117 lines
3.1 KiB
Go
117 lines
3.1 KiB
Go
package wasm
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import (
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"errors"
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"reflect"
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"syscall/js"
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)
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// ErrInvalidArgumentType is returned when a generated Go function wrapper receives invalid argument types from JS.
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var ErrInvalidArgumentType = errors.New("invalid argument passed into Go function")
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var errorType = reflect.TypeOf((*error)(nil)).Elem()
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type goThrowable struct {
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Result js.Value `wasm:"result"`
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Error js.Value `wasm:"error"`
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}
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// toJSFunc takes a reflect.Value of a Go function and converts it to a JS function that:
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// Errors if the parameter types do not conform to the Go function signature,
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// Throws an error if the last returned value is an error and is non-nil,
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// Return an array if there's multiple non-error return values.
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func toJSFunc(x reflect.Value) js.Value {
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funcType := x.Type()
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var hasError bool
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if funcType.NumOut() != 0 {
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hasError = funcType.Out(funcType.NumOut()-1) == errorType
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}
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return funcWrapper.Invoke(js.FuncOf(func(this js.Value, args []js.Value) interface{} {
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in, err := conformJSValueToType(funcType, this, args)
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if err != nil {
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return ToJSValue(goThrowable{
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Error: NewError(err),
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})
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}
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out := x.Call(in)
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if !hasError {
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return ToJSValue(goThrowable{
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Result: returnValue(out),
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})
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}
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lastParam := out[len(out)-1]
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if !lastParam.IsNil() {
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return ToJSValue(goThrowable{
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Error: NewError(lastParam.Interface().(error)),
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})
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}
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return ToJSValue(goThrowable{
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Result: returnValue(out[:len(out)-1]),
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})
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}))
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}
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var jsValueType = reflect.TypeOf(js.Value{})
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// conformJSValueToType attempts to convert the provided JS values to reflect.Values that match the
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// types expected for the parameters of funcType.
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func conformJSValueToType(funcType reflect.Type, this js.Value, values []js.Value) ([]reflect.Value, error) {
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if funcType.NumIn() == 0 {
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if len(values) != 0 {
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return nil, ErrInvalidArgumentType
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}
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return []reflect.Value{}, nil
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}
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if funcType.In(0) == jsValueType {
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// If the first parameter is a js.Value, it is assumed to be the value of `this`.
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values = append([]js.Value{this}, values...)
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}
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if funcType.IsVariadic() && funcType.NumIn()-1 > len(values) {
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return nil, ErrInvalidArgumentType
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}
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if !funcType.IsVariadic() && funcType.NumIn() != len(values) {
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return nil, ErrInvalidArgumentType
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}
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in := make([]reflect.Value, 0, len(values))
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for i, v := range values {
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paramType := funcType.In(i)
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x := reflect.Zero(paramType).Interface()
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err := FromJSValue(v, &x)
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if err != nil {
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return nil, err
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}
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in = append(in, reflect.ValueOf(x))
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}
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return in, nil
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}
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// returnValue wraps returned values by Go in a JS-friendly way.
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// If there are no returned values, it returns undefined.
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// If there is exactly one, it returns the JS equivalent.
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// If there is more than one, it returns an array containing the JS equivalent of every returned value.
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func returnValue(x []reflect.Value) js.Value {
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switch len(x) {
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case 0:
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return js.Undefined()
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case 1:
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return ToJSValue(x[0].Interface())
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}
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xInterface := make([]interface{}, 0, len(x))
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for _, v := range x {
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xInterface = append(xInterface, v.Interface())
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}
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return ToJSValue(xInterface)
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}
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