transfer::receiver(3tcl) Data transfer facilities transfer::receiver(3tcl)
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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
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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 Ob-
ject methods. The set of supported options is explained in sec-
tion 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 com-
ing 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 Op-
tions 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 mes-
sage. 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 re-
ceiver object is listening on otherwise, i.e when it is config-
ured to connect passively. See also the package transfer::con-
nect 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 fol-
lowing general form:
objectName method ?arg arg ...?
The method method and its arg'uments determine the exact behav-
ior 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 com-
pletes and tries to access the now missing data structures of
the destroyed object.
objectName start
This method initiates the data reception, setting up the connec-
tion 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 ob-
ject 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 recep-
tion 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 trans-
fer::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 con-
nect to. The host is given by either name or IP address.
passive
In this mode the option -host has no relevance and is ig-
nored should it be configured. The only option the ob-
ject needs is -port, and it specifies the TCP port on
which the listening socket is opened to await the connec-
tion from the partner.
-host hostname-or-ipaddr
This option specifies the host to connect to in active mode, ei-
ther 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 ex-
pected to connect to. For passive mode however it is the port
where the object creates the listening socket waiting for a con-
nection. It defaults to 0, which allows the OS to choose the ac-
tual 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 com-
mand fconfigure. They provide the configuration to be set for
the channel between the two partners after it has been estab-
lished, 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 chan-
nel 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 re-
ceived so far.
SECURE CONNECTIONS
One way to secure connections made by objects of this package is to re-
quire 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 applica-
tion 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://googleonli-
nesecurity.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.
When proposing code changes, please provide unified diffs, i.e the out-
put of diff -u.
Note further that attachments are strongly preferred over inlined
patches. Attachments can be made by going to the Edit form of the
ticket immediately after its creation, and then using the left-most
button in the secondary navigation bar.
KEYWORDS
channel, copy, data destination, receiver, secure, ssl, tls, transfer
CATEGORY
Transfer module
COPYRIGHT
Copyright (c) 2006 Andreas Kupries <andreas_kupries@users.sourceforge.net>
tcllib 0.2 transfer::receiver(3tcl)