Re: Ada and Internet stuff

[Darren New <dnew@san.rr.com>]

> > Also, what's the mechanism for dealing with things like UTF-8?
>   Base64 is specifically designed to work across various character
> encodings.  Thus an 'A' means 6 bits of zeroes, regardless of how
> that 'A' is represented.

Actually, I think it's that ASCII 64 means 6 bits of zeros, but I'd have
to double-check the RFC specifically. :-) But I understand what you're
saying, that the text-io routines are responsible for mapping 'A' in the
source to 'A' in your input file.

>  You *should* be able to replace String
> with Wide_String and Character with Wide_Character appropriately
> and have it work.  Of course your 24 bits of input would then be
> 64, rather than 32 bits, encoded, for an expansion factor of 2.66,
> which would rather argue against it.

Sorry. That second question was kind of a non-sequitar. Not asking about
its relation to base64 as such, but in general about character encoding
problems. Like, if I were to deal with XML, how could I expect to handle
wide characters in the input stream?

> >   -- Target'length must be at least:
> >   -- Output_Quad_Count: constant := (Source'length + 2) / 3;
> >   -- Output_Byte_Count: constant := 4 * Output_Quad_Count;
> >   -- Target'length = Output_Byte_Count + 2 * (Output_Byte_Count / 76)
> >
> > This should be a function. :-) Probably, it would be best to have a
> > function that takes an input length and returns the output length in
> > both directions, so you can allocate your buffers properly before
> > calling the functions.
>   Extra whitespace and missing line breaks are both allowed in encoded
> data, so you can't tell without looking at it, ie running the decoding,
> just what it will decode into. 

True. But that might be useful anyway, even if inefficient.

> No such problem on encoding.

Yes.

> You could make
>     function Encode(X : Stream_Element_Array) return String;
>     function Decode(S : String) return Stream_Element_Array;
> and let them generate and return the correct size results.  That's
> not terribly hard but is surely less speedy, which may matter.

I was fiddling around with variable length strings, and I thought I
understood but I apparently don't. What would I *do* with such a
returned result? There isn't a variable I could assign it to, is there?
The only thing I could do is to pass it to some other routine that takes
unconstrained strings as an in parameter, yes?

I thought I could do
  declare
    s : String;
  begin
    s := Encode(yadda);
  end;
but that doesn't work. Bummer.

(Yes, as you can tell, I'm all the way up to "Hello World". :-)

-- 
Darren New 
San Diego, CA, USA (PST). Cryptokeys on demand.