Rhai¶

Rhai is a small embedded scripting language for Rust. It runs in-process, supports a configurable execution budget, and is the default choice for short transforms.

Minimal example¶

[[pipelines.transforms]]
type = "script"
runtime = "rhai"
on_error = "drop"
script = """
fn transform(env) {
  if env.payload["userId"] == 1 {
    env.meta.headers["priority"] = "high";
  }

  env.payload["processed"] = true;
  env
}
"""

`script_file`¶

Load the script from disk instead of inlining it:

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

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 () (or no return value) — filter the envelope out.

Execution limits¶

Rhai exposes a number of safety knobs. All are optional and have sensible defaults:

Field	Default	Purpose
`max_operations`	`100000`	Operation budget per call. Prevents infinite loops.
`max_call_levels`	`32`	Max function call depth.
`max_expr_depth`	`64`	Max expression nesting in top-level scope.
`max_function_expr_depth`	`32`	Max expression nesting inside function bodies.
`max_variables`	`64`	Max number of variables in scope.

A budget exhaustion is reported as a runtime error and follows the transform's on_error policy.

These fields are Rhai-only. Setting them under runtime = "lua" or runtime = "python" is rejected at config-load time.

`env` binding¶

Field	Access
Logical key	`env.meta.key`
Source node id	`env.meta.source_id`
Producer timestamp (ms)	`env.meta.timestamp_ms`
Headers map	`env.meta.headers`
Payload	`env.payload`

env.payload is the parsed JSON value — index into it with the usual [] syntax.