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From: adiabat <rx@awsomnet.org>
Date: Sun, 4 Dec 2016 15:00:00 -0500
Message-ID: <CAKEeUhjYPL+kO6RCc8UDZWeAEmFuX1NRfkv22uqR4K+FiGosDA@mail.gmail.com>
To: Johnson Lau <jl2012@xbt.hk>, 
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Forcenet: an experimental network with a new
	header format
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Interesting stuff! I have some comments, mostly about the header.

The header of forcenet is mostly described in Luke=E2=80=99s BIP, but I hav=
e made
> some amendments as I implemented it. The format is (size in parentheses;
> little endian):
>
> Height (4), BIP9 signalling field (4), hardfork signalling field (3),
> merge-mining hard fork signalling field (1), prev hash (32), timestamp (4=
),
> nonce1 (4), nonce2 (4), nonce3 (compactSize + variable), Hash TMR (32),
> Hash WMR (32), total tx size (8) , total tx weight (8), total sigops (8),
> number of tx (4), merkle branches leading to header C (compactSize + 32 b=
it
> hashes)
>

First, I'd really rather not have variable length fields in the header.
It's so much nicer to just have a fixed size.

Is having both TMR and WMR really needed?  As segwit would be required with
this header type, and the WMR covers a superset of the data that the TMR
does, couldn't you get rid of the TMR?  The only disadvantage I can see is
that light clients may want a merkle proof of a transaction without having
to download the witnesses for that transaction.  This seems pretty minor,
especially as once they're convinced of block inclusion they can discard
the witness data, and also the tradeoff is that light clients will have to
download and store and extra 32 bytes per block, likely offsetting any
savings from omitting witness data.

The other question is that there's a bit that's redundant: height is also
committed to in the coinbase tx via bip 34 (speaking of which, if there's a
hard-fork, how about reverting bip 34 and committing to the height with
coinbase tx nlocktime instead?)

Total size / weight / number of txs also feels pretty redundant.  Not a lot
of space but it's hard to come up with a use for them.  Number of tx could
be useful if you want to send all the leaves of a merkle tree, but you
could also do that by committing to the depth of the merkle tree in the
header, which is 1 byte.

Also how about making timestamp 8 bytes?  2106 is coming up soon :)

Maybe this is too nit-picky; maybe it's better to put lots of stuff in for
testing the forcenet and then take out all the stuff that wasn't used or
had issues as it progresses.

Thanks and looking forward to trying out forcenet!

-Tadge

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<div dir=3D"ltr">Interesting stuff! I have some comments, mostly about the =
header.<div><br></div><div class=3D"gmail_extra"><div class=3D"gmail_quote"=
><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1=
px #ccc solid;padding-left:1ex">
The header of forcenet is mostly described in Luke=E2=80=99s BIP, but I hav=
e made some amendments as I implemented it. The format is (size in parenthe=
ses; little endian):<br>
<br>
Height (4), BIP9 signalling field (4), hardfork signalling field (3), merge=
-mining hard fork signalling field (1), prev hash (32), timestamp (4), nonc=
e1 (4), nonce2 (4), nonce3 (compactSize + variable), Hash TMR (32), Hash WM=
R (32), total tx size (8) , total tx weight (8), total sigops (8), number o=
f tx (4), merkle branches leading to header C (compactSize + 32 bit hashes)=
<br></blockquote><div><br></div><div>First, I&#39;d really rather not have =
variable length fields in the header.=C2=A0 It&#39;s so much nicer to just =
have a fixed size.</div><div><br></div><div>Is having both TMR and WMR real=
ly needed?=C2=A0 As segwit would be required with this header type, and the=
 WMR covers a superset of the data that the TMR does, couldn&#39;t you get =
rid of the TMR?=C2=A0 The only disadvantage I can see is that light clients=
 may want a merkle proof of a transaction without having to download the wi=
tnesses for that transaction.=C2=A0 This seems pretty minor, especially as =
once they&#39;re convinced of block inclusion they can discard the witness =
data, and also the tradeoff is that light clients will have to download and=
 store and extra 32 bytes per block, likely offsetting any savings from omi=
tting witness data.</div><div><br></div><div>The other question is that the=
re&#39;s a bit that&#39;s redundant: height is also committed to in the coi=
nbase tx via bip 34 (speaking of which, if there&#39;s a hard-fork, how abo=
ut reverting bip 34 and committing to the height with coinbase tx nlocktime=
 instead?)</div><div><br></div><div>Total size / weight / number of txs als=
o feels pretty redundant.=C2=A0 Not a lot of space but it&#39;s hard to com=
e up with a use for them.=C2=A0 Number of tx could be useful if you want to=
 send all the leaves of a merkle tree, but you could also do that by commit=
ting to the depth of the merkle tree in the header, which is 1 byte.</div><=
div><br></div><div>Also how about making timestamp 8 bytes? =C2=A02106 is c=
oming up soon :)</div><div><br></div><div>Maybe this is too nit-picky; mayb=
e it&#39;s better to put lots of stuff in for testing the forcenet and then=
 take out all the stuff that wasn&#39;t used or had issues as it progresses=
.</div><div><br>Thanks and looking forward to trying out forcenet!</div><di=
v><br></div><div>-Tadge</div></div></div></div>

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