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libcjson: LuaJIT FFI-based cJSON library for nginx-module-lua

Installation

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CentOS/RHEL 7 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua-resty-libcjson

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua5.1-resty-libcjson

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-libcjson v1.4 released on Jul 04 2016.

lua-resty-libcjson is a LuaJIT FFI-based cJSON library (tested with OpenResty too).

Lua API

mixed json.decode(value)

Decodes JSON value or structure (JSON array or object), and returns either Lua table or some simple value (e.g. boolean, string, number, nil or json.null (when running in context of OpenResty the json.null is the same as ngx.null).

Example
local json = require "resty.libcjson"
local obj = json.decode "{}"       -- table (with obj.__jsontype == "object")
local arr = json.decode "[]"       -- table (with arr.__jsontype == "array")
local nbr = json.decode "1"        -- 1
local bln = json.decode "true"     -- true
local str = json.decode '"test"'   -- "test"
local str = json.decode '""'       -- ""
local num = json.decode(5)         -- 5
local num = json.decode(math)      -- math
local num = json.decode(json.null) -- json.null
local nul = json.decode "null"     -- json.null
local nul = json.decode ""         -- nil
local nul = json.decode(nil)       -- nil
local nul = json.decode()          -- nil

Nested JSON structures are parsed as nested Lua tables.

string json.encode(value, formatted)

Encodes Lua value or table, and returns equivalent JSON value or structure as a string. Optionally you may pass formatted argument with value of false to get unformatted JSON string as output.

Example
local json = require "resty.libcjson"
local str = json.encode{}                              -- "[]"
local str = json.encode(setmetatable({}, json.object)) -- "{}"
local str = json.encode(1)                             -- "1"
local str = json.encode(1.1)                           -- "1.100000"
local str = json.encode "test"                         -- '"test"'
local str = json.encode ""                             -- '""'
local str = json.encode(false)                         -- "false"
local str = json.encode(nil)                           -- "null"
local str = json.encode(json.null)                     -- "null"
local str = json.encode()                              -- "null"
local str = json.encode{ a = "b" }                     -- '{ "a": "b" }'
local str = json.encode{ "a", b = 1 }                  -- '{ "1": "a", "b": 1 }'
local str = json.encode{ 1, 1.1, "a", "", false }      -- '[1, 1.100000, "a", "", false]'

Nested Lua tables are encoded as nested JSON structures (JSON objects or arrays).

About JSON Arrays and Object Encoding and Decoding

See this comment: https://github.com/bungle/lua-resty-libcjson/issues/1#issuecomment-38567447.

Benchmarks

About 190 MB citylots.json:

## Lua cJSON
Decoding Time: 5.882825
Encoding Time: 4.902301
## lua-resty-libcjson
Decoding Time: 6.409872
Encoding Time: (takes forever)

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-libcjson.