Get a Lightning Channel’s Address

Lightning channels are built on Bitcoin’s foundation, specifically using a 2-of-2 multisignature structure. While checking a channel’s address and balance might seem straightforward, it requires understanding how to derive Bitcoin addresses from transaction scripts.

The Bitcoin-Lightning Connection

When two parties create a Lightning channel, they lock their funds in a specialized Bitcoin transaction output. This output requires both parties’ signatures to spend and contains a script rather than a conventional address. This creates an interesting challenge: while Bitcoin node APIs and block explorers expect standard addresses for balance queries, Lightning channels use scripts. To monitor channel balances effectively, you need to convert the funding output’s script into its corresponding Bitcoin address.

Working with the Funding Script

To access the funding script, you’ll need the channelpoint – a combination of the funding transaction hash and output index. These components allow you to query transaction details and perform the necessary conversion.

Here’s a Java implementation using BitcoinJ that handles this process:

public BitcoinAddress getAddressForChannel(String channelPoint) throws IOException {

        if (channelPoint == null) {
            throw new IllegalArgumentException("channelPoint cannot be null");
        }
        if (!channelPoint.contains(":")) {
            throw new IllegalArgumentException("channelPoint must contain ':'");
        }
        String[] parts = channelPoint.split(":");
        if (parts.length != 2) {
            throw new IllegalArgumentException("channelPoint must contain exactly one  ':'");
        }
        String txHash = parts[0];
        int outputIndex = Integer.parseInt(parts[1]);

        RawTransactionInfo rawTransactionInfo = bitcoinClient.getRawTransactionInfo(Sha256Hash.wrap(txHash));

        if (rawTransactionInfo.getVout().isEmpty() || rawTransactionInfo.getVout().size() < outputIndex + 1) {
            throw new IllegalArgumentException("Transaction doesn't contains a VOUT for index " + outputIndex);
        }

        Vout vout = rawTransactionInfo.getVout().get(outputIndex);
        ScriptPubKeyInfo tempPubKeyInfo = vout.getScriptPubKey();
        Script script = new Script(Hex.decode(tempPubKeyInfo.getHex()));
        Address toAddress = script.getToAddress(MAINNET, true);

        return new BitcoinAddress(script.getScriptType().toString(), toAddress.toString());
}
Code language: Java (java)