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