runtime: support syscall/js

runtime/internal/lib/syscall/js/func.go

@@ -0,0 +1,106 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build js && wasm
+// +build js,wasm
+
+package js
+
+import (
+	"sync"
+)
+
+var (
+	funcsMu    sync.Mutex
+	funcs             = make(map[uint32]func(Value, []Value) any)
+	nextFuncID uint32 = 1
+)
+
+// Func is a wrapped Go function to be called by JavaScript.
+type Func struct {
+	Value // the JavaScript function that invokes the Go function
+	id    uint32
+}
+
+// FuncOf returns a function to be used by JavaScript.
+//
+// The Go function fn is called with the value of JavaScript's "this" keyword and the
+// arguments of the invocation. The return value of the invocation is
+// the result of the Go function mapped back to JavaScript according to ValueOf.
+//
+// Invoking the wrapped Go function from JavaScript will
+// pause the event loop and spawn a new goroutine.
+// Other wrapped functions which are triggered during a call from Go to JavaScript
+// get executed on the same goroutine.
+//
+// As a consequence, if one wrapped function blocks, JavaScript's event loop
+// is blocked until that function returns. Hence, calling any async JavaScript
+// API, which requires the event loop, like fetch (http.Client), will cause an
+// immediate deadlock. Therefore a blocking function should explicitly start a
+// new goroutine.
+//
+// Func.Release must be called to free up resources when the function will not be invoked any more.
+func FuncOf(fn func(this Value, args []Value) any) Func {
+	funcsMu.Lock()
+	id := nextFuncID
+	nextFuncID++
+	funcs[id] = fn
+	funcsMu.Unlock()
+	var buf [20]byte
+	sid := string(itoa(buf[:], uint64(id)))
+	wrap := functionConstructor.New(ValueOf(`
+		const event = { id:` + sid + `, this: this, args: arguments };
+		Module._llgo_invoke(event);
+		return event.result;
+	`))
+	return Func{
+		id:    id,
+		Value: wrap,
+	}
+}
+
+func itoa(buf []byte, val uint64) []byte {
+	i := len(buf) - 1
+	for val >= 10 {
+		buf[i] = byte(val%10 + '0')
+		i--
+		val /= 10
+	}
+	buf[i] = byte(val + '0')
+	return buf[i:]
+}
+
+// Release frees up resources allocated for the function.
+// The function must not be invoked after calling Release.
+// It is allowed to call Release while the function is still running.
+func (c Func) Release() {
+	funcsMu.Lock()
+	delete(funcs, c.id)
+	funcsMu.Unlock()
+}
+
+//export llgo_export_invoke
+func llgo_export_invoke(cb Value) bool {
+	id := uint32(cb.Get("id").Int())
+	funcsMu.Lock()
+	f, ok := funcs[id]
+	funcsMu.Unlock()
+	if !ok {
+		Global().Get("console").Call("error", "call to released function")
+		return true
+	}
+
+	// Call the js.Func with arguments
+	this := cb.Get("this")
+	argsObj := cb.Get("args")
+	args := make([]Value, argsObj.Length())
+	for i := range args {
+		args[i] = argsObj.Index(i)
+	}
+	result := f(this, args)
+
+	// Return the result to js
+	cb.Set("result", result)
+	return true
+}