feat(closeOnContextDone): Add the ability to close the wasm execution…

… based on context

engine.go

@@ -35,6 +35,17 @@ type (
 		Stdout io.Writer
 		// Stderr is the writer WASI uses for `fd_write` to file descriptor 2.
 		Stderr io.Writer
+		// CloseOnContextDone ensures the executions of functions to be closed under one of the following circumstances:
+		//
+		// 	- context.Context passed to the Call method of api.Function is canceled during execution. (i.e. ctx by context.WithCancel)
+		// 	- context.Context passed to the Call method of api.Function reaches timeout during execution. (i.e. ctx by context.WithTimeout or context.WithDeadline)
+		// 	- Close or CloseWithExitCode of api.Module is explicitly called during execution.
+		//
+		// This is especially useful when one wants to run untrusted Wasm binaries since otherwise, any invocation of
+		// api.Function can potentially block the corresponding Goroutine forever. Moreover, it might block the
+		// entire underlying OS thread which runs the api.Function call. See "Why it's safe to execute runtime-generated
+		// machine codes against async Goroutine preemption" section in internal/engine/compiler/RATIONALE.md for detail.
+		CloseOnContextDone bool
 	}
 
 	// Module is a WebAssembly Module.

engines/wazero/wazero.go

@@ -117,9 +117,17 @@ func DefaultRuntime(ctx context.Context) (wazero.Runtime, error) {
 
 // New implements the same method as documented on wapc.Engine.
 func (e *engine) New(ctx context.Context, host wapc.HostCallHandler, guest []byte, config *wapc.ModuleConfig) (mod wapc.Module, err error) {
-	r, err := e.newRuntime(ctx)
-	if err != nil {
-		return nil, err
+	//runtime conf changes
+	var r wazero.Runtime
+	if config.CloseOnContextDone {
+		runtimeConfig := wazero.NewRuntimeConfig().WithCloseOnContextDone(true)
+		r = wazero.NewRuntimeWithConfig(ctx, runtimeConfig)
+		wasi_snapshot_preview1.MustInstantiate(ctx, r)
+	} else {
+		r, err = e.newRuntime(ctx)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	m := &Module{runtime: r, wapcHostCallHandler: host}