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
  • decode_big_numbers_as_strings

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.

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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").

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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": []
}

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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": []
}

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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).

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decode_big_numbers_as_strings

syntax: cjson.decode_big_numbers_as_strings(true|false)

Aas you know, Lua 5.1 uses one single number representation which can be chosen at compile time and since it is often set to IEEE 754 double precision floating point, one cannot store a 64 bit integer with full precision.

Default false. If this is set to true, then any numbers that may result in a precision loss will be preserved as a string.

Base on the commit: https://github.com/brimworks/lua-cjson/commit/48ab7055a1fa13a8f7e9a6242237a40f68f0f847 :))

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