#moonbit: backend: js

#ryota0624/circuit_breaker_mbt

#supported backends

• js
• native

#Overview

• Closed: Normal operation, requests pass through
• Open: Too many failures detected, requests are rejected immediately
• HalfOpen: Testing if the system has recovered, limited requests allowed

#Basic Usage

///|
test "basic circuit breaker usage" {
  // Create a circuit breaker with default settings
  let settings : @ryota0624/circuit_breaker.Settings[Int, String] = @ryota0624/circuit_breaker.Settings::default()

  let cb = @ryota0624/circuit_breaker.CircuitBreaker::new(settings)

  // Execute a function through the circuit breaker
  let result = cb.run_sync(fn() -> Result[Int, String] { Ok(42) })

  inspect(result, content="Success(42)")
}

#Custom Configuration

///|
test "custom circuit breaker configuration" {
  let mut current_time = 0L

  let settings : @ryota0624/circuit_breaker.Settings[Int, String] = @ryota0624/circuit_breaker.Settings::default()
    .with_name("MyService")
    .with_timeout(5000L) // 5 seconds timeout in Open state
    .with_max_requests(3L) // Allow 3 requests in HalfOpen state
    .with_get_now(fn() { current_time }) // Custom time source for testing

  let cb = @ryota0624/circuit_breaker.CircuitBreaker::new(settings)

  // Simulate failures to trip the circuit
  for i = 0; i < 6; i = i + 1 {
    let _ = cb.run_sync(fn() -> Result[Int, String] {
      Err("service unavailable")
    })
  }

  // Circuit should be open now
  inspect(cb.state(), content="Open")

  // Requests are rejected in Open state
  let result = cb.run_sync(fn() -> Result[Int, String] { Ok(1) })
  inspect(result, content="Rejected(OpenCircuit)")

  // Advance time past timeout
  current_time = 5000L

  // Circuit transitions to HalfOpen and allows request
  let result2 = cb.run_sync(fn() -> Result[Int, String] { Ok(1) })
  inspect(result2, content="Success(1)")
}

#Error Handling

///|
test "error handling with circuit breaker" {
  let settings : @ryota0624/circuit_breaker.Settings[String, String] = @ryota0624/circuit_breaker.Settings::default()

  let cb = @ryota0624/circuit_breaker.CircuitBreaker::new(settings)

  // Handle different result types
  let result = cb.run_sync(fn() -> Result[String, String] { Err("error") })

  inspect(result, content="Failure(\"error\")")
}