db: avoid the only failing db_exec.

Replace with an explicit test for existence.  This simplifies our db interface.

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

wallet/db.c

@@ -496,21 +496,6 @@ static void PRINTF_FMT(3, 4)
 	tal_free(cmd);
 }
 
-bool db_exec_prepared_mayfail_(const char *caller UNUSED, struct db *db, sqlite3_stmt *stmt)
-{
-	assert(db->in_transaction);
-
-	if (sqlite3_step(stmt) != SQLITE_DONE) {
-		goto fail;
-	}
-
-	db_stmt_done(stmt);
-	return true;
-fail:
-	db_stmt_done(stmt);
-	return false;
-}
-
 sqlite3_stmt *PRINTF_FMT(3, 4)
     db_query_(const char *location, struct db *db, const char *fmt, ...)
 {

wallet/db.h

@@ -109,15 +109,6 @@ sqlite3_stmt *db_prepare_(const char *location, struct db *db, const char *query
 #define db_exec_prepared(db,stmt) db_exec_prepared_(__func__,db,stmt)
 void db_exec_prepared_(const char *caller, struct db *db, sqlite3_stmt *stmt);
 
-/**
- * db_exec_prepared_mayfail - db_exec_prepared, but don't fatal() it fails.
- */
-#define db_exec_prepared_mayfail(db,stmt) \
-	db_exec_prepared_mayfail_(__func__,db,stmt)
-bool db_exec_prepared_mayfail_(const char *caller,
-			       struct db *db,
-			       sqlite3_stmt *stmt);
-
 /* Wrapper around sqlite3_finalize(), for tracking statements. */
 void db_stmt_done(sqlite3_stmt *stmt);
 

wallet/wallet.c

@@ -67,12 +67,24 @@ struct wallet *wallet_new(struct lightningd *ld,
 	"channel_id, peer_id, commitment_point, confirmation_height, "	\
 	"spend_height, scriptpubkey"
 
-/* We actually use the db constraints to uniquify, so OK if this fails. */
+/* This can fail if we've already seen UTXO. */
 bool wallet_add_utxo(struct wallet *w, struct utxo *utxo,
 		     enum wallet_output_type type)
 {
 	sqlite3_stmt *stmt;
 
+	stmt = db_prepare(w->db,
+			  "SELECT * from outputs WHERE prev_out_tx=? AND prev_out_index=?");
+	sqlite3_bind_blob(stmt, 1, &utxo->txid, sizeof(utxo->txid), SQLITE_TRANSIENT);
+	sqlite3_bind_int(stmt, 2, utxo->outnum);
+
+	/* If we get a result, that means a clash. */
+	if (sqlite3_step(stmt) == SQLITE_ROW) {
+		db_stmt_done(stmt);
+		return false;
+	}
+	db_stmt_done(stmt);
+
 	stmt = db_prepare(w->db, "INSERT INTO outputs ("
 			  UTXO_FIELDS
 			  ") VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?);");
@@ -109,9 +121,8 @@ bool wallet_add_utxo(struct wallet *w, struct utxo *utxo,
 	else
 		sqlite3_bind_null(stmt, 12);
 
-	/* May fail if we already know about the tx, e.g., because
-	 * it's change or some internal tx. */
-	return db_exec_prepared_mayfail(w->db, stmt);
+	db_exec_prepared(w->db, stmt);
+	return true;
 }
 
 /**