Re: XML parsing problems

[Per Bothner]

Chris Burdess wrote:
> As I understand it, the problem can occur when the position in the buffer is
> near the end. If the mark is set at position 2047 in the buffer, then we read
> 2 bytes and reset, then refill() will have been called and the position is
> actually reset to position 2047 in the new buffer, 2K further along in the
> original stream.
> ...
> If anyone has a robust solution to this problem please apply it; I will try
> to address it but may not have much free time before the new year/release.

Three choices, assuming the mark is active and at position M
in a buffer of size S:
(1) Move S-M bytes to the start of the buffer and read upto M bytes.
Advantage: doesn't need to grow the buffer.
Disadvantage: we lose buffer alignment, which probably doesn't matter
except with a highly tuned (an nio-based?) implementation.
Also, can fail if the readAheadLimit > S.
(2) Grow the buffer to S+(S-M).
Disadvantage: Same alignment issue as (1).
(3) Use two buffers, one old and a new buffer.  The old buffer doesn't
need to be full-size, as long as it can handle the readAheadLimit
(in the general case) or at least S-M in this case.
Advantage: Preserves alignment.
Disadvantage: More complex.  After a reset, then a read(byte[],int, int)
will only get S-M bytes.

Assuming buffer alignment isn't an issue, then I'd say use a combination
of (1) if possible and (2) if needed.
--
        --Per Bothner
address@hidden   http://per.bothner.com/