle

  This option specifies that the source of the data is a channel, and its associated argument is the handle of the channel containing the data.

-file path

  This option specifies that the source of the data is a file, and its associated argument is the path of the file containing the data.

-variable varname

  This option specifies that the source of the data is a string stored in a variable, and its associated argument contains the name of the variable in question. The variable is assumed to be global or namespaced, anchored at the global namespace.

-size int

  This option specifies the size of the data transfer. It is optional and defaults to -1. This value, and any other value less than zero signals to transfer all the data from the source.

-progress command

  This option, if specified, defines a command to be invoked for each chunk of bytes transmitted, allowing the user to monitor the progress of the transmission of the data. The callback is always invoked with one additional argument, the number of bytes transmitted 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. Please also report any ideas for enhancements you may have for either package and/or documentation.

## Keywords

channel, copy, data source, transfer

## Category

Transfer module

## Copyright

Copyright © 2006-2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>