luci-base: improve string format error reporting

In mod metamethod, execute string format under pcall() and rethrow error in
caller context to report caller of function in errors and not the meta
method itself.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 16 insertions, 3 deletions

diff --git a/modules/luci-base/luasrc/util.lua b/modules/luci-base/luasrc/util.lua
index 896e36b45f..0e7334be87 100644
--- a/modules/luci-base/luasrc/util.lua
+++ b/modules/luci-base/luasrc/util.lua
@@ -16,7 +16,7 @@ local _ubus_connection = nil
 
 local getmetatable, setmetatable = getmetatable, setmetatable
 local rawget, rawset, unpack = rawget, rawset, unpack
-local tostring, type, assert = tostring, type, assert
+local tostring, type, assert, error = tostring, type, assert, error
 local ipairs, pairs, next, loadstring = ipairs, pairs, next, loadstring
 local require, pcall, xpcall = require, pcall, xpcall
 local collectgarbage, get_memory_limit = collectgarbage, get_memory_limit
@@ -27,14 +27,27 @@ module "luci.util"
 -- Pythonic string formatting extension
 --
 getmetatable("").__mod = function(a, b)
+	local ok, res
+
 	if not b then
 		return a
 	elseif type(b) == "table" then
+		local k, _
 		for k, _ in pairs(b) do if type(b[k]) == "userdata" then b[k] = tostring(b[k]) end end
-		return a:format(unpack(b))
+
+		ok, res = pcall(a.format, a, unpack(b))
+		if not ok then
+			error(res, 2)
+		end
+		return res
 	else
 		if type(b) == "userdata" then b = tostring(b) end
-		return a:format(b)
+
+		ok, res = pcall(a.format, a, b)
+		if not ok then
+			error(res, 2)
+		end
+		return res
 	end
 end