Function ExampleConfig_fuel

example_test.go:17–91

Example of limiting a WebAssembly function's runtime using "fuel consumption".

()

// Example of limiting a WebAssembly function's runtime using "fuel consumption".
func ExampleConfig_fuel() {
	config := wasmtime.NewConfig()
	config.SetConsumeFuel(true)
	engine := wasmtime.NewEngineWithConfig(config)
	store := wasmtime.NewStore(engine)
	err := store.SetFuel(10000)
	if err != nil {
		log.Fatal(err)
	}

	// Compile and instantiate a small example with an infinite loop.
	wasm, err := wasmtime.Wat2Wasm(`
	(module
	  (func $fibonacci (param $n i32) (result i32)
	    (if
	      (i32.lt_s (local.get $n) (i32.const 2))
	      (then (return (local.get $n)))
	    )
	    (i32.add
	      (call $fibonacci (i32.sub (local.get $n) (i32.const 1)))
	      (call $fibonacci (i32.sub (local.get $n) (i32.const 2)))
	    )
	  )
	  (export "fibonacci" (func $fibonacci))
	)
	`)
	if err != nil {
		log.Fatal(err)
	}
	module, err := wasmtime.NewModule(store.Engine, wasm)
	if err != nil {
		log.Fatal(err)
	}
	instance, err := wasmtime.NewInstance(store, module, []wasmtime.AsExtern{})
	if err != nil {
		log.Fatal(err)
	}

	// Invoke `fibonacci` export with higher and higher numbers until we exhaust our fuel.
	fibonacci := instance.GetFunc(store, "fibonacci")
	if fibonacci == nil {
		log.Fatal("Failed to find function export `fibonacci`")
	}
	fuel := uint64(10000)
	for n := 0; ; n++ {
		err := store.SetFuel(fuel)
		if err != nil {
			log.Fatal(err)
		}
		output, err := fibonacci.Call(store, n)
		if err != nil {
			break
		}
		fuelAfter, err := store.GetFuel()
		if err != nil {
			log.Fatal(err)
		}
		fmt.Printf("fib(%d) = %d [consumed %d fuel]\n", n, output, fuel-fuelAfter)