RE: Base64 question

["John Allen" <jallen@xxxxxxxxxxx>]

Scott, 

Maybe I have something wrong in my test code:
I am testing with "ABC"
I translate this to ASCII and get the correct value
X'414243'
I do Base64 encode and get QkJD
Then when I decode it I get X'424243'
Which is BBC

D W$Before        S              8A                       
D W$After         S             12A                       
D W$AfterLen      S             10I 0                     
 *                                                        
D W$After2        S             12A                       
D W$AfterLen2     S             10I 0                     
 *                                                        
D P$LEN           S              4  0                     
D P$Table         S             10A                       
 *                                                        
C                   eval      W$Before = 'ABC'            
 * Calculate length of PCL commnd string                  
C     ' '           CHECKR    W$Before      P$Len         
 * Convert string to ascii                                
C                   CALL      'QDCXLATE'                  
C                   PARM                    P$len           
C                   PARM                    W$Before        
C                   PARM      'QASCII'      P$table         
 *                                                          
 * W$Before = 'ABC'; after translation debug shows x'414243'

 /free                                                      
                                                            
     W$AfterLen = B64_Encode( %ADDR(W$Before)               
                            : %LEN(%TRIMR(W$Before))        
                            : %ADDR(W$After)                
                            : %SIZE(W$After) );             
                                                            
     W$AfterLen2 = B64_Decode( %ADDR(W$After)               
                             : %LEN(%TRIMR(W$After))        
                             : %ADDR(W$After2)              
                             : %SIZE(W$After2) );           
                                                            
     *INLR = *ON;                                           
/end-free

WAfter2 = debug shows x'424243' (which is BBC)



-----Original Message-----
From: Scott Klement [mailto:midrange-l@xxxxxxxxxxxxxxxx] 
Sent: Thursday, November 06, 2008 3:13 PM
To: Midrange Systems Technical Discussion
Subject: Re: Base64 question

hi John,

I don't think it makes sense to store in ASCII in the
database.  After 
all, you're likely to want to do other things with your
database besides 
this one program.

Why not just add code to your RPG program to convert it to
ASCII prior 
to base64 encoding it?

Here's a trivial example in ILE RPG, that uses the
IBM-supplied QDCXLATE 
program to convert from EBCDIC to ASCII:

      D QDCXLATE        PR
ExtPgm('QDCXLATE')
      D   Len                          5p 0 const
      D   data                     32702a
options(*varsize)
      D   table                       10a   const

      D data            s              5
       /free
          data = 'Hello';
          QDCXLATE( %len(data)
                  : data
                  : 'QTCPASC' );

The above method is really easy to do, and it works. It can
be used with 
any of the translation tables (*TBL objects) on your system.
QTCPASC is 
an IBM-supplied table that translates to ASCII.

There are two big problems with QDCXLATE:

a) You can't use it to translate a single-byte character set
to a double 
or mixed-byte character set.

b) In order to make it work properly with variant
characters, you have 
to find (or create) a table that translates exactly the way
you want. 
(there are many versions of ASCII and many versions of
EBCDIC.  Which 
one are you translating from?  Which one are you translating
to?)

A more sophisticated method of doing the translation (and
one that 
requires more code) is to use the iconv() API.  With iconv()
you can 
provide the exact from/to CCSID and it'll translate between
them.  It 
also lets you work with double-byte and multi-byte character
sets.  But 
the code is more complex, so I'll leave you with the
QDCXLATE API for 
now, and if you find that lacking, let me know and I'll post
an iconv 
example.

But, at any rate, ASCII/EBCDIC translation is hardly part of
Base64 
encoding!  Indeed, most of the time you use base64 encoding
expressly 
because your data isn't text data!



John Allen wrote:
> 1)If I have the value "Hello" in my database field on the
> System i (in EBCDIC) isn't there some method I can convert
> it to an ASCII value before encoding it to Base64 so I end
> up with the correct Base64 value the ASCII machine is
> expecting, or just store it in my database field in ASCII
> format (although it is actually an EBCDIC System)?
> Example If the value were 123 in EBCDIC it would be stored
> as x'F1F2F3' Could I store it as ASCII x'313233' then
could
> it be encoded to Base64 to be read in correctly by ASCII
> system?