feat: Add reflection to create JS value from Go value

wasm/error.go

@@ -0,0 +1,13 @@
+package wasm
+
+import "syscall/js"
+
+// NewError returns a JS Error with the provided Go error's error message.
+func NewError(goErr error) js.Value {
+	errConstructor, err := Global().Expect(js.TypeFunction, "Error")
+	if err != nil {
+		panic("Error constructor not found")
+	}
+
+	return errConstructor.New(goErr.Error())
+}

wasm/function.go

@@ -0,0 +1,87 @@
+package wasm
+
+import (
+	"errors"
+	"reflect"
+	"syscall/js"
+)
+
+// ErrInvalidArgumentType is returned when a generated Go function wrapper receives invalid argument types from JS.
+var ErrInvalidArgumentType = errors.New("invalid argument passed into Go function")
+
+var errorType = reflect.TypeOf(error(nil))
+
+func toJSFunc(x reflect.Value) js.Value {
+	funcType := x.Type()
+	var hasError bool
+	if funcType.NumOut() != 0 {
+		hasError = funcType.Out(funcType.NumOut()-1) == errorType
+	}
+
+	return js.FuncOf(func(this js.Value, args []js.Value) interface{} {
+		in, err := conformJSValueToType(funcType, this, args)
+		if err != nil {
+			throwWrapper.Invoke(NewError(err))
+			return nil
+		}
+
+		out := x.Call(in)
+
+		if !hasError {
+			return ToJSValue(returnValue(out))
+		}
+
+		lastParam := out[len(out)-1]
+		if !lastParam.IsNil() {
+			throwWrapper.Invoke(NewError(err))
+			return nil
+		}
+		return ToJSValue(returnValue(out[:len(out)-1]))
+	}).JSValue()
+}
+
+var jsValueType = reflect.TypeOf(js.Value{})
+
+func conformJSValueToType(funcType reflect.Type, this js.Value, values []js.Value) ([]reflect.Value, error) {
+	if funcType.NumIn() == 0 {
+		if len(values) != 0 {
+			return nil, ErrInvalidArgumentType
+		}
+		return []reflect.Value{}, nil
+	}
+
+	if funcType.In(0) == jsValueType {
+		values = append([]js.Value{this}, values...)
+	}
+
+	if !funcType.IsVariadic() && funcType.NumIn() != len(values) {
+		return nil, ErrInvalidArgumentType
+	}
+
+	in := make([]reflect.Value, 0, len(values))
+	for i, v := range values {
+		paramType := funcType.In(i)
+		x := reflect.Zero(paramType).Interface()
+		err := FromJSValue(v, &x)
+		if err != nil {
+			return nil, err
+		}
+
+		in = append(in, reflect.ValueOf(x))
+	}
+
+	return in, nil
+}
+
+func returnValue(x []reflect.Value) js.Value {
+	if len(x) == 1 {
+		return ToJSValue(x[0])
+	}
+
+	xInterface := make([]interface{}, 0, len(x))
+	for _, v := range x {
+		xInterface = append(xInterface, v.Interface())
+	}
+
+	return ToJSValue(x)
+}

wasm/go.mod

@@ -0,0 +1,3 @@
+module gitea.teamortix.com/Team-Ortix/go-mod-wasm/wasm
+
+go 1.16

wasm/object.go

@@ -0,0 +1,137 @@
+package wasm
+
+import (
+	"fmt"
+	"syscall/js"
+)
+
+// TypeMismatchError is returned when a function is called with a js.Value that has the incorrect type.
+type TypeMismatchError struct {
+	Expected js.Type
+	Actual   js.Type
+}
+
+func (e TypeMismatchError) Error() string {
+	return fmt.Sprintf("expected %v type, got %v type instead", e.Expected, e.Actual)
+}
+
+// Global returns the global object as a Object.
+// If the global object is not an object, it panics.
+func Global() Object {
+	global, err := NewObject(js.Global())
+	if err != nil {
+		panic(err)
+	}
+	return global
+}
+
+// Object is a statically typed Object instance of js.Value.
+// It should be instantiated with NewObject where it is checked for type instead of directly.
+// Calling methods on a zero Object is undefined behaviour.
+type Object struct {
+	value js.Value
+}
+
+// NewObject instantiates a new Object with the provided js.Value.
+// If the js.Value is not an Object, it returns a TypeMismatchError.
+func NewObject(raw js.Value) (Object, error) {
+	if raw.Type() != js.TypeObject {
+		return Object{}, TypeMismatchError{
+			Expected: js.TypeObject,
+			Actual:   raw.Type(),
+		}
+	}
+
+	return Object{raw}, nil
+}
+
+// Get recursively gets the Object's properties, returning a TypeMismatchError if it encounters a non-object while
+// descending through the object.
+func (o Object) Get(path ...string) (js.Value, error) {
+	current := o.value
+	for _, v := range path {
+		if current.Type() != js.TypeObject {
+			return js.Value{}, TypeMismatchError{
+				Expected: js.TypeObject,
+				Actual:   current.Type(),
+			}
+		}
+
+		current = current.Get(v)
+	}
+	return current, nil
+}
+
+// Expect is a helper function that calls Get and checks the type of the result.
+// It returns a TypeMismatchError if a non-object is encountered while descending the path or the final type does not
+// match with the provided expected type.
+func (o Object) Expect(expectedType js.Type, path ...string) (js.Value, error) {
+	value, err := o.Get(path...)
+	if err != nil {
+		return js.Value{}, err
+	}
+
+	if value.Type() != expectedType {
+		return js.Value{}, TypeMismatchError{
+			Expected: expectedType,
+			Actual:   value.Type(),
+		}
+	}
+
+	return value, nil
+}
+
+// Delete deletes the property from the object.
+func (o Object) Delete(p string) {
+	o.value.Delete(p)
+}
+
+// Equal checks if the object is equal to another value.
+func (o Object) Equal(v js.Value) bool {
+	return o.value.Equal(v)
+}
+
+// Index indexes into the object.
+func (o Object) Index(i int) js.Value {
+	return o.value.Index(i)
+}
+
+// InstanceOf implements the instanceof operator in JavaScript.
+func (o Object) InstanceOf(t js.Value) bool {
+	return o.value.InstanceOf(t)
+}
+
+// JSValue implements the js.Wrapper interface.
+func (o Object) JSValue() js.Value {
+	return o.value
+}
+
+// Length returns the "length" property of the object.
+func (o Object) Length() int {
+	return o.value.Length()
+}
+
+// Set sets the property p to the value of js.ValueOf(x).
+func (o Object) Set(p string, x interface{}) {
+	o.value.Set(p, x)
+}
+
+// SetIndex sets the index i to the value of js.ValueOf(x).
+func (o Object) SetIndex(i int, x interface{}) {
+	o.value.SetIndex(i, x)
+}
+
+// String returns the object marshalled as a JSON string for debugging purposes.
+func (o Object) String() string {
+	stringify, err := Global().Expect(js.TypeFunction, "JSON", "stringify")
+	if err != nil {
+		panic(err)
+	}
+
+	jsonStr := stringify.Invoke(o)
+	if jsonStr.Type() != js.TypeString {
+		panic("JSON.stringify returned a " + jsonStr.Type().String())
+	}
+
+	return jsonStr.String()
+}

wasm/promise.go

@@ -0,0 +1,150 @@
+package wasm
+
+import "syscall/js"
+
+// Promise is an instance of a JS promise.
+// The zero value of this struct is not a valid Promise.
+type Promise struct {
+	Object
+}
+
+// FromJSValue turns a JS value to a Promise.
+func (p *Promise) FromJSValue(value js.Value) error {
+	var err error
+	p.Object, err = NewObject(value)
+	return err
+}
+
+// JSValue turns a Promise to a JS value.
+func (p Promise) JSValue() js.Value {
+	return p.Object.JSValue()
+}
+
+// NewPromise returns a promise that is fulfilled or rejected when the provided handler returns.
+// The handler is spawned in its own goroutine.
+func NewPromise(handler func() (interface{}, error)) Promise {
+	resultChan := make(chan interface{})
+	errChan := make(chan error)
+
+	// Invoke the handler in a new goroutine.
+	go func() {
+		result, err := handler()
+		if err != nil {
+			errChan <- err
+			return
+		}
+		resultChan <- result
+	}()
+
+	// Create a JS promise handler.
+	var jsHandler js.Func
+	jsHandler = js.FuncOf(func(this js.Value, args []js.Value) interface{} {
+		if len(args) < 2 {
+			panic("not enough arguments are passed to the Promise constructor handler")
+		}
+
+		resolve := args[0]
+		reject := args[1]
+
+		if resolve.Type() != js.TypeFunction || reject.Type() != js.TypeFunction {
+			panic("invalid type passed to Promise constructor handler")
+		}
+
+		go func() {
+			select {
+			case r := <-resultChan:
+				resolve.Invoke(r)
+			case err := <-errChan:
+				reject.Invoke(NewError(err))
+			}
+
+			// Free up resources now that we are done.
+			jsHandler.Release()
+		}()
+
+		return nil
+	})
+
+	promise, err := Global().Expect(js.TypeFunction, "Promise")
+	if err != nil {
+		panic("Promise constructor not found")
+	}
+
+	return mustJSValueToPromise(promise.New(jsHandler))
+}
+
+// PromiseAll creates a promise that is fulfilled when all the provided promises have been fulfilled.
+// The promise is rejected when any of the promises provided rejects.
+// It is implemented by calling Promise.all on JS.
+func PromiseAll(promise ...Promise) Promise {
+	promiseAll, err := Global().Expect(js.TypeFunction, "Promise", "all")
+	if err != nil {
+		panic("Promise.all not found")
+	}
+
+	pInterface := make([]interface{}, 0, len(promise))
+	for _, v := range promise {
+		pInterface = append(pInterface, v)
+	}
+
+	return mustJSValueToPromise(promiseAll.Invoke(pInterface))
+}
+
+// PromiseAllSettled creates a promise that is fulfilled when all the provided promises have been fulfilled or rejected.
+// It is implemented by calling Promise.allSettled on JS.
+func PromiseAllSettled(promise ...Promise) Promise {
+	promiseAllSettled, err := Global().Expect(js.TypeFunction, "Promise", "allSettled")
+	if err != nil {
+		panic("Promise.allSettled not found")
+	}
+
+	pInterface := make([]interface{}, 0, len(promise))
+	for _, v := range promise {
+		pInterface = append(pInterface, v)
+	}
+
+	return mustJSValueToPromise(promiseAllSettled.Invoke(pInterface))
+}
+
+// PromiseAny creates a promise that is fulfilled when any of the provided promises have been fulfilled.
+// The promise is rejected when all of the provided promises gets rejected.
+// It is implemented by calling Promise.any on JS.
+func PromiseAny(promise ...Promise) Promise {
+	promiseAny, err := Global().Expect(js.TypeFunction, "Promise", "any")
+	if err != nil {
+		panic("Promise.any not found")
+	}
+
+	pInterface := make([]interface{}, 0, len(promise))
+	for _, v := range promise {
+		pInterface = append(pInterface, v)
+	}
+
+	return mustJSValueToPromise(promiseAny.Invoke(pInterface))
+}
+
+// PromiseRace creates a promise that is fulfilled or rejected when one of the provided promises fulfill or reject.
+// It is implemented by calling Promise.race on JS.
+func PromiseRace(promise ...Promise) Promise {
+	promiseRace, err := Global().Expect(js.TypeFunction, "Promise", "race")
+	if err != nil {
+		panic("Promise.race not found")
+	}
+
+	pInterface := make([]interface{}, 0, len(promise))
+	for _, v := range promise {
+		pInterface = append(pInterface, v)
+	}
+
+	return mustJSValueToPromise(promiseRace.Invoke(pInterface))
+}
+
+func mustJSValueToPromise(v js.Value) Promise {
+	var p Promise
+	err := p.FromJSValue(v)
+	if err != nil {
+		panic("Expected a Promise from JS standard library")
+	}
+
+	return p
+}

wasm/reflect_from.go

@@ -0,0 +1,11 @@
+package wasm
+
+import (
+	"fmt"
+	"syscall/js"
+)
+
+func FromJSValue(x js.Value, out interface{}) error {
+	// TODO
+	return fmt.Errorf("unimplemented")
+}

wasm/reflect_to.go

@@ -0,0 +1,155 @@
+package wasm
+
+import (
+	"fmt"
+	"reflect"
+	"syscall/js"
+	"unsafe"
+)
+
+// ToJSValue converts a given Go value into its equivalent JS form.
+//
+// One special case is that complex numbers (complex64 and complex128) are converted into objects with a real and imag
+// property holding a number each.
+//
+// A function is converted into a JS function where the function returns an error if the provided arguments do not conform
+// to the Go equivalent but otherwise calls the Go function.
+//
+// The "this" argument of a function is always passed to the Go function if its first parameter is of type js.Value.
+// Otherwise, it is simply ignored.
+//
+// If the last return value of a function is an error, it will be thrown in JS if it's non-nil.
+// If the function returns multiple non-error values, it is converted to an array when returning to JS.
+//
+// It panics when a channel or a map with keys other than string and integers are passed in.
+func ToJSValue(x interface{}) js.Value {
+	if x == nil {
+		return js.Undefined()
+	}
+
+	// Fast path for basic types that do not require reflection.
+	switch x := x.(type) {
+	case js.Value:
+		return x
+	case js.Wrapper, bool, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, uintptr,
+		unsafe.Pointer, float32, float64, string:
+		return js.ValueOf(x)
+	case complex64:
+		return js.ValueOf(map[string]interface{}{
+			"real": real(x),
+			"imag": imag(x),
+		})
+	case complex128:
+		return js.ValueOf(map[string]interface{}{
+			"real": real(x),
+			"imag": imag(x),
+		})
+	}
+
+	value := reflect.ValueOf(x)
+
+	if value.Kind() == reflect.Ptr {
+		value = reflect.Indirect(value)
+		if !value.IsValid() {
+			return js.Undefined()
+		}
+	}
+
+	switch value.Kind() {
+	case reflect.Array, reflect.Slice:
+		return toJSArray(value)
+	case reflect.Func:
+		return toJSFunc(value)
+	case reflect.Map:
+		return mapToJSObject(value)
+	case reflect.Struct:
+		return structToJSObject(value)
+	default:
+		panic(fmt.Sprintf("cannot convert %T to a JS value", x))
+	}
+}
+
+func toJSArray(x reflect.Value) js.Value {
+	arrayConstructor, err := Global().Get("Array")
+	if err != nil {
+		panic("Array constructor not found")
+	}
+
+	array := arrayConstructor.New()
+	for i := 0; i < x.Len(); i++ {
+		array.SetIndex(i, ToJSValue(x.Index(i).Interface()))
+	}
+
+	return array
+}
+
+func mapToJSObject(x reflect.Value) js.Value {
+	objectConstructor, err := Global().Get("Object")
+	if err != nil {
+		panic("Object constructor not found")
+	}
+
+	obj := objectConstructor.New()
+	iter := x.MapRange()
+	for {
+		key := iter.Key()
+		value := iter.Value().Interface()
+		switch key := key.Interface().(type) {
+		case int:
+			obj.SetIndex(key, ToJSValue(value))
+		case int8:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case int16:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case int32:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case int64:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case uint:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case uint8:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case uint16:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case uint32:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case uint64:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case uintptr:
+			obj.SetIndex(int(key), ToJSValue(value))
+		case string:
+			obj.Set(key, ToJSValue(value))
+		default:
+			panic(fmt.Sprintf("cannot convert %T into a JS value as its key is not a string or an integer",
+				x.Interface()))
+		}
+
+		if !iter.Next() {
+			break
+		}
+	}
+
+	return obj
+}
+
+func structToJSObject(x reflect.Value) js.Value {
+	objectConstructor, err := Global().Get("Object")
+	if err != nil {
+		panic("Object constructor not found")
+	}
+
+	obj := objectConstructor.New()
+
+	structType := x.Type()
+	for i := 0; i < structType.NumField(); i++ {
+		field := structType.Field(i)
+		name := field.Name
+		if tagName, ok := field.Tag.Lookup("wasm"); ok {
+			name = tagName
+		}
+
+		obj.Set(name, ToJSValue(x.Field(i)))
+	}
+
+	return obj
+}

wasm/wasm.go

@@ -0,0 +1,15 @@
+package wasm
+
+import "syscall/js"
+
+const globalIdent = "__go_wasm__"
+
+var throwWrapper js.Value
+
+func init() {
+	var err error
+	throwWrapper, err = Global().Get(globalIdent, "__throw__")
+	if err != nil {
+		panic("JS wrapper __go_wasm__.__throw__ not found")
+	}
+}