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package flyscrape
import (
"log"
"strings"
"sync"
"time"
"github.com/PuerkitoBio/goquery"
"github.com/cornelk/hashmap"
"github.com/nlnwa/whatwg-url/url"
)
type ScrapeParams struct {
HTML string
URL string
}
type ScrapeOptions struct {
URL string `json:"url"`
AllowedDomains []string `json:"allowedDomains"`
BlockedDomains []string `json:"blockedDomains"`
Depth int `json:"depth"`
Rate float64 `json:"rate"`
}
type ScrapeResult struct {
URL string `json:"url"`
Data any `json:"data,omitempty"`
Links []string `json:"-"`
Error error `json:"error,omitempty"`
Timestamp time.Time `json:"timestamp"`
}
func (s *ScrapeResult) omit() bool {
return s.Error == nil && s.Data == nil
}
type ScrapeFunc func(ScrapeParams) (any, error)
type FetchFunc func(url string) (string, error)
type target struct {
url string
depth int
}
type Scraper struct {
ScrapeOptions ScrapeOptions
ScrapeFunc ScrapeFunc
FetchFunc FetchFunc
visited *hashmap.Map[string, struct{}]
wg *sync.WaitGroup
jobs chan target
results chan ScrapeResult
}
func (s *Scraper) init() {
s.visited = hashmap.New[string, struct{}]()
s.wg = &sync.WaitGroup{}
s.jobs = make(chan target, 1024)
s.results = make(chan ScrapeResult)
if s.FetchFunc == nil {
s.FetchFunc = Fetch()
}
if s.ScrapeOptions.Rate == 0 {
s.ScrapeOptions.Rate = 100
}
if len(s.ScrapeOptions.AllowedDomains) == 0 {
u, err := url.Parse(s.ScrapeOptions.URL)
if err == nil {
s.ScrapeOptions.AllowedDomains = []string{u.Host()}
}
}
}
func (s *Scraper) Scrape() <-chan ScrapeResult {
s.init()
s.enqueueJob(s.ScrapeOptions.URL, s.ScrapeOptions.Depth)
go s.worker()
go s.waitClose()
return s.results
}
func (s *Scraper) worker() {
var (
rate = time.Duration(float64(time.Second) / s.ScrapeOptions.Rate)
leakyjobs = leakychan(s.jobs, rate)
)
for job := range leakyjobs {
go func(job target) {
defer s.wg.Done()
res := s.process(job)
if !res.omit() {
s.results <- res
}
if job.depth <= 0 {
return
}
for _, l := range res.Links {
if _, ok := s.visited.Get(l); ok {
continue
}
if !s.isURLAllowed(l) {
continue
}
s.enqueueJob(l, job.depth-1)
}
}(job)
}
}
func (s *Scraper) process(job target) (res ScrapeResult) {
res.URL = job.url
res.Timestamp = time.Now()
html, err := s.FetchFunc(job.url)
if err != nil {
res.Error = err
return
}
res.Links = links(html, job.url)
res.Data, err = s.ScrapeFunc(ScrapeParams{HTML: html, URL: job.url})
if err != nil {
res.Error = err
return
}
return
}
func (s *Scraper) enqueueJob(url string, depth int) {
s.wg.Add(1)
select {
case s.jobs <- target{url: url, depth: depth}:
s.visited.Set(url, struct{}{})
default:
log.Println("queue is full, can't add url:", url)
s.wg.Done()
}
}
func (s *Scraper) isURLAllowed(rawurl string) bool {
u, err := url.Parse(rawurl)
if err != nil {
return false
}
host := u.Host()
ok := false
for _, domain := range s.ScrapeOptions.AllowedDomains {
if domain == "*" || host == domain {
ok = true
break
}
}
for _, domain := range s.ScrapeOptions.BlockedDomains {
if host == domain {
ok = false
break
}
}
return ok
}
func (s *Scraper) waitClose() {
s.wg.Wait()
close(s.jobs)
close(s.results)
}
func links(html string, origin string) []string {
var links []string
doc, err := goquery.NewDocumentFromReader(strings.NewReader(html))
if err != nil {
return nil
}
urlParser := url.NewParser(url.WithPercentEncodeSinglePercentSign())
uniqueLinks := make(map[string]bool)
doc.Find("a").Each(func(i int, s *goquery.Selection) {
link, _ := s.Attr("href")
parsedLink, err := urlParser.ParseRef(origin, link)
if err != nil || !isValidLink(parsedLink) {
return
}
absLink := parsedLink.Href(true)
if !uniqueLinks[absLink] {
links = append(links, absLink)
uniqueLinks[absLink] = true
}
})
return links
}
func isValidLink(link *url.Url) bool {
if link.Scheme() != "" && link.Scheme() != "http" && link.Scheme() != "https" {
return false
}
if strings.HasPrefix(link.String(), "javascript:") {
return false
}
return true
}
func leakychan[T any](in chan T, rate time.Duration) chan T {
ticker := time.NewTicker(rate)
sem := make(chan struct{}, 1)
c := make(chan T)
go func() {
for range ticker.C {
sem <- struct{}{}
}
}()
go func() {
for v := range in {
<-sem
c <- v
}
ticker.Stop()
close(c)
}()
return c
}
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