Source: unmarshal.go in package github.com/aws/aws-sdk-go/private/protocol/xml/xmlutil

package xmlutil

import (
	"bytes"
	"encoding/base64"
	"encoding/xml"
	"fmt"
	"io"
	"reflect"
	"strconv"
	"strings"
	"time"

	"github.com/aws/aws-sdk-go/aws/awserr"
	"github.com/aws/aws-sdk-go/private/protocol"
)

UnmarshalXMLError unmarshals the XML error from the stream into the value type specified. The value must be a pointer. If the message fails to unmarshal, the message content will be included in the returned error as a awserr.UnmarshalError.

func UnmarshalXMLError(v interface{}, stream io.Reader) error {
	var errBuf bytes.Buffer
	body := io.TeeReader(stream, &errBuf)

	err := xml.NewDecoder(body).Decode(v)
	if err != nil && err != io.EOF {
		return awserr.NewUnmarshalError(err,
			"failed to unmarshal error message", errBuf.Bytes())
	}

	return nil
}

UnmarshalXML deserializes an xml.Decoder into the container v. V needs to match the shape of the XML expected to be decoded. If the shape doesn't match unmarshaling will fail.

func UnmarshalXML(v interface{}, d *xml.Decoder, wrapper string) error {
	n, err := XMLToStruct(d, nil)
	if err != nil {
		return err
	}
	if n.Children != nil {
		for _, root := range n.Children {
			for _, c := range root {
				if wrappedChild, ok := c.Children[wrapper]; ok {
					c = wrappedChild[0] // pull out wrapped element
				}

				err = parse(reflect.ValueOf(v), c, "")
				if err != nil {
					if err == io.EOF {
						return nil
					}
					return err
				}
			}
		}
		return nil
	}
	return nil
}

parse deserializes any value from the XMLNode. The type tag is used to infer the type, or reflect will be used to determine the type from r.

func parse(r reflect.Value, node *XMLNode, tag reflect.StructTag) error {
	xml := tag.Get("xml")
	if len(xml) != 0 {
		name := strings.SplitAfterN(xml, ",", 2)[0]
		if name == "-" {
			return nil
		}
	}

	rtype := r.Type()
	if rtype.Kind() == reflect.Ptr {
		rtype = rtype.Elem() // check kind of actual element type
	}

	t := tag.Get("type")
	if t == "" {
		switch rtype.Kind() {

also it can't be a time object

			if _, ok := r.Interface().(*time.Time); !ok {
				t = "structure"
			}

also it can't be a byte slice

			if _, ok := r.Interface().([]byte); !ok {
				t = "list"
			}
		case reflect.Map:
			t = "map"
		}
	}

	switch t {
	case "structure":
		if field, ok := rtype.FieldByName("_"); ok {
			tag = field.Tag
		}
		return parseStruct(r, node, tag)
	case "list":
		return parseList(r, node, tag)
	case "map":
		return parseMap(r, node, tag)
	default:
		return parseScalar(r, node, tag)
	}
}

parseStruct deserializes a structure and its fields from an XMLNode. Any nested types in the structure will also be deserialized.

func parseStruct(r reflect.Value, node *XMLNode, tag reflect.StructTag) error {
	t := r.Type()
	if r.Kind() == reflect.Ptr {
		if r.IsNil() { // create the structure if it's nil
			s := reflect.New(r.Type().Elem())
			r.Set(s)
			r = s
		}

		r = r.Elem()
		t = t.Elem()
	}

unwrap any payloads

	if payload := tag.Get("payload"); payload != "" {
		field, _ := t.FieldByName(payload)
		return parseStruct(r.FieldByName(payload), node, field.Tag)
	}

	for i := 0; i < t.NumField(); i++ {
		field := t.Field(i)
		if c := field.Name[0:1]; strings.ToLower(c) == c {
			continue // ignore unexported fields
		}

figure out what this field is called

		name := field.Name
		if field.Tag.Get("flattened") != "" && field.Tag.Get("locationNameList") != "" {
			name = field.Tag.Get("locationNameList")
		} else if locName := field.Tag.Get("locationName"); locName != "" {
			name = locName
		}

try to find the field by name in elements

		elems := node.Children[name]

		if elems == nil { // try to find the field in attributes
			if val, ok := node.findElem(name); ok {
				elems = []*XMLNode{{Text: val}}
			}
		}

		member := r.FieldByName(field.Name)
		for _, elem := range elems {
			err := parse(member, elem, field.Tag)
			if err != nil {
				return err
			}
		}
	}
	return nil
}

parseList deserializes a list of values from an XML node. Each list entry will also be deserialized.

func parseList(r reflect.Value, node *XMLNode, tag reflect.StructTag) error {
	t := r.Type()

	if tag.Get("flattened") == "" { // look at all item entries
		mname := "member"
		if name := tag.Get("locationNameList"); name != "" {
			mname = name
		}

		if Children, ok := node.Children[mname]; ok {
			if r.IsNil() {
				r.Set(reflect.MakeSlice(t, len(Children), len(Children)))
			}

			for i, c := range Children {
				err := parse(r.Index(i), c, "")
				if err != nil {
					return err
				}
			}
		}
	} else { // flattened list means this is a single element
		if r.IsNil() {
			r.Set(reflect.MakeSlice(t, 0, 0))
		}

		childR := reflect.Zero(t.Elem())
		r.Set(reflect.Append(r, childR))
		err := parse(r.Index(r.Len()-1), node, "")
		if err != nil {
			return err
		}
	}

	return nil
}

parseMap deserializes a map from an XMLNode. The direct children of the XMLNode will also be deserialized as map entries.

func parseMap(r reflect.Value, node *XMLNode, tag reflect.StructTag) error {
	if r.IsNil() {
		r.Set(reflect.MakeMap(r.Type()))
	}

	if tag.Get("flattened") == "" { // look at all child entries
		for _, entry := range node.Children["entry"] {
			parseMapEntry(r, entry, tag)
		}
	} else { // this element is itself an entry
		parseMapEntry(r, node, tag)
	}

	return nil
}

parseMapEntry deserializes a map entry from a XML node.

func parseMapEntry(r reflect.Value, node *XMLNode, tag reflect.StructTag) error {
	kname, vname := "key", "value"
	if n := tag.Get("locationNameKey"); n != "" {
		kname = n
	}
	if n := tag.Get("locationNameValue"); n != "" {
		vname = n
	}

	keys, ok := node.Children[kname]
	values := node.Children[vname]
	if ok {
		for i, key := range keys {
			keyR := reflect.ValueOf(key.Text)
			value := values[i]
			valueR := reflect.New(r.Type().Elem()).Elem()

			parse(valueR, value, "")
			r.SetMapIndex(keyR, valueR)
		}
	}
	return nil
}

parseScaller deserializes an XMLNode value into a concrete type based on the interface type of r. Error is returned if the deserialization fails due to invalid type conversion, or unsupported interface type.

func parseScalar(r reflect.Value, node *XMLNode, tag reflect.StructTag) error {
	switch r.Interface().(type) {
	case *string:
		r.Set(reflect.ValueOf(&node.Text))
		return nil
	case []byte:
		b, err := base64.StdEncoding.DecodeString(node.Text)
		if err != nil {
			return err
		}
		r.Set(reflect.ValueOf(b))
	case *bool:
		v, err := strconv.ParseBool(node.Text)
		if err != nil {
			return err
		}
		r.Set(reflect.ValueOf(&v))
	case *int64:
		v, err := strconv.ParseInt(node.Text, 10, 64)
		if err != nil {
			return err
		}
		r.Set(reflect.ValueOf(&v))
	case *float64:
		v, err := strconv.ParseFloat(node.Text, 64)
		if err != nil {
			return err
		}
		r.Set(reflect.ValueOf(&v))
	case *time.Time:
		format := tag.Get("timestampFormat")
		if len(format) == 0 {
			format = protocol.ISO8601TimeFormatName
		}

		t, err := protocol.ParseTime(format, node.Text)
		if err != nil {
			return err
		}
		r.Set(reflect.ValueOf(&t))
	default:
		return fmt.Errorf("unsupported value: %v (%s)", r.Interface(), r.Type())
	}
	return nil