lightning-splice_update -- Command to initiate a channel to a peer


(WARNING: experimental-splicing only)

splice_update channel_id psbt


splice_update is a low level RPC command which updates the active channel
splice associated with channel_id.

channel_id is the channel id of the channel being spliced.

psbt is the base 64 encoded PSBT returned from splice_init with any changes
added by the user.

splice_update must be called repeatidly until the result commitments_secured
is true. Each time splice_update is called, it will return a new PSBT that
may have changes. In the simplest case, you take the returned psbt and pass
it back into splice_update for the incoming psbt field.

For more complex use cases, you may modify the psbt both before calling
splice_update and inbetween subsequent calls until commitments_secured is
true. After which point you can no long make modifications to the PSBT (beyond
signing, which comes later with splice_signed).

Each splice_update result may include changes to the PSBT specified by your
channel peer. You can review these changes between calls to splice_update to
perform additional validation or strategy adjustment.

Typically, splice_update will return commitments_secured true after one call
but you should assume it will need multiple calls. Here is an example way to
call splice_update

while [[ $(echo $RESULT | jq -r ".commitments_secured") == "false" ]]
	RESULT=$(lightning-cli splice_update $CHANNEL_ID $PSBT)
	PSBT=$(echo $RESULT | jq -r ".psbt")
	echo $RESULT

Before each call to splice_update you have the opportunity
to make additional changes.

Here is a full example set of splice commands that will splice in 100,000 sats
to the first channel that comes out of listpeerchannels. The example assumes
you already have at least one confirmed channel.

RESULT=$(lightning-cli listpeerchannels)
CHANNEL_ID=$(echo $RESULT| jq -r ".channels[0].channel_id")
echo $RESULT

RESULT=$(lightning-cli fundpsbt -k satoshi=100000sat feerate=urgent startweight=800 excess_as_change=true)
INITIALPSBT=$(echo $RESULT | jq -r ".psbt")
echo $RESULT

RESULT=$(lightning-cli splice_init $CHANNEL_ID 100000 $INITIALPSBT)
PSBT=$(echo $RESULT | jq -r ".psbt")
echo $RESULT

while [[ $(echo $RESULT | jq -r ".commitments_secured") == "false" ]]
	RESULT=$(lightning-cli splice_update $CHANNEL_ID $PSBT)
	PSBT=$(echo $RESULT | jq -r ".psbt")
	echo $RESULT

RESULT=$(lightning-cli signpsbt -k psbt="$PSBT")
PSBT=$(echo $RESULT | jq -r ".signed_psbt")
echo $RESULT

lightning-cli splice_signed $CHANNEL_ID $PSBT


On success, an object is returned, containing:

  • psbt (string): the (incomplete) PSBT of the splice transaction
  • commitments_secured (boolean): whether or not the commitments were secured





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