Re: Base64 question

[Scott Klement <midrange-l@xxxxxxxxxxxxxxxx>]

Hi John,

The purpose behind base64 is to allow binary data to be sent through a 
text transfer medium.  For example, if you have a JPEG picture and want 
to send it through e-mail, you have a problem.  Pictures aren't made up 
of letters and numbers, instead the actual bit values of the bytes 
control what the picture looks like.  However, e-mail was designed for 
text.  If you send e-mail from a computer running ASCII to a computer 
running EBCDIC, all of the bytes in the message will be translated from 
ASCII to EBCDIC -- so a picture would become a corrupt mess.

Base64 is a solution to that problem.   Base64 takes the actual bit 
values that make up a string of data, and converts them to to a 
text-safe format.  The text can then be translated to 
ASCII/EBCDIC/Unicode, whatever, it doesn't matter.  When it's decoded, 
the data will be decoded back to the exact same binary values that you 
started with.

That being the case, a text string encoded on an EBCDIC platform will 
CERTAINLY encode to a different string than a text string encoded on an 
ASCII platform!   Of course it will, since the underlying bit values are 
different.

If you take the string 'Hello' and encode it on an EBCDIC platform, 
you've encoded x'C885939396' into base64.  When you decode it on an 
ASCII platform, it'll decode to x'C885939396' -- which is NOT the word 
Hello in ASCII (If it did that, there'd be no point to base64) but 
rather, it's the exact same bit values you started with...

Hope you understand.

John Allen wrote:
> I am doing a test to see of I can convert a character string
> to B64 from within an RPG program
>
> There are programs on the web that convert files in the IFS,
> but I need to convert a database field
>
>  
>
> So I am using a B64 encode/decode program from Scott Klement
> (Thanks Scott)
>
> However I am getting a completely different value then what
> I get using a Web based B64 encode decode program
>
> AND when I try to convert it back it does not convert back
> correctly
>
>  
>
> Can anyone point me to what I may be doing wrong? 
>
> Does the encode.decode expect ASCII characters? 
>
> Should the example below work fine? 
>
>  
>
> W$Before = 'ABCDEFGH';                             
>
>                                                    
>
> W$AfterLen = B64_Encode( %ADDR(W$Before)           
>
>                        : %LEN(%TRIMR(W$Before))    
>
>                        : %ADDR(W$After)            
>
>                        : %SIZE(W$After) );         
>
>  
>
> (Using Debug I see that W$AFTER = 'wsLDxcXGxMgg')
>
> (Web based encodes to QUJDREVGR0gNCg==)
>
>                                                 
>
>  W$AfterLen2 = B64_Decode( %ADDR(W$After)       
>
>                          : %LEN(%TRIMR(W$After))
>
>                          : %ADDR(W$After2)      
>
>                          : %SIZE(W$After2) );   
>
>                                                 
>
>  
>
> (Using Debug I see that decodes back to W$AFTER2 =
> 'BBCEEFDH-   ')
>
>   
>
> Any ideas on what I might be doing wrong?
>
>  
>
> Thanks
>
>  
>
> John
>
>  
>
>