[bitcoin-dev] Introcing a side memory network to bitcoin for ads

[Tamas Blummer <tamas.blummer@gmail.com>]

I introduced you to the pattern of a side memory to bitcoin in [1] and
promised an implementation of it.

Here you are.

defiads is a side memory network to bitcoin, implemented in Rust, built
on top of rust-bitcoin, murmel, hammersbald, rust-bitcoinconsenus,
rust-wallet, all Rust open source free to grab at
https://github.com/defiads/defiads

defiads builds a peer-to-peer network to distribute textual ads, as
first suggested by ZmnSCPxj[4]. I hope that it will serve 
decentralized finance applications with an infrastructure to distribute
ads, order books, coinjoin proposals etc.

Every defiads node maintains a copy of a network-wide shared 1GB memory
pool of current ads.

An ad is replicated to other nodes as long as there is some bitcoin
locked to it on the bitcoin network. Locking means someone transferred
some sats to an address that is associated with the ad using the
pay-to-contract protocol[2]. The address does not release the bitcoins
until a predefined time span that is the duration of the advertizement,
this is accomplished with OP_CSV. The ad will be evicted from the pool
as soon as the coins locked to it are spendable again.

defiads  ranks advertizements by the ratio of used space divided by
bitcoins locked and will only replicate the top 1GB of this ranked list.

You may read the ads by starting a defiads process of your own and
the query the content through its JSON-RPC API.

You may place ads by performing the following steps, with its JSON-RPC API

1. deposit some bitcoins into your defiads node's wallet
2. prepare an ad, providing its category, abstract and content
3. fund the ad by locking some of the bitcoins to it for a limited term
of the advertizement
4. you may withdraw your coins from the defiads node's wallet after the
advertizement expires

defiads handles the association with ads, locking and unlocking coins.

Implementation notes
defiads connects to both the bitcoin and its own peer-to-peer network.
You do not need to run a bitcoin node as defiads  only needs a small
fraction of the information on the bictoin blockchain and retrieves that
on its own, as an SPV node. 

The defiads node's wallet is compatibe with that of TREZOR, Ledger,
Greenwallet and many other wallets that support BIP38, BIP44, BIP48,
BIP84 key generation and use standards.

defiads uses Invertible Bloom Lookup Tables[3] to synchronize the ads
pool with its peers.

Status
It seems to work, but you should not yet use with real bitcoins,
therefore by default it connects the bitcoin's test network.

There is no discovery for the network yet, so you will have to know some
peer in the network to see other than your own ads. Write me a direct
email if you'd like to connect to my node.


Future developent
Should the use become popular then 1GB pool become tight, then people
will have to compete for its use. Some might not have enough bitcoin's
to lock and might therefore pay others to lock theirs to fund an
advertizement. defiads network could match both sides and thereby give
rise to bitcoin's first truly risk less interest rate market.

defiads is currently downloading, but not storing, 
the blocks after its birth date. This will no longer be needed once
BIP158 filters are served and committed by Bitcoin Core.

I hope that someone builds a nice UI on top of the JSON RPC as that is
not my area of expertise.

Tamas Blummer

[1] https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2019-August/017264.html

[2] https://arxiv.org/pdf/1212.3257.pdf

[3] https://arxiv.org/pdf/1101.2245.pdf

[4] https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2019-July/017083.html