Add support for testnet4

[sstone]

See bitcoin/bitcoin#29775.
It basically adds a new genesis block the testnet4 (addresses uses the same prefixes/encoding as testnet3).

[t-bast]

If I understand correctly, we're waiting for a release of Bitcoin Core that includes testnet4 to merge this, right?

[sstone]

If I understand correctly, we're waiting for a release of Bitcoin Core that includes testnet4 to merge this, right?

Bitcoin core's master branch already includes support for testnet4, there are testnet4 explorers and electrum servers, and it's unlikely that the testnet4 genesis block will change so we could also merge now. There would not be much of a LN testnet4 network so we'd probably need to keep running a testnet3 node for a while, but it would help a lot to have a testnet4 version of Phoenix for our own tests.

[t-bast]

There would not be much of a LN testnet4 network so we'd probably need to keep running a testnet3 node for a while, but it would help a lot to have a testnet4 version of Phoenix for our own tests.

I don't understand how it can help with our tests: we require a trampoline node for phoenix and phoenixd, and that trampoline node requires a Bitcoin Core node. So we'd need a Bitcoin Core node that supports testnet4, right? The Bitcoin Core master branch is notoriously buggy, we're going to have issues unrelated to lightning if we run with a non-released version (Richard tried that recently and had coin selection issues that made eclair unusable), so it's not going to help us much? Or do you want to try that option anyway and run a testnet4 node based on Bitcoin Core master?

[sstone]

There would not be much of a LN testnet4 network so we'd probably need to keep running a testnet3 node for a while, but it would help a lot to have a testnet4 version of Phoenix for our own tests.

I don't understand how it can help with our tests: we require a trampoline node for phoenix and phoenixd, and that trampoline node requires a Bitcoin Core node. So we'd need a Bitcoin Core node that supports testnet4, right? The Bitcoin Core master branch is notoriously buggy, we're going to have issues unrelated to lightning if we run with a non-released version (Richard tried that recently and had coin selection issues that made eclair unusable), so it's not going to help us much? Or do you want to try that option anyway and run a testnet4 node based on Bitcoin Core master?

Yes most LN tests would be done on testnet3, but for specific phoenix tests we'd run Bitcoin Core's master branch with all the caveats you mentioned.

[t-bast]

Sounds good, let's do that then 👍