initial 'driveClient' based on 'github.com/emersion/go-webdav' (#511)

util/sync/driveClient/internal/xml.go

@@ -0,0 +1,175 @@
+package internal
+
+import (
+	"encoding/xml"
+	"fmt"
+	"io"
+	"reflect"
+	"strings"
+)
+
+// RawXMLValue is a raw XML value. It implements xml.Unmarshaler and
+// xml.Marshaler and can be used to delay XML decoding or precompute an XML
+// encoding.
+type RawXMLValue struct {
+	tok      xml.Token // guaranteed not to be xml.EndElement
+	children []RawXMLValue
+
+	// Unfortunately encoding/xml doesn't offer TokenWriter, so we need to
+	// cache outgoing data.
+	out interface{}
+}
+
+// NewRawXMLElement creates a new RawXMLValue for an element.
+func NewRawXMLElement(name xml.Name, attr []xml.Attr, children []RawXMLValue) *RawXMLValue {
+	return &RawXMLValue{tok: xml.StartElement{name, attr}, children: children}
+}
+
+// EncodeRawXMLElement encodes a value into a new RawXMLValue. The XML value
+// can only be used for marshalling.
+func EncodeRawXMLElement(v interface{}) (*RawXMLValue, error) {
+	return &RawXMLValue{out: v}, nil
+}
+
+// UnmarshalXML implements xml.Unmarshaler.
+func (val *RawXMLValue) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
+	val.tok = start
+	val.children = nil
+	val.out = nil
+
+	for {
+		tok, err := d.Token()
+		if err != nil {
+			return err
+		}
+		switch tok := tok.(type) {
+		case xml.StartElement:
+			child := RawXMLValue{}
+			if err := child.UnmarshalXML(d, tok); err != nil {
+				return err
+			}
+			val.children = append(val.children, child)
+		case xml.EndElement:
+			return nil
+		default:
+			val.children = append(val.children, RawXMLValue{tok: xml.CopyToken(tok)})
+		}
+	}
+}
+
+// MarshalXML implements xml.Marshaler.
+func (val *RawXMLValue) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
+	if val.out != nil {
+		return e.Encode(val.out)
+	}
+
+	switch tok := val.tok.(type) {
+	case xml.StartElement:
+		if err := e.EncodeToken(tok); err != nil {
+			return err
+		}
+		for _, child := range val.children {
+			// TODO: find a sensible value for the start argument?
+			if err := child.MarshalXML(e, xml.StartElement{}); err != nil {
+				return err
+			}
+		}
+		return e.EncodeToken(tok.End())
+	case xml.EndElement:
+		panic("unexpected end element")
+	default:
+		return e.EncodeToken(tok)
+	}
+}
+
+var _ xml.Marshaler = (*RawXMLValue)(nil)
+var _ xml.Unmarshaler = (*RawXMLValue)(nil)
+
+func (val *RawXMLValue) Decode(v interface{}) error {
+	return xml.NewTokenDecoder(val.TokenReader()).Decode(&v)
+}
+
+func (val *RawXMLValue) XMLName() (name xml.Name, ok bool) {
+	if start, ok := val.tok.(xml.StartElement); ok {
+		return start.Name, true
+	}
+	return xml.Name{}, false
+}
+
+// TokenReader returns a stream of tokens for the XML value.
+func (val *RawXMLValue) TokenReader() xml.TokenReader {
+	if val.out != nil {
+		panic("webdav: called RawXMLValue.TokenReader on a marshal-only XML value")
+	}
+	return &rawXMLValueReader{val: val}
+}
+
+type rawXMLValueReader struct {
+	val         *RawXMLValue
+	start, end  bool
+	child       int
+	childReader xml.TokenReader
+}
+
+func (tr *rawXMLValueReader) Token() (xml.Token, error) {
+	if tr.end {
+		return nil, io.EOF
+	}
+
+	start, ok := tr.val.tok.(xml.StartElement)
+	if !ok {
+		tr.end = true
+		return tr.val.tok, nil
+	}
+
+	if !tr.start {
+		tr.start = true
+		return start, nil
+	}
+
+	for tr.child < len(tr.val.children) {
+		if tr.childReader == nil {
+			tr.childReader = tr.val.children[tr.child].TokenReader()
+		}
+
+		tok, err := tr.childReader.Token()
+		if err == io.EOF {
+			tr.childReader = nil
+			tr.child++
+		} else {
+			return tok, err
+		}
+	}
+
+	tr.end = true
+	return start.End(), nil
+}
+
+var _ xml.TokenReader = (*rawXMLValueReader)(nil)
+
+func valueXMLName(v interface{}) (xml.Name, error) {
+	t := reflect.TypeOf(v)
+	for t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+	if t.Kind() != reflect.Struct {
+		return xml.Name{}, fmt.Errorf("webdav: %T is not a struct", v)
+	}
+	nameField, ok := t.FieldByName("XMLName")
+	if !ok {
+		return xml.Name{}, fmt.Errorf("webdav: %T is missing an XMLName struct field", v)
+	}
+	if nameField.Type != reflect.TypeOf(xml.Name{}) {
+		return xml.Name{}, fmt.Errorf("webdav: %T.XMLName isn't an xml.Name", v)
+	}
+	tag := nameField.Tag.Get("xml")
+	if tag == "" {
+		return xml.Name{}, fmt.Errorf(`webdav: %T.XMLName is missing an "xml" tag`, v)
+	}
+	name := strings.Split(tag, ",")[0]
+	nameParts := strings.Split(name, " ")
+	if len(nameParts) != 2 {
+		return xml.Name{}, fmt.Errorf("webdav: expected a namespace and local name in %T.XMLName's xml tag", v)
+	}
+	return xml.Name{nameParts[0], nameParts[1]}, nil
+}