Go language implementation of web crawler instances
- 2020-05-26 09:17:14
- OfStack
This article illustrates the web crawler method implemented by Go. Share with you for your reference. The specific analysis is as follows:
Go's concurrency feature is used here to execute web crawlers in parallel.
Modify the Crawl function to grab URLs in parallel without repeating it.
package main
import (
"fmt"
)
type Fetcher interface {
// Fetch return URL the body Content, and will be found on this page URL In the 1 a slice In the.
Fetch(url string) (body string, urls []string, err error)
}
// Crawl use fetcher From a certain URL Start recursively crawling the page until the maximum depth is reached.
func Crawl(url string, depth int, fetcher Fetcher) {
// TODO: Parallel fetching URL .
// TODO: Do not repeatedly crawl pages.
// The following is not the case:
if depth <= 0 {
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 {
Crawl(u, depth-1, fetcher)
}
return
}
func main() {
Crawl("http://golang.org/", 4, fetcher)
}
// fakeFetcher Returns several results Fetcher .
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 It's filled 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/",
},
},
}I hope this article has been helpful to your programming of Go language.