stable table keys iteration order by tools.sortedpairs helper

mqtt/protocol.lua

@@ -56,6 +56,7 @@ local rshift = bit.rshift
 
 local tools = require("mqtt.tools")
 local div = tools.div
+local sortedpairs = tools.sortedpairs
 
 --- Create bytes of the uint8 value
 -- @tparam number val - integer value to convert to bytes
@@ -489,7 +490,7 @@ local function value_tostring(value)
 		return str_format("%q", value)
 	elseif t == "table" then
 		local res = {}
-		for k, v in pairs(value) do
+		for k, v in sortedpairs(value) do
 			if type(k) == "number" then
 				res[#res + 1] = value_tostring(v)
 			else
@@ -511,7 +512,7 @@ end
 -- @treturn string human-readable string representation of the packet
 function protocol.packet_tostring(packet)
 	local res = {}
-	for k, v in pairs(packet) do
+	for k, v in sortedpairs(packet) do
 		res[#res + 1] = str_format("%s=%s", k, value_tostring(v))
 	end
 	return str_format("%s{%s}", tostring(packet_type[packet.type]), tbl_concat(res, ", "))

mqtt/protocol5.lua

@@ -26,6 +26,9 @@ local string = require("string")
 local str_char = string.char
 local fmt = string.format
 
+local tools = require("mqtt.tools")
+local sortedpairs = tools.sortedpairs
+
 local bit = require("mqtt.bitwrap")
 local bor = bit.bor
 local band = bit.band
@@ -321,7 +324,7 @@ local function make_properties(ptype, args)
 		assert(type(args.properties) == "table", "expecting .properties to be a table")
 		-- validate all properties and append them to order list
 		local order = {}
-		for name, value in pairs(args.properties) do
+		for name, value in sortedpairs(args.properties) do
 			assert(type(name) == "string", "expecting property name to be a string: "..tostring(name))
 			-- detect property identifier and check it's allowed for that packet type
 			local prop_id = assert(properties[name], "unknown property: "..tostring(name))
@@ -360,7 +363,7 @@ local function make_properties(ptype, args)
 		assert(type(args.user_properties) == "table", "expecting .user_properties to be a table")
 		assert(allowed[uprop_id], "user_property is not allowed for packet type "..ptype)
 		local order = {}
-		for name, val in pairs(args.user_properties) do
+		for name, val in sortedpairs(args.user_properties) do
 			local ntype = type(name)
 			if ntype == "string" then
 				if type(val) ~= "string" then

mqtt/tools.lua

@@ -10,6 +10,11 @@ local str_byte = string.byte
 
 local table = require("table")
 local tbl_concat = table.concat
+local tbl_sort = table.sort
+
+local type = type
+local error = error
+local pairs = pairs
 
 local math = require("math")
 local math_floor = math.floor
@@ -29,6 +34,42 @@ function tools.div(x, y)
 	return math_floor(x / y)
 end
 
+-- table.sort callback for tools.sortedpairs()
+local function sortedpairs_compare(a, b)
+	local a_type = type(a)
+	local b_type = type(b)
+	if (a_type == "string" and b_type == "string") or (a_type == "number" and b_type == "number") then
+		return a < b
+	elseif a_type == "number" then
+		return true
+	elseif b_type == "number" then
+		return false
+	else
+		error("sortedpairs failed to make a stable keys comparison of types "..a_type.." and "..b_type)
+	end
+end
+
+-- Iterate through table keys and values in stable (sorted) order
+function tools.sortedpairs(tbl)
+	local keys = {}
+	for k in pairs(tbl) do
+		local k_type = type(k)
+		if k_type ~= "string" and k_type ~= "number" then
+			error("sortedpairs failed to make a stable iteration order for key of type "..type(k))
+		end
+		keys[#keys + 1] = k
+	end
+	tbl_sort(keys, sortedpairs_compare)
+	local i = 0
+	return function()
+		i = i + 1
+		local key = keys[i]
+		if key then
+			return key, tbl[key]
+		end
+	end
+end
+
 -- export module table
 return tools
 

tests/spec/module-basics.lua

@@ -34,6 +34,29 @@ describe("MQTT lua library component test:", function()
 		assert.are.equal("FF00FF", tools.hex("\255\000\255"))
 	end)
 
+	it("tools.sortedpairs", function()
+		assert.are.equal(type(tools.sortedpairs), "function")
+
+		-- naive table-to-string implementation with stable table key iteration order
+		local function tbl_tostring(tbl)
+			local res = {"{"}
+			for k, v in tools.sortedpairs(tbl) do
+				res[#res + 1] = string.format("%s=%s,", k, v)
+			end
+			res[#res + 1] = "}"
+			return table.concat(res)
+		end
+
+		assert.are.equal("{}", tbl_tostring{})
+		assert.are.equal('{a=1,}', tbl_tostring{a=1,})
+		assert.are.equal('{a=1,b=2,}', tbl_tostring{b=2,a=1,})
+		assert.are.equal('{a=1,b=2,}', tbl_tostring{b=2,a=1,})
+		assert.are.equal('{1=1,2=2,3=3,}', tbl_tostring{1,2,3,})
+		assert.are.equal('{1=1,2=2,3=3,}', tbl_tostring{[3]=3,[2]=2,[1]=1,})
+		assert.are.equal('{1=1,a=1,}', tbl_tostring{1,a=1,})
+		assert.are.equal('{1=1,2=2,3=3,a=1,b=2,}', tbl_tostring{b=2,a=1,[3]=3,[2]=2,[1]=1,})
+	end)
+
 	it("extract_hex", function()
 		assert.are.equal("", extract_hex(""))
 		assert.are.equal("", extract_hex(" "))