External Funding

TL;DR

Call open_channel_with_external_funding to get an unsigned transaction, sign it with your external wallet, then submit via submit_signed_funding_tx. Do not modify the transaction structure after it is returned.

External funding allows you to open a payment channel using funds from an external wallet (e.g., a third-party CKB wallet) rather than requiring the channel parties themselves to provide the funding. This is useful when you want to delegate the funding transaction to a separate wallet application.

How It Works

1. Call open_channel_with_external_funding to negotiate the channel parameters. This returns an unsigned_funding_tx.
2. The external wallet signs the CKB cells it contributed for funding.
3. Submit the signed transaction via submit_signed_funding_tx.

Important Constraints

Signing the Funding Transaction

For Rust Developers

If you are using secp256k1-sighash locks, refer to the development-only sign_external_funding_tx implementation for how to sign the transaction. This helper only covers secp256k1 signing — it resolves previous outputs, groups matching lock scripts, signs each script group, and writes the signature into WitnessArgs.lock.

For JavaScript Developers

Refer to the fiber-wallet example using @ckb-ccc/ccc. The main signing flow is signFundingTx, with toCccTransaction for JSON-RPC to CCC conversion and withFundingTxWitnesses for copying signed witnesses back to the original transaction.

The example supports:

• Standard CCC signers
• OmniLock witness preparation
• JoyID redirect signing

RPC Example

{
  "jsonrpc": "2.0",
  "method": "open_channel_with_external_funding",
  "params": [
    {
      "pubkey": "<peer_pubkey>",
      "funding_amount": "0x77359400",
      "funding_type_script": null
    }
  ],
  "id": 1
}