receiver man page

transfer::receiver — Data source


package require Tcl  8.4

package require snit  ?1.0?

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

package require transfer::connect  ?0.2?

package require transfer::receiver  ?0.2?

transfer::receiver object ?options...?

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

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

objectName method ?arg arg ...?

objectName destroy

objectName start

objectName busy


This package pulls data destinations and connection setup together into a combined object for the reception of information coming in over a socket. These objects understand all the options from objects created by the packages transfer::data::destination and transfer::connect.


Package Commands

transfer::receiver object ?options...?

This command creates a new receiver 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::receiver stream channel chan host port ?arg...?

This method creates a fire-and-forget transfer for the data coming from the source at host/port (details below) and writing to 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 not closed when the transfer has completed. This is left to the completion callback.

If both host and port are provided an active connection to the data source is made. If only a port is specified (with host the empty string) then a passive connection is made instead, i.e. the receiver then waits for a conneciton by the transmitter.

Any arguments after the port are treated as options and are used to configure the internal receiver 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 receiver object. This callback is only given the number of bytes and transfered, and possibly an error message. No reference to the internally used receiver 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 receiver 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::receiver stream file path host port ?arg...?

This method is like stream channel, except that the received data is written to the file path, replacing any prior content.

Object Command

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

objectName start

This method initiates the data reception, setting up the connection first and then copying the received information into the destination. The method will throw an error if a reception is already/still in progress. I.e. it is not possible to run two receptions in parallel, only in sequence. Errors will also be thrown if the configuration of the data destination 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 reception is in progress (True), or not (False).


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

-command cmdprefix

This option specifies the command to invoke when the reception 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:


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.


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).

-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.

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::receiver R -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.


channel, copy, data destination, receiver, secure, ssl, tls, transfer


Transfer module


0.2 tcllib Data transfer facilities