lightning-fundpsbt -- Command to populate PSBT inputs from the wallet

SYNOPSIS

fundpsbt satoshi feerate startweight [minconf] [reserve] [locktime] [min_witness_weight] [excess_as_change] [nonwrapped] [opening_anchor_channel]

DESCRIPTION

fundpsbt is a low-level RPC command which creates a PSBT using unreserved inputs in the wallet, optionally reserving them as well.

• satoshi (sat_or_all): The minimum satoshi value of the output(s) needed (or the string all meaning use all unreserved inputs). If a value, it can be a whole number, a whole number ending in sat, a whole number ending in 000msat, or a number with 1 to 8 decimal places ending in btc.
• feerate (feerate): Used for the transaction as initial feerate. The default is normal.
• startweight (u32): The weight of the transaction before fundpsbt has added any inputs.
• minconf (u32, optional): The minimum number of confirmations that used outputs should have. The default is 1.
• reserve (u32, optional): If not zero, then reserveinputs is called (successfully, with exclusive true) on the returned PSBT for this number of blocks. The default is 72 blocks.
• locktime (u32, optional): The locktime of the transaction. if not set, it is set to a recent block height.
• min_witness_weight (u32, optional): Minimum weight to use for a UTXO's witness. If the actual witness weight is greater than the provided minimum, the actual witness weight will be used.
• excess_as_change (boolean, optional): Flag to add a change output for the excess sats.
• nonwrapped (boolean, optional): To signal to filter out any p2sh-wrapped inputs from funding this PSBT. (added v23.02)
• opening_anchor_channel (boolean, optional): To signel that it needs emergency reserve for anchors so that we can lowball our commitment tx fees, and min-emergency-msat for reserving some sats for closing anchor channels. (added v23.08)

USAGE

Let's assume the caller is trying to produce a 100,000 satoshi output.

First, the caller estimates the weight of the core (typically 42) and known outputs of the transaction (typically (9 + scriptlen) * 4). For a simple P2WPKH it's a 22 byte scriptpubkey, so that's 124 weight.

It calls "fundpsbt 100000sat slow 166", which succeeds, and returns the psbt and feerate_per_kw it used, the estimated_final_weight and any excess_msat.

If excess_msat is greater than the cost of adding a change output, the caller adds a change output randomly to position 0 or 1 in the PSBT. Say feerate_per_kw is 253, and the change output is a P2WPKH (weight 124), the cost is around 31 sats. With the dust limit disallowing payments below 546 satoshis, we would only create a change output if excess_msat was greater or equal to 31 + 546.

RETURN VALUE

On success, an object is returned, containing:

• psbt (string): Unsigned PSBT which fulfills the parameters given.
• feerate_per_kw (u32): The feerate used to create the PSBT, in satoshis-per-kiloweight.
• estimated_final_weight (u32): The estimated weight of the transaction once fully signed.
• excess_msat (msat): The amount above satoshi which is available. This could be zero, or dust; it will be zero if change_outnum is also returned.
• change_outnum (u32, optional): The 0-based output number where change was placed (only if parameter excess_as_change was true and there was sufficient funds).
• reservations (array of objects, optional): If reserve was true or a non-zero number, just as per lightning- reserveinputs(7).:
  • txid (txid): The txid of the transaction.
  • vout (u32): The 0-based output number.
  • was_reserved (boolean) (always false): Whether this output was previously reserved.
  • reserved (boolean) (always true): Whether this output is now reserved.
  • reserved_to_block (u32): The blockheight the reservation will expire.

If excess_as_change is true and the excess is enough to cover an additional output above the dust_limit, then an output is added to the PSBT for the excess amount. The excess_msat will be zero. A change_outnum will be returned with the index of the change output.

ERRORS

On error the returned object will contain code and message properties, with code being one of the following:

• -32602: If the given parameters are wrong.
• -1: Catchall nonspecific error.
• 301: Insufficient UTXOs to meet satoshi value.

AUTHOR

Rusty Russell <[email protected]> is mainly responsible.

SEE ALSO

lightning-utxopsbt(7), lightning-reserveinputs(7), lightning-unreserveinputs(7)

RESOURCES

Main web site: https://github.com/ElementsProject/lightning

lightning-cli fundpsbt -k "satoshi"=1000000 "feerate"="253perkw" "startweight"=250 "reserve"=0

{
  "id": "example:fundpsbt#1",
  "method": "fundpsbt",
  "params": {
    "satoshi": 1000000,
    "feerate": "253perkw",
    "startweight": 250,
    "reserve": 0
  }
}

{
  "psbt": "cHNidP8BAgQCAAAAAQMEbwAAAAEEAQpsbt310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000310000",
  "feerate_per_kw": 253,
  "estimated_final_weight": 693,
  "excess_msat": 196962507000,
  "change_outnum": 0
}

lightning-cli fundpsbt -k "satoshi"=500000 "feerate"="urgent" "startweight"=166 "reserve"=0 "excess_as_change"=True "min_witness_weight"=110

{
  "id": "example:fundpsbt#2",
  "method": "fundpsbt",
  "params": {
    "satoshi": 500000,
    "feerate": "urgent",
    "startweight": 166,
    "reserve": 0,
    "excess_as_change": true,
    "min_witness_weight": 110
  }
}

{
  "psbt": "cHNidP8BAgQCAAAAAQMEbwAAAAEEAQpsbt410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000410000",
  "feerate_per_kw": 11000,
  "estimated_final_weight": 612,
  "excess_msat": 0,
  "change_outnum": 0
}