Softpanorama defensive error diagnostic framework

Many people independently came to the subset of ideas of Defensive programming so it is impossible to attribute this concept to a single author.

One of fundamental principles of defensive programming is that the program should always provide meaningful diagnostics and logging. Meaningful diagnostic is typically a weak spot of many Unix utilities, which were written when every byte of storage was a premium and the computer used to have just one 1M bytes of memory or less (Xenix -- one of the early Unixes worked well on 2MB IBM PCs)

If messages you get in case of errors or crashes are cryptic it typically takes a lot of efforts to relate the message to the root case. If you are the user of the program that you yourself have written that might be viewed as a case of "insult after injury" :-)

Here we strive to the quality of diagnostics that is typically demonstrated by debugging complier. Defensive programming also presume presence of a sophisticated logging infrastructure within the program. Logs should are easy to parse and filter for relevant information.

Softpanorama defensive diagnostic framework module Softpano.pm provides  the following functionality:

1. All messages are produced with the line in which they occurred.
    
2. Messages are generated using subroutine logme which has two parameters (error code and the text of the message). They are printed with the error code, which signify the severity and the line number at which logme subroutine was invoked. Four error levels levels are distinguished:
   1. Warnings: informational messages that do not affect the validly of the program output or any results of its execution. Still the situation that deserve some attention
   2. Errors: (correctable errors) Messages that something went wrong but the results execution of the program is still OK and/or output of the program most probably is still valid
   3. Severe errors (failures). Program can continue but the results are most probably a garbage and should be discarded. Diagnostic messages provides after this point might still have a value.
   4. Terminal or internal errors (called abends - abnomal ends). Those are unrecoverable errors. Program iether ontinue at this point ir the results are garabage. In Cans ethe program run as a cron job, for such abnormal situations you can even try to email the developer.

   To achieve this this level of functionality the programmed needs to have a special messages generation subroutine. which is waht we present in this project.

   For example, the subroutine logmes, which is the key part of Softpano.pm module is modeled after one used in compilers. The first parameter passes to this subroutines should be the one byte code of the error (or its number equivalent), the second is the test of dignostic message. The subroutine prints this message to consol and log  along with the line in which error was detected. 

   The errors codes used are as following

   • W -- warning --  the program can continue; most probably results will be correct, but in rare cases this situation can lead to incorrct or incomplete results.
   • E -- error  -- continuation of the program possible and the result most probably will be correct (correctable errors)
   • S -- failure (serious error)  -- continuation of program possible but the result most probably will be useless or wrong.
   • T -- internal error 

   NOTE: The abbreviated string for those codes has the mnemonic string WEST
    

3. Terminal errors (abends) represent a special case, for which some additional diagnostic should be provided. They are invoked with a special subroutine (called abend), which can provide extended context for the error
    
4. Output of those message is regulated by option verbosity (-v). The highest level is 3 which produces all errors. 
    
5. There are also two types of informational messages that can be produced  (which are not suppressible):
   • "I" (informational) messages produced with the error code. They can be generated using logme subroutine
   • Regular output which is produced without error code, as is. They can be generated using out subroutine
      
6. There is  a possibility to output of the summary of the messages at the end of execution of programs

Testing the Softpano.pm module

To test Softpano.pm module please use softpano_test.pl provided. This test re-implements basic functionality of cat command in Perl. Invocation is:

perl softpano_test.pl softpano_test.pl

The text of softpano_test.pl can serve as a user manual for the module.

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It provides the following functionality:

1. All messages are produced with the line in which they occurred.
2. Messages are generated using subroutine logme which has two parameters (error code and the text of the message). They are printed with the error code, which signify the severity and the line number at which logme subroutine was involved. Four levels are distinguished:
   • Warnings: informational messages that do not affect the validly of the program output or any results of its execution. Still the situation that deserve some attention
   • Errors: (correctable errors) Messages that something went wrong but the results execution of the program is still OK and/or output of the program most probably is still valid
   • Severe errors (failures). Program can continue but the results are most probably a garbage and should be discarded. Diagnostic messages provides after this point might still have a value.
   • Terminal or internal errors (abends). Program can't continue at this point and need to exit. In case of cron jobs, for such abnormal situations you can even try to email the developer.

   To achieve this one needs to write or borrow and adapt a special messages generation subroutine for example logmes, modeled after one used in compilers. One of the parameters passes to this subroutines should be the one byte code of the error (or its number equivalent) along with the line in which error was detected. For example

   • W -- warning -- the program can continue; most probably results will be correct, but in rare cases this situation can lead to incorrct or incomplete results.
   • E -- error -- continuation of the program possible and the result most probably will be correct (correctable errors)
   • S -- failure (serious error) -- continuation of program possible but the result most probably will be useless or wrong.
   • T -- internal error

   The abbreviated string for those codes has the mnemonic string WEST

3. Terminal errors (abends) represent a special case, for which some additional diagnostic should be provided. They are invoked with a special subroutine (called abend), which can provide extended context for the error
4. Output of those message is regulated by option verbosity (-v). The highest level is 3 which produces all errors.
5. There are also two types of informational messages that can be produced (which are not suppressible):
   • "I" (informational) messages produced with the error code. They can be generated using logme subroutine
   • Regular output which is produced without error code, as is. They can be generated using out subroutine
6. There is a possibility to output of the summary of the messages at the end of execution of programs

Testing the Softpano.pm module

To test Softpano.pm module please use softpano_test.pl provided. This test re-implements basic functionality of cat command in Perl. Invocation is:

perl softpano_test.pl softpano_test.pl

The text of softpano_test.pl can serve as a user manual for the module.

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Last modified: June 04, 2021