FreeTDS Development Group

[Frediano Ziglio <freddy77 AT gmail.com>]

Hi,
  I forgot to say. If you look at test results you'll note that
get_send_data (dblib), t0013 and t0014 (dblib) tests fail with tds 7.3.
These tests cannot work with this version of the protocol as Microsoft
changed the network protocol removing textptr when BLOBs (text/image) are
returned.

Frediano



2013/5/20 Frediano Ziglio <freddy77 AT gmail.com>

> Hi,
>   trying to sort the problem of supporting protocol 7.2/7.3 in dblib/ctlib
> I came to the problem of varchar(max). The problem was that dblib wants
> conversion to single char while varchar(max) was implemented not converting
> it. This was fine for ODBC which disable conversions in libTDS to support
> getting raw data but not for dblib. To fix the issue a new iconv function
> which deal with varchar(max) (which can be streamed having multiple chunks
> so tds_get_char_data was not helpful in this case (as only support
> contiguous data from the net). I then decided to write code which could
> handle conversion from an input stream to an output stream so I can reuse
> for  every conversion (for instance from bcp file to memory!).
>
> I ended up with this branch:
>
> http://gitorious.org/~freddy77/freetds/mars-freetds/commits/unify_iconv
>
> I'm actually running tests again to publish on nightly.
>
> The reason I didn't pushed is that although code is quite good there are
> some things to decide and sort out! Structures/functions to deal with
> streams are in include/freetds/stream.h. Input stream it's just a function
> to read data while output have a buffer contained in it.
>
> Good things of these patches:
> - only a single code to convert characters, better for test and
> maintenance;
> - bit less copy of data;
> - allow dblib/ctlib to support up to protocol 7.3;
> - allow bcp to support direct streaming, no fseek require
>
> Things to sort out:
> - I added a new stream.h in include/freetds. The idea is to move freetds
> internal includes in such directory to be able to include with
> <freetds/name.h>. Are there any objections? The main reason is to avoid
> using the tds prefix for every include;
> - tds_stream_convert (in the new src/tds/stream.c) should perhaps be moved
> in iconv.c?
> - tds_iconv_fread (in src/tds/iconv.c) should be moved to only bcp code?
> Now handle termination directly so is very bcp only related. It's also true
> that was used only for bcp even before. Now however has very few things to
> deal with iconv as conversions are done by tds_stream_convert;
>
> Small todos and optimizations:
> - check EINVAL error during conversion, should be ok;
> - optimize file terminator detection (is not slower than before);
> - reuse buffer reading data from file to avoid too much
> allocation/reallocation/free;
> - limit reallocation starting allocating a suitable buffer (not too big
> but not even fixed);
> - reuse tds_stream_convert more, even to read into blobs.
>
> Frediano
>
>