zsync internals (was: Compressing packages with bzip2 instead gzip)

Paul Sladen ubuntu at paul.sladen.org
Thu Jan 19 09:46:50 GMT 2006

On Thu, 19 Jan 2006, John C. McCabe-Dansted wrote:
> Zsync uses a clever trick which I think goes basically like this:
> $gzip_opts=detect which options were used to create data.tar.gz

Unfortunately the 'clever trick' turns out to be pretty dumb:

  if file_recompressed_with_options("gzip --best") == original_file:
    options = "--best"
    panic("zsyncmake: Cannot detect options used!")

Whereas it *should* instead use the sizes from the Zmap to compress each
block at a time.  This would cope with dpkg chunking stuff in 8kB and then
the only guessing would be to get the compression level and search window
size (these will be constant in 99.97% of cases).

This country is covered in white fluffy snow.  Helsinki, FI

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