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Charms

Cast a Spell

Now that we have implemented an app, we’re ready to cast a spell onto a real Bitcoin transaction. We’re going to use bitcoin-cli to interact with the Bitcoin network.

Quick note: Check if you have pre-requisites installed.

Important: we assume bitcoin-cli is aliased as b:

Terminal window
alias b=bitcoin-cli

Using an app

We’ve just tested the app with an NFT-minting spell. Let’s use it on Bitcoin testnet4 (we have a node set up in pre-requisites).

Terminal window
app_bins=$(charms app build)


# pick from the output of `bitcoin-cli listunspent`
# should NOT be the same as the one you used for minting the NFT
funding_utxo_id="2d6d1603f0738085f2035d496baf2b91a639d204b414ea180beb417a3e09f84e:1"


cat ./spells/mint-nft.yaml | envsubst | RUST_LOG=info charms wallet cast --app-bins=${app_bins} --funding-utxo-id=${funding_utxo_id}

This will create and sign (but not yet submit to the network) two Bitcoin transactions:

  • commit transaction and
  • cast transaction.

The commit transaction creates exactly one output (committing to a spell and its proof) which is then spent by the cast transaction. The cast transaction contains the spell and proof (in the witness spending the output created by the commit tx), and it cannot exist without the commit transaction.

charms wallet cast prints the 2 hex-encoded signed transactions at the end of its output, which looks like a JSON array (because it is a JSON array):

["020000000001015f...57505efa00000000", "020000000001025f...e14c656300000000"]

You can copy this JSON array of hex strings and submit both transaction to the network as a package:

Terminal window
b submitpackage '["020000000001015f...57505efa00000000", "020000000001025f...e14c656300000000"]'