code.dwrz.net

xml_decoder.go (4390B)

---

 package xml
 
 import (
 	"encoding/xml"
 	"fmt"
 	"strings"
 )
 
 // NodeDecoder is a XML decoder wrapper that is responsible to decoding
 // a single XML Node element and it's nested member elements. This wrapper decoder
 // takes in the start element of the top level node being decoded.
 type NodeDecoder struct {
 	Decoder *xml.Decoder
 	StartEl xml.StartElement
 }
 
 // WrapNodeDecoder returns an initialized XMLNodeDecoder
 func WrapNodeDecoder(decoder *xml.Decoder, startEl xml.StartElement) NodeDecoder {
 	return NodeDecoder{
 		Decoder: decoder,
 		StartEl: startEl,
 	}
 }
 
 // Token on a Node Decoder returns a xml StartElement. It returns a boolean that indicates the
 // a token is the node decoder's end node token; and an error which indicates any error
 // that occurred while retrieving the start element
 func (d NodeDecoder) Token() (t xml.StartElement, done bool, err error) {
 	for {
 		token, e := d.Decoder.Token()
 		if e != nil {
 			return t, done, e
 		}
 
 		// check if we reach end of the node being decoded
 		if el, ok := token.(xml.EndElement); ok {
 			return t, el == d.StartEl.End(), err
 		}
 
 		if t, ok := token.(xml.StartElement); ok {
 			return restoreAttrNamespaces(t), false, err
 		}
 
 		// skip token if it is a comment or preamble or empty space value due to indentation
 		// or if it's a value and is not expected
 	}
 }
 
 // restoreAttrNamespaces update XML attributes to restore the short namespaces found within
 // the raw XML document.
 func restoreAttrNamespaces(node xml.StartElement) xml.StartElement {
 	if len(node.Attr) == 0 {
 		return node
 	}
 
 	// Generate a mapping of XML namespace values to their short names.
 	ns := map[string]string{}
 	for _, a := range node.Attr {
 		if a.Name.Space == "xmlns" {
 			ns[a.Value] = a.Name.Local
 			break
 		}
 	}
 
 	for i, a := range node.Attr {
 		if a.Name.Space == "xmlns" {
 			continue
 		}
 		// By default, xml.Decoder will fully resolve these namespaces. So if you had <foo xmlns:bar=baz bar:bin=hi/>
 		// then by default the second attribute would have the `Name.Space` resolved to `baz`. But we need it to
 		// continue to resolve as `bar` so we can easily identify it later on.
 		if v, ok := ns[node.Attr[i].Name.Space]; ok {
 			node.Attr[i].Name.Space = v
 		}
 	}
 	return node
 }
 
 // GetElement looks for the given tag name at the current level, and returns the element if found, and
 // skipping over non-matching elements. Returns an error if the node is not found, or if an error occurs while walking
 // the document.
 func (d NodeDecoder) GetElement(name string) (t xml.StartElement, err error) {
 	for {
 		token, done, err := d.Token()
 		if err != nil {
 			return t, err
 		}
 		if done {
 			return t, fmt.Errorf("%s node not found", name)
 		}
 		switch {
 		case strings.EqualFold(name, token.Name.Local):
 			return token, nil
 		default:
 			err = d.Decoder.Skip()
 			if err != nil {
 				return t, err
 			}
 		}
 	}
 }
 
 // Value provides an abstraction to retrieve char data value within an xml element.
 // The method will return an error if it encounters a nested xml element instead of char data.
 // This method should only be used to retrieve simple type or blob shape values as []byte.
 func (d NodeDecoder) Value() (c []byte, err error) {
 	t, e := d.Decoder.Token()
 	if e != nil {
 		return c, e
 	}
 
 	endElement := d.StartEl.End()
 
 	switch ev := t.(type) {
 	case xml.CharData:
 		c = ev.Copy()
 	case xml.EndElement: // end tag or self-closing
 		if ev == endElement {
 			return []byte{}, err
 		}
 		return c, fmt.Errorf("expected value for %v element, got %T type %v instead", d.StartEl.Name.Local, t, t)
 	default:
 		return c, fmt.Errorf("expected value for %v element, got %T type %v instead", d.StartEl.Name.Local, t, t)
 	}
 
 	t, e = d.Decoder.Token()
 	if e != nil {
 		return c, e
 	}
 
 	if ev, ok := t.(xml.EndElement); ok {
 		if ev == endElement {
 			return c, err
 		}
 	}
 
 	return c, fmt.Errorf("expected end element %v, got %T type %v instead", endElement, t, t)
 }
 
 // FetchRootElement takes in a decoder and returns the first start element within the xml body.
 // This function is useful in fetching the start element of an XML response and ignore the
 // comments and preamble
 func FetchRootElement(decoder *xml.Decoder) (startElement xml.StartElement, err error) {
 	for {
 		t, e := decoder.Token()
 		if e != nil {
 			return startElement, e
 		}
 
 		if startElement, ok := t.(xml.StartElement); ok {
 			return startElement, err
 		}
 	}
 }