Commit using a blueprint

This guide provides a walkthrough on using cardano-cli to assemble the necessary components for committing funds to a head using a blueprint transaction.

Prerequisites

You should have access to the following repositories:

• hydra-node
• hydra-tui
• cardano-cli, and
• curl binaries.

Step 1

You can use cardano-cli to create a blueprint transaction from some UTXO you own. First, initiate a Cardano node on the pre-production network:

./testnets/cardano-node.sh ~/code/hydra/testnets/preprod

Step 2

Determine which UTXO you intend to commit to the head. This example uses Alice's external wallet key to identify her address:

cardano-cli address build \
 --payment-verification-key-file hydra-cluster/config/credentials/alice-funds.vk \
 --testnet-magic 1

addr_test1vp5cxztpc6hep9ds7fjgmle3l225tk8ske3rmwr9adu0m6qchmx5z

Next, query to see what UTXO Alice has:

cardano-cli query utxo \
   --socket-path testnets/preprod/node.socket \
   --address addr_test1vp5cxztpc6hep9ds7fjgmle3l225tk8ske3rmwr9adu0m6qchmx5z \
   --testnet-magic 1 \
   --output-json

{
    "14ab373afb1112d925b0f6a84518ac26d4a8cfcc99231e1f47e6996182e843a9#0": {
        "address": "addr_test1vp5cxztpc6hep9ds7fjgmle3l225tk8ske3rmwr9adu0m6qchmx5z",
        "datum": null,
        "datumhash": null,
        "inlineDatum": null,
        "referenceScript": null,
        "value": {
            "lovelace": 8000000
        }
    },
    "14ab373afb1112d925b0f6a84518ac26d4a8cfcc99231e1f47e6996182e843a9#1": {
        "address": "addr_test1vp5cxztpc6hep9ds7fjgmle3l225tk8ske3rmwr9adu0m6qchmx5z",
        "datum": null,
        "datumhash": null,
        "inlineDatum": null,
        "referenceScript": null,
        "value": {
            "lovelace": 1828427
        }
    },
}

Step 3

Select the first UTXO, which has eight ada available. Use five ada to commit and rely on hydra-node to balance the commit transaction:

cardano-cli transaction build-raw \
  --babbage-era \
  --tx-in 14ab373afb1112d925b0f6a84518ac26d4a8cfcc99231e1f47e6996182e843a9#0 \
  --tx-out addr_test1vp5cxztpc6hep9ds7fjgmle3l225tk8ske3rmwr9adu0m6qchmx5z+5000000 \
  --fee 0 \
  --out-file tx.json

Step 4

You should now have the blueprint transaction in the tx.json file. For hydra-node to provide a draft commit transaction, you need to:

• Obtain the protocol parameters needed to run the hydra-node
• Ensure the hydra-node is up and running
• Have the head in the initializing state
• Submit the HTTP request to the hydra-node API server using the blueprint transaction you just created and the UTXO used for its input.

Query the protocol parameters:

cardano-cli query protocol-parameters \
  --testnet-magic 1 \
  --socket-path testnets/preprod/node.socket \
  --out-file pp-preprod.json

Step 5

Start the hydra-node as a single party head instance.

Note: The value 6264cee4d5eab3fb58ab67f3899ecbcc0d7e72732a2d9c1c5d638115db6ca711 comes from the hydra-node release 0.16.0.

hydra-node \
  --node-id 1 --port 5001 --api-port 4001 \
  --hydra-signing-key demo/alice.sk \
  --hydra-scripts-tx-id 6264cee4d5eab3fb58ab67f3899ecbcc0d7e72732a2d9c1c5d638115db6ca711 \
  --cardano-signing-key hydra-cluster/config/credentials/alice.sk \
  --ledger-protocol-parameters pp-preprod.json \
  --testnet-magic 1 \
  --node-socket testnets/preprod/node.socket \
  --persistence-dir .

Now you can start hydra-tui and initialize the head:

hydra-tui \
  --connect 0.0.0.0:4001 \
  --cardano-signing-key hydra-cluster/config/credentials/alice-funds.sk \
  --testnet-magic 1 \
  --node-socket testnets/preprod/node.socket

Press i to initialize the head. Once the head is in the Initializing state, you can send the HTTP request to the /commit API path. Assemble the request body using the cborHex field from the tx-body file tx.json and the JSON representation of the UTXO you used as input.

This is the valid JSON request:

{
  "blueprintTx": {
    "cborHex": "84a3008182582014ab373afb1112d925b0f6a84518ac26d4a8cfcc99231e1f47e6996182e843a900018182581d6069830961c6af9095b0f2648dff31fa9545d8f0b6623db865eb78fde81a007a12000200a0f5f6",
    "description": "",
    "type": "Tx BabbageEra"
  },
  "utxo": {
    "14ab373afb1112d925b0f6a84518ac26d4a8cfcc99231e1f47e6996182e843a9#0": {
      "address": "addr_test1vp5cxztpc6hep9ds7fjgmle3l225tk8ske3rmwr9adu0m6qchmx5z",
      "datum": null,
      "datumhash": null,
      "inlineDatum": null,
      "referenceScript": null,
      "value": {
        "lovelace": 8000000
      }
    }
  }
}

Save this JSON to a commit-request.json file.

You can now prompt the running hydra-node to draft a commit transaction:

curl -X POST 127.0.0.1:4001/commit \
  --data @commit-request.json

This yields a large CBOR blob, which you can save to the commit-tx.json file.

Next, sign and submit the draft of the commit transaction:

cardano-cli transaction sign \
  --tx-file commit-tx.json \
  --signing-key-file hydra-cluster/config/credentials/alice-funds.sk \
  --out-file signed-tx.json


cardano-cli transaction submit \
  --tx-file signed-tx.json \
  --socket-path testnets/preprod/node.socket \
  --testnet-magic 1

If you start the hydra-tui and wait until the transaction you just sent is re-observed by the hydra-node, you should see that the head is now open.