fundpsbt satoshi feerate startweight [minconf] [reserve] [locktime] [min_witness_weight] [excess_as_change]
fundpsbt is a low-level RPC command which creates a PSBT using unreserved
inputs in the wallet, optionally reserving them as well.
satoshi is 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
feerate is an optional feerate: see NOTES in lightning-feerates(7)
for possible values. The default is normal.
startweight is the weight of the transaction before fundpsbt has
added any inputs.
minconf specifies the minimum number of confirmations that used
outputs should have. Default is 1.
If reserve if not zero, then reserveinputs is called (successfully, with
exclusive true) on the returned PSBT for this number of blocks (default
72 blocks if unspecified).
locktime is an optional locktime: if not set, it is set to a recent
min_witness_weight is an 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 is an optional boolean to flag to add a change output
for the excess sats.
nonwrapped is an optional boolean to signal to filter out any p2sh-wrapped
inputs from funding this PSBT.
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.
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): Whether this output was previously reserved (always false)
- reserved (boolean): Whether this output is now reserved (always true)
- 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.
On error the returned object will contain
code being one of the following:
- -32602: If the given parameters are wrong.
- -1: Catchall nonspecific error.
- 301: Insufficient UTXOs to meet satoshi value.
Rusty Russell <[email protected]> is mainly responsible.
lightning-utxopsbt(7), lightning-reserveinputs(7), lightning-unreserveinputs(7).
Main web site: https://github.com/ElementsProject/lightning