wallet: Change db_select_prepare to check for select instead

`db_select_prepare` was prepending the "SELECT" part in an attempt to limit
its use to read-only statements. This is leads to the queries in the code not
actually being well-formed, which we'll need in a later commit, and was also
resulting in extra allocations. This switches the behavior to just enforce a
"SELECT" prefix being present which allows us to have well-formed queries in
the code again and avoids the extra allocation.

Signed-off-by: Christian Decker <[email protected]>

wallet/db.c

@@ -479,17 +479,18 @@ sqlite3_stmt *db_select_prepare_(const char *location, struct db *db, const char
 {
 	int err;
 	sqlite3_stmt *stmt;
-	const char *full_query = tal_fmt(db, "SELECT %s", query);
 
+	/* Since these queries will be treated as read-only they need to start
+	 * with "SELECT" and have no side-effects. */
+	assert(strncmp(query, "SELECT", 6) == 0);
 	assert(db->in_transaction);
 
-	err = sqlite3_prepare_v2(db->sql, full_query, -1, &stmt, NULL);
+	err = sqlite3_prepare_v2(db->sql, query, -1, &stmt, NULL);
 
 	if (err != SQLITE_OK)
-		db_fatal("%s: %s: %s", location, full_query, sqlite3_errmsg(db->sql));
+		db_fatal("%s: %s: %s", location, query, sqlite3_errmsg(db->sql));
 
 	dev_statement_start(stmt, location);
-	tal_free(full_query);
 	return stmt;
 }
 

wallet/invoices.c

@@ -179,7 +179,7 @@ static void trigger_expiration(struct invoices *invoices)
 	/* Acquire all expired invoices and save them in a list */
 	list_head_init(&idlist);
 	stmt = db_select_prepare(invoices->db,
-				 "id"
+				 "SELECT id"
 				 "  FROM invoices"
 				 " WHERE state = ?"
 				 "   AND expiry_time <= ?;");
@@ -218,7 +218,7 @@ static void install_expiration_timer(struct invoices *invoices)
 
 	/* Find unpaid invoice with nearest expiry time */
 	stmt = db_select_prepare(invoices->db,
-				 "MIN(expiry_time)"
+				 "SELECT MIN(expiry_time)"
 				 "  FROM invoices"
 				 " WHERE state = ?;");
 	sqlite3_bind_int(stmt, 1, UNPAID);
@@ -330,7 +330,7 @@ bool invoices_find_by_label(struct invoices *invoices,
 	sqlite3_stmt *stmt;
 
 	stmt = db_select_prepare(invoices->db,
-				 "id"
+				 "SELECT id"
 				 "  FROM invoices"
 				 " WHERE label = ?;");
 	sqlite3_bind_json_escape(stmt, 1, label);
@@ -349,7 +349,7 @@ bool invoices_find_by_rhash(struct invoices *invoices,
 	sqlite3_stmt *stmt;
 
 	stmt = db_select_prepare(invoices->db,
-				 "id"
+				 "SELECT id"
 				 "  FROM invoices"
 				 " WHERE payment_hash = ?;");
 	sqlite3_bind_blob(stmt, 1, rhash, sizeof(*rhash), SQLITE_TRANSIENT);
@@ -368,7 +368,7 @@ bool invoices_find_unpaid(struct invoices *invoices,
 	sqlite3_stmt *stmt;
 
 	stmt = db_select_prepare(invoices->db,
-				 " id"
+				 "SELECT id"
 				 "  FROM invoices"
 				 " WHERE payment_hash = ?"
 				 "   AND state = ?;");
@@ -421,6 +421,7 @@ bool invoices_iterate(struct invoices *invoices,
 
 	if (!it->p) {
 		stmt = db_select_prepare(invoices->db,
+					 "SELECT"
 					 "  state"
 					 ", payment_key"
 					 ", payment_hash"
@@ -470,7 +471,7 @@ static enum invoice_status invoice_get_status(struct invoices *invoices, struct
 	bool res;
 
 	stmt = db_select_prepare(invoices->db,
-				 "state FROM invoices WHERE id = ?;");
+				 "SELECT state FROM invoices WHERE id = ?;");
 	sqlite3_bind_int64(stmt, 1, invoice.id);
 	res = db_select_step(invoices->db, stmt);
 	assert(res);
@@ -552,7 +553,7 @@ void invoices_waitany(const tal_t *ctx,
 
 	/* Look for an already-paid invoice. */
 	stmt = db_select_prepare(invoices->db,
-				 "id"
+				 "SELECT id"
 				 "  FROM invoices"
 				 " WHERE pay_index NOT NULL"
 				 "   AND pay_index > ?"
@@ -602,6 +603,7 @@ const struct invoice_details *invoices_get_details(const tal_t *ctx,
 	struct invoice_details *details;
 
 	stmt = db_select_prepare(invoices->db,
+				 "SELECT"
 				 "  state"
 				 ", payment_key"
 				 ", payment_hash"