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lightning-fundpsbt -- Command to populate PSBT inputs from the wallet
================================================================
SYNOPSIS
--------
**fundpsbt** *satoshi* *feerate* *startweight* \[*minconf*\] \[*reserve*\] \[*locktime*\] \[*min_witness_weight*\]
DESCRIPTION
-----------
`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
*btc*.
*feerate* can be one of the feerates listed in lightning-feerates(7),
or one of the strings *urgent* (aim for next block), *normal* (next 4
blocks or so) or *slow* (next 100 blocks or so) to use lightningd’s
internal estimates. It can also be a *feerate* is a number, with an
optional suffix: *perkw* means the number is interpreted as
satoshi-per-kilosipa (weight), and *perkb* means it is interpreted
bitcoind-style as satoshi-per-kilobyte. Omitting the suffix is
equivalent to *perkb*.
*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.
*reserve* is a boolean: if true (the default), then *reserveinputs* is
called (successfully, with *exclusive* true) on the returned PSBT.
*locktime* is an optional locktime: if not set, it is set to a recent
block height.
*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.
EXAMPLE 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, returns the *psbt* containing the inputs, *feerate_per_kw*
showing the exact numeric feerate it used, *estimated_final_weight* for
the estimated weight of the transaction once fully signed, and
*excess_msat* containing the amount above *satoshi* which is
available. This could be zero, or dust. If *satoshi* was "all",
then *excess_msat* is the entire amount once fees are subtracted
for the weights of the inputs and startweight.
If *reserve* was true, then a *reservations* array is returned,
exactly like *reserveinputs*.
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 <<rusty@rustcorp.com.au>> is mainly responsible.
SEE ALSO
--------
lightning-utxopsbt(7), lightning-reserveinputs(7), lightning-unreserveinputs(7).
RESOURCES
---------
Main web site: <https://github.com/ElementsProject/lightning>