suppose you want to send a critical message that must be received
exactly as it was sent, or maybe you want to send a data file where
it's highly unlikely that even a trained operator could tell that there
was an error in receiving the data. Or perhaps you need to
broadcast a weather bulletin or situation report to multiple stations
and allow each station to verify that the message was received exactly
as it was sent.
is an application that is designed to take
care of each of these situations. Flwrap allows you to transmit a
text message, image, or binary file to either single or multiple
stations and allow each receiving station to verify that the
transmission was received without error. In the discussion which
follows the application name is Flwrap, the file encapsulation process
is called wrap, wrapping and the encapsulated file is said to be
executable is a small desktop application that encapsulates a text file, an image
file, or a binary file within a set of identifier blocks. These
blocks include a 16 bit checksum that is used to test the encapsulated
file for integrity. Flwrap is designed to be used to best advantage
with fldigi but can be used with any digital modem program.
Fldigi can recognize an wrapped transmission in the Rx data
stream and automatically save the file. Fldigi can process
multiple wrapped files that are sent in rapid succession. Fldigi
does this without operator intervention. The conversion of files
to and from the wrapped format do still require an operator.
A text file is encapsulated without changes
to the text. Images and other binary files are first converted to
a base-64 format. The converted file is then encapsulated.
The header blocks identify the type of file and whether or not it
has been converted to base-64. Files with any of the following
extensions will be treated as binary data files and converted to the
Using flwrap is very simple. Install the executable file and then create a short cut to the executable on the desktop.
users may find it a bit confusing to install a program that does not
have an installation wizard, but it really is very easy to do.
The flwrap.exe program is contained in the zipped fldigi archive
that also contains fldigi.exe and flarq.exe. If you have already
installed fldigi from this archive then you already have flwrap.exe
installed. The installer creates a desktop icon for the application. Additional shortcuts to flwrap may be
dragged into any convenient folder where files to be wrapped are
(or double click) to launch the application and you will see a brief
description of usage.
You may wrap/unwrap a file using three different techniques.
1) Drag and drop the file to be wrapped onto the desktop icon
2) Drag and drop the file into the drop box in the flwrap dialog
3) Invoke the application from a command line
All three can be used on Linux and Windows, but (1) and (2) are the most user friendly.
(2) and (3) can be used on OS X, but (2) is prefered. OS X users should not expect technique (1) to work. This is a limitation of the OS X desktop manager and not flwrap.
Either technique will yield the following when successful.
and you will see the following results :
!! FLWRAPPED FILES ARE ALWAYS PLACED IN THE SAME FOLDER AS THE SOURCE FILE !!
file "Scottie_small.jpg" has been wrapped by the drag and drop technique.
The results of the flwrap appear in the flwrap info dialog and you
can see the new file in the original source directory (all on a Linux
computer). The original file was an image and so it was converted
to ASCII format using base-64 encoding before it was wrapped.
t9zOJ117omOU0L/w9j2ace8X3+DAO/4C54Tr6Xuru1g4tiuMU2oaA2+R2tLXaNEkTeUYKgWG ... removed data for this example
GwFcGQIpP8wA6WQTbzmx5ggV7Qj524JWO2cEcS2nRFTG6EeoQdvmGsLwXwMIeQA= [b64:end][WRAP:chksum 8710][WRAP:end]
[WRAP:beg] ... [WRAP:end] bracket the contents of the file
[WRAP:lf] specifies that the single line feed character delineates lines
[WRAP:fn Scottie_small.jpg] specifies that the source (and destination) filename is "Scottie_small.jpg"
[b64:start] ... [b64:end] bracket the base-64 encoded contents
[WRAP:chksum 8710] is the checksum associated with the file and it's contents
the receiving end the file might be named "wrap-090318-001.wrap."
Drag and drop it onto the flwrap launch icon to unwrap the file.
If the transfer had errors then the unwrap process would fail. The message dialog would so indicate:
You can continue to drop files into the drop box and each new file will be treated independently.
flwrap with compression
flwrap also compresses and expands files in addition to encapsulating
them. Binary files such as a MS Word file or an executable must
be converted to base 64 before being wrapped. Those files are
first compressed before the base64 encoding is applied. A Word
by flwrap it is 3.1 kB in size.
The wrapped file is an ASCII text file suitable for transmission using
any of the fldigi modes other than CW, RTTY or the fuzzy modes such as
The compression method used in flwrap is called LZMA, Lempel–Ziv–Markov
chain algorithm, a form of dictionary compression. There are
times that LZMA cannot compress the data. The data set might be
too small or have zero redundancy. Under those circumstances you
will warned with a appropriate message: