Implement a simple stateless observation executable

[ghost]

📋 Created a hydra-chain-observer executable, which prints a few basic observations of the head life-cycle.

📋 The chain observer does connect directly to a cardano-node just the same as a ydra-node` would.

📋 Refactored low-level observation functions to only take UTxO and Tx (especially the observeCommitTx).

---

• CHANGELOG updated or not needed

• Documentation updated or not needed

• Haddocks updated or not needed

• No new TODOs introduced or explained herafter

  • One TODO in State.hs about a stateful generator - this will be removed once we get rid of stateful observation anyways

[ch1bo]

@abailly-iohk Do we need this? It's no harm if the UTxO is always updated, even when nothing is observed. I think it would simplify the implementation a bit if we remove this constraint.

[ch1bo]

It's an optimization. That is, we do not accumulate memory on unrelated transactions.

[ch1bo]

SB: Shouldn't we make sure we only process commits of "our head" now?

Yes. This is implicit here (as only UTxO of our head are resolvable), but could be improved by an explicit guard $ headId == commitHeadId or so.

[ch1bo]

Done

[github-actions]

Test Results

366 tests  +3   361 ✔️ +3   21m 38s ⏱️ + 1m 8s
124 suites +2       5 💤 ±0 
    5 files   ±0       0 ❌ ±0 

Results for commit 61ead85. ± Comparison against base commit 6a95190.

♻️ This comment has been updated with latest results.

[v0d1ch]

Good work guys!

[ch1bo]

Tested this manually against preprod to find the currently open head we use in our tactical meetings:

cabal run hydra-chain-observer -- --node-socket testnets/preprod/node.socket --testnet-magic 1 --start-chain-from "43251332.9ea784cd95687e3c90a17b6f3633b5554f25a3ceba82f860c2e4d3cb57a0b236" | jq 'select(.message.tag == "HeadInitTx")'

Will output:

{
  "timestamp": "2023-11-13T14:17:57.570680734Z",
  "threadId": 6,
  "namespace": "hydra-chain-observer",
  "message": {
    "headId": "1185347034540e3a9c60c69a73185ebdcd3b06cd243047aea289e6b6",
    "tag": "HeadInitTx"
  }
}