Don't fail if there is no journal to recover

src/lib/autoload/a_07_transaction.lua

 --[[
-Copyright 2016, CZ.NIC z.s.p.o. (http://www.nic.cz/)
+Copyright 2016-2017, CZ.NIC z.s.p.o. (http://www.nic.cz/)
 
 This file is part of the turris updater.
 
@@ -39,6 +39,7 @@ local utils = require "utils"
 local journal = require "journal"
 local DBG = DBG
 local WARN = WARN
+local INFO = INFO
 local state_dump = state_dump
 local sync = sync
 local log_event = log_event
@@ -349,6 +350,10 @@ end
 function recover()
 	local run_state = backend.run_state()
 	local previous = journal.recover()
+	if not previous then
+		INFO("No journal to recover");
+		return {}
+	end
 	local status = {}
 	for _, value in ipairs(previous) do
 		assert(not status[value.type])

src/lib/journal.c

 /*
- * Copyright 2016, CZ.NIC z.s.p.o. (http://www.nic.cz/)
+ * Copyright 2016-2017, CZ.NIC z.s.p.o. (http://www.nic.cz/)
  *
  * This file is part of the turris updater.
  *
@@ -119,7 +119,7 @@ static void journal_write(enum record_type type, size_t num_params, const size_t
 	ASSERT_MSG(!error, "Failed to write journal: %s", strerror(errno));
 }
 
-static void journal_open(lua_State *L, int flags) {
+static bool journal_open(lua_State *L, int flags) {
 	DBG("Opening journal");
 	if (fd != -1)
 		luaL_error(L, "Journal already open");
@@ -133,7 +133,7 @@ static void journal_open(lua_State *L, int flags) {
 				luaL_error(L, "Unfinished journal exists");
 			case ENOENT:
 				if (!(flags & O_CREAT))
-					luaL_error(L, "No journal to recover");
+					return false;
 				// Otherwise ‒ fall through to the default section
 			default:
 				luaL_error(L, "Error opening journal: %s", strerror(errno));
@@ -142,6 +142,7 @@ static void journal_open(lua_State *L, int flags) {
 	ASSERT_MSG(fcntl(fd, F_SETFD, (long)FD_CLOEXEC) != -1, "Failed to set close on exec on journal FD: %s", strerror(errno));
 	// Keep a copy of the journal path, someone might change it and we want to remove the correct journal on finish
 	journal_path = strdup(path);
+	return true;
 }
 
 static int lua_fresh(lua_State *L) {
@@ -255,7 +256,8 @@ FAIL:
 }
 
 static int lua_recover(lua_State *L) {
-	journal_open(L, 0);
+	if (!journal_open(L, 0))
+		return 0;
 	lua_newtable(L);
 	size_t i = 0;
 	off_t offset = 0;

src/lib/lua_funcs.txt

@@ -190,7 +190,7 @@ There are following functions:
   fresh():: Open a new journal. It fails if there's a journal file
     already.
   recover():: Open a previous journal. It returns table with the
-    content of the journal. It fails in case there's no journal.
+    content of the journal. If there is no journal nil is returned.
   finish([keep]):: Close the journal. If the keep is set to true,
     it keeps the journal in place, otherwise it is deleted. The idea
     is that the application would close the journal when it succeeds,

tests/journal.lua

 --[[
-Copyright 2016, CZ.NIC z.s.p.o. (http://www.nic.cz/)
+Copyright 2016-2017, CZ.NIC z.s.p.o. (http://www.nic.cz/)
 
 This file is part of the turris updater.
 
@@ -79,7 +79,7 @@ function test_recover_empty()
 	local dir = dir_init()
 	assert_table_equal({}, ls(dir))
 	-- Nothing to recover
-	assert_error(function () J.recover() end)
+	assert_nil(J.recover())
 	J.fresh()
 	-- Keep the journal file
 	J.finish(true)