Okay, zsync 0.0.4 is out. I found the stupid bug in the HTTP fetcher that was causing some redundant information to be transferred. The download efficiency improves by between 5 to 25 percent with this fix.

I have also put in a very simple first heuristic for using both compressed and uncompressed source URLs. By using uncompressed for small blocks (where available), zsync saves downloading the inflate table at the start of the block and the intervening data ahead of the bit you want to download. While for large blocks it continues to use the compressed data. This cuts another 100k off the inter-day Debian Packages update - in fact I have increased the block size on the two streams being offered now, as the .zsync was now bigger than the required transfer of real data.

I must update the technical paper with some new figures now these changes are in...

On the practical front, zsync-0.0.4 now allows relative URLs in the .zsync file, and follows HTTP redirects when downloading the control file. Get it here.