df: use estimated witness weight, not fixed 110 value

Persist the estimated-witness-weight thru via the PSBT object.
Use this to calculate the estimated fee burden of a peer.

For now we just re-use the 110 "default" witness weight.

FIXME: use BIP322 and send proofs/use that as estimate

common/psbt_open.c

@@ -24,6 +24,22 @@ bool psbt_get_serial_id(const struct wally_map *map, u64 *serial_id)
 	return true;
 }
 
+static bool psbt_map_get_u32(const struct wally_map *map, u32 type, u32 *val)
+{
+	size_t value_len;
+	beint32_t bev;
+	void *result = psbt_get_lightning(map, type, &value_len);
+	if (!result)
+		return false;
+
+	if (value_len != sizeof(bev))
+		return false;
+
+	memcpy(&bev, result, value_len);
+	*val = be32_to_cpu(bev);
+	return true;
+}
+
 static int compare_serials(const struct wally_map *map_a,
 			   const struct wally_map *map_b)
 {
@@ -72,7 +88,6 @@ static const u8 *linearize_input(const tal_t *ctx,
 	psbt->inputs[0] = *in;
 	psbt->num_inputs++;
 
-
 	/* Sort the inputs, so serializing them is ok */
 	wally_map_sort(&psbt->inputs[0].unknowns, 0);
 
@@ -320,6 +335,22 @@ struct psbt_changeset *psbt_get_changeset(const tal_t *ctx,
 	return set;
 }
 
+void psbt_set_est_witness_weight(const tal_t *ctx,
+				 struct wally_psbt_input *input,
+				 u32 est_witness_weight)
+{
+	u8 *key = psbt_make_key(tmpctx, PSBT_TYPE_EST_WITNESS_WEIGHT, NULL);
+	beint32_t bev = cpu_to_be32(est_witness_weight);
+
+	psbt_input_set_unknown(ctx, input, key, &bev, sizeof(bev));
+}
+
+bool psbt_get_est_witness_weight(const struct wally_psbt_input *input,
+				 u32 *est_witness_weight)
+{
+	return psbt_map_get_u32(&input->unknowns, PSBT_TYPE_EST_WITNESS_WEIGHT,
+				est_witness_weight);
+}
 
 void psbt_input_set_serial_id(const tal_t *ctx,
 			      struct wally_psbt_input *input,

common/psbt_open.h

@@ -38,6 +38,7 @@ struct psbt_changeset {
 #define PSBT_TYPE_SERIAL_ID 0x01
 #define PSBT_TYPE_INPUT_MARKER 0x02
 #define PSBT_TYPE_OUTPUT_EXTERNAL 0x04
+#define PSBT_TYPE_EST_WITNESS_WEIGHT 0x08
 
 /* psbt_get_serial_id - Returns the serial_id from an unknowns map
  *
@@ -46,8 +47,27 @@ struct psbt_changeset {
  *
  * Returns false if serial_id is not present
  */
-WARN_UNUSED_RESULT bool psbt_get_serial_id(const struct wally_map *map,
-					   u64 *serial_id);
+bool psbt_get_serial_id(const struct wally_map *map, u64 *serial_id);
+
+/* psbt_set_est_witness_weight - Set the estimated witness weight for an input
+ *
+ * @ctx - the allocation context
+ * @input - the psbt input to annotate with it's estimated witness weight
+ * @est_witness_weight - the estimated witness weight
+ * */
+void psbt_set_est_witness_weight(const tal_t *ctx,
+				 struct wally_psbt_input *input,
+				 u32 est_witness_weight);
+
+/* psbt_get_est_witness_weight - Get estimated witness weight from input
+ *
+ * @input - psbt input to retreive the estimated wintess weight annotation of
+ * @est_witness_weight - witness weight, if present
+ *
+ * Returns false if est_witness_weight not present
+ */
+WARN_UNUSED_RESULT bool psbt_get_est_witness_weight(const struct wally_psbt_input *input,
+						    u32 *est_witness_weight);
 
 /* psbt_sort_by_serial_id - Sort PSBT by serial_ids
  *

lightningd/dual_open_control.c

@@ -810,7 +810,7 @@ openchannel2_hook_deserialize(struct openchannel2_payload *payload,
 	    !lease_rates_set_chan_fee_base_msat(payload->rates, fee_max_base))
 		fatal("Plugin sent overflowing `channel_fee_max_base_msat`");
 
-	/* Add a serial_id to everything that doesn't have one yet */
+	/* Add a serial_id + est_weight to everything that doesn't have one yet */
 	if (payload->psbt)
 		psbt_add_serials(payload->psbt, TX_ACCEPTER);
 
@@ -867,7 +867,7 @@ openchannel2_changed_deserialize(struct openchannel2_psbt_payload *payload,
 			       false, &psbt))
 		return false;
 
-	/* Add serials to PSBT, before checking for required fields */
+	/* Add serials + est_weights to PSBT, before checking for required fields */
 	psbt_add_serials(psbt, TX_ACCEPTER);
 
 	/* We require the PSBT to meet certain criteria such as
@@ -2446,7 +2446,7 @@ json_openchannel_bump(struct command *cmd,
 	oa->our_upfront_shutdown_script
 		= channel->shutdown_scriptpubkey[LOCAL];
 
-	/* Add serials to any input that's missing them */
+	/* Add serials+est-weight to any input that's missing them */
 	psbt_add_serials(psbt, TX_INITIATOR);
 
 	/* We require the PSBT to meet certain criteria such as
@@ -2703,7 +2703,7 @@ static struct command_result *json_openchannel_update(struct command *cmd,
 				    "Another openchannel command"
 				    " is in progress");
 
-	/* Add serials to PSBT */
+	/* Add serials+est-weight to PSBT */
 	psbt_add_serials(psbt, TX_INITIATOR);
 
 	/* We require the PSBT to meet certain criteria such as
@@ -2881,7 +2881,7 @@ static struct command_result *json_openchannel_init(struct command *cmd,
 				    type_to_string(tmpctx, struct amount_sat,
 						   &chainparams->max_funding));
 
-	/* Add serials to any input that's missing them */
+	/* Add serials+weights to any input that's missing them */
 	psbt_add_serials(psbt, TX_INITIATOR);
 
 	/* We require the PSBT to meet certain criteria such as

openingd/dualopend.c

@@ -238,11 +238,12 @@ static u8 *psbt_changeset_get_next(const tal_t *ctx,
 				   struct psbt_changeset *set)
 {
 	u64 serial_id;
+	/* FIXME: actually estimate this? */
+	u32 est_witness_weight = 110;
 	u8 *msg;
 
 	if (tal_count(set->added_ins) != 0) {
 		const struct input_set *in = &set->added_ins[0];
-		u32 est_witness_weight = 0;
 
 		if (!psbt_get_serial_id(&in->input.unknowns, &serial_id))
 			abort();
@@ -601,18 +602,22 @@ static size_t psbt_input_weight(struct wally_psbt *psbt,
 				size_t in)
 {
 	size_t weight;
+	u32 est_witness_weight;
 
 	/* txid + txout + sequence */
 	weight = (32 + 4 + 4) * 4;
+	/* This should be just one 00 byte,
+	 * pre-Segwit inputs aren't allowed */
 	weight +=
 		(psbt->inputs[in].redeem_script_len +
 			(varint_t) varint_size(psbt->inputs[in].redeem_script_len)) * 4;
 
-	/* BOLT-f53ca2301232db780843e894f55d95d512f297f9 #3:
-	 *
-	 * The minimum witness weight for an input is 110.
-	 */
-	weight += 110;
+	/* Add input's estimated witness weight */
+	if (!psbt_get_est_witness_weight(&psbt->inputs[in], &est_witness_weight))
+		/* Default to 110 */
+		est_witness_weight = 110;
+
+	weight += est_witness_weight;
 	return weight;
 }
 
@@ -1498,7 +1503,6 @@ static bool run_tx_interactive(struct state *state,
 						   cast_const2(u8 **,
 							       &tx_bytes),
 						   &outpoint.n, &sequence,
-						   /* FIXME: use this */
 						   &est_witness_weight))
 				open_err_fatal(state,
 					       "Parsing tx_add_input %s",
@@ -1630,6 +1634,7 @@ static bool run_tx_interactive(struct state *state,
 							      &asset);
 			}
 			psbt_input_set_serial_id(psbt, in, serial_id);
+			psbt_set_est_witness_weight(psbt, in, est_witness_weight);
 
 			break;
 		}