Created
November 14, 2015 08:58
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My solution for "Exercise: Web Crawler" in "A Tour of Go" - https://tour.golang.org/concurrency/9
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| package main | |
| import ( | |
| "fmt" | |
| ) | |
| 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) | |
| } | |
| // Crawl uses fetcher to recursively crawl | |
| // pages starting with url, to a maximum of depth. | |
| func Crawl(url string, depth int, fetcher Fetcher) { | |
| // DONE: Fetch URLs in parallel. | |
| // DONE: Don't fetch the same URL twice. | |
| ch := make(chan Fetched) | |
| n := 1 | |
| cache := map[string]bool{url: true} | |
| go Fetch(url, depth, fetcher, ch) | |
| for n > 0 { | |
| n-- | |
| fetched := <-ch | |
| if fetched.err != nil { | |
| fmt.Println(fetched.err) | |
| continue | |
| } | |
| fmt.Printf("found: %s %q\n", fetched.url, fetched.body) | |
| if fetched.depth > 1 { | |
| for _, u := range fetched.urls { | |
| if !cache[u] { | |
| n++ | |
| cache[u] = true | |
| go Fetch(u, fetched.depth-1, fetcher, ch) | |
| } | |
| } | |
| } | |
| } | |
| } | |
| func Fetch(url string, depth int, fetcher Fetcher, ch chan Fetched) { | |
| body, urls, err := fetcher.Fetch(url) | |
| ch <- Fetched{url, depth, body, urls, err} | |
| } | |
| type Fetched struct { | |
| url string | |
| depth int | |
| body string | |
| urls []string | |
| err error | |
| } | |
| func main() { | |
| Crawl("http://golang.org/", 4, fetcher) | |
| } | |
| // 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/", | |
| }, | |
| }, | |
| } |
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