lightning/doc/lightning-fundpsbt.7

.TH "LIGHTNING-FUNDPSBT" "7" "" "" "lightning-fundpsbt"
.SH NAME
lightning-fundpsbt - Command to populate PSBT inputs from the wallet
.SH SYNOPSIS

\fBfundpsbt\fR \fIsatoshi\fR \fIfeerate\fR \fIstartweight\fR [\fIminconf\fR] [\fIreserve\fR]

.SH DESCRIPTION

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


\fIsatoshi\fR 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 \fIsat\fR, a whole number
ending in \fI000msat\fR, or a number with 1 to 8 decimal places ending in
\fIbtc\fR\.


\fIfeerate\fR can be one of the feerates listed in \fBlightning-feerates\fR(7),
or one of the strings \fIurgent\fR (aim for next block), \fInormal\fR (next 4
blocks or so) or \fIslow\fR (next 100 blocks or so) to use lightningd’s
internal estimates\.  It can also be a \fIfeerate\fR is a number, with an
optional suffix: \fIperkw\fR means the number is interpreted as
satoshi-per-kilosipa (weight), and \fIperkb\fR means it is interpreted
bitcoind-style as satoshi-per-kilobyte\. Omitting the suffix is
equivalent to \fIperkb\fR\.


\fIstartweight\fR is the weight of the transaction before \fIfundpsbt\fR has
added any inputs\.


\fIminconf\fR specifies the minimum number of confirmations that used
outputs should have\. Default is 1\.


\fIreserve\fR is a boolean: if true (the default), then \fIreserveinputs\fR is
called (successfully, with \fIexclusive\fR true) on the returned PSBT\.

.SH 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 164 weight\.


It calls "\fIfundpsbt\fR 100000sat slow 206", which succeeds, and returns
the \fIpsbt\fR and \fIfeerate_per_kw\fR it used, the \fIestimated_final_weight\fR
and any \fIexcess_msat\fR\.


If \fIexcess_msat\fR 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 \fIfeerate_per_kw\fR is 253, and the change output is a P2WPKH
(weight 164), that would cost the cost is around 41 sats\.  With the
dust limit disallowing payments below 546 satoshis, we would only create
a change output if \fIexcess_msat\fR was greater or equal to 41 + 546\.

.SH RETURN VALUE

On success, returns the \fIpsbt\fR containing the inputs, \fIfeerate_per_kw\fR
showing the exact numeric feerate it used, \fIestimated_final_weight\fR for
the estimated weight of the transaction once fully signed, and
\fIexcess_msat\fR containing the amount above \fIsatoshi\fR which is
available\.  This could be zero, or dust\.  If \fIsatoshi\fR was "all",
then \fIexcess_msat\fR is the entire amount once fees are subtracted
for the weights of the inputs and startweight\.


If \fIreserve\fR was true, then a \fIreservations\fR array is returned,
exactly like \fIreserveinputs\fR\.


On error the returned object will contain \fBcode\fR and \fBmessage\fR properties,
with \fBcode\fR being one of the following:

.RS
.IP \[bu]
-32602: If the given parameters are wrong\.
.IP \[bu]
-1: Catchall nonspecific error\.
.IP \[bu]
301: Insufficient UTXOs to meet \fIsatoshi\fR value\.

.RE
.SH AUTHOR

Rusty Russell \fI<rusty@rustcorp.com.au\fR> is mainly responsible\.

.SH SEE ALSO

\fBlightning-reserveinputs\fR(7), \fBlightning-unreserveinputs\fR(7)\.

.SH RESOURCES

Main web site: \fIhttps://github.com/ElementsProject/lightning\fR