reserveinputs: add exclusive flag.

This is the normal case: you only want to reserve inputs which
are not already reserved.  This saves you iterating through the
results and unreserving some if you weren't exclusive.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

doc/lightning-reserveinputs.7

@@ -3,7 +3,7 @@
 lightning-reserveinputs - Construct a transaction and reserve the UTXOs it spends
 .SH SYNOPSIS
 
-\fBreserveinputs\fR \fIpsbt\fR
+\fBreserveinputs\fR \fIpsbt\fR [\fIexclusive\fR]
 
 .SH DESCRIPTION
 
@@ -11,6 +11,11 @@ The \fBreserveinputs\fR RPC command places (or increases) reservations on any
 inputs specified in \fIpsbt\fR which are known to lightningd\.  It will fail
 with an error it any of the inputs are known to be spent\.
 
+
+Normally the command will fail (with no reservations made) if an input
+is already reserved\.  If \fIexclusive\fR is set to \fIFalse\fR, then existing
+reservations are simply extended, rather than causing failure\.
+
 .SH RETURN VALUE
 
 On success, an \fIreservations\fR array is returned, with an entry for each input
@@ -37,7 +42,7 @@ The following error codes may occur:
 
 .RS
 .IP \[bu]
--32602: Invalid parameter, such as specifying a spent input in \fIpsbt\fR\.
+-32602: Invalid parameter, such as specifying a spent/reserved input in \fIpsbt\fR\.
 
 .RE
 .SH AUTHOR

doc/lightning-reserveinputs.7.md

@@ -4,7 +4,7 @@ lightning-reserveinputs -- Construct a transaction and reserve the UTXOs it spen
 SYNOPSIS
 --------
 
-**reserveinputs** *psbt*
+**reserveinputs** *psbt* [*exclusive*]
 
 DESCRIPTION
 -----------
@@ -13,6 +13,10 @@ The **reserveinputs** RPC command places (or increases) reservations on any
 inputs specified in *psbt* which are known to lightningd.  It will fail
 with an error it any of the inputs are known to be spent.
 
+Normally the command will fail (with no reservations made) if an input
+is already reserved.  If *exclusive* is set to *False*, then existing
+reservations are simply extended, rather than causing failure.
+
 
 RETURN VALUE
 ------------
@@ -29,7 +33,7 @@ which was reserved:
 On failure, an error is reported and no UTXOs are reserved.
 
 The following error codes may occur:
-- -32602: Invalid parameter, such as specifying a spent input in *psbt*.
+- -32602: Invalid parameter, such as specifying a spent/reserved input in *psbt*.
 
 AUTHOR
 ------

wallet/reservation.c

@@ -44,12 +44,16 @@ static struct command_result *json_reserveinputs(struct command *cmd,
 	struct json_stream *response;
 	struct wally_psbt *psbt;
 	struct utxo **utxos = tal_arr(cmd, struct utxo *, 0);
+	bool *exclusive;
+	u32 current_height;
 
 	if (!param(cmd, buffer, params,
 		   p_req("psbt", param_psbt, &psbt),
+		   p_opt_def("exclusive", param_bool, &exclusive, true),
 		   NULL))
 		return command_param_failed();
 
+	current_height = get_block_height(cmd->ld->topology);
 	for (size_t i = 0; i < psbt->tx->num_inputs; i++) {
 		struct bitcoin_txid txid;
 		struct utxo *utxo;
@@ -59,6 +63,14 @@ static struct command_result *json_reserveinputs(struct command *cmd,
 				       &txid, psbt->tx->inputs[i].index);
 		if (!utxo)
 			continue;
+		if (*exclusive && is_reserved(utxo, current_height)) {
+			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+					    "%s:%u already reserved",
+					    type_to_string(tmpctx,
+							   struct bitcoin_txid,
+							   &utxo->txid),
+					    utxo->outnum);
+		}
 		if (utxo->status == output_state_spent)
 			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 					    "%s:%u already spent",
@@ -80,7 +92,7 @@ static struct command_result *json_reserveinputs(struct command *cmd,
 
 		if (!wallet_reserve_utxo(cmd->ld->wallet,
 					 utxos[i],
-					 get_block_height(cmd->ld->topology))) {
+					 current_height)) {
 			fatal("Unable to reserve %s:%u!",
 			      type_to_string(tmpctx,
 					     struct bitcoin_txid,
@@ -88,7 +100,7 @@ static struct command_result *json_reserveinputs(struct command *cmd,
 			      utxos[i]->outnum);
 		}
 		json_add_reservestatus(response, utxos[i], oldstatus, old_res,
-				       get_block_height(cmd->ld->topology));
+				       current_height);
 	}
 	json_array_end(response);
 	return command_success(cmd, response);