fundchannel: Add a new 'utxo' parameter

This new parameter takes a list of outpoints (as txid:vout) and fund a channel from the corresponding utxos.
Example : fundchannel <id> 10000 normal 1 [10767f0db0e568127fffd7f70a154d4599f42d62babf63230a7c3378bfce3cb0:0, c9e040e0b5fc8c59d5e7834108fbc5583001f414dd83faf0a05cff9d1a92d32c:0]

common/wallet_tx.c

@@ -1,4 +1,7 @@
+#include <ccan/ccan/opt/opt.h>
+#include <ccan/tal/str/str.h>
 #include <common/json_command.h>
+#include <common/json_helpers.h>
 #include <common/jsonrpc_errors.h>
 #include <common/wallet_tx.h>
 #include <inttypes.h>
@@ -23,13 +26,14 @@ struct command_result *param_wtx(struct command *cmd,
 		return NULL;
 	}
 	wtx->all_funds = false;
+
 	if (!parse_amount_sat(&wtx->amount,
 			      buffer + tok->start, tok->end - tok->start))
 		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
-				    "'%s' should be satoshis or 'all', not '%.*s'",
-				    name,
-				    tok->end - tok->start,
-				    buffer + tok->start);
+					"'%s' should be an amount in satoshis or all, not '%.*s'",
+					name,
+					tok->end - tok->start,
+					buffer + tok->start);
 
 	if (amount_sat_greater(wtx->amount, max))
                 return command_fail(wtx->cmd, FUND_MAX_EXCEEDED,
@@ -39,6 +43,66 @@ struct command_result *param_wtx(struct command *cmd,
         return NULL;
 }
 
+struct command_result *param_utxos(struct command *cmd,
+				 const char *name,
+				 const char *buffer,
+				 const jsmntok_t *tok,
+				 const struct utxo ***utxos)
+{
+	size_t i;
+	const jsmntok_t *curr;
+	struct bitcoin_txid **txids = tal_arr(cmd, struct bitcoin_txid*, 0);
+	unsigned int **outnums = tal_arr(cmd, unsigned int*, 0);
+
+	json_for_each_arr(i, curr, tok) {
+		jsmntok_t txid_tok, outnum_tok;
+		if (!split_tok(buffer, curr, ':', &txid_tok, &outnum_tok))
+			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+								"Could not decode the outpoint from \"%s\""
+								" The utxos should be specified as"
+								" 'txid:output_index'.",
+								json_strdup(tmpctx, buffer, curr));
+
+		struct bitcoin_txid *txid = tal(txids, struct bitcoin_txid);
+		unsigned int *outnum = tal(txids, unsigned int);
+		if (!json_to_txid(buffer, (const jsmntok_t*)&txid_tok, txid)) {
+			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+								"Could not get a txid out of \"%s\"",
+								json_strdup(tmpctx, buffer, &txid_tok));
+		}
+		if(!json_to_number(buffer, (const jsmntok_t*)&outnum_tok, outnum))
+			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+								"Could not get a vout out of \"%s\"",
+								json_strdup(tmpctx, buffer, &outnum_tok));
+
+		tal_arr_expand(&txids, txid);
+		tal_arr_expand(&outnums, outnum);
+	}
+
+	if (!tal_count(txids) || !tal_count(outnums))
+		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+							"Please specify an array of 'txid:output_index',"
+							" not \"%.*s\"",
+							tok->end - tok->start,
+							buffer + tok->start);
+
+	*utxos = wallet_select_specific(cmd, cmd->ld->wallet, txids, outnums);
+	tal_free(txids);
+	tal_free(outnums);
+
+	if (!*utxos)
+		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+							"Could not decode all of the outpoints. The utxos"
+							" should be specified as an array of "
+							" 'txid:output_index'.");
+	if (tal_count(*utxos) == 0)
+		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+							"No matching utxo was found from the wallet."
+							"You can get a list of the wallet utxos with"
+							" the `listfunds` RPC call.");
+	return NULL;
+}
+
 static struct command_result *check_amount(const struct wallet_tx *wtx,
 					   struct amount_sat amount)
 {
@@ -104,3 +168,64 @@ struct command_result *wtx_select_utxos(struct wallet_tx *tx,
 	}
 	return NULL;
 }
+
+struct command_result *wtx_from_utxos(struct wallet_tx *tx,
+					u32 fee_rate_per_kw,
+					size_t out_len,
+					u32 maxheight,
+					const struct utxo **utxos)
+{
+	size_t weight;
+	struct amount_sat total_amount, fee_estimate;
+
+	tx->change = AMOUNT_SAT(0);
+	tx->change_key_index = 0;
+	total_amount = AMOUNT_SAT(0);
+
+	/* The transaction has `tal_count(tx.utxos)` inputs and one output */
+	/* (version + in count + out count + locktime)  (index + value + script length) */
+	weight = 4 * (4 + 1 + 1 + 4) + 4 * (8 + 1 + out_len);
+	for (size_t i = 0; i < tal_count(utxos); i++) {
+		if (!*utxos[i]->blockheight || *utxos[i]->blockheight > maxheight) {
+			tal_arr_remove(&utxos, i);
+			continue;
+		}
+		/* txid + index + sequence + script_len */
+		weight += (32 + 4 + 4 + 1) * 4;
+		/* P2SH variants include push of <0 <20-byte-key-hash>> */
+		if (utxos[i]->is_p2sh)
+			weight += 23 * 4;
+		/* Account for witness (1 byte count + sig + key) */
+		weight += 1 + (1 + 73 + 1 + 33);
+		if (!amount_sat_add(&total_amount, total_amount, utxos[i]->amount))
+			fatal("Overflow when computing input amount");
+	}
+	tx->utxos = utxos;
+
+	if (!tx->all_funds && amount_sat_less(tx->amount, total_amount)
+			&& !amount_sat_sub(&tx->change, total_amount, tx->amount))
+		fatal("Overflow when computing change");
+	if (amount_sat_greater_eq(tx->change, get_chainparams(tx->cmd->ld)->dust_limit)) {
+		tx->change_key_index = wallet_get_newindex(tx->cmd->ld);
+		/* Add the change output's weight */
+		weight += (8 + 1 + out_len) * 4;
+	}
+
+	fee_estimate = amount_tx_fee(fee_rate_per_kw, weight);
+
+	if (tx->all_funds || amount_sat_eq(tx->change, AMOUNT_SAT(0))) {
+		tx->amount = total_amount;
+		if (!amount_sat_sub(&tx->amount, tx->amount, fee_estimate))
+			return command_fail(tx->cmd, FUND_CANNOT_AFFORD,
+								"Cannot afford transaction with %s sats of fees",
+								type_to_string(tmpctx, struct amount_sat,
+									&fee_estimate));
+	} else {
+		if (!amount_sat_sub(&tx->change, tx->change, fee_estimate))
+			return command_fail(tx->cmd, FUND_CANNOT_AFFORD,
+								"Cannot afford transaction with %s sats of fees",
+								type_to_string(tmpctx, struct amount_sat,
+									&fee_estimate));
+	}
+	return check_amount(tx, tx->amount);
+}

common/wallet_tx.h

@@ -27,11 +27,23 @@ struct command_result *param_wtx(struct command *cmd,
 				 const jsmntok_t *tok,
 				 struct wallet_tx *wtx);
 
+struct command_result *param_utxos(struct command *cmd,
+				 const char *name,
+				 const char *buffer,
+				 const jsmntok_t *tok,
+				 const struct utxo ***utxos);
+
 struct command_result *wtx_select_utxos(struct wallet_tx *tx,
 					u32 fee_rate_per_kw,
 					size_t out_len,
 					u32 maxheight);
 
+struct command_result *wtx_from_utxos(struct wallet_tx *tx,
+					u32 fee_rate_per_kw,
+					size_t out_len,
+					u32 maxheight,
+					const struct utxo **utxos);
+
 static inline u32 minconf_to_maxheight(u32 minconf, struct lightningd *ld)
 {
 	/* No confirmations is special, we need to disable the check in the

lightningd/opening_control.c

@@ -996,6 +996,7 @@ static struct command_result *json_fund_channel(struct command *cmd,
 	bool *announce_channel;
 	u8 *msg;
 	struct amount_sat max_funding_satoshi;
+	const struct utxo **chosen_utxos;
 
 	max_funding_satoshi = get_chainparams(cmd->ld)->max_funding;
 
@@ -1009,6 +1010,7 @@ static struct command_result *json_fund_channel(struct command *cmd,
 		   p_opt("feerate", param_feerate, &feerate_per_kw),
 		   p_opt_def("announce", param_bool, &announce_channel, true),
 		   p_opt_def("minconf", param_number, &minconf, 1),
+		   p_opt("utxos", param_utxos, &chosen_utxos),
 		   NULL))
 		return command_param_failed();
 
@@ -1055,8 +1057,12 @@ static struct command_result *json_fund_channel(struct command *cmd,
 	}
 
 	maxheight = minconf_to_maxheight(*minconf, cmd->ld);
-	res = wtx_select_utxos(fc->wtx, *feerate_per_kw,
-			       BITCOIN_SCRIPTPUBKEY_P2WSH_LEN, maxheight);
+	if (chosen_utxos)
+		res = wtx_from_utxos(fc->wtx, *feerate_per_kw,
+				BITCOIN_SCRIPTPUBKEY_P2WSH_LEN, maxheight, chosen_utxos);
+	else
+		res = wtx_select_utxos(fc->wtx, *feerate_per_kw,
+				BITCOIN_SCRIPTPUBKEY_P2WSH_LEN, maxheight);
 	if (res)
 		return res;
 

wallet/wallet.c

@@ -380,6 +380,36 @@ const struct utxo **wallet_select_coins(const tal_t *ctx, struct wallet *w,
 	return utxo;
 }
 
+const struct utxo **wallet_select_specific(const tal_t *ctx, struct wallet *w,
+					struct bitcoin_txid **txids,
+                    u32 **outnums)
+{
+	size_t i, j;
+	struct utxo **available;
+	const struct utxo **utxos = tal_arr(ctx, const struct utxo*, 0);
+	tal_add_destructor2(utxos, destroy_utxos, w);
+
+	available = wallet_get_utxos(ctx, w, output_state_available);
+	for (i = 0; i < tal_count(txids); i++) {
+		for (j = 0; j < tal_count(available); j++) {
+
+			if (bitcoin_txid_eq(&available[j]->txid, txids[i])
+					&& available[j]->outnum == *outnums[i]) {
+				struct utxo *u = tal_steal(utxos, available[j]);
+				tal_arr_expand(&utxos, u);
+
+				if (!wallet_update_output_status(
+					w, &available[j]->txid, available[j]->outnum,
+					output_state_available, output_state_reserved))
+					fatal("Unable to reserve output");
+			}
+		}
+	}
+	tal_free(available);
+
+	return utxos;
+}
+
 const struct utxo **wallet_select_all(const tal_t *ctx, struct wallet *w,
 				      const u32 feerate_per_kw,
 				      size_t outscriptlen,

wallet/wallet.h

@@ -371,6 +371,15 @@ const struct utxo **wallet_select_all(const tal_t *ctx, struct wallet *w,
 				      struct amount_sat *sat,
 				      struct amount_sat *fee_estimate);
 
+/**
+ * wallet_select_specific - Select utxos given an array of txids and an array of outputs index
+ *
+ * Returns an array of `utxo` structs.
+ */
+const struct utxo **wallet_select_specific(const tal_t *ctx, struct wallet *w,
+					struct bitcoin_txid **txids,
+					u32 **outnums);
+
 /**
  * wallet_confirm_utxos - Once we've spent a set of utxos, mark them confirmed.
  *