Lua¶

The Lua runtime is embedded in-process via mlua. Use it when you want familiar Lua syntax for small transforms.

Minimal example¶

[[pipelines.transforms]]
type = "script"
runtime = "lua"
on_error = "drop"
script = """
function transform(env)
  if env.payload.userId == 1 then
    env.meta.headers.priority = "high"
  end

  env.payload.processed = true
  return env
end
"""

script_file¶

[[pipelines.transforms]]
type = "script"
runtime = "lua"
script_file = "./transforms/enrich.lua"

function transform(env)
  env.payload.processed = true
  return env
end

script and script_file are mutually exclusive — set exactly one. Relative script_file paths are resolved from the config file's directory.

Return semantics¶

• return env — emit the (possibly mutated) envelope downstream.
• return nil (or no return) — filter the envelope out.

Limits¶

The Lua runtime does not expose an execution budget today. The Rhai-only limit fields (max_operations, max_call_levels, etc.) are rejected at config-load time when runtime = "lua" — the transform fails to register rather than silently ignoring them.

env binding¶

env.payload is exposed as a Lua table mirroring the JSON structure.