Kafka Connector 26.3
Kafka Connector Help

# Write a Lua Script

A Lua script that is run from a connector must have the following structure:

    function handler(config, document, params)
    	...
    end

The `handler` function is called for each document and is passed the following arguments:

Argument | Description
--- | ---
`config` | A `LuaConfig` object that you can use to retrieve the values of configuration parameters from the connector’s configuration file.
`document` | A `LuaDocument` object. The document object is an internal representation of the document being processed. Modifying this object changes the document.
`params` | The `params` argument is a table that contains additional information provided by the connector: TYPE. The type of task being performed. The possible values are `ADD`, `UPDATE`, `DELETE`, or `COLLECT`. SECTION. The name of the section in the configuration file that contains configuration parameters for the task. FILENAME. The document filename. The Lua script can modify this file, but must not delete it. OWNFILE. Indicates whether the connector (and CFS) has ownership of the file. A value of `true` means that CFS deletes the file after it has been processed.

For the connector to continue processing the document, the `handler` function must return `true`. If the function returns `false`, the document is discarded.

The following script demonstrates how you can use the `config` and `params` arguments:

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    function handler(config, document, params)
        -- Write all of the additional information to a log file
        for k,v in pairs(params) do
            log("logfile.txt", k..": "..tostring(v))
        end

        -- The following lines set variables from the params argument
        type = params["TYPE"]
        section = params["SECTION"]
        filename = params["FILENAME"]

        -- Read a configuration parameter from the configuration file
        -- If the parameter is not set, "DefaultValue" is returned
        val = config:getValue(section, "Parameter", "DefaultValue")

        -- If the document is not being deleted, set the field FieldName
        -- to the value of the configuration parameter
        if type ~= "DELETE" then
            document:setFieldValue("FieldName", val)
        end

        -- If the document has a file (that is, not just metadata),
        -- copy the file to a new location and write a stub idx file
        -- containing the metadata.
        if filename ~= "" then
            copytofilename = "./out/"..create_uuid(filename)
            copy_file(filename, copytofilename)
            document:writeStubIdx(copytofilename..".idx")
        end

        return true
    end

TIP: You can write a library of useful functions to share between multiple scripts. To include a library of functions in a script, add the code `dofile("library.lua")` to the top of the lua script, outside of the `handler` function.

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Version 26.3 | Last updated July 2026

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Product: Knowledge Discovery Kafka Connector 26.3

Topic Title: Write a Lua Script