From 50ff0b26fd48e0b495990ac55a2b72d1735873d9 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Wed, 15 Jul 2020 05:00:26 +0930
Subject: [PATCH] wallet: explicit routines to reserve/unreserve a UTXO.

These keep the struct utxo in sync with the database, explicitly:
these will be the only places where utxo->status is set.

The old routines will be removed at the end.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 wallet/wallet.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++
 wallet/wallet.h | 17 ++++++++++
 2 files changed, 101 insertions(+)

diff --git a/wallet/wallet.c b/wallet/wallet.c
index 1dfce9445..3f096e7c0 100644
--- a/wallet/wallet.c
+++ b/wallet/wallet.c
@@ -28,6 +28,9 @@
  * to prune? */
 #define UTXO_PRUNE_DEPTH 144
 
+/* 12 hours is usually enough reservation time */
+#define RESERVATION_INC (6 * 12)
+
 static void outpointfilters_init(struct wallet *w)
 {
 	struct db_stmt *stmt;
@@ -418,6 +421,87 @@ void wallet_confirm_utxos(struct wallet *w, const struct utxo **utxos)
 	}
 }
 
+static void db_set_utxo(struct db *db, const struct utxo *utxo)
+{
+	struct db_stmt *stmt;
+
+	if (utxo->status == output_state_reserved)
+		assert(utxo->reserved_til);
+	else
+		assert(!utxo->reserved_til);
+
+	stmt = db_prepare_v2(
+		db, SQL("UPDATE outputs SET status=?, reserved_til=?"
+			"WHERE prev_out_tx=? AND prev_out_index=?"));
+	db_bind_int(stmt, 0, output_status_in_db(utxo->status));
+	if (utxo->reserved_til)
+		db_bind_int(stmt, 1, *utxo->reserved_til);
+	else
+		db_bind_null(stmt, 1);
+	db_bind_txid(stmt, 2, &utxo->txid);
+	db_bind_int(stmt, 3, utxo->outnum);
+	db_exec_prepared_v2(take(stmt));
+}
+
+bool wallet_reserve_utxo(struct wallet *w, struct utxo *utxo, u32 current_height)
+{
+	u32 reservation_height;
+
+	if (utxo->status == output_state_reserved)
+		assert(utxo->reserved_til);
+	else
+		assert(!utxo->reserved_til);
+
+	switch (utxo->status) {
+	case output_state_spent:
+		return false;
+	case output_state_available:
+	case output_state_reserved:
+		break;
+	case output_state_any:
+		abort();
+	}
+
+	/* We simple increase existing reservations, which DTRT if we unreserve */
+	if (utxo->reserved_til
+	    && *utxo->reserved_til >= current_height)
+		reservation_height = *utxo->reserved_til + RESERVATION_INC;
+	else
+		reservation_height = current_height + RESERVATION_INC;
+
+	utxo->status = output_state_reserved;
+	tal_free(utxo->reserved_til);
+	utxo->reserved_til = tal_dup(utxo, u32, &reservation_height);
+
+	db_set_utxo(w->db, utxo);
+
+	return true;
+}
+
+void wallet_unreserve_utxo(struct wallet *w, struct utxo *utxo, u32 current_height)
+{
+	if (utxo->status == output_state_reserved) {
+		/* FIXME: old code didn't set reserved_til, so fake it here */
+		if (!utxo->reserved_til)
+			utxo->reserved_til = tal_dup(utxo, u32, &current_height);
+		assert(utxo->reserved_til);
+	} else
+		assert(!utxo->reserved_til);
+
+	if (utxo->status != output_state_reserved)
+		fatal("UTXO %s:%u is not reserved",
+		      type_to_string(tmpctx, struct bitcoin_txid, &utxo->txid),
+		      utxo->outnum);
+
+	if (*utxo->reserved_til <= current_height + RESERVATION_INC) {
+		utxo->status = output_state_available;
+		utxo->reserved_til = tal_free(utxo->reserved_til);
+	} else
+		*utxo->reserved_til -= RESERVATION_INC;
+
+	db_set_utxo(w->db, utxo);
+}
+
 bool wallet_add_onchaind_utxo(struct wallet *w,
 			      const struct bitcoin_txid *txid,
 			      u32 outnum,
diff --git a/wallet/wallet.h b/wallet/wallet.h
index 19ef4fe58..34e76989c 100644
--- a/wallet/wallet.h
+++ b/wallet/wallet.h
@@ -392,6 +392,23 @@ bool wallet_add_onchaind_utxo(struct wallet *w,
 			      /* NULL if option_static_remotekey */
 			      const struct pubkey *commitment_point);
 
+/**
+ * wallet_reserve_utxo - set a reservation on a UTXO.
+ *
+ * If the reservation is already reserved, refreshes the reservation,
+ * otherwise if it's not available, returns false.
+ */
+bool wallet_reserve_utxo(struct wallet *w,
+			 struct utxo *utxo,
+			 u32 reservation_blocknum);
+
+/* wallet_unreserve_utxo - make a reserved UTXO available again.
+ *
+ * Must be reserved.
+ */
+void wallet_unreserve_utxo(struct wallet *w, struct utxo *utxo,
+			   u32 current_height);
+
 /** wallet_utxo_get - Retrive a utxo.
  *
  * Returns a utxo, or NULL if not found.