Provided by: tcllib_1.17-dfsg-1_all 
NAME
transfer::receiver - Data source
SYNOPSIS
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
_________________________________________________________________________________________________
DESCRIPTION
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.
API
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).
OPTIONS
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:
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).
-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
[http://googleonlinesecurity.blogspot.co.uk/2014/10/this-poodle-bites-exploiting-
ssl-30.html] 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
[http://core.tcl.tk/tcllib/reportlist]. Please also report any ideas for enhancements you
may have for either package and/or documentation.
KEYWORDS
channel, copy, data destination, receiver, secure, ssl, tls, transfer
CATEGORY
Transfer module
COPYRIGHT
Copyright (c) 2006 Andreas Kupries <andreas_kupries@users.sourceforge.net>