fundpsbt/utxopsbt: new `min_witness_weight` param

Needed for v2 of channel opens, where the minimum weight is 110; a
'simple utxo' (sig + key) weighs in at 107, so we a need a way to
establish a floor for this case.

Changelog-Added: JSON-RPC: fundpsbt/utxopsbt have new param, `min_witness_utxo`, which sets a floor for the weight calculation of an added input

common/utxo.c

@@ -64,7 +64,14 @@ struct utxo *fromwire_utxo(const tal_t *ctx, const u8 **ptr, size_t *max)
 	return utxo;
 }
 
-size_t utxo_spend_weight(const struct utxo *utxo)
+size_t utxo_spend_weight(const struct utxo *utxo, size_t min_witness_weight)
 {
-	return bitcoin_tx_simple_input_weight(utxo->is_p2sh);
+	size_t wit_weight = bitcoin_tx_simple_input_witness_weight();
+	/* If the min is less than what we'd use for a 'normal' tx,
+	 * we return the value with the greater added/calculated */
+	if (wit_weight < min_witness_weight)
+		return bitcoin_tx_input_weight(utxo->is_p2sh,
+					       min_witness_weight);
+
+	return bitcoin_tx_input_weight(utxo->is_p2sh, wit_weight);
 }

common/utxo.h

@@ -74,5 +74,5 @@ void towire_utxo(u8 **pptr, const struct utxo *utxo);
 struct utxo *fromwire_utxo(const tal_t *ctx, const u8 **ptr, size_t *max);
 
 /* Estimate of (signed) UTXO weight in transaction */
-size_t utxo_spend_weight(const struct utxo *utxo);
+size_t utxo_spend_weight(const struct utxo *utxo, size_t min_witness_weight);
 #endif /* LIGHTNING_COMMON_UTXO_H */

doc/lightning-fundpsbt.7

@@ -3,7 +3,7 @@
 lightning-fundpsbt - Command to populate PSBT inputs from the wallet
 .SH SYNOPSIS
 
-\fBfundpsbt\fR \fIsatoshi\fR \fIfeerate\fR \fIstartweight\fR [\fIminconf\fR] [\fIreserve\fR] [\fIlocktime\fR]
+\fBfundpsbt\fR \fIsatoshi\fR \fIfeerate\fR \fIstartweight\fR [\fIminconf\fR] [\fIreserve\fR] [\fIlocktime\fR] [\fImin_witness_weight\fR]
 
 .SH DESCRIPTION
 
@@ -43,6 +43,11 @@ called (successfully, with \fIexclusive\fR true) on the returned PSBT\.
 \fIlocktime\fR is an optional locktime: if not set, it is set to a recent
 block height\.
 
+
+\fImin_witness_weight\fR 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\.
+
 .SH EXAMPLE USAGE
 
 Let's assume the caller is trying to produce a 100,000 satoshi output\.
@@ -104,4 +109,4 @@ Rusty Russell \fI<rusty@rustcorp.com.au\fR> is mainly responsible\.
 
 Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 
-\" SHA256STAMP:8eb6970e2d625198db9b8e5ab7f90f9fb141744a837f58ee68ef54d28c7066b0
+\" SHA256STAMP:a8b9705274638127c2f5ec4e97ed94e6d7f6b6b10a76c2248e8bc8b36dd804ff

doc/lightning-fundpsbt.7.md

@@ -4,7 +4,7 @@ lightning-fundpsbt -- Command to populate PSBT inputs from the wallet
 SYNOPSIS
 --------
 
-**fundpsbt** *satoshi* *feerate* *startweight* \[*minconf*\] \[*reserve*\] \[*locktime*\]
+**fundpsbt** *satoshi* *feerate* *startweight* \[*minconf*\] \[*reserve*\] \[*locktime*\] \[*min_witness_weight*\]
 
 DESCRIPTION
 -----------
@@ -39,6 +39,10 @@ called (successfully, with *exclusive* true) on the returned PSBT.
 *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.
+
 EXAMPLE USAGE
 -------------
 

doc/lightning-utxopsbt.7

@@ -3,7 +3,7 @@
 lightning-utxopsbt - Command to populate PSBT inputs from given UTXOs
 .SH SYNOPSIS
 
-\fButxopsbt\fR \fIsatoshi\fR \fIfeerate\fR \fIstartweight\fR \fIutxos\fR [\fIreserve\fR] [\fIreservedok\fR] [\fIlocktime\fR]
+\fButxopsbt\fR \fIsatoshi\fR \fIfeerate\fR \fIstartweight\fR \fIutxos\fR [\fIreserve\fR] [\fIreservedok\fR] [\fIlocktime\fR] [\fImin_witness_weight\fR]
 
 .SH DESCRIPTION
 
@@ -31,6 +31,11 @@ if any of the \fIutxos\fR are already reserved\.
 \fIlocktime\fR is an optional locktime: if not set, it is set to a recent
 block height\.
 
+
+\fImin_witness_weight\fR 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\.
+
 .SH RETURN VALUE
 
 On success, returns the \fIpsbt\fR containing the inputs, \fIfeerate_per_kw\fR
@@ -70,4 +75,4 @@ Rusty Russell \fI<rusty@rustcorp.com.au\fR> is mainly responsible\.
 
 Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 
-\" SHA256STAMP:e47331be08a0911c74e142f2255bf62a83b70b818c1cf39a9314aab8c17a6e47
+\" SHA256STAMP:777710bb963f435193e92a55344c740c123d7aa4d54bf573c99a616f59eeee54

doc/lightning-utxopsbt.7.md

@@ -4,7 +4,7 @@ lightning-utxopsbt -- Command to populate PSBT inputs from given UTXOs
 SYNOPSIS
 --------
 
-**utxopsbt** *satoshi* *feerate* *startweight* *utxos* \[*reserve*\] \[*reservedok*\] \[*locktime*\]
+**utxopsbt** *satoshi* *feerate* *startweight* *utxos* \[*reserve*\] \[*reservedok*\] \[*locktime*\] \[*min_witness_weight*\]
 
 DESCRIPTION
 -----------
@@ -29,6 +29,10 @@ if any of the *utxos* are already reserved.
 *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.
+
 RETURN VALUE
 ------------
 

wallet/reservation.c

@@ -386,7 +386,7 @@ static struct command_result *json_fundpsbt(struct command *cmd,
 {
 	struct utxo **utxos;
 	u32 *feerate_per_kw;
-	u32 *minconf, *weight;
+	u32 *minconf, *weight, *min_witness_weight;
 	struct amount_sat *amount, input, diff;
 	bool all, *reserve;
 	u32 *locktime, maxheight;
@@ -398,6 +398,8 @@ static struct command_result *json_fundpsbt(struct command *cmd,
 		   p_opt_def("minconf", param_number, &minconf, 1),
 		   p_opt_def("reserve", param_bool, &reserve, true),
 		   p_opt("locktime", param_number, &locktime),
+		   p_opt_def("min_witness_weight", param_number,
+			     &min_witness_weight, 0),
 		   NULL))
 		return command_param_failed();
 
@@ -427,7 +429,9 @@ static struct command_result *json_fundpsbt(struct command *cmd,
 						    "impossible UTXO value");
 
 			/* But also adds weight */
-			*weight += utxo_spend_weight(utxo);
+			fprintf(stderr, "min_witness_weight is %u\n",
+					*min_witness_weight);
+			*weight += utxo_spend_weight(utxo, *min_witness_weight);
 			continue;
 		}
 
@@ -555,7 +559,7 @@ static struct command_result *json_utxopsbt(struct command *cmd,
 					    const jsmntok_t *params)
 {
 	struct utxo **utxos;
-	u32 *feerate_per_kw, *weight;
+	u32 *feerate_per_kw, *weight, *min_witness_weight;
 	bool all, *reserve, *reserved_ok;
 	struct amount_sat *amount, input, excess;
 	u32 current_height, *locktime;
@@ -568,6 +572,8 @@ static struct command_result *json_utxopsbt(struct command *cmd,
 		   p_opt_def("reserve", param_bool, &reserve, true),
 		   p_opt_def("reservedok", param_bool, &reserved_ok, false),
 		   p_opt("locktime", param_number, &locktime),
+		   p_opt_def("min_witness_weight", param_number,
+			     &min_witness_weight, 0),
 		   NULL))
 		return command_param_failed();
 
@@ -592,7 +598,7 @@ static struct command_result *json_utxopsbt(struct command *cmd,
 					    "impossible UTXO value");
 
 		/* But also adds weight */
-		*weight += utxo_spend_weight(utxo);
+		*weight += utxo_spend_weight(utxo, *min_witness_weight);
 	}
 
 	/* For all, anything above 0 is "excess" */