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# transfer::transmitter(n) 0.2 tcllib "Data transfer facilities"

## Name

transfer::transmitter - 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?
- package require transfer::connect ?0.2?
- package require transfer::transmitter ?0.2?

- transfer::transmitter objectName ?options...?
- transfer::transmitter stream channel chan host port ?arg...?
- transfer::transmitter stream file path host port ?arg...?
- objectName method ?arg arg ...?
- objectName destroy
- objectName start
- objectName busy

## Description

This package pulls data sources and connection setup together into a combined object for the transmission of information over a socket. These objects understand all the options from objects created by the packages transfer::data::source and transfer::connect.

## API

### Package commands

transfer::transmitter objectName ?options...?

  This command creates a new transmitter 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.

transfer::transmitter stream channel chan host port ?arg...?

  This method creates a fire-and-forget transfer for the data contained in the channel chan, starting at the current seek location. The channel is configured to use binary translation and encoding for the transfer. The channel is automatically closed when the transfer has completed.

  If both host and port are provided an active connection to the destination is made. If only a port is specified (with host the empty string) then a passive connection is made instead.

  Any arguments after the port are treated as options and are used to configure the internal transmitter object. See the section Options for a list of the supported options and their meaning. Note however that the signature of the command prefix specified for the -command callback differs from the signature for the same option of the transmitter object. This callback is only given the number of bytes and transfered, and possibly an error message. No reference to the internally used transmitter object is made.

  The result returned by the command is the empty string if it was set to make an active connection, and the port the internal transmitter object is listening on otherwise, i.e when it is configured to connect passively. See also the package transfer::connect and the description of the method connect for where this behaviour comes from.

transfer::transmitter stream file path host port ?arg...?

  This method is like stream channel, except that the data contained in the file path is transfered.

### Object command

All objects created by the ::transfer::transmitter 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 transmission is in progress will cause errors later on, when the transmission completes and tries to access the now missing data structures of the destroyed object.

objectName start

  This method initiates the data transmission, setting up the connection first and then copying the information. The method will throw an error if a transmission is already/still in progress. I.e. it is not possible to run two transmissions in parallel on a single object, only in sequence. Multiple transmitter objects are needed to manage parallel transfers, one per transmission. Errors will also be thrown if the configuration of the data source is invalid, or if no completion callback was specified.

  The result returned by the method is the empty string for an object configured to make an active connection, and the port the object is listening on otherwise, i.e when it is configured to connect passively. See also the package transfer::connect and the description of the method connect for where this behaviour comes from.

objectName busy

  This method returns a boolean value telling us whether a transmission is in progress (True), or not (False).

### Options

All transmitter objects support the union of the options supported by their connect and data source components, plus two of their own. See also the documentation for the packages transfer::data::source and transfer::connect.

-blocksize int

  This option specifies the size of the chunks to be transmitted in one block. Usage is optional, its default value is 1024.

-command cmdprefix

  This option specifies the command to invoke when the transmission of the information has been completed. The arguments given to this command are the same as given to the completion callback of the command transfer::copy::do provided by the package transfer::copy.

-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).

-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.

## Secure connections

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::transmitter T -socketcmd tls::socket ...
        ...

## TLS Security Considerations

This package uses the TLS package to handle the security for https urls and other socket connections.

Policy decisions like the set of protocols to support and what ciphers to use are not the responsibility of TLS, nor of this package itself however. Such decisions are the responsibility of whichever application is using the package, and are likely influenced by the set of servers the application will talk to as well.

For example, in light of the recent POODLE attack discovered by Google many servers will disable support for the SSLv3 protocol. To handle this change the applications using TLS must be patched, and not this package, nor TLS itself. Such a patch may be as simple as generally activating tls1 support, as shown in the example below.

        package require tls
        tls::init -tls1 1 ;# forcibly activate support for the TLS1 protocol
        ... your own application code ...

## 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, secure, ssl, tls, transfer, transmitter

## Category

Transfer module

## Copyright

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