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dex/vendor/github.com/beevik/etree/path.go
2017-01-09 18:30:58 -08:00

471 lines
12 KiB
Go

// Copyright 2015 Brett Vickers.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package etree
import (
"strconv"
"strings"
)
/*
A Path is an object that represents an optimized version of an
XPath-like search string. Although path strings are XPath-like,
only the following limited syntax is supported:
. Selects the current element
.. Selects the parent of the current element
* Selects all child elements
// Selects all descendants of the current element
tag Selects all child elements with the given tag
[#] Selects the element of the given index (1-based,
negative starts from the end)
[@attrib] Selects all elements with the given attribute
[@attrib='val'] Selects all elements with the given attribute set to val
[tag] Selects all elements with a child element named tag
[tag='val'] Selects all elements with a child element named tag
and text equal to val
Examples:
Select the title elements of all descendant book elements having a
'category' attribute of 'WEB':
//book[@category='WEB']/title
Select the first book element with a title child containing the text
'Great Expectations':
.//book[title='Great Expectations'][1]
Starting from the current element, select all children of book elements
with an attribute 'language' set to 'english':
./book/*[@language='english']
Select all descendant book elements whose title element has an attribute
'language' set to 'french':
//book/title[@language='french']/..
*/
type Path struct {
segments []segment
}
// ErrPath is returned by path functions when an invalid etree path is provided.
type ErrPath string
// Error returns the string describing a path error.
func (err ErrPath) Error() string {
return "etree: " + string(err)
}
// CompilePath creates an optimized version of an XPath-like string that
// can be used to query elements in an element tree.
func CompilePath(path string) (Path, error) {
var comp compiler
segments := comp.parsePath(path)
if comp.err != ErrPath("") {
return Path{nil}, comp.err
}
return Path{segments}, nil
}
// MustCompilePath creates an optimized version of an XPath-like string that
// can be used to query elements in an element tree. Panics if an error
// occurs. Use this function to create Paths when you know the path is
// valid (i.e., if it's hard-coded).
func MustCompilePath(path string) Path {
p, err := CompilePath(path)
if err != nil {
panic(err)
}
return p
}
// A segment is a portion of a path between "/" characters.
// It contains one selector and zero or more [filters].
type segment struct {
sel selector
filters []filter
}
func (seg *segment) apply(e *Element, p *pather) {
seg.sel.apply(e, p)
for _, f := range seg.filters {
f.apply(p)
}
}
// A selector selects XML elements for consideration by the
// path traversal.
type selector interface {
apply(e *Element, p *pather)
}
// A filter pares down a list of candidate XML elements based
// on a path filter in [brackets].
type filter interface {
apply(p *pather)
}
// A pather is helper object that traverses an element tree using
// a Path object. It collects and deduplicates all elements matching
// the path query.
type pather struct {
queue fifo
results []*Element
inResults map[*Element]bool
candidates []*Element
scratch []*Element // used by filters
}
// A node represents an element and the remaining path segments that
// should be applied against it by the pather.
type node struct {
e *Element
segments []segment
}
func newPather() *pather {
return &pather{
results: make([]*Element, 0),
inResults: make(map[*Element]bool),
candidates: make([]*Element, 0),
scratch: make([]*Element, 0),
}
}
// traverse follows the path from the element e, collecting
// and then returning all elements that match the path's selectors
// and filters.
func (p *pather) traverse(e *Element, path Path) []*Element {
for p.queue.add(node{e, path.segments}); p.queue.len() > 0; {
p.eval(p.queue.remove().(node))
}
return p.results
}
// eval evalutes the current path node by applying the remaining
// path's selector rules against the node's element.
func (p *pather) eval(n node) {
p.candidates = p.candidates[0:0]
seg, remain := n.segments[0], n.segments[1:]
seg.apply(n.e, p)
if len(remain) == 0 {
for _, c := range p.candidates {
if in := p.inResults[c]; !in {
p.inResults[c] = true
p.results = append(p.results, c)
}
}
} else {
for _, c := range p.candidates {
p.queue.add(node{c, remain})
}
}
}
// A compiler generates a compiled path from a path string.
type compiler struct {
err ErrPath
}
// parsePath parses an XPath-like string describing a path
// through an element tree and returns a slice of segment
// descriptors.
func (c *compiler) parsePath(path string) []segment {
// If path starts or ends with //, fix it
if strings.HasPrefix(path, "//") {
path = "." + path
}
if strings.HasSuffix(path, "//") {
path = path + "*"
}
// Paths cannot be absolute
if strings.HasPrefix(path, "/") {
c.err = ErrPath("paths cannot be absolute.")
return nil
}
// Split path into segment objects
var segments []segment
for _, s := range splitPath(path) {
segments = append(segments, c.parseSegment(s))
if c.err != ErrPath("") {
break
}
}
return segments
}
func splitPath(path string) []string {
pieces := make([]string, 0)
start := 0
inquote := false
for i := 0; i+1 <= len(path); i++ {
if path[i] == '\'' {
inquote = !inquote
} else if path[i] == '/' && !inquote {
pieces = append(pieces, path[start:i])
start = i + 1
}
}
return append(pieces, path[start:])
}
// parseSegment parses a path segment between / characters.
func (c *compiler) parseSegment(path string) segment {
pieces := strings.Split(path, "[")
seg := segment{
sel: c.parseSelector(pieces[0]),
filters: make([]filter, 0),
}
for i := 1; i < len(pieces); i++ {
fpath := pieces[i]
if fpath[len(fpath)-1] != ']' {
c.err = ErrPath("path has invalid filter [brackets].")
break
}
seg.filters = append(seg.filters, c.parseFilter(fpath[:len(fpath)-1]))
}
return seg
}
// parseSelector parses a selector at the start of a path segment.
func (c *compiler) parseSelector(path string) selector {
switch path {
case ".":
return new(selectSelf)
case "..":
return new(selectParent)
case "*":
return new(selectChildren)
case "":
return new(selectDescendants)
default:
return newSelectChildrenByTag(path)
}
}
// parseFilter parses a path filter contained within [brackets].
func (c *compiler) parseFilter(path string) filter {
if len(path) == 0 {
c.err = ErrPath("path contains an empty filter expression.")
return nil
}
// Filter contains [@attr='val'] or [tag='val']?
eqindex := strings.Index(path, "='")
if eqindex >= 0 {
rindex := nextIndex(path, "'", eqindex+2)
if rindex != len(path)-1 {
c.err = ErrPath("path has mismatched filter quotes.")
return nil
}
switch {
case path[0] == '@':
return newFilterAttrVal(path[1:eqindex], path[eqindex+2:rindex])
default:
return newFilterChildText(path[:eqindex], path[eqindex+2:rindex])
}
}
// Filter contains [@attr], [N] or [tag]
switch {
case path[0] == '@':
return newFilterAttr(path[1:])
case isInteger(path):
pos, _ := strconv.Atoi(path)
switch {
case pos > 0:
return newFilterPos(pos - 1)
default:
return newFilterPos(pos)
}
default:
return newFilterChild(path)
}
}
// selectSelf selects the current element into the candidate list.
type selectSelf struct{}
func (s *selectSelf) apply(e *Element, p *pather) {
p.candidates = append(p.candidates, e)
}
// selectParent selects the element's parent into the candidate list.
type selectParent struct{}
func (s *selectParent) apply(e *Element, p *pather) {
if e.parent != nil {
p.candidates = append(p.candidates, e.parent)
}
}
// selectChildren selects the element's child elements into the
// candidate list.
type selectChildren struct{}
func (s *selectChildren) apply(e *Element, p *pather) {
for _, c := range e.Child {
if c, ok := c.(*Element); ok {
p.candidates = append(p.candidates, c)
}
}
}
// selectDescendants selects all descendant child elements
// of the element into the candidate list.
type selectDescendants struct{}
func (s *selectDescendants) apply(e *Element, p *pather) {
var queue fifo
for queue.add(e); queue.len() > 0; {
e := queue.remove().(*Element)
p.candidates = append(p.candidates, e)
for _, c := range e.Child {
if c, ok := c.(*Element); ok {
queue.add(c)
}
}
}
}
// selectChildrenByTag selects into the candidate list all child
// elements of the element having the specified tag.
type selectChildrenByTag struct {
space, tag string
}
func newSelectChildrenByTag(path string) *selectChildrenByTag {
s, l := spaceDecompose(path)
return &selectChildrenByTag{s, l}
}
func (s *selectChildrenByTag) apply(e *Element, p *pather) {
for _, c := range e.Child {
if c, ok := c.(*Element); ok && spaceMatch(s.space, c.Space) && s.tag == c.Tag {
p.candidates = append(p.candidates, c)
}
}
}
// filterPos filters the candidate list, keeping only the
// candidate at the specified index.
type filterPos struct {
index int
}
func newFilterPos(pos int) *filterPos {
return &filterPos{pos}
}
func (f *filterPos) apply(p *pather) {
if f.index >= 0 {
if f.index < len(p.candidates) {
p.scratch = append(p.scratch, p.candidates[f.index])
}
} else {
if -f.index <= len(p.candidates) {
p.scratch = append(p.scratch, p.candidates[len(p.candidates)+f.index])
}
}
p.candidates, p.scratch = p.scratch, p.candidates[0:0]
}
// filterAttr filters the candidate list for elements having
// the specified attribute.
type filterAttr struct {
space, key string
}
func newFilterAttr(str string) *filterAttr {
s, l := spaceDecompose(str)
return &filterAttr{s, l}
}
func (f *filterAttr) apply(p *pather) {
for _, c := range p.candidates {
for _, a := range c.Attr {
if spaceMatch(f.space, a.Space) && f.key == a.Key {
p.scratch = append(p.scratch, c)
break
}
}
}
p.candidates, p.scratch = p.scratch, p.candidates[0:0]
}
// filterAttrVal filters the candidate list for elements having
// the specified attribute with the specified value.
type filterAttrVal struct {
space, key, val string
}
func newFilterAttrVal(str, value string) *filterAttrVal {
s, l := spaceDecompose(str)
return &filterAttrVal{s, l, value}
}
func (f *filterAttrVal) apply(p *pather) {
for _, c := range p.candidates {
for _, a := range c.Attr {
if spaceMatch(f.space, a.Space) && f.key == a.Key && f.val == a.Value {
p.scratch = append(p.scratch, c)
break
}
}
}
p.candidates, p.scratch = p.scratch, p.candidates[0:0]
}
// filterChild filters the candidate list for elements having
// a child element with the specified tag.
type filterChild struct {
space, tag string
}
func newFilterChild(str string) *filterChild {
s, l := spaceDecompose(str)
return &filterChild{s, l}
}
func (f *filterChild) apply(p *pather) {
for _, c := range p.candidates {
for _, cc := range c.Child {
if cc, ok := cc.(*Element); ok &&
spaceMatch(f.space, cc.Space) &&
f.tag == cc.Tag {
p.scratch = append(p.scratch, c)
}
}
}
p.candidates, p.scratch = p.scratch, p.candidates[0:0]
}
// filterChildText filters the candidate list for elements having
// a child element with the specified tag and text.
type filterChildText struct {
space, tag, text string
}
func newFilterChildText(str, text string) *filterChildText {
s, l := spaceDecompose(str)
return &filterChildText{s, l, text}
}
func (f *filterChildText) apply(p *pather) {
for _, c := range p.candidates {
for _, cc := range c.Child {
if cc, ok := cc.(*Element); ok &&
spaceMatch(f.space, cc.Space) &&
f.tag == cc.Tag &&
f.text == cc.Text() {
p.scratch = append(p.scratch, c)
}
}
}
p.candidates, p.scratch = p.scratch, p.candidates[0:0]
}