Function Extension

Note

Go C-shared native .so dynamic plugins are unsupported in rekuiper. High-performance connectors are compiled directly into the rekuiper Rust binary. Custom function extensions run through WebAssembly (Wasm) or External Services. This guide is preserved as a technical reference for legacy eKuiper installations.

rekuiper provides built-in functions for data processing. You can create custom function extensions to implement domain-specific business logic.

Development

Develop a Custom Function

To create a custom function, implement the api.Function interface and export it from a Go plugin.

Before developing, configure the plugin development environment.

1. Implement Validate:

   Validate(args []interface{}) error

   The engine calls Validate during SQL plan verification. The parameter is a slice of AST expressions. Check argument counts and types. Return nil if validation succeeds; otherwise, return an error.

2. Implement IsAggregate:

   IsAggregate() bool

   Return true if the function operates as an aggregate function over grouped window slices; otherwise, return false.

3. Implement Exec:

   Exec(args []interface{}) (interface{}, bool)

   The engine calls Exec to compute the function result. The args parameter contains the runtime argument values. Return the result and true on success, or return nil and false on failure.

4. Export the Symbol:

   The plugin must reside in the main package. Export the function as a variable symbol:

   var MyFunction myFunction

Refer to the Echo Function implementation for a complete reference.

Export Multiple Functions

A single plugin can export multiple functions:

var (
    Function1 function1
    Function2 function2
    FunctionN functionN
)

Combining related functions into one plugin simplifies distribution and deployment.

Package the Plugin

Compile the function into a Go plugin .so file in the plugins/functions directory:

go build -trimpath --buildmode=plugin -o plugins/functions/MyFunction.so extensions/functions/my_function.go

Register Functions

The engine automatically loads plugins in the plugin directory. If a plugin exports multiple functions, register them explicitly:

1. Development: Place the compiled .so file into plugins/functions, then invoke the CLI register command or the REST register API.
2. Production: Package the plugin into a zip archive, then invoke the CLI create command or the REST create API with the function list.

Usage in SQL Rules

Invoke the custom function directly in SQL:

{
  "id": "rule1",
  "sql": "SELECT myFunction(name) FROM demo",
  "actions": [
    {
      "log": {}
    }
  ]
}