[Http-crcsync] crccache ready for some testing I think

[Rusty Russell]

On Sunday 05 April 2009 07:33:06 Alex Wulms wrote:
> Hi Rusty,
> 
> Many thanks!!!
> 
> I'll adapt crccache code this sunday to support the improved algorithm and 
> submit all to the git repo.
> 
> Hi Toby,
> 
> I'll change the crccache-client to send the original file size in stead  of 
> the blocksize in the header. In that way, the crccache-server can calculate 
> the blocksize and the tailsize by itself. It is more efficient then using two 
> headers (one with blocksize, one with tailsize). I'll also adapt the client 
> to put the crc of all 21 blocks (the 20 full blocks + the 1 tail block) in 
> the header. I must still figure out what to do in case that the tail has a 
> zero size (e.g. if filesize is exact multiple of 20) but I think that while 
> writing the code, the answer will crystalize by itself.

I think Toby's draft, which suggested just leaving the trailing block as
a literal, is an interesting possibility.  Worst case, it's 19 bytes.

I also think we should go to 60-bit csums (but needs new CRC algo).

Finally, I think the strong hash sent in request in Toby's draft is not useful
as the block signature + size can be used for caching in exactly the same way.

Cheers,
Rusty.