Re: Stdio.Buffer, need a way to revisit old positions in the output

Per Hedbor () @ Pike (-) importm?te f?r mailinglistan wrote:
>> Yes, well, apart from the fact that you can't use the add_int32(),
>> there is another difficulty here: the sizeof() and the [] operators
>> are relative to the start of the buffer.  The start is a moving
>> target however, since some of it might have been flushed to the
>> descriptor already.

>That would very much be true with your solution as well, unless as a
>side effect it stopped the data from moving around.

Well, no, the positions my original solution returns and accepts
are offset+len.

>I could implement _a_ deluxe version rather quickly, actually:

>|  object k1 = buffer->start_hstring(size_size);
>|  buffer->add()
>|  .. add stuff ..
>|  k1->end([adjust]);
>|  // updates buffer[k1..k1+size-1] to (size_diff+adjust) or if
>|  // specified to end an explicit value
>!  // if k1 is out of scope, undo sub-adds.

>The main difference is that it is not really a sub-buffer, it is a
>sort-of pointer. It would also need to block reading past the new add
>position.

This sounds just about like the ideal solution to me.

>This is a somewhat over-specialized API, but I have also found myself
>wishing for something along those lines, so perhaps it would be useful.

Yes, please!

>Note that it does not really take all that much time to create new
>buffer objects and add those to the buffer:

Yes, I realise that, but I would like to stick to the don't-copy-data-
around-unless-necessary paradigm.

>buffer->start... solution unless the packets are very large
>(basically, if the memcpy time is bigger than the time it takes to
>create and free the object)

Unfortunately, in the database driver, I have to deal with small (<256 bytes)
and large (>32MB) packets, so it will matter.
-- 
Stephen.