[freetds] pbcb: replacing strcpy(3)

Lowden, James K LowdenJK at bernstein.com
Thu May 8 10:02:23 EDT 2003


> From: Frediano Ziglio [mailto:freddyz77 at tin.it]
> Sent: May 8, 2003 2:24 AM
> Il gio, 2003-05-08 alle 06:51, James K.Lowden ha scritto:
> 
> James, dstr_* was designed to be extended in such way...

Yes, I thought that might be the case.  Honestly, I don't like the opacity
of DSTR, nor the casts, and I'm not convinced of the advantage of never
pointing to NULL.  I realize those could all be fixed, but you seem to think
they're good things.... :-)  I'd like a more transparent, less manhandled
approach.  

Still, I think we should all discuss this.  However we address counted
strings, they're going to be a pervasive metaphor, and it would be nice if
we all liked the way they're done.  

I've thought many times of adding a C++ module to use basic_string<>.  That
to me would be the most elegant approach, but at a heavy cost of
dependencies and, I fear, portability.  I'm not aware of a generalized
standalone counted string library for C, something that would happy dealing
in UCS-2, and that ideally could engage iconv.  

> TDS_PBCB* pbcb_cpy (iconv_t cd, TDS_PBCB* dest, const TDS_PBCB* src);
> TDS_PBCB* pbcb_strcpy (iconv_t cd, TDS_PBCB* pbcb, const char *src);
> 
> Why pass iconv_t just to copy a buffer?

Not just to copy a buffer, to convert a buffer.  If cd == -1, copy.  Else
use iconv to convert from src to dest.  

I think perhaps rather than returning a pointer, the functions should return
inbytesleft from iconv (normally 0).  If nonzero, the caller can examine
errno and decide what to do.  

> All I need (in query.c) is a function to return byte count of 
> converted
> string... Something like tds_get_converted_length(TDSICONVINFO * ic,
> const char* s, size_t length);

We could do that, it's true.  The advantage of your idea is that there's no
buffer allocation.  

I think it's a very loose design, though: here we use iconv to count the
length of the converted string (discarding the output), there we call
tds_put_string() and expect it to do the same conversion.  For every
tds_put_string(), two independent calls to iconv() in two different
functions.  

For all data except [n]text, the maximum buffer size is 8000 bytes; for
metadata, 512 bytes.  For that reason, I would avoid malloc(3), favoring
fixed buffers instead.  Let iconv convert once, preserve the output, send
the length and the data as required by the protocol.  That would require
e.g. tds_submit_query() to maintain 3 such buffers, but I think that's a
good trade-off for the simplicity.  

Regards, 

--jkl


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