58 lines
2.2 KiB
Go
58 lines
2.2 KiB
Go
package ndr
|
|
|
|
import (
|
|
"errors"
|
|
"fmt"
|
|
"reflect"
|
|
)
|
|
|
|
// Union interface must be implemented by structs that will be unmarshaled into from the NDR byte stream union representation.
|
|
// The union's discriminating tag will be passed to the SwitchFunc method.
|
|
// The discriminating tag field must have the struct tag: `ndr:"unionTag"`
|
|
// If the union is encapsulated the discriminating tag field must have the struct tag: `ndr:"encapsulated"`
|
|
// The possible value fields that can be selected from must have the struct tag: `ndr:"unionField"`
|
|
type Union interface {
|
|
SwitchFunc(t interface{}) string
|
|
}
|
|
|
|
// Union related constants such as struct tag values
|
|
const (
|
|
unionSelectionFuncName = "SwitchFunc"
|
|
TagEncapsulated = "encapsulated"
|
|
TagUnionTag = "unionTag"
|
|
TagUnionField = "unionField"
|
|
)
|
|
|
|
func (dec *Decoder) isUnion(field reflect.Value, tag reflect.StructTag) (r reflect.Value) {
|
|
ndrTag := parseTags(tag)
|
|
if !ndrTag.HasValue(TagUnionTag) {
|
|
return
|
|
}
|
|
r = field
|
|
// For a non-encapsulated union, the discriminant is marshalled into the transmitted data stream twice: once as the
|
|
// field or parameter, which is referenced by the switch_is construct, in the procedure argument list; and once as
|
|
// the first part of the union representation.
|
|
if !ndrTag.HasValue(TagEncapsulated) {
|
|
dec.r.Discard(int(r.Type().Size()))
|
|
}
|
|
return
|
|
}
|
|
|
|
// unionSelectedField returns the field name of which of the union values to fill
|
|
func unionSelectedField(union, discriminant reflect.Value) (string, error) {
|
|
if !union.Type().Implements(reflect.TypeOf(new(Union)).Elem()) {
|
|
return "", errors.New("struct does not implement union interface")
|
|
}
|
|
args := []reflect.Value{discriminant}
|
|
// Call the SelectFunc of the union struct to find the name of the field to fill with the value selected.
|
|
sf := union.MethodByName(unionSelectionFuncName)
|
|
if !sf.IsValid() {
|
|
return "", fmt.Errorf("could not find a selection function called %s in the unions struct representation", unionSelectionFuncName)
|
|
}
|
|
f := sf.Call(args)
|
|
if f[0].Kind() != reflect.String || f[0].String() == "" {
|
|
return "", fmt.Errorf("the union select function did not return a string for the name of the field to fill")
|
|
}
|
|
return f[0].String(), nil
|
|
}
|