Name

lua-cjson - Fast JSON encoding/parsing

Table of Contents

• Name
• Description
• Additions to mpx/lua
  • encode_empty_table_as_object
  • empty_array
  • empty_array_mt
  • encode_number_precision

Description

This fork of mpx/lua-cjson is included in the OpenResty bundle and includes a few bugfixes and improvements, especially to facilitate the encoding of empty tables as JSON Arrays.

Please refer to the lua-cjson documentation for standard usage, this README only provides informations regarding this fork's additions.

See mpx/master..openresty/master for the complete history of changes.

Back to TOC

Additions

encode_empty_table_as_object

syntax: cjson.encode_empty_table_as_object(true|false|"on"|"off")

Change the default behavior when encoding an empty Lua table.

By default, empty Lua tables are encoded as empty JSON Objects ({}). If this is set to false, empty Lua tables will be encoded as empty JSON Arrays instead ([]).

This method either accepts a boolean or a string ("on", "off").

Back to TOC

empty_array

syntax: cjson.empty_array

A lightuserdata, similar to cjson.null, which will be encoded as an empty JSON Array by cjson.encode().

For example, since encode_empty_table_as_object is true by default:

local cjson = require "cjson"

local json = cjson.encode({
    foo = "bar",
    some_object = {},
    some_array = cjson.empty_array
})

This will generate:

{
    "foo": "bar",
    "some_object": {},
    "some_array": []
}

Back to TOC

empty_array_mt

syntax: setmetatable({}, cjson.empty_array_mt)

A metatable which can "tag" a table as a JSON Array in case it is empty (that is, if the table has no elements, cjson.encode() will encode it as an empty JSON Array).

Instead of:

local function serialize(arr)
    if #arr < 1 then
        arr = cjson.empty_array
    end

    return cjson.encode({some_array = arr})
end

This is more concise:

local function serialize(arr)
    setmetatable(arr, cjson.empty_array_mt)

    return cjson.encode({some_array = arr})
end

Both will generate:

{
    "some_array": []
}

Back to TOC

encode_number_precision

syntax: cjson.encode_number_precision(precision)

This fork allows encoding of numbers with a precision up to 16 decimals (vs. 14 in mpx/lua-cjson).

Back to TOC