Re: [bitcoin-dev] Libconsensus separated repository (was Bitcoin Core and hard forks)

From: Eric Lombrozo <elombrozo@gmail•com>
To: "Jorge Timón" <jtimon@jtimon•cc>,
	"Tamas Blummer" <tamas@bitsofproof•com>
Cc: Bitcoin Dev <bitcoin-dev@lists•linuxfoundation.org>,
	Libbitcoin <libbitcoin@lists•dyne.org>
Subject: Re: [bitcoin-dev] Libconsensus separated repository (was Bitcoin Core and hard forks)
Date: Fri, 21 Aug 2015 20:07:15 +0000	[thread overview]
Message-ID: <CABr1YTfKFzdJ5DuWrb_ua+s16Px9sgSrdLcYxAjEDujnbiy76Q@mail.gmail.com> (raw)
In-Reply-To: <CABm2gDpcEmiPNQWeUk5aTjuTSRAJSPYfgAKc7B_qrqw0w04xoA@mail.gmail.com>

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Unfortunately we have no way of rigorously proving functional equivalence
other than code review and unit testing. The simpler the consensus code
(and the more we can write it in a style that affords provability of
correctness) the easier it will be in the future to compare implementations.

Prior to swapping out implementations, we should at the least run it
through the gauntlet and perhaps run both implementations side-by-side.

All I/O should be treated abstractly in the API.

In C++ I really like using a nearly bare-bones signal template for most
async message handling, i.e.
https://github.com/ciphrex/mSIGNA/blob/master/deps/Signals/src/Signals.h

This greatly facilitates support for async bidirectional I/O, etc...with
minimal overhead.

But others might have other stylistic preferences.

- Eric

On Fri, Aug 21, 2015, 12:46 PM Jorge Timón <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> On Thu, Aug 20, 2015 at 10:35 AM, Tamas Blummer <tamas@bitsofproof•com>
> wrote:
> > Every re-implementation, re-factoring even copy-paste introduces a risk
> of disagreement,
> > but also open the chance of doing the work better, in the sense of
> software engineering.
>
> But you don't want something better, you want something functionally
> identical.
> You may want to watch sipa's explanation on why "the implementation is
> the specification" and the reasons to separate libconsensus:
> https://youtu.be/l3O4nh79CUU?t=764
>
> >> On Aug 20, 2015, at 10:06, Jorge Timón <jtimon@jtimon•cc> wrote:
> >>
> >>
> >> But the goal is not reimplementing the consensus rules but rather
> >> extract them from Bitcoin Core so that nobody needs to re-implement
> >> them again.
> >
> >
> >
> > My goal is different. Compatibility with Bitcoin is important as I also
> want to deal with Bitcoins,
> > but it is also imperative to be able to create and serve other block
> chains with other rules and for those
> > I do not want to carry on the legacy of an antique tool set and a
> spaghetti style.
> >
> > Bits of Proof uses scala (akka networking), java (api service), c++
> (leveledb and now libconsensus)
> > and I am eager to integrate secp256k1 (c) as soon as part of consensus.
> The choices were
> > made because each piece appears best in what they do.
>
> Since you already depend on libconsensus for VerifyScript, wouldn't it
> be nice that it also offered VerifyTx, VerifyHeader and VerifyBlock?
> You would still have complete control over storage, concurrency,
> networking, policy...
> My plan is for the C API to interface with the external storage by
> passing a function pointer to it.
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