md5_IX.py

by D@CC
on 2023ISep25
Purpose: to create a hash-total verification program
 that will ensure the integrity of a subject file.

The Hash total of a subject-file is often calculated in order
 to ensure that the file's contents have not been changed.
Normally, the hash total of the file is stored in a second
 file located in the same folder as the first.
My issue with this process is that the procedure is
 compromised if the "hash-total" file is lost or
 separated from the subject-file.
My solution is to insert one line at the beginning of the file.
 This can easily be done with a python program file by
 prefacing the "hash-total" with "##########_MD5_IX01:".
 Any Python compiler or interpreter will ignore this
 record because it is flagged as a comment by its initial "#".
 This can also be done with any text file.  If the programs
 using this text file know that this special hash record
 should be ignored, then the fileName can be the same
 name as the text file without the "hash record". If
 the program reading the text file cannot "ignore" 
 the initial hash record, then the file must be changed
 before being used. The change is merely that the first
 record will be removed from the text file. It is suggested
 that for these cases, the extension of the file contaning
 the hash total will be ".tx5" .  If the program using the data
 file can ignore a first data record with the prefix of
 "##########_MD5_IX01:" followed by a hash total, then the
 hash file can use the extension of ".txt"
This file will be named 

The initial md5_IX.py program will
be given three parameters:
 the first parameter is -f to signify that a file is to be hashed
                     or -r to signify that a file is to be validated.
 If this parameter is missing, it defaults to -r.
 Files to be validated are "read-only" and will NOT be changed,
 the second parameter is the name of the subject-file.
 the third parameter is the name designating the hash total.
   This third parameter, if missing, is understood to be "_MD5_IX01"
Examples of a subject-file name are "PiR2F.txt" or "Prog01.py".
The "Prog01.py" example will be used in the remainder of this article.

Case -r Verify if the subject file has a valid hash total.

 The md5_IX.py program will read the first record of the subject file.
 If it does not begin with "##########_MD5_IX01:", then it cannot
  be validated and a log error "fileName nnn: no Hash record" will be raised and
  the program will abort.
 If it does begin with a hash record, the hash total in the record
  will be saved as a string named "strMD5old" 
 The hash total of the remaining records will be calculated and
  saving in "strMD5curr".
 If strMD5old==strMD5curr no error will be raised.
 If strMD5old differs from strMD5curr a log error will result
  saying "fileName nnn: bad Hash record"
 If an error occurs, an error file explaining the error will be
  written to the disk.  The error file will be named 
  "fileName_unixtime.err"
 The program will exit without error.

 Note that Case -r will decide if a file has an improper hash total
  an an error file will be created.

Case -f Convert the subject file to a valid "has" file with a hash 
   total in the first record.
  But leave unchanged any subject file with a valid hash total.

 The md5_IX.py program will read the first record of the subject file.
 If it does begin with a hash record, the hash total in the record
  will be saved as a string named "strMD5old"
 If it doesn't begin with a hash record, then "strMD5old" will be
  set to "none"
 In either case, the hash total of the remaining records will be 
  calculated and saved in "strMD5curr".
 If strMD5old==strMD5curr then no error will be raised and the 
  program will exit without error.
 If strMD5old differs from strMD5curr, then
  1. the subject file will be renamed by adding the suffix 
       "yyyyMmmmdd" to the fileName.
  2. a log message will say "fileName: hash total was updated.
  2. a new file will be created with a new first record containing
       "strMD5curr" as the hash total
  3. the name of the new file will be the unchanged subject fileName.
  4. The program will exit without error.

 Note that Case -f never fails and NO error file will be created.
 However, the subject file may be changed.  If so, a copy of the
  old subject file is kept with a slight name change.  The
  resulting subject file always has a valid "hash total" record.

This is the end of program definition of md5_IX.py
/md5_IX.txt