Node handshakes and features

[adiabat]

There are a bunch of possible things a node can do. I'll enumerate them here and see if it can be pared down a bit.

P Proofs
B Blocks
S Set
F Forest
R Roots

Proofs - utreexo proofs for all blocks. ~1TB
Blocks - the blockchain. ~1TB
Set - the UTXO set. ~ 10GB
Forest - the whole utreexo forest. ~10GB
Roots - utreexo forest roots. ~1KB

Set and Forest "go together", Blocks and Proofs "go together".
5 bits, so 32 possible nodes? But you can't have forest without having roots, which reduces it to 24.
(Forest without roots is impossible / contradiction so we'll eliminate. The others... will enumerate)

Currently, Set and Forest are coupled. Do they have to be? Could there be any use to having the forest but not having the set...? Feels like no? Which would reduce it again. To 20.

Trying to make it somewhat MSB ... LSB here. At least in terms of size.

no PBS FR Useless?

00 000 00
01 000 01
02 000 11 *
03 001 00
04 001 01 *
05 001 11
06 010 00
07 010 01
08 010 11 *
09 011 00
10 011 01 *
11 011 11
12 100 00
13 100 01
14 100 11 *
15 101 00
16 101 01 *
17 101 11
18 110 00
19 110 01 
20 110 11 *
21 111 00
22 111 01 *
23 111 11

Enumeration of all types!! Do these make sense?
no PBS FR
00 000 00 - Nothing. Electrum node. (Ah but electrum node has headers...? Should we add that? ugh)
01 000 01 - Roots only. The CSN - the whole point of utreexo!
02 000 11 - Non-archive half-bridge. Can't prove anything. Useless?
03 001 00 - Set only. A "pruned" bitcoin node.
04 001 01 - Set and roots. Seems pointless.
05 001 11 - Set and forest. A real-time bridge node with no archive.
06 010 00 - Blocks only. I don't know if there's software out there to support this, but it would be useful! Call it "cloud node"
07 010 01 - Blocks and roots. For if you only have a hard drive. Maybe a bit niche but some use cases.
08 010 11 - Blocks, no set, and forest. Seems useless.
09 011 00 - Blocks and set. Satoshi's Vision, the only option Satoshi coded, the One True Full Node.
10 011 01 - Blocks and set and roots. Seems useless? What's the point of having the roots if you have the set, same as 04.
11 011 11 - Blocks, set, forest. A bridge node with non-utreexo archive. Could make sense.
12 100 00 - Proofs only. A utreexo-only "cloud node", sure.
13 100 01 - Proofs and roots. Similar to 07, could make sense with hard drive only; can prove old blocks and validate.
14 100 11 - Proofs and forest. Forest without set is pointless.
15 101 00 - Proofs and set. Doesn't really make much sense, it's a pruned node that also has utreexo proofs? But you could.
16 101 01 - Proofs, set, roots. Same as 04/10, pointless.
17 101 11 - Proofs, set, forest. It's a bridge, and also has utreexo proofs. Call this a "pure utreexo bridge archive"
18 110 00 - Proofs and blocks. A total archive cloud node.
19 110 01 - Proofs, blocks, set. Makes sense, you've got a hard drive and bandwidth but no iops.
20 110 11 - like 02/08
21 111 00 - Proofs, blocks, set. Weird because you know about utreexo but don't have roots, but possible. Like 15.
22 111 01 - Proofs, blocks, set, roots. Like 4/10, useless.
23 111 11 - Proofs, blocks, set, forest. Ultranode, utreexo bridge total archive.

So 24 possible node types, looks like 8 of which are pointless, leaving 16 useful node types.