読者です 読者をやめる 読者になる 読者になる

A Tour of Go #71 をやってみた

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/",
		},
	},
}