BOO FILE FORMAT, ENCODING AND DECODING

Many Kermit programs are often distributed using a special encoding called
"boo" (short for "bootstrap") format, developed especially for distribution of
Kermit binaries over networks, e-mail, and communication lines.

A common practice is to encode .EXE and other binary files into printable
characters, such as hexadecimal digits, for transportability.  A simple "hex"
encoding results in two characters per 8-bit binary byte, plus CRLFs added
every 80 (or less) hex characters to allow the file to pass through
card-oriented networks like BITNET.  A hex file is therefore more than twice
as large as the original binary file.

A .BOO file is a more compact, but somewhat more complicated, encoding.  Every
three binary bytes (24 bits) are split up into four 6-bit bytes with 48 (ASCII
character "0") added to each, resulting in four ASCII characters ranging from
"0" (ASCII 48) to "o" (ASCII 111), with CRLFs added at or near "column 76".
The resulting file size would therefore be about 4/3 the .EXE file size.  This
is still quite large, so .BOO files also compress consecutive null (zero)
bytes.  Up to 78 consecutive nulls are compressed into two characters.  Tilde
("~") is the null-compression lead-in, and the following character indicates
how many nulls are represented (subtract 48 from this character's ASCII
value).  For instance "~A" means 17 consecutive nulls; "~~" means 78 of them.
Repeated nulls are very common in binary executable files.

4-for-3 encoding combined with null compression reduces the size of the
encoded file to approximately the same size as the original .EXE file, and
sometimes even smaller.  The first line of a .BOO file is the name (in plain
text) of the original file.  Here's what the first few lines of a typical .BOO
file look like:

  CKERMIT.EXE
  CEYP0Id05@0P~3oomo2Y01FWeP8@007P000040HB4001`W~28bL005\W~2JBP00722V0ZHPYP:
  \8:H2]R2V0[`PYP:68>H2S23V0YHPiP:Xg800;Qd~2UWD006Yg~2Ogl009]o~2L8000;20~~~~
  ~~~~~~~:R2H008TV?P761T410<H6@P40j4l6RRH0083l17@PP?`1M@?YSP20o0Ee0nUD0h3l
  1WD3jO@3]0VjW03=8L?X4`N0o01h1\H6~20l>0i7n0o1]e7[@2\PO=8LH60@00Raj>04^97Xh0

Executable C-Kermit programs are distributed in BOO format for the Commodore
Amiga, OS/2, and possibly others.  BOO format is also used for MS-DOS Kermit,
Microsoft Windows Kermit, and other Kermit versions that are not part of
C-Kermit.

The program for converting a binary executable (or any other) file into
BOO format is:

  CKBMKB.C

Compile this program using your C compiler and then run it, giving the name
of the input (binary) and output (boo) files as a command-line arguments, for
example:

  ckbmkb ckermit.exe ckermit.boo

The program for converting a BOO file back into its original form (such as
binary executable) is:

  CKBUNB.C

Compile this program using your C compiler and then run it, giving the name
of the input (boo) file as a command-line argument, for example:

  ckbunb ckermit.boo

This will re-create the file with its original name (as stored in the first
line of the BOO file).

These two programs are identical to the MSBMKB and MSBPCT programs that are
distributed with MS-DOS Kermit.  BOO-file makers and decoders are also
available in other languages (Fortran, Pascal, Assembler, etc) in the MS-DOS
Kermit file collection under the MSB prefix.
