[Monotone-devel] Re: RFC: Fake IDs

[Graydon Hoare]

Zack Weinberg wrote:
> There are a small number of places that need a fake ID of some variety
> (ignoring all the unit tests, which use 'em heavily) and we currently
> just pick a "random" 160-bit number.   I need to add a few more of
> these, so I thought it would be a good idea to have a principled way
> of generating them.  The  implementation I've picked is to have
> vocab.hh provide a fake_id() function/macro that hashes __FILE__ and
> __LINE__.

Eh.. I'd prefer to turn those cases where we pick fake IDs to actually 
loop, checking the db for a collision. It feels weird to be hard-coding 
collision conditions into the binary, however unlikely.

It's easy enough to start with the "all zero" SHA1 and count upwards. 
It's probably even fine if you just run through the first 2^64 of them 
for now; you can't store anywhere near that much data in an sqlite 
database. Something like this should do:

u8 buf[41];
for (u64 i = 0; i < UINT64_MAX; ++i)
  sprintf(buf, 41, "%40.40" PRIX64, i);

or something slightly more tasteful, if you prefer.

-graydon