{ "$schema": "../rpc-schema-draft.json", "type": "object", "additionalProperties": false, "rpc": "fundpsbt", "title": "Command to populate PSBT inputs from the wallet", "description": [ "`fundpsbt` is a low-level RPC command which creates a PSBT using unreserved inputs in the wallet, optionally reserving them as well." ], "request": { "required": [ "satoshi", "feerate", "startweight" ], "properties": { "satoshi": { "type": "sat_or_all", "description": [ "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": { "type": "feerate", "description": [ "Used for the transaction as initial feerate." ], "default": "*normal*" }, "startweight": { "type": "u32", "description": [ "The weight of the transaction before *fundpsbt* has added any inputs." ] }, "minconf": { "type": "u32", "description": [ "The minimum number of confirmations that used outputs should have." ], "default": "1" }, "reserve": { "type": "u32", "description": [ "If not zero, then *reserveinputs* is called (successfully, with *exclusive* true) on the returned PSBT for this number of blocks." ], "default": "72 blocks" }, "locktime": { "type": "u32", "description": [ "The locktime of the transaction. if not set, it is set to a recent block height." ] }, "min_witness_weight": { "type": "u32", "description": [ "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": { "type": "boolean", "description": [ "Flag to add a change output for the excess sats." ] }, "nonwrapped": { "added": "v23.02", "type": "boolean", "description": [ "To signal to filter out any p2sh-wrapped inputs from funding this PSBT." ] }, "opening_anchor_channel": { "added": "v23.08", "type": "boolean", "description": [ "To signel that it needs emergency reserve for anchors so that we can lowball our commitment tx fees, and min-emergency-msat for reserving some sats for closing anchor channels." ] } } }, "response": { "required": [ "psbt", "feerate_per_kw", "estimated_final_weight", "excess_msat" ], "properties": { "psbt": { "type": "string", "description": [ "Unsigned PSBT which fulfills the parameters given." ] }, "feerate_per_kw": { "type": "u32", "description": [ "The feerate used to create the PSBT, in satoshis-per-kiloweight." ] }, "estimated_final_weight": { "type": "u32", "description": [ "The estimated weight of the transaction once fully signed." ] }, "excess_msat": { "type": "msat", "description": [ "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": { "type": "u32", "description": [ "The 0-based output number where change was placed (only if parameter *excess_as_change* was true and there was sufficient funds)." ] }, "reservations": { "type": "array", "description": [ "If *reserve* was true or a non-zero number, just as per lightning- reserveinputs(7)." ], "items": { "type": "object", "required": [ "txid", "vout", "was_reserved", "reserved", "reserved_to_block" ], "additionalProperties": false, "properties": { "txid": { "type": "txid", "description": [ "The txid of the transaction." ] }, "vout": { "type": "u32", "description": [ "The 0-based output number." ] }, "was_reserved": { "type": "boolean", "enum": [ false ], "description": [ "Whether this output was previously reserved." ] }, "reserved": { "type": "boolean", "enum": [ true ], "description": [ "Whether this output is now reserved." ] }, "reserved_to_block": { "type": "u32", "description": [ "The blockheight the reservation will expire." ] } } } } }, "post_return_value_notes": [ "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." ] }, "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." ], "errors": [ "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: " ], "examples": [ { "request": { "id": "example:fundpsbt#1", "method": "fundpsbt", "params": { "satoshi": 1000000, "feerate": "253perkw", "startweight": 250, "reserve": 0 } }, "response": { "psbt": "cHNidP8BAF4CAAAAAZiQf/mEs4NcFFfD4K8xauOgSpbz/xeetoXVWAPCI0h6AQAAAAD9////AahhAAAAAAAAIlEg+3d9jpNmK0getyg5W+Mp31CPIRDKcJg/mZs/uaVrQ+GZAAAAAAEAiQIAAAABswU80whDZOoIHS/lfyxwmHh5USHBwbcjWHaJ9/XU+78BAAAAAP3///8CgIQeAAAAAAAiACDJvFwGPK7796bHgUQHtWJ7T4GotW7L6TLGgvnLrA0Z32INzQsAAAAAIlEgyRg+3pEh88b9FJiCLEenYCcyJ2ackJUIhDusW72BP2iYAAAAAQErYg3NCwAAAAAiUSDJGD7ekSHzxv0UmIIsR6dgJzInZpyQlQiEO6xbvYE/aAAA", "feerate_per_kw": 253, "estimated_final_weight": 693, "excess_msat": 196962507000, "change_outnum": 0 } }, { "request": { "id": "example:fundpsbt#2", "method": "fundpsbt", "params": { "satoshi": 500000, "feerate": "urgent", "startweight": 166, "reserve": 0, "excess_as_change": true, "min_witness_weight": 110 } }, "response": { "psbt": "cHNidP8BAF4CAAAAAZiQf/mEs4NcFFfD4K8xauOgSpbz/xeetoXVWAPCI0h6AQAAAAD9////AfZRxQsAAAAAIlEg21kTTo7K2doCG6F2JqgaDjc1kRCrH7AL08oPVVJhuE+ZAAAAAAEAiQIAAAABswU80whDZOoIHS/lfyxwmHh5USHBwbcjWHaJ9/XU+78BAAAAAP3///8CgIQeAAAAAAAiACDJvFwGPK7796bHgUQHtWJ7T4GotW7L6TLGgvnLrA0Z32INzQsAAAAAIlEgyRg+3pEh88b9FJiCLEenYCcyJ2ackJUIhDusW72BP2iYAAAAAQErYg3NCwAAAAAiUSDJGD7ekSHzxv0UmIIsR6dgJzInZpyQlQiEO6xbvYE/aAAA", "feerate_per_kw": 11000, "estimated_final_weight": 612, "excess_msat": 0, "change_outnum": 0 } } ] }