astarte_flow
astarte_flow v0.1.0

lua_map

  • type: producer_consumer
  • accepted input: any kind of message
  • output: transformed input message

This is a producer and consumer block that takes an incoming message and it transforms it using the given Lua script.

This block supports Lua 5.2 scripts ( luerl scripting engine is used under the hood). The incoming message will be provided to the script as message.

This block name is not related to the map abstract data type and it should be not confused with it, instead it is related to the function (our script) application to a sequence of items (the messages).

Properties

  • script: Lua script. (required, string)
  • config: Lua script configuration object. (optional, object)

script

 script

A Lua Lua 5.2 script. The most simple script is "return message;" which returns an unmodified message.

See also luerl documentation.

config

 config

Any object. Config parameter is meant as a method to provide parameters to the Lua script, without hard-coding them. It can be accessed using config.

Output message

An input message transformation which depends on the script implementation. Missing message attributes are taken from the input message, therefore some fields are kept unchanged.

Examples

The following example uses lua_map block for Fahrenheit to Celsius degrees conversion. A key prefix is provided through config object and prepended to the string "/celsius". All other existing message attributes are taken as-is from the input message.

[...]
| lua_map
  .script("""
    new_message = {};
    new_message.key = config.prefix .. "/celsius";
    new_message.data = (message.data - 32) / 1.8;
    return new_message;
  """)
  .config(${config})
[...]