Lets
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.
Wrap is an application that is designed to take
care of each of these situations. Wrap 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.
The wrap
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. Wrap is designed to be used to best advantage
with fldigi but can be used with any digital modem program.
Fldigi can recognize a 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
base-64 format:
Using wrap is very simple. Install the executable file and then create a short cut to the executable on the desktop.
Windows
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 wrap.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 wrap.exe
installed. Keep all the executable files together. If you
are installing wrap by itself you unzip the wrap-1.0.zip file and
extract its contents to a folder that is convenient to locate.
Then right-click on the extracted wrap.exe, hold the mouse button
down, drag a shortcut from wrap.exe to the Desktop, and release the
mouse button. You can also right-click on wrap.exe and choose "Send to
Desktop (create a shortcut)". Additional shortcuts to Wrap may be
dragged into any convenient folder where files to be wrapped are
located.
Left click
(or double click) to launch the application and you will see a brief
description of usage: Open
a file browser to the folder (directory) that contains the files that are to be wrapped .
Drag and drop the file to be wrapped onto the desktop icon
and you will see the following results :
!! WRAPPED FILES ARE ALWAYS PLACED IN THE SAME FOLDER AS THE SOURCE FILE !!
The
file "testbars-bw.png" has been wrapped by the drag and drop technique.
The results of the wrap appear in the wrap info dialog and you
can see the new file in the WrapTest 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.
This file is small enough to examine to see how the wrapped file
is formated:
[WRAP:beg] ... [WRAP:end] bracket the contents of the file
[WRAP:lf] specifies that the single line feed character delineates lines
[WRAP:fn testbars-bw.png] specifies that the source (and destination) filename is "testbars-bw.png"
[b64:start] ... [b64:end] bracket the base-64 encoded contents
[WRAP:chksum DB95] is the checksum associated with the file and it's contents
At
the receiving end the file might be named "wrap-090318-001.wrap."
Drag and drop it onto the wrap launch icon and the following
results:
Notice that the original filename is used for the unwrapped file.
If the transfer had errors then the unwrap process would fail. The message dialog would so indicate:
Certain
files probably should not be considered for transfer without first
compressing them. All of the Microsoft Office files fall into
this category. You can satisfy yourself that this is true.
Try creating two documents
Document type
Size of file
Compressed with Zip
Excel spreadsheet with a single entry in the A1 cell = "1"
13,824 bytes
1,321 bytes
Word document with a single character "1" entered as the text
24,064 bytes
1,862 bytes
The
original files are also binary files and should not be sent in the
plain using any digital mode. You would first have to compress
the file and then wrap the compressed version before transmission.
But there is absolutely no good reason for transferring this type
of a file over HF or VHF radio.
Oh yes that single character
word document that contained the number "1". It compressed to 1,862
bytes and then grew to 2,627 bytes after being converted to base-64 and wrapped
for transmission. 2627 to 1 ... I sure would like those odds in
the stock market !
The best practice with WRAP file transmission is to save messages as
plain text files (txt) and spreadsheets or databases as comma delimited
files (csv), both of which are common formats for any software packages,
including the free Open Office suite.
