これだけだと1つのgoroutineの中で再帰しているだけで、ちゃんと並列になっていない気がする…
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) } func CallCrawl(url string, depth int, fetcher Fetcher, fetched map[string]bool, ch chan string) { Crawl(url, depth, fetcher, fetched, ch) close(ch) } // Crawl uses fetcher to recursively crawl // pages starting with url, to a maximum of depth. func Crawl(url string, depth int, fetcher Fetcher, fetched map[string]bool, ch chan string) { // TODO: Fetch URLs in parallel. // TODO: Don't fetch the same URL twice. // This implementation doesn't do either: if depth <= 0 { return } if fetched[url] == true { return } fetched[url] = true body, urls, err := fetcher.Fetch(url) if err != nil { ch <- fmt.Sprintf("%s", err) return } ch <- fmt.Sprintf("found: %s %q", url, body) for _, u := range urls { Crawl(u, depth-1, fetcher, fetched, ch) } return } func main() { fetched := make(map[string]bool) ch := make(chan string) go CallCrawl("http://golang.org/", 4, fetcher, fetched, ch) for v := range ch { fmt.Println(v) } } // 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/", }, }, }
