393 lines
12 KiB
Go
393 lines
12 KiB
Go
// Package ndr provides the ability to unmarshal NDR encoded byte steams into Go data structures
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package ndr
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import (
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"bufio"
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"fmt"
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"io"
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"reflect"
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"strings"
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)
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// Struct tag values
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const (
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TagConformant = "conformant"
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TagVarying = "varying"
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TagPointer = "pointer"
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TagPipe = "pipe"
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)
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// Decoder unmarshals NDR byte stream data into a Go struct representation
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type Decoder struct {
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r *bufio.Reader // source of the data
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size int // initial size of bytes in buffer
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ch CommonHeader // NDR common header
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ph PrivateHeader // NDR private header
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conformantMax []uint32 // conformant max values that were moved to the beginning of the structure
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s interface{} // pointer to the structure being populated
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current []string // keeps track of the current field being populated
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}
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type deferedPtr struct {
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v reflect.Value
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tag reflect.StructTag
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}
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// NewDecoder creates a new instance of a NDR Decoder.
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func NewDecoder(r io.Reader) *Decoder {
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dec := new(Decoder)
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dec.r = bufio.NewReader(r)
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dec.r.Peek(int(commonHeaderBytes)) // For some reason an operation is needed on the buffer to initialise it so Buffered() != 0
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dec.size = dec.r.Buffered()
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return dec
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}
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// Decode unmarshals the NDR encoded bytes into the pointer of a struct provided.
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func (dec *Decoder) Decode(s interface{}) error {
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dec.s = s
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err := dec.readCommonHeader()
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if err != nil {
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return err
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}
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err = dec.readPrivateHeader()
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if err != nil {
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return err
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}
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_, err = dec.r.Discard(4) //The next 4 bytes are an RPC unique pointer referent. We just skip these.
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if err != nil {
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return Errorf("unable to process byte stream: %v", err)
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}
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return dec.process(s, reflect.StructTag(""))
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}
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func (dec *Decoder) process(s interface{}, tag reflect.StructTag) error {
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// Scan for conformant fields as their max counts are moved to the beginning
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// http://pubs.opengroup.org/onlinepubs/9629399/chap14.htm#tagfcjh_37
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err := dec.scanConformantArrays(s, tag)
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if err != nil {
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return err
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}
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// Recursively fill the struct fields
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var localDef []deferedPtr
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err = dec.fill(s, tag, &localDef)
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if err != nil {
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return Errorf("could not decode: %v", err)
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}
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// Read any deferred referents associated with pointers
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for _, p := range localDef {
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err = dec.process(p.v, p.tag)
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if err != nil {
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return fmt.Errorf("could not decode deferred referent: %v", err)
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}
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}
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return nil
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}
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// scanConformantArrays scans the structure for embedded conformant fields and captures the maximum element counts for
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// dimensions of the array that are moved to the beginning of the structure.
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func (dec *Decoder) scanConformantArrays(s interface{}, tag reflect.StructTag) error {
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err := dec.conformantScan(s, tag)
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if err != nil {
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return fmt.Errorf("failed to scan for embedded conformant arrays: %v", err)
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}
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for i := range dec.conformantMax {
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dec.conformantMax[i], err = dec.readUint32()
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if err != nil {
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return fmt.Errorf("could not read preceding conformant max count index %d: %v", i, err)
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}
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}
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return nil
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}
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// conformantScan inspects the structure's fields for whether they are conformant.
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func (dec *Decoder) conformantScan(s interface{}, tag reflect.StructTag) error {
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ndrTag := parseTags(tag)
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if ndrTag.HasValue(TagPointer) {
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return nil
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}
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v := getReflectValue(s)
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switch v.Kind() {
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case reflect.Struct:
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for i := 0; i < v.NumField(); i++ {
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err := dec.conformantScan(v.Field(i), v.Type().Field(i).Tag)
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if err != nil {
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return err
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}
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}
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case reflect.String:
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if !ndrTag.HasValue(TagConformant) {
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break
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}
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dec.conformantMax = append(dec.conformantMax, uint32(0))
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case reflect.Slice:
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if !ndrTag.HasValue(TagConformant) {
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break
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}
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d, t := sliceDimensions(v.Type())
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for i := 0; i < d; i++ {
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dec.conformantMax = append(dec.conformantMax, uint32(0))
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}
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// For string arrays there is a common max for the strings within the array.
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if t.Kind() == reflect.String {
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dec.conformantMax = append(dec.conformantMax, uint32(0))
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}
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}
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return nil
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}
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func (dec *Decoder) isPointer(v reflect.Value, tag reflect.StructTag, def *[]deferedPtr) (bool, error) {
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// Pointer so defer filling the referent
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ndrTag := parseTags(tag)
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if ndrTag.HasValue(TagPointer) {
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p, err := dec.readUint32()
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if err != nil {
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return true, fmt.Errorf("could not read pointer: %v", err)
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}
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ndrTag.delete(TagPointer)
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if p != 0 {
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// if pointer is not zero add to the deferred items at end of stream
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*def = append(*def, deferedPtr{v, ndrTag.StructTag()})
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}
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return true, nil
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}
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return false, nil
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}
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func getReflectValue(s interface{}) (v reflect.Value) {
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if r, ok := s.(reflect.Value); ok {
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v = r
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} else {
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if reflect.ValueOf(s).Kind() == reflect.Ptr {
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v = reflect.ValueOf(s).Elem()
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}
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}
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return
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}
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// fill populates fields with values from the NDR byte stream.
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func (dec *Decoder) fill(s interface{}, tag reflect.StructTag, localDef *[]deferedPtr) error {
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v := getReflectValue(s)
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//// Pointer so defer filling the referent
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ptr, err := dec.isPointer(v, tag, localDef)
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if err != nil {
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return fmt.Errorf("could not process struct field(%s): %v", strings.Join(dec.current, "/"), err)
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}
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if ptr {
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return nil
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}
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// Populate the value from the byte stream
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switch v.Kind() {
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case reflect.Struct:
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dec.current = append(dec.current, v.Type().Name()) //Track the current field being filled
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// in case struct is a union, track this and the selected union field for efficiency
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var unionTag reflect.Value
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var unionField string // field to fill if struct is a union
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// Go through each field in the struct and recursively fill
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for i := 0; i < v.NumField(); i++ {
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fieldName := v.Type().Field(i).Name
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dec.current = append(dec.current, fieldName) //Track the current field being filled
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//fmt.Fprintf(os.Stderr, "DEBUG Decoding: %s\n", strings.Join(dec.current, "/"))
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structTag := v.Type().Field(i).Tag
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ndrTag := parseTags(structTag)
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// Union handling
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if !unionTag.IsValid() {
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// Is this field a union tag?
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unionTag = dec.isUnion(v.Field(i), structTag)
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} else {
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// What is the selected field value of the union if we don't already know
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if unionField == "" {
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unionField, err = unionSelectedField(v, unionTag)
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if err != nil {
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return fmt.Errorf("could not determine selected union value field for %s with discriminat"+
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" tag %s: %v", v.Type().Name(), unionTag, err)
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}
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}
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if ndrTag.HasValue(TagUnionField) && fieldName != unionField {
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// is a union and this field has not been selected so will skip it.
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dec.current = dec.current[:len(dec.current)-1] //This field has been skipped so remove it from the current field tracker
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continue
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}
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}
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// Check if field is a pointer
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if v.Field(i).Type().Implements(reflect.TypeOf(new(RawBytes)).Elem()) &&
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v.Field(i).Type().Kind() == reflect.Slice && v.Field(i).Type().Elem().Kind() == reflect.Uint8 {
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//field is for rawbytes
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structTag, err = addSizeToTag(v, v.Field(i), structTag)
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if err != nil {
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return fmt.Errorf("could not get rawbytes field(%s) size: %v", strings.Join(dec.current, "/"), err)
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}
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ptr, err := dec.isPointer(v.Field(i), structTag, localDef)
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if err != nil {
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return fmt.Errorf("could not process struct field(%s): %v", strings.Join(dec.current, "/"), err)
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}
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if !ptr {
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err := dec.readRawBytes(v.Field(i), structTag)
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if err != nil {
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return fmt.Errorf("could not fill raw bytes struct field(%s): %v", strings.Join(dec.current, "/"), err)
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}
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}
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} else {
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err := dec.fill(v.Field(i), structTag, localDef)
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if err != nil {
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return fmt.Errorf("could not fill struct field(%s): %v", strings.Join(dec.current, "/"), err)
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}
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}
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dec.current = dec.current[:len(dec.current)-1] //This field has been filled so remove it from the current field tracker
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}
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dec.current = dec.current[:len(dec.current)-1] //This field has been filled so remove it from the current field tracker
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case reflect.Bool:
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i, err := dec.readBool()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Uint8:
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i, err := dec.readUint8()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Uint16:
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i, err := dec.readUint16()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Uint32:
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i, err := dec.readUint32()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Uint64:
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i, err := dec.readUint64()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Int8:
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i, err := dec.readInt8()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Int16:
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i, err := dec.readInt16()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Int32:
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i, err := dec.readInt32()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Int64:
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i, err := dec.readInt64()
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if err != nil {
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return fmt.Errorf("could not fill %s: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.String:
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ndrTag := parseTags(tag)
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conformant := ndrTag.HasValue(TagConformant)
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// strings are always varying so this is assumed without an explicit tag
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var s string
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var err error
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if conformant {
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s, err = dec.readConformantVaryingString(localDef)
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if err != nil {
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return fmt.Errorf("could not fill with conformant varying string: %v", err)
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}
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} else {
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s, err = dec.readVaryingString(localDef)
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if err != nil {
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return fmt.Errorf("could not fill with varying string: %v", err)
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}
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}
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v.Set(reflect.ValueOf(s))
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case reflect.Float32:
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i, err := dec.readFloat32()
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if err != nil {
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return fmt.Errorf("could not fill %v: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Float64:
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i, err := dec.readFloat64()
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if err != nil {
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return fmt.Errorf("could not fill %v: %v", v.Type().Name(), err)
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}
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v.Set(reflect.ValueOf(i))
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case reflect.Array:
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err := dec.fillFixedArray(v, tag, localDef)
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if err != nil {
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return err
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}
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case reflect.Slice:
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if v.Type().Implements(reflect.TypeOf(new(RawBytes)).Elem()) && v.Type().Elem().Kind() == reflect.Uint8 {
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//field is for rawbytes
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err := dec.readRawBytes(v, tag)
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if err != nil {
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return fmt.Errorf("could not fill raw bytes struct field(%s): %v", strings.Join(dec.current, "/"), err)
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}
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break
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}
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ndrTag := parseTags(tag)
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conformant := ndrTag.HasValue(TagConformant)
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varying := ndrTag.HasValue(TagVarying)
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if ndrTag.HasValue(TagPipe) {
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err := dec.fillPipe(v, tag)
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if err != nil {
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return err
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}
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break
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}
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_, t := sliceDimensions(v.Type())
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if t.Kind() == reflect.String && !ndrTag.HasValue(subStringArrayValue) {
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// String array
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err := dec.readStringsArray(v, tag, localDef)
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if err != nil {
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return err
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}
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break
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}
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// varying is assumed as fixed arrays use the Go array type rather than slice
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if conformant && varying {
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err := dec.fillConformantVaryingArray(v, tag, localDef)
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if err != nil {
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return err
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}
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} else if !conformant && varying {
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err := dec.fillVaryingArray(v, tag, localDef)
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if err != nil {
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return err
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}
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} else {
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//default to conformant and not varying
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err := dec.fillConformantArray(v, tag, localDef)
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if err != nil {
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return err
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}
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}
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default:
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return fmt.Errorf("unsupported type")
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}
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return nil
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}
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// readBytes returns a number of bytes from the NDR byte stream.
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func (dec *Decoder) readBytes(n int) ([]byte, error) {
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//TODO make this take an int64 as input to allow for larger values on all systems?
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b := make([]byte, n, n)
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m, err := dec.r.Read(b)
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if err != nil || m != n {
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return b, fmt.Errorf("error reading bytes from stream: %v", err)
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}
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return b, nil
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}
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