lovr-msgpack

lua-mp - Yet another msgpack implement for Lua

Lua-mp is a simple C module for Lua to manipulate msgpack encoding/decoding.

Install

The simplest way to install it is using Luarocks:

luarocks install --server=https://luarocks.org/dev lua-mp

Or, just compile the single C file:

# Linux
gcc -o mp.so -O3 -fPIC -shared mp.c
# macOS
gcc -o mp.so -O3 -fPIC -shared -undefined dynamic_lookup mp.c
# Windows
cl /Fe mp.dll /LD /MT /O2 /DLUA_BUILD_AS_DLL /Ipath/to/lua/include mp.c path/to/lua/lib

Example

local mp = require "mp"
local serpent = require "serpent" -- just for print table

local bytes = mp.encode {
  name = "alice",
  phone_list = { "1311234", "1310024" }
}
print(mp.tohex(bytes))

local t = mp.decode(bytes)
print(serpent.block(t))

## Document

Routine	Returns	Description
decode(string[, i[, j[, ext_handler]]])	object, pos	decode a msgpack string into object, returns the decoded object and unread position
encode(...)	string	Accept any values and create a msgpack encoding string
null	-	the null object can be used in array/map
array(...)	...	mark all it's arguments to array
map(...)	...	mark all it's arguments to map
meta(type, ...)	...	mark all it's arguments to type
tohex(string)	string	convert a binary string into hexadigit mode for human reading
fromhex(string)	string	convert hexadigit back into binary string

Decoding mapping

Msgpack Type	Lua Type
null	nil
true, false	boolean
int, uint, float32, float64	number
bin, string	string
ext	{ type = number, value = string }

decode() accepts a string, and optional two pos i and j (based on 1), and a optionl env_handler function for arguments. if there is ext type in msgpack string, the ext_handler will be called with type and value and returns a object for use. if the handler returns nothing, the default type/value table will be used.

It returns the decoded object, and if there is any remain bytes in string, returns the current reading position for next reading. So you can iterate all object in a string using a loop:

local pos = 1
local values = {}
while pos do
  values[#values+1], pos = mp.decode(data, pos)
end

Encoding Mapping

Lua Type	Msgpack Type
nil	null
boolean	true, false
number	int, float32, float64
string	string
function	A handler function returns the actually values to encode
table	array or map or any other (using meta types)

Meta types

meta type is a table, that has a metatable, which has a field "msgpack.type" with below values:

"msgpack.type"	"Description"
"null"	encode a null
"True", "False"	encode a true or false
"int", "uint", "float", "double"	reads the value field of table, and encode a number value
"string", "binary"	same as above, but encoding a string or binary value
"value"	same as above, but encode using the Lua type of value field
"handler"	reads the pack field as a function, call with table itself, and returns the actually values to encode
"array"	treat table as a array
"map"	treat table as a map
"extension"	reads the type and value fields in table and encode a ext value

meta value can get by mp.meta() or mp.array(), mp.map() routines:

-- get a meta value of uint:
local uint = mp.meta("uint", 123)
-- get a array:
local array = mp.array { 1,2,3,4 }
-- set all tables to map:
mp.map(map1, map2, map3)

Handler function

A handler should first returns a "msgpack.type" string, and if needed, return the actual value to be encoded. for "entension" type, handler should returns both type and value:

local function handler_to_get_a_uint() return "uint", 123 end
local function handler_to_get_a_ext() return "extension", 1, "foo" end
local function handler_to_get_a_true() return "True" end
local function handler_to_another_handler() return "handler", { pack = handler } end