267 lines
6.8 KiB
Go
267 lines
6.8 KiB
Go
package robotstxt
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// Comments explaining the logic are taken from either the google's spec:
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// https://developers.google.com/webmasters/control-crawl-index/docs/robots_txt
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//
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// or the Wikipedia's entry on robots.txt:
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// http://en.wikipedia.org/wiki/Robots.txt
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import (
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"fmt"
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"io"
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"regexp"
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"strconv"
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"strings"
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"time"
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)
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type lineType uint
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const (
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lIgnore lineType = iota
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lUnknown
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lUserAgent
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lAllow
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lDisallow
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lCrawlDelay
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lSitemap
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lHost
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)
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type parser struct {
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tokens []string
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pos int
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}
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type lineInfo struct {
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t lineType // Type of line key
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k string // String representation of the type of key
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vs string // String value of the key
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vf float64 // Float value of the key
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vr *regexp.Regexp // Regexp value of the key
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}
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func newParser(tokens []string) *parser {
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return &parser{tokens: tokens}
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}
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func parseGroupMap(groups map[string]*Group, agents []string, fun func(*Group)) {
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var g *Group
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for _, a := range agents {
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if g = groups[a]; g == nil {
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g = new(Group)
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groups[a] = g
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}
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fun(g)
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}
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}
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func (p *parser) parseAll() (groups map[string]*Group, host string, sitemaps []string, errs []error) {
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groups = make(map[string]*Group, 16)
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agents := make([]string, 0, 4)
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isEmptyGroup := true
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// Reset internal fields, tokens are assigned at creation time, never change
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p.pos = 0
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for {
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if li, err := p.parseLine(); err != nil {
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if err == io.EOF {
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break
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}
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errs = append(errs, err)
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} else {
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switch li.t {
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case lUserAgent:
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// Two successive user-agent lines are part of the same group.
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if !isEmptyGroup {
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// End previous group
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agents = make([]string, 0, 4)
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}
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if len(agents) == 0 {
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isEmptyGroup = true
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}
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agents = append(agents, li.vs)
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case lDisallow:
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// Error if no current group
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if len(agents) == 0 {
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errs = append(errs, fmt.Errorf("Disallow before User-agent at token #%d.", p.pos))
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} else {
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isEmptyGroup = false
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var r *rule
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if li.vr != nil {
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r = &rule{"", false, li.vr}
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} else {
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r = &rule{li.vs, false, nil}
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}
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parseGroupMap(groups, agents, func(g *Group) { g.rules = append(g.rules, r) })
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}
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case lAllow:
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// Error if no current group
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if len(agents) == 0 {
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errs = append(errs, fmt.Errorf("Allow before User-agent at token #%d.", p.pos))
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} else {
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isEmptyGroup = false
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var r *rule
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if li.vr != nil {
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r = &rule{"", true, li.vr}
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} else {
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r = &rule{li.vs, true, nil}
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}
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parseGroupMap(groups, agents, func(g *Group) { g.rules = append(g.rules, r) })
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}
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case lHost:
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host = li.vs
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case lSitemap:
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sitemaps = append(sitemaps, li.vs)
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case lCrawlDelay:
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if len(agents) == 0 {
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errs = append(errs, fmt.Errorf("Crawl-delay before User-agent at token #%d.", p.pos))
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} else {
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isEmptyGroup = false
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delay := time.Duration(li.vf * float64(time.Second))
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parseGroupMap(groups, agents, func(g *Group) { g.CrawlDelay = delay })
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}
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}
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}
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}
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return
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}
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func (p *parser) parseLine() (li *lineInfo, err error) {
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t1, ok1 := p.popToken()
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if !ok1 {
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// proper EOF
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return nil, io.EOF
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}
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t2, ok2 := p.peekToken()
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if !ok2 {
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// EOF, no value associated with the token, so ignore token and return
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return nil, io.EOF
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}
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// Helper closure for all string-based tokens, common behaviour:
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// - Consume t2 token
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// - If empty, return unknown line info
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// - Otherwise return the specified line info
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returnStringVal := func(t lineType) (*lineInfo, error) {
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p.popToken()
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if t2 != "" {
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return &lineInfo{t: t, k: t1, vs: t2}, nil
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}
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return &lineInfo{t: lIgnore}, nil
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}
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// Helper closure for all path tokens (allow/disallow), common behaviour:
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// - Consume t2 token
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// - If empty, return unknown line info
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// - Otherwise, normalize the path (add leading "/" if missing, remove trailing "*")
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// - Detect if wildcards are present, if so, compile into a regexp
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// - Return the specified line info
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returnPathVal := func(t lineType) (*lineInfo, error) {
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p.popToken()
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if t2 != "" {
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if !strings.HasPrefix(t2, "*") && !strings.HasPrefix(t2, "/") {
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t2 = "/" + t2
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}
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if strings.HasSuffix(t2, "*") {
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t2 = strings.TrimRight(t2, "*")
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}
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// From google's spec:
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// Google, Bing, Yahoo, and Ask support a limited form of
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// "wildcards" for path values. These are:
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// * designates 0 or more instances of any valid character
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// $ designates the end of the URL
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if strings.ContainsAny(t2, "*$") {
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// Must compile a regexp, this is a pattern.
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// Escape string before compile.
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t2 = regexp.QuoteMeta(t2)
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t2 = strings.Replace(t2, `\*`, `.*`, -1)
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t2 = strings.Replace(t2, `\$`, `$`, -1)
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if r, e := regexp.Compile(t2); e != nil {
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return nil, e
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} else {
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return &lineInfo{t: t, k: t1, vr: r}, nil
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}
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} else {
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// Simple string path
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return &lineInfo{t: t, k: t1, vs: t2}, nil
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}
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}
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return &lineInfo{t: lIgnore}, nil
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}
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switch strings.ToLower(t1) {
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case tokEOL:
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// Don't consume t2 and continue parsing
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return &lineInfo{t: lIgnore}, nil
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case "user-agent", "useragent":
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// From google's spec:
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// Handling of <field> elements with simple errors / typos (eg "useragent"
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// instead of "user-agent") is undefined and may be interpreted as correct
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// directives by some user-agents.
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// The user-agent is non-case-sensitive.
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t2 = strings.ToLower(t2)
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return returnStringVal(lUserAgent)
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case "disallow":
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// From google's spec:
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// When no path is specified, the directive is ignored (so an empty Disallow
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// CAN be an allow, since allow is the default. The actual result depends
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// on the other rules in the group).
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return returnPathVal(lDisallow)
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case "allow":
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// From google's spec:
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// When no path is specified, the directive is ignored.
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return returnPathVal(lAllow)
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case "host":
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// Host directive to specify main site mirror
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// Read more: https://help.yandex.com/webmaster/controlling-robot/robots-txt.xml#host
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return returnStringVal(lHost)
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case "sitemap":
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// Non-group field, applies to the host as a whole, not to a specific user-agent
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return returnStringVal(lSitemap)
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case "crawl-delay", "crawldelay":
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// From http://en.wikipedia.org/wiki/Robots_exclusion_standard#Nonstandard_extensions
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// Several major crawlers support a Crawl-delay parameter, set to the
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// number of seconds to wait between successive requests to the same server.
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p.popToken()
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if cd, e := strconv.ParseFloat(t2, 64); e != nil {
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return nil, e
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} else {
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return &lineInfo{t: lCrawlDelay, k: t1, vf: cd}, nil
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}
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}
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// Consume t2 token
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p.popToken()
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return &lineInfo{t: lUnknown, k: t1}, nil
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}
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func (p *parser) popToken() (tok string, ok bool) {
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tok, ok = p.peekToken()
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if !ok {
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return
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}
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p.pos++
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return tok, true
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}
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func (p *parser) peekToken() (tok string, ok bool) {
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if p.pos >= len(p.tokens) {
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return "", false
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}
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return p.tokens[p.pos], true
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}
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