txprepare: Use param_outpoint_arr helper to validate input

common/json_helpers.c

@@ -193,6 +193,14 @@ void json_add_txid(struct json_stream *result, const char *fieldname,
 	json_add_string(result, fieldname, hex);
 }
 
+void json_add_outpoint(struct json_stream *result, const char *fieldname,
+		       const struct bitcoin_outpoint *out)
+{
+	char hex[hex_str_size(sizeof(out->txid))];
+	bitcoin_txid_to_hex(&out->txid, hex, sizeof(hex));
+	json_add_member(result, fieldname, true, "%s:%d", hex, out->n);
+}
+
 void json_add_short_channel_id(struct json_stream *response,
 			       const char *fieldname,
 			       const struct short_channel_id *scid)

common/json_helpers.h

@@ -102,6 +102,10 @@ void json_add_channel_id(struct json_stream *response,
 void json_add_txid(struct json_stream *result, const char *fieldname,
 		   const struct bitcoin_txid *txid);
 
+/* '"fieldname" : "txid:n" */
+void json_add_outpoint(struct json_stream *result, const char *fieldname,
+		       const struct bitcoin_outpoint *out);
+
 /* '"fieldname" : "1234:5:6"' */
 void json_add_short_channel_id(struct json_stream *response,
 			       const char *fieldname,

plugins/txprepare.c

@@ -324,7 +324,7 @@ static struct command_result *txprepare_continue(struct command *cmd,
 						 struct txprepare *txp,
 						 const char *feerate,
 						 unsigned int *minconf,
-						 const char *utxos,
+						 struct bitcoin_outpoint *utxos,
 						 bool is_withdraw)
 {
 	struct out_req *req;
@@ -341,7 +341,11 @@ static struct command_result *txprepare_continue(struct command *cmd,
 		req = jsonrpc_request_start(cmd->plugin, cmd, "utxopsbt",
 					    psbt_created, forward_error,
 					    txp);
-		json_add_jsonstr(req->js, "utxos", utxos);
+		json_array_start(req->js, "utxos");
+		for (size_t i = 0; i < tal_count(utxos); i++) {
+			json_add_outpoint(req->js, NULL, &utxos[i]);
+		}
+		json_array_end(req->js);
 	} else {
 		req = jsonrpc_request_start(cmd->plugin, cmd, "fundpsbt",
 					    psbt_created, forward_error,
@@ -365,14 +369,15 @@ static struct command_result *json_txprepare(struct command *cmd,
 					     const jsmntok_t *params)
 {
 	struct txprepare *txp = tal(cmd, struct txprepare);
-	const char *feerate, *utxos;
+	const char *feerate;
+	struct bitcoin_outpoint *utxos;
 	unsigned int *minconf;
 
 	if (!param(cmd, buffer, params,
 		   p_req("outputs", param_outputs, txp),
 		   p_opt("feerate", param_string, &feerate),
 		   p_opt_def("minconf", param_number, &minconf, 1),
-		   p_opt("utxos", param_string, &utxos),
+		   p_opt("utxos", param_outpoint_arr, &utxos),
 		   NULL))
 		return command_param_failed();
 
@@ -472,7 +477,8 @@ static struct command_result *json_withdraw(struct command *cmd,
 	struct txprepare *txp = tal(cmd, struct txprepare);
 	struct amount_sat *amount;
 	const u8 *scriptpubkey;
-	const char *feerate, *utxos;
+	const char *feerate;
+	struct bitcoin_outpoint *utxos;
 	unsigned int *minconf;
 
 	if (!param(cmd, buffer, params,
@@ -481,7 +487,7 @@ static struct command_result *json_withdraw(struct command *cmd,
 		   p_req("satoshi", param_sat_or_all, &amount),
 		   p_opt("feerate", param_string, &feerate),
 		   p_opt_def("minconf", param_number, &minconf, 1),
-		   p_opt("utxos", param_string, &utxos),
+		   p_opt("utxos", param_outpoint_arr, &utxos),
 		   NULL))
 		return command_param_failed();