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Add encoding of nil values in tables and of empty maps #2

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Add encoding of nil values in tables and of empty maps #2

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110 changes: 64 additions & 46 deletions msgpack.lua
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Original file line number Diff line number Diff line change
Expand Up @@ -43,15 +43,58 @@ local type, pcall, pairs, select = type, pcall, pairs, select
--]]----------------------------------------------------------------------------
local encode_value -- forward declaration

local NIL = {} -- unique object to represent nil

local EMPTY_MAP = {} -- unique object to represent an empty map

local function get_type(value)
if value == NIL then return 'nil' end
if value == EMPTY_MAP then return 'map' end
return type(value)
end

local function is_an_array(value)
local expected = 1
for k in pairs(value) do
if k ~= expected then
return false
end
expected = expected + 1
end
return true
local expected = 1
for k in pairs(value) do
if k ~= expected then
return false
end
expected = expected + 1
end
return true
end

local function encode_array(value)
local elements = {}
for i, v in pairs(value) do
elements[i] = encode_value(v)
end

local length = #elements
if length < 16 then
return pack('>B', 0x90 + length) .. tconcat(elements)
elseif length < 65536 then
return pack('>BI2', 0xdc, length) .. tconcat(elements)
else
return pack('>BI4', 0xdd, length) .. tconcat(elements)
end
end

local function encode_map(value)
local elements = {}
for k, v in pairs(value) do
elements[#elements + 1] = encode_value(k)
elements[#elements + 1] = encode_value(v)
end

local length = #elements // 2
if length < 16 then
return pack('>B', 0x80 + length) .. tconcat(elements)
elseif length < 65536 then
return pack('>BI2', 0xde, length) .. tconcat(elements)
else
return pack('>BI4', 0xdf, length) .. tconcat(elements)
end
end

local encoder_functions = {
Expand Down Expand Up @@ -125,51 +168,20 @@ local encoder_functions = {
end,
['table'] = function(value)
if is_an_array(value) then -- it seems to be a proper Lua array
local elements = {}
for i, v in pairs(value) do
elements[i] = encode_value(v)
end

local length = #elements
if length < 16 then
return pack('>B', 0x90 + length) .. tconcat(elements)
elseif length < 65536 then
return pack('>BI2', 0xdc, length) .. tconcat(elements)
else
return pack('>BI4', 0xdd, length) .. tconcat(elements)
end
return encode_array(value)
else -- encode as a map
local elements = {}
for k, v in pairs(value) do
elements[#elements + 1] = encode_value(k)
elements[#elements + 1] = encode_value(v)
end

local length = #elements // 2
if length < 16 then
return pack('>B', 0x80 + length) .. tconcat(elements)
elseif length < 65536 then
return pack('>BI2', 0xde, length) .. tconcat(elements)
else
return pack('>BI4', 0xdf, length) .. tconcat(elements)
end
end
return encode_map(value)
end
end,
['map'] = function(value)
return encode_map(value)
end,
}

encode_value = function(value)
return encoder_functions[type(value)](value)
return encoder_functions[get_type(value)](value)
end

local function encode(...)
local data = {}
for i = 1, select('#', ...) do
data[#data + 1] = encode_value(select(i, ...))
end
return tconcat(data)
end


--[[----------------------------------------------------------------------------

Decoder
Expand Down Expand Up @@ -368,6 +380,12 @@ return {
return nil, 'cannot decode MessagePack'
end
end,

--- an object that is packed as a nil value
NIL = NIL,

--- an object that is packed as an empty map
EMPTY_MAP = EMPTY_MAP
}

--[[----------------------------------------------------------------------------
Expand Down