Skip to content

Instantly share code, notes, and snippets.

@krstp
Forked from harryhare/exercise-web-crawler.go
Created February 14, 2021 20:57
Show Gist options
  • Save krstp/447cb89b4163c2ad09a23b3aef36cd32 to your computer and use it in GitHub Desktop.
Save krstp/447cb89b4163c2ad09a23b3aef36cd32 to your computer and use it in GitHub Desktop.
Solution to Exercise: Web Crawler https://tour.golang.org/concurrency/10
package main
import (
"fmt"
"time"
"sync"
)
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
type SafeCounter struct {
v map[string]bool
mux sync.Mutex
}
var c SafeCounter = SafeCounter{v: make(map[string]bool)}
func (s SafeCounter)checkvisited(url string)bool{
s.mux.Lock()
defer s.mux.Unlock()
_,ok:=s.v[url]
if ok==false {
s.v[url]=true
return false
}
return true
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
// TODO: Fetch URLs in parallel.
// TODO: Don't fetch the same URL twice.
// This implementation doesn't do either:
if depth <= 0 {
return
}
if c.checkvisited(url) {
return;
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("found: %s %q\n", url, body)
for _, u := range urls {
go Crawl(u, depth-1, fetcher)
}
return
}
func main() {
Crawl("http://golang.org/", 4, fetcher)
time.Sleep(5*time.Second)
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"http://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"http://golang.org/pkg/",
"http://golang.org/cmd/",
},
},
"http://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"http://golang.org/",
"http://golang.org/cmd/",
"http://golang.org/pkg/fmt/",
"http://golang.org/pkg/os/",
},
},
"http://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
"http://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"http://golang.org/",
"http://golang.org/pkg/",
},
},
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment