starbind.go

package server

import (
	"fmt"
	"reflect"

	"go.starlark.net/starlark"
)

func toValue(v interface{}) starlark.Value {
	switch v := v.(type) {
	case uint8:
		return starlark.MakeUint64(uint64(v))
	case uint16:
		return starlark.MakeUint64(uint64(v))
	case uint32:
		return starlark.MakeUint64(uint64(v))
	case uint64:
		return starlark.MakeUint64(v)
	case uintptr:
		return starlark.MakeUint64(uint64(v))
	case uint:
		return starlark.MakeUint64(uint64(v))
	case int8:
		return starlark.MakeInt64(int64(v))
	case int16:
		return starlark.MakeInt64(int64(v))
	case int32:
		return starlark.MakeInt64(int64(v))
	case int64:
		return starlark.MakeInt64(v)
	case int:
		return starlark.MakeInt64(int64(v))
	case string:
		return starlark.String(v)
	case map[string]uint64:
		// this is the only map type that we use in the api, if we ever want to
		// add more maps to the api a more general approach will be necessary.
		var r starlark.Dict
		for k, v := range v {
			r.SetKey(starlark.String(k), starlark.MakeUint64(v))
		}
		return &r
	case nil:
		return starlark.None
	case error:
		return starlark.String(v.Error())
	default:
		vval := reflect.ValueOf(v)
		switch vval.Type().Kind() {
		case reflect.Ptr:
			if vval.IsNil() {
				return starlark.None
			}
			vval = vval.Elem()
			if vval.Type().Kind() == reflect.Struct {
				return structAsStarlarkValue{vval}
			}
		case reflect.Struct:
			return structAsStarlarkValue{vval}
		case reflect.Slice:
			return sliceAsStarlarkValue{vval}
		}
		return starlark.String(fmt.Sprintf("%v", v))
	}
}

// sliceAsStarlarkValue converts a reflect.Value containing a slice
// into a starlark value.
// The public methods of sliceAsStarlarkValue implement the Indexable and
// Sequence starlark interfaces.
type sliceAsStarlarkValue struct {
	v reflect.Value
}

var _ starlark.Indexable = sliceAsStarlarkValue{}
var _ starlark.Sequence = sliceAsStarlarkValue{}

func (v sliceAsStarlarkValue) Freeze() {
}

func (v sliceAsStarlarkValue) Hash() (uint32, error) {
	return 0, fmt.Errorf("not hashable")
}

func (v sliceAsStarlarkValue) String() string {
	return fmt.Sprintf("%#v", v.v)
}

func (v sliceAsStarlarkValue) Truth() starlark.Bool {
	return v.v.Len() != 0
}

func (v sliceAsStarlarkValue) Type() string {
	return v.v.Type().String()
}

func (v sliceAsStarlarkValue) Index(i int) starlark.Value {
	if i >= v.v.Len() {
		return nil
	}
	return toValue(v.v.Index(i).Interface())
}

func (v sliceAsStarlarkValue) Len() int {
	return v.v.Len()
}

func (v sliceAsStarlarkValue) Iterate() starlark.Iterator {
	return &sliceAsStarlarkValueIterator{0, v.v}
}

type sliceAsStarlarkValueIterator struct {
	cur int
	v   reflect.Value
}

func (it *sliceAsStarlarkValueIterator) Done() {
}

func (it *sliceAsStarlarkValueIterator) Next(p *starlark.Value) bool {
	if it.cur >= it.v.Len() {
		return false
	}
	*p = toValue(it.v.Index(it.cur).Interface())
	it.cur++
	return true
}

// structAsStarlarkValue converts any Go struct into a starlark.Value.
// The public methods of structAsStarlarkValue implement the
// starlark.HasAttrs interface.
type structAsStarlarkValue struct {
	v reflect.Value
}

func (v structAsStarlarkValue) AttrNames() []string {
	var out []string
	for i := 0; i < v.v.NumField(); i++ {
		out = append(out, v.v.Type().Field(i).Name)
	}
	return out
}

var _ starlark.HasAttrs = structAsStarlarkValue{}

func (v structAsStarlarkValue) Freeze() {
}

func (v structAsStarlarkValue) Hash() (uint32, error) {
	return 0, fmt.Errorf("not hashable")
}

func (v structAsStarlarkValue) String() string {
	return fmt.Sprintf("%#v", v.v)
}

func (v structAsStarlarkValue) Truth() starlark.Bool {
	return true
}

func (v structAsStarlarkValue) Type() string {
	return v.v.Type().String()
}

func (v structAsStarlarkValue) Attr(name string) (starlark.Value, error) {
	r := v.v.FieldByName(name)
	if r == (reflect.Value{}) {
		return starlark.None, fmt.Errorf("no field named %q in %T", name, v.v.Interface())
	}
	return toValue(r.Interface()), nil
}