asl

This library provides an implementation of Amazon States Language (ASL) in Rust.

The library can parse and execute state machines defined in ASL.

Example: Hello world

This example will print the strings Hello and World:

struct TaskHandler {}
impl StateExecutionHandler for TaskHandler {
    type TaskExecutionError = String;

    fn execute_task(
        &self,
        resource: &str,
        input: &Value,
        credentials: Option<&Value>,
    ) -> Result<Option<Value>, Self::TaskExecutionError> {
        let result = match resource {
            "SayHello" => "Hello",
            "SayWorld" => "World",
            _ => Err("Unknown resource!")?,
        };
        println!("{}", result);
        Ok(None) // We opt into returning nothing
    }
}

fn main() {
    let definition = r#"{
          "Comment": "A simple minimal example of the States language",
          "StartAt": "State: Hello",
          "States": {
            "State: Hello": {
              "Type": "Task",
              "Resource": "SayHello",
              "Next": "State: World"
            },
            "State: World": {
              "Type": "Task",
              "Resource": "SayWorld",
              "End": true
            }
          }
        }"#;
    let state_machine = StateMachine::parse(definition).unwrap();
    let input = Value::Null;
    let execution: Execution<TaskHandler, EmptyContext> = state_machine.start(&input, TaskHandler {}, EmptyContext {});
    // the Execution type implements Iterator, so we can iterate until there are no more states to execute
    let steps: Vec<StateExecutionOutput> = execution.collect();
}

See: test_hello_world.rs.

Amazon States Language (ASL)

The Amazon States Language is a JSON-based, structured language used to define your state machine, a collection of states, that can do work (Task states), determine which states to transition to next (Choice states), stop an execution with an error (Fail states), and so on.

For a complete definition of ASL, refer to the Amazon States Language Specification.

IMPORTANT: This project is NOT affiliated with Amazon in any way.

ASL is deeply connected to AWS Step Functions. This means that in many places, the definition from the language specification is not specified, so this library opts into following the results from AWS Step Functions.

Feature Matrix

The main features that are already implemented or missing are listed in the following table:

License

This project is licensed under the MIT License.