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// Extract links from HTML/CSS content.
package analysis
import (
"fmt"
"io/ioutil"
"net/http"
"net/url"
"regexp"
"strings"
"github.com/PuerkitoBio/goquery"
)
var (
urlcssRx = regexp.MustCompile(`.*:.*url\(["']?([^'"\)]+)["']?\)`)
linkMatches = []struct {
tag string
attr string
}{
{"a", "href"},
{"link", "href"},
{"img", "src"},
{"script", "src"},
}
)
// GetLinks returns all the links found in a document. Currently only
// parses HTML pages and CSS stylesheets.
func GetLinks(resp *http.Response) ([]*url.URL, error) {
var outlinks []string
ctype := resp.Header.Get("Content-Type")
if strings.HasPrefix(ctype, "text/html") {
// Use goquery to extract links from the parsed HTML
// contents (query patterns are described in the
// linkMatches table).
doc, err := goquery.NewDocumentFromResponse(resp)
if err != nil {
return nil, err
}
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, val)
})
}
} else if strings.HasPrefix(ctype, "text/css") {
// Use a simple (and actually quite bad) regular
// expression to extract "url()" links from CSS.
if data, err := ioutil.ReadAll(resp.Body); err == nil {
for _, val := range urlcssRx.FindAllStringSubmatch(string(data), -1) {
outlinks = append(outlinks, val[1])
}
}
}
// Parse outbound links relative to the request URI, and
// return unique results.
var result []*url.URL
links := make(map[string]*url.URL)
for _, val := range outlinks {
if linkurl, err := resp.Request.URL.Parse(val); err == nil {
links[linkurl.String()] = linkurl
}
}
for _, u := range links {
result = append(result, u)
}
return result, nil
}
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