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package crawl
import (
"fmt"
"net/url"
"strings"
)
type Scope interface {
Check(*url.URL, int) bool
}
type maxDepthScope struct {
maxDepth int
}
func (s *maxDepthScope) Check(uri *url.URL, depth int) bool {
return depth < s.maxDepth
}
// NewDepthScope returns a Scope that will limit crawls to a
// maximum link depth with respect to the crawl seeds.
func NewDepthScope(maxDepth int) Scope {
return &maxDepthScope{maxDepth}
}
type schemeScope struct {
allowedSchemes map[string]struct{}
}
func (s *schemeScope) Check(uri *url.URL, depth int) bool {
_, ok := s.allowedSchemes[uri.Scheme]
return ok
}
// NewSchemeScope limits the crawl to the specified URL schemes.
func NewSchemeScope(schemes []string) Scope {
m := make(map[string]struct{})
for _, s := range schemes {
m[s] = struct{}{}
}
return &schemeScope{m}
}
// A URLPrefixMap makes it easy to check for URL prefixes (even for
// very large lists). The URL scheme is ignored, along with an
// eventual "www." prefix.
type URLPrefixMap map[string]struct{}
func normalizeUrlPrefix(uri *url.URL) string {
return strings.TrimPrefix(uri.Host, "www.") + strings.TrimSuffix(uri.Path, "/")
}
func (m URLPrefixMap) Add(uri *url.URL) {
m[normalizeUrlPrefix(uri)] = struct{}{}
}
func (m URLPrefixMap) Contains(uri *url.URL) bool {
s := strings.TrimPrefix(uri.Host, "www.")
if _, ok := m[s]; ok {
return true
}
for _, p := range strings.Split(uri.Path, "/") {
if p == "" {
continue
}
s = fmt.Sprintf("%s/%s", s, p)
if _, ok := m[s]; ok {
return true
}
}
return false
}
type urlPrefixScope struct {
prefixes URLPrefixMap
}
func (s *urlPrefixScope) Check(uri *url.URL, depth int) bool {
return s.prefixes.Contains(uri)
}
// NewURLPrefixScope returns a Scope that limits the crawl to a set of
// allowed URL prefixes.
func NewURLPrefixScope(prefixes URLPrefixMap) Scope {
return &urlPrefixScope{prefixes}
}
// NewSeedScope returns a Scope that will only allow crawling the seed
// prefixes.
func NewSeedScope(seeds []*url.URL) Scope {
pfx := make(URLPrefixMap)
for _, s := range seeds {
pfx.Add(s)
}
return NewURLPrefixScope(pfx)
}
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