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Example Project

This directory contains an example project, written in both Motoko and Rust, to showcase how to:

  1. Get the balance of a Bitcoin address.

  2. Get transaction outputs and use them to build a transaction.

  3. Sign a transaction and send it to the Bitcoin network.

Note
 The example project contains a hard-coded ECDSA key for demonstration purposes. The mainnet release will offer the functionality for canisters to securely generate ECDSA keys.

Deployment

After going through the initial setup, you have the choice of either deploying the Rust or the Motoko example.

Rust

To deploy the Rust example:

dfx deploy btc-example-rust --no-wallet --argument "(record { bitcoin_canister_id = principal \"$(dfx canister --no-wallet id btc)\" })" --mode=reinstall

Motoko

To deploy the Motoko example:

dfx deploy btc-example-motoko --no-wallet --argument "(record { bitcoin_canister_id = principal \"$(dfx canister --no-wallet id btc)\" })"

To reinstall the Motoko example:

dfx deploy btc-example-motoko --no-wallet --argument "(record { bitcoin_canister_id = principal \"$(dfx canister --no-wallet id btc)\" })" --mode=reinstall
Note

Many crypto primitives are still missing in Motoko, and that makes some fundamental operations, such as computing a Bitcoin address and signing a transaction, impossible.

These primitives are actively being built. In the meantime, as a work-around until the crypto primitives become available, we wrap all the functionality requiring cryptography into a "common" canister, which is deployed along with and used by the Motoko example.

Endpoints

The example provides the following endpoints:

  • Retrieve the canister’s BTC address.

dfx canister --no-wallet call btc-example-rust btc_address
dfx canister --no-wallet call btc-example-motoko btc_address

  • Retrieve the canister’s balance.

# Using the Rust example.
dfx canister --no-wallet call btc-example-rust balance

# Using the Motoko example.
dfx canister --no-wallet call btc-example-motoko balance

  • Retrieve the canister’s UTXOs.

# Using the Rust example.
dfx canister --no-wallet call btc-example-rust get_utxos

# Using the Motoko example.
dfx canister --no-wallet call btc-example-motoko get_utxos

  • Send Bitcoin (in Satoshi) from the canister to a destination address.

# Using the Rust example.
dfx canister --no-wallet call btc-example-rust send "(1_0000_0000, \"DESTINATION_ADDRESS\")"

# Using the Motoko example.
dfx canister --no-wallet call btc-example-motoko send "(1_0000_0000, \"DESTINATION_ADDRESS\")"

For the transaction to be processed, you’ll need to mine a new block using the command below. The new block will contain the newly sent transaction.

./bin/bitcoin-cli -conf=$(pwd)/bitcoin.conf generatetoaddress 1 $BTC_ADDRESS

Sending bitcoin to the example canister

To top up the example canister with Bitcoin, run the following:

# The canister's BTC address.
# This can be retrieved using the canister's "balance" endpoint.
export CANISTER_BTC_ADDRESS=mmdoAzumgjbvAJjVGg7fkQmtvDNFd2wjjH

# Send a transaction that transfers 10 BTC to the canister.
./bin/bitcoin-cli -conf=$(pwd)/bitcoin.conf -datadir=$(pwd)/data sendtoaddress $CANISTER_BTC_ADDRESS 10 "" "" true true null "unset" null 1.1

# Mine a block that contains the transaction.
./bin/bitcoin-cli -conf=$(pwd)/bitcoin.conf generatetoaddress 1 $BTC_ADDRESS

If successful, querying the balance endpoint of the canister should return the updated balance.