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b07327a687
It's *possible* to do this using various RPC calls, but it's unfriendly: 1. Call getinfo to get the current block height. 2. Call listfunds to map the UTXOs. 3. Create the PSBT and hope you get all the fields correct. Instead, this presents an interface just like `fundpsbt`, with identical returns. I think it's different enough to justify a new command (though it shares much internally, of course). In particular, it's now quite simple to create a command which uses specified utxos, and then adds more to meet any shortfall. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
94 lines
3.4 KiB
Markdown
94 lines
3.4 KiB
Markdown
lightning-fundpsbt -- Command to populate PSBT inputs from the wallet
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================================================================
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SYNOPSIS
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--------
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**fundpsbt** *satoshi* *feerate* *startweight* \[*minconf*\] \[*reserve*\]
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DESCRIPTION
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-----------
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`fundpsbt` is a low-level RPC command which creates a PSBT using unreserved
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inputs in the wallet, optionally reserving them as well.
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*satoshi* is the minimum satoshi value of the output(s) needed (or the
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string "all" meaning use all unreserved inputs). If a value, it can
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be a whole number, a whole number ending in *sat*, a whole number
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ending in *000msat*, or a number with 1 to 8 decimal places ending in
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*btc*.
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*feerate* can be one of the feerates listed in lightning-feerates(7),
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or one of the strings *urgent* (aim for next block), *normal* (next 4
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blocks or so) or *slow* (next 100 blocks or so) to use lightningd’s
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internal estimates. It can also be a *feerate* is a number, with an
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optional suffix: *perkw* means the number is interpreted as
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satoshi-per-kilosipa (weight), and *perkb* means it is interpreted
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bitcoind-style as satoshi-per-kilobyte. Omitting the suffix is
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equivalent to *perkb*.
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*startweight* is the weight of the transaction before *fundpsbt* has
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added any inputs.
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*minconf* specifies the minimum number of confirmations that used
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outputs should have. Default is 1.
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*reserve* is a boolean: if true (the default), then *reserveinputs* is
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called (successfully, with *exclusive* true) on the returned PSBT.
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EXAMPLE USAGE
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-------------
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Let's assume the caller is trying to produce a 100,000 satoshi output.
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First, the caller estimates the weight of the core (typically 42) and
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known outputs of the transaction (typically (9 + scriptlen) * 4). For
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a simple P2WPKH it's a 22 byte scriptpubkey, so that's 164 weight.
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It calls "*fundpsbt* 100000sat slow 206", which succeeds, and returns
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the *psbt* and *feerate_per_kw* it used, the *estimated_final_weight*
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and any *excess_msat*.
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If *excess_msat* is greater than the cost of adding a change output,
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the caller adds a change output randomly to position 0 or 1 in the
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PSBT. Say *feerate_per_kw* is 253, and the change output is a P2WPKH
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(weight 164), that would cost the cost is around 41 sats. With the
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dust limit disallowing payments below 546 satoshis, we would only create
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a change output if *excess_msat* was greater or equal to 41 + 546.
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RETURN VALUE
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------------
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On success, returns the *psbt* containing the inputs, *feerate_per_kw*
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showing the exact numeric feerate it used, *estimated_final_weight* for
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the estimated weight of the transaction once fully signed, and
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*excess_msat* containing the amount above *satoshi* which is
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available. This could be zero, or dust. If *satoshi* was "all",
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then *excess_msat* is the entire amount once fees are subtracted
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for the weights of the inputs and startweight.
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If *reserve* was true, then a *reservations* array is returned,
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exactly like *reserveinputs*.
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On error the returned object will contain `code` and `message` properties,
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with `code` being one of the following:
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- -32602: If the given parameters are wrong.
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- -1: Catchall nonspecific error.
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- 301: Insufficient UTXOs to meet *satoshi* value.
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AUTHOR
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------
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Rusty Russell <<rusty@rustcorp.com.au>> is mainly responsible.
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SEE ALSO
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--------
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lightning-utxopsbt(7), lightning-reserveinputs(7), lightning-unreserveinputs(7).
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RESOURCES
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---------
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Main web site: <https://github.com/ElementsProject/lightning>
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