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// Extract links from HTML/CSS content.
package analysis
import (
"fmt"
"io/ioutil"
"net/http"
"regexp"
"strings"
"github.com/PuerkitoBio/goquery"
"git.autistici.org/ale/crawl"
)
var (
urlcssRx = regexp.MustCompile(`(?:@import|:).*url\(["']?([^'"\)]+)["']?\)`)
linkMatches = []struct {
tag string
attr string
linkTag int
}{
{"a", "href", crawl.TagPrimary},
{"link", "href", crawl.TagRelated},
{"img", "src", crawl.TagRelated},
{"script", "src", crawl.TagRelated},
{"iframe", "src", crawl.TagRelated},
}
)
// The unparsed version of an Outlink.
type rawOutlink struct {
URL string
Tag int
}
// GetLinks returns all the links found in a document. Currently only
// parses HTML pages and CSS stylesheets.
func GetLinks(resp *http.Response) ([]crawl.Outlink, error) {
// Parse outbound links relative to the request URI, and
// return unique results.
var result []crawl.Outlink
links := make(map[string]crawl.Outlink)
for _, l := range extractLinks(resp) {
// Skip data: URLs altogether.
if strings.HasPrefix(l.URL, "data:") {
continue
}
if linkurl, err := resp.Request.URL.Parse(l.URL); err == nil {
links[linkurl.String()] = crawl.Outlink{
URL: linkurl,
Tag: l.Tag,
}
}
}
for _, l := range links {
result = append(result, l)
}
return result, nil
}
func extractLinks(resp *http.Response) []rawOutlink {
ctype := resp.Header.Get("Content-Type")
switch {
case strings.HasPrefix(ctype, "text/html"):
return extractLinksFromHTML(resp)
case strings.HasPrefix(ctype, "text/css"):
return extractLinksFromCSS(resp)
default:
return nil
}
}
func extractLinksFromHTML(resp *http.Response) []rawOutlink {
var outlinks []rawOutlink
// Use goquery to extract links from the parsed HTML
// contents (query patterns are described in the
// linkMatches table).
doc, err := goquery.NewDocumentFromReader(resp.Body)
if err != nil {
return nil
}
for _, lm := range linkMatches {
doc.Find(fmt.Sprintf("%s[%s]", lm.tag, lm.attr)).Each(func(i int, s *goquery.Selection) {
val, _ := s.Attr(lm.attr)
outlinks = append(outlinks, rawOutlink{URL: val, Tag: lm.linkTag})
})
}
return outlinks
}
func extractLinksFromCSS(resp *http.Response) []rawOutlink {
// Use a simple (and actually quite bad) regular
// expression to extract "url()" links from CSS.
var outlinks []rawOutlink
if data, err := ioutil.ReadAll(resp.Body); err == nil {
for _, val := range urlcssRx.FindAllStringSubmatch(string(data), -1) {
outlinks = append(outlinks, rawOutlink{URL: val[1], Tag: crawl.TagRelated})
}
}
return outlinks
}
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