Модуль msgpack


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Модуль msgpack

Общие сведения

The msgpack module takes strings in MsgPack format and decodes them, or takes a series of non-MsgPack values and encodes them. Tarantool makes heavy internal use of MsgPack because tuples in Tarantool are stored as MsgPack arrays.


Below is a list of all msgpack functions and members.

Name Use
msgpack.encode() Convert a Lua object to an MsgPack string
msgpack.decode() Convert an MsgPack string to a Lua object
msgpack.NULL Analog of Lua’s «nil»

Convert a Lua object to a MsgPack string.

  • lua_value – either a scalar value or a Lua table value.

the original value reformatted as a MsgPack string.




Convert a MsgPack string to a Lua object.

  • string – a string formatted as MsgPack.
  • the original contents formatted as a Lua table;
  • the number of bytes that were decoded.
Rtype:lua object

A value comparable to Lua «nil» which may be useful as a placeholder in a tuple.


tarantool> msgpack = require('msgpack')
tarantool> y = msgpack.encode({'a',1,'b',2})
tarantool> z = msgpack.decode(y)
tarantool> z[1], z[2], z[3], z[4]
- a
- 1
- b
- 2
tarantool> box.space.tester:insert{20, msgpack.NULL, 20}
- [20, null, 20]

The MsgPack output structure can be specified with __serialize:

  • __serialize = "seq" or "sequence" for an array
  • __serialize = "map" or "mapping" for a map

Serializing „A“ and „B“ with different __serialize values causes different results. To show this, here is a routine which encodes {„A“,“B“} both as an array and as a map, then displays each result in hexadecimal.

function hexdump(bytes)
    local result = ''
    for i = 1, #bytes do
        result = result .. string.format("%x", string.byte(bytes, i)) .. ' '
    return result

msgpack = require('msgpack')
m1 = msgpack.encode(setmetatable({'A', 'B'}, {
                             __serialize = "seq"
m2 = msgpack.encode(setmetatable({'A', 'B'}, {
                             __serialize = "map"
print('array encoding: ', hexdump(m1))
print('map encoding: ', hexdump(m2))


array encoding: 92 a1 41 a1 42
map encoding:   82 01 a1 41 02 a1 42

The MsgPack Specification page explains that the first encoding means:

fixarray(2), fixstr(1), "A", fixstr(1), "B"

and the second encoding means:

fixmap(2), key(1), fixstr(1), "A", key(2), fixstr(2), "B".

Here are examples for all the common types, with the Lua-table representation on the left, with the MsgPack format name and encoding on the right.

Common Types and MsgPack Encodings

{} „fixmap“ if metatable is „map“ = 80 otherwise „fixarray“ = 90
„a“ „fixstr“ = a1 61
false „false“ = c2
true „true“ = c3
127 „positive fixint“ = 7f
65535 „uint 16“ = cd ff ff
4294967295 „uint 32“ = ce ff ff ff ff
nil „nil“ = c0
msgpack.NULL same as nil
[0] = 5 „fixmap(1)“ + „positive fixint“ (for the key) + „positive fixint“ (for the value) = 81 00 05
[0] = nil „fixmap(0)“ = 80 – nil is not stored when it is a missing map value
1.5 „float 64“ = cb 3f f8 00 00 00 00 00 00

Also, some MsgPack configuration settings for encoding can be changed, in the same way that they can be changed for JSON.