Commit using blueprint transaction

This is a small walk-through on how to use cardano-cli to assemble everything needed to commit funds to a Head using blueprint transaction.

Example assumes you have the hydra-node repo at your disposal together with hydra-node, hydra-tui, cardano-cli and curl binaries.

We can use cardano-cli to create a blueprint transaction from some UTxO we own.

First we need a running cardano-node so let's spin one on the preprod network:

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

Now we need to find the UTxO you want to commit to the Head

In this example we will use Alice and her external wallet key so first let's find out the address:

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

addr_test1vp5cxztpc6hep9ds7fjgmle3l225tk8ske3rmwr9adu0m6qchmx5z

and 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
        }
    },
}

Let's pick the first UTxO which has total of 8 ADA available. Let's use 5 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

So now we have the blueprint transaction present in the tx.json file.

In order to have hydra-node give us a draft commit transaction we need to:

• Obtain protocol-parameters needed to run the hydra-node
• Have the hydra-node up and running
• Have the Head in the initializing state
• Submit the http request to the hydra-node api server using the blueprint transaction we just created and the UTxO used for it's input.

Query the preview protocol-parameters:

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

Start the hydra-node in as a single party Head instance.

Note: The value 6264cee4d5eab3fb58ab67f3899ecbcc0d7e72732a2d9c1c5d638115db6ca711 comes from 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 we 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

Now press i to initialize the Head.

Once we see that the head is in the Initializing state we are ready to send the HTTP request to the /commit API path.

To assemble the request body we will use the cborHex field from the tx-body file tx.json.

To get the json representation of the UTxO we used as the input we can just copy/paste the output we got from cardano-cli when we did a UTxO query:

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
      }
    }
  }
}

Let's save this json to commit-request.json file.

Now, it is time to ask the running hydra-node to draft a commit transaction for us:

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

This yields a large cbor blob which we can save to commit-tx.json file.

Now we need to sign and submit the draft 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 we start the hydra-tui and wait a bit until the transaction we just sent is re-observed by the hydra-node we should see that the Head is now open.