lightning-fundpsbt -- Command to populate PSBT inputs from the wallet ================================================================ SYNOPSIS -------- **fundpsbt** *satoshi* *feerate* *startweight* [*minconf*] [*reserve*] [*locktime*] [*min_witness_weight*] [*excess_as_change*] 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. 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 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. *excess_as_change* is an optional boolean to flag to add a change output for the excess sats. 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 ------------ [comment]: # (GENERATE-FROM-SCHEMA-START) 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 [comment]: # (GENERATE-FROM-SCHEMA-END) 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` 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 <> is mainly responsible. SEE ALSO -------- lightning-utxopsbt(7), lightning-reserveinputs(7), lightning-unreserveinputs(7). RESOURCES --------- Main web site: [comment]: # ( SHA256STAMP:0cd239969d70c9261f0d7309762e3d2e646ddd0c62dc7dd8b08515c03cc5385b)