Re: [boost] [serialization] Base64 padding in basic_text_oprimitive

From: Robert Ramey (ramey_at_[hidden])
Date: 2008-06-10 12:43:08

The problem with ths fix is that the current system reads the number of 
bytes and advances
the iterator only that number of bytes.  So if I were to make this change, I 
would also have to make another change on the base64 input.  But then I 
would have a problem with reading old archives which woudn't have the extra
byte.

Nevertheless, I would much like to see a correct,  portable and more widely 
usable version of this iterator.

So, If you would like to see this do the following:

a) open up a track ticket on this.
b) post patch for output AND input
c) run tests - at least test_bas64 iterator

Then I'll look at rolling it in - along with tweaks to make it backward 
compatible
for existing archives.

Let no good deed go unpunished.

Robert Ramey

Vyacheslav E. Andrejev wrote:
> Hello,
>
> Code that pads base64 output with '=' looks in
> basic_text_oprimitive.ipp like following:
>
>    std::size_t padding = 2 - count % 3;
>    if(padding > 1)
>        *oi = '=';
>        if(padding > 2)
>            *oi = '=';
>
> It will give the following transformations of a few simple strings:
>
> "012" -> "MDEy="
> "0123" -> "MDEyMw"
> "01234" -> "MDEyMzQ"
> "012345" -> "MDEyMzQ1="
>
> Which violates the principle of the base 64 that the encoded output
> length is multiple of 4 bytes. Right output for the samples above
> should be:
>
> "012" -> "MDEy"
> "0123" -> "MDEyMw=="
> "01234" -> "MDEyMzQ="
> "012345" -> "MDEyMzQ1"
>
>
> The problem with the code above is that the condition (padding > 2)
> is never satisfied. I think that the proper code should look like
>
>        std::size_t padding = 2 - count % 3;
>        if (padding < 2) {
>          *oi = '=';
>          if (padding > 0)
>            *oi = '=';
>        }