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scanner.go
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scanner.go
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package xx
import (
"encoding/xml"
"errors"
"strings"
)
// ScanFunc is a callback that accepts an xml.StartElement, an
// xml.CharData, and an optional interface{} value for private use.
//
// The function is called for two XML tokens: xml.StartElement
// and xml.CharData. The xml.StartElement will always be the last
// StartElement parsed. CharData may be nil.
type ScanFunc func(ctx *Context) error
// Scanner scans XML from an xml.Decoder, looking for specific paths.
type Scanner struct {
tree map[xml.Name]*Scanner
se ScanFunc
cd ScanFunc
}
// NewScanner returns an initialized Scanner, ready to use.
func NewScanner() *Scanner {
return &Scanner{tree: make(map[xml.Name]*Scanner)}
}
// MustHandleStartElement initializes an XML StartElement handler.
// It panics if it cannot create a path handler.
func (s *Scanner) MustHandleStartElement(path string, f ScanFunc) {
must(s.HandleStartElement(path, f))
}
func must(err error) {
if err != nil {
panic(err)
}
}
// HandleStartElement initializes an XML StartElement handler.
//
// Paths must be in the form of "foo>bar" or "uri foo>uri bar".
// The path is delimited by > characters, and individual path
// elements are split on whitespace into a namespace and local
// tag name.
//
// HandleStartElement returns ErrInvalidPath if the specified path
// is malformed.
func (s *Scanner) HandleStartElement(path string, f ScanFunc) error {
s2, err := s.makePath(path)
if err != nil {
return err
}
s2.se = f
return nil
}
// MustHandleCharData initializes an XML CharData handler.
// It panics if it cannot create a path handler.
func (s *Scanner) MustHandleCharData(path string, f ScanFunc) {
must(s.HandleCharData(path, f))
}
// HandleCharData initializes an XML CharData handler.
func (s *Scanner) HandleCharData(path string, f ScanFunc) error {
s2, err := s.makePath(path)
if err != nil {
return err
}
s2.cd = f
return nil
}
// makePath finds or creates a tree of Scanners.
// It returns the leaf node Scanner for the path or an error.
func (s *Scanner) makePath(path string) (*Scanner, error) {
names := strings.SplitN(path, ">", 2)
fields := strings.Fields(names[0])
var name xml.Name
switch len(fields) {
case 0:
if len(names) > 1 {
return nil, ErrInvalidPath
}
return s, nil
case 1:
name.Local = fields[0]
case 2:
name.Space = fields[0]
name.Local = fields[1]
default:
return nil, ErrInvalidPath
}
s2, ok := s.tree[name]
if !ok {
s2 = NewScanner()
s.tree[name] = s2
}
if len(names) == 1 {
return s2.makePath("")
}
return s2.makePath(names[1])
}
// ErrInvalidPath describes an invalid Scanner path
// returned by Scanner.Handle.
var ErrInvalidPath = errors.New("invalid scan path")
// Scan reads xml.Tokens from Decoder d, passing matching
// xml.StartElement or xml.CharData tokens and an optional
// value from the caller to the matching ScanFuncs in s.
// It returns any errors encountered.
// It will return if it encounters an xml.EndElement that matches
// the corresponding xml.StartElement it attempted to scan.
func (s *Scanner) Scan(d *xml.Decoder, ctxValue interface{}) error {
ctx := Context{
Decoder: d,
Value: ctxValue,
}
return s.scan(&ctx)
}
func (s *Scanner) scan(ctx *Context) error {
for {
t, err := ctx.Decoder.Token()
if err != nil {
return err
}
switch node := t.(type) {
case xml.StartElement:
s2, ok := s.tree[node.Name]
if !ok {
s2, ok = s.tree[xml.Name{Space: "", Local: node.Name.Local}]
if !ok {
err = ctx.Decoder.Skip()
break
}
}
child := *ctx
child.Parent = ctx
child.StartElement = node
if s2.se != nil {
err = s2.se(&child)
if err != nil {
return err
}
}
err = s2.scan(&child)
case xml.EndElement:
return nil
case xml.CharData:
if s.cd != nil {
ctx.CharData = node
err = s.cd(ctx)
ctx.CharData = nil
}
}
if err != nil {
return err
}
}
}