Lua Filter

The luafilter is a filter that calls a set of functions in a Lua script.

Read the Lua language documentation for information on how to write Lua scripts.

Note: This module is experimental and must be built from source. The module is deprecated in MaxScale 23.08 and might be removed in a future release.

• Lua Filter

Filter Parameters

The luafilter has two parameters. They control which scripts will be called by the filter. Both parameters are optional but at least one should be defined. If both global_script and session_script are defined, the entry points in both scripts will be called.

global_script

The global Lua script. The parameter value is a path to a readable Lua script which will be executed.

This script will always be called with the same global Lua state and it can be used to build a global view of the whole service.

session_script

The session level Lua script. The parameter value is a path to a readable Lua script which will be executed once for each session.

Each session will have its own Lua state meaning that each session can have a unique Lua environment. Use this script to do session specific tasks.

Lua Script Calling Convention

The entry points for the Lua script expect the following signatures:

• nil createInstance(name) - global script only, called when the script is first loaded

  • When the global script is loaded, it first executes on a global level before the luafilter calls the createInstance function in the Lua script with the filter's name as its argument.

• nil newSession(string, string) - new session is created

These functions, if found in the script, will be called whenever a call to the matching entry point is made.

Script Template

Here is a script template that can be used to try out the luafilter. Copy it into a file and add global_script=<path to script> into the filter configuration. Make sure the file is readable by the maxscale user.

Functions Exposed by the Luafilter

The luafilter exposes the following functions that can be called inside the Lua script API endpoints.

• string mxs_get_type_mask()

• Returns the type of the current query being executed as a string. The values are the string versions of the query types defined in query_classifier.h are separated by vertical bars (|). This function can only be called from the routeQuery entry point.

Example Configuration and Script

Here is a minimal configuration entry for a luafilter definition.

And here is a script that opens a file in /tmp/ and logs output to it.

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