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transfer::transmitter(n) Data transfer facilities transfer::transmitter(n) 





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



  

  
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.

  

  

  
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.

  

  

  
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:



  

  
The method method and its arg'uments determine the exact
      behavior of the command. See section Object methods for the
      detailed specifications.








OBJECT METHODS



  

  
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.

  

  
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.

  

  

  
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.



  

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

  

  
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.

  

  
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.







  

  
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.

  

  
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.

  

  
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.

  

  

  

  

  

  

  
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).

  

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

  

  
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.

  

  
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.

  

  
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.

  

  
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.

  

  
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
    [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.


When proposing code changes, please provide unified diffs,
    i.e the output 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 source, secure, ssl, tls, transfer,
    transmitter






CATEGORY


Transfer module






COPYRIGHT


Copyright (c) 2006-2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>








  

    0.2
    tcllib