heka json decoder

json_decoder.lua

-- This Source Code Form is subject to the terms of the Mozilla Public
-- License, v. 2.0. If a copy of the MPL was not distributed with this
-- file, You can obtain one at http://mozilla.org/MPL/2.0/.

--[[
Parses a payload containing JSON.

Config:

- type (string, optional, default nil):
    Sets the message 'Type' header to the specified value

- payload_keep (bool, optional, default false)
    Always preserve the original log line in the message payload.


.. code-block:: javascript

    {
      "msg": "Start Request",
      "event": "artemis.web.ensure-running",
      "extra": {
        "workspace-id": "hpl4daza2f"
      },
      "time": "2015-05-06T20:40:05.509926234Z",
      "severity": 1
    }

*Example Heka Configuration*

.. code-block:: ini

    [ArtemisLogInput]
    type = "LogstreamerInput"
    log_directory = "/srv/artemis/current/logs"
    file_match = 'artemis\.log'
    decoder = "JsonDecoder"

    [JsonDecoder]
    type = "SandboxDecoder"
    filename = "lua_decoders/json_decoder.lua"

        [JsonDecoder.config]
        type = "artemis"
        payload_keep = true
--]]

require "cjson"
local util = require("util")

local msg_type     = read_config("type")
local payload_keep = read_config("payload_keep")

local msg = {
    Type       = msg_type,
    Payload    = nil,
    Fields     = nil,
    Severity   = nil
}

function process_message()
    local ok, json = pcall(cjson.decode, read_message("Payload"))
    if not ok then
        return -1
    end

    if payload_keep then
        msg.Payload = read_message("Payload")
    end

    msg.Severity = json["severity"]

    local flat = {}
    util.table_to_fields(json, flat, nil)
    msg.Fields = flat
 
    if not pcall(inject_message, msg) then return -1 end
 
    return 0
end