Lightning loop

[nixbitcoin]

This PR integrates lightning-loop in nix-bitcoin. Lightning Loop is a Non-Custodial Off/On Chain Bridge. It can be used for improvised CoinSwaps that utilize the privacy properties of LN.

Details

• Based on Update: nixpkgs and elementsd #201.
• For testing purposes it includes lnd: 0.10.0 -> 0.10.3, enable same features as upstream NixOS/nixpkgs#89668 in 7d512a5. This can be removed as soon as lnd: 0.10.0 -> 0.10.3, enable same features as upstream NixOS/nixpkgs#89668 is merged, and the pinned nixpkgs in 3cbb691 are bumped.
• AFAICT the datadir can't be specified for loopd, but because of ReadWritePaths it's created in /var/lib/lnd/.loopd with the right permissions, which is kind of what we want.

Tested with a succesful loop out tx f8178663a03d5b492d756f43b9989c1e7f42640b0c837d4957f29080d025d3bd

[nixbitcoin]

Rebased with upstream lnd

[sputn1ck]

I have not looked at the code, but tested a loop in and loop out in my krops setup and it worked great!

[nixbitcoin]

Thank you for the blind trust!

[nixbitcoin]

Check that lightning-loop fails with the right error, making sure lightning-loop can connect to lnd

[jonasnick]

ACK e920494

[Kixunil]

Today I attempted to integrate loop into my deb repository and found out it doesn't support authentication yet How did you secure it? Do you rely on namespaces only?

[nixbitcoin]

Yes, lightning-loop relies on running inside its own network namespace for security. Only users inside the nb-lightning-loop namespace can reach the loopd daemon, and only the semi-privileged operator user can place processes into that namespace. Ideally we would get defense-in-depth with authentication. Thank you for linking the issue, we will update lightning-loop as soon as the issue is closed.