《Go 指南》 练习：Web 爬虫 || A Tour of Go , Exercise: Web Crawler

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type SafeCounter struct {
	mp   map[string]bool
	mux sync.Mutex
	wg sync.WaitGroup
}

// Crawl 使用 fetcher 从某个 URL 开始递归的爬取页面，直到达到最大深度。
func (sc *SafeCounter)Crawl(url string, depth int, fetcher Fetcher) {
	defer sc.wg.Done()
	
	sc.mux.Lock()	
	sc.mp[url] = true
	defer sc.mux.Unlock()
	
	
	if depth <= 0 {
		return
	}
	body, urls, err := fetcher.Fetch(url)
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Printf("found: %s %qn", url, body)
	for _, u := range urls {
		if sc.mp[u] == false{
			sc.wg.Add(1)
			go sc.Crawl(u, depth-1, fetcher)
		}
	}
	
	return
}

func main() {
	c := SafeCounter{mp: make(map[string]bool)}
	c.wg.Add(1)
	c.Crawl( "https://golang.org/", 4, fetcher)
	c.wg.Wait()
}

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package main

import (
	"fmt"
	"sync"
)

type Fetcher interface {
	// Fetch 返回 URL 的 body 内容，并且将在这个页面上找到的 URL 放到一个 slice 中。
	Fetch(url string) (body string, urls []string, err error)
}

type SafeCounter struct {
	mp   map[string]bool
	mux sync.Mutex
	wg sync.WaitGroup
}

// Crawl 使用 fetcher 从某个 URL 开始递归的爬取页面，直到达到最大深度。
func (sc *SafeCounter)Crawl(url string, depth int, fetcher Fetcher) {
	defer sc.wg.Done()
	
	sc.mux.Lock()	
	sc.mp[url] = true
	defer sc.mux.Unlock()
	
	
	if depth <= 0 {
		return
	}
	body, urls, err := fetcher.Fetch(url)
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Printf("found: %s %qn", url, body)
	for _, u := range urls {
		if sc.mp[u] == false{
			sc.wg.Add(1)
			go sc.Crawl(u, depth-1, fetcher)
		}
	}
	
	return
}

func main() {
	c := SafeCounter{mp: make(map[string]bool)}
	c.wg.Add(1)
	c.Crawl( "https://golang.org/", 4, fetcher)
	c.wg.Wait()
}

// fakeFetcher 是返回若干结果的 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 是填充后的 fakeFetcher。
var fetcher = fakeFetcher{
	"https://golang.org/": &fakeResult{
		"The Go Programming Language",
		[]string{
			"https://golang.org/pkg/",
			"https://golang.org/cmd/",
		},
	},
	"https://golang.org/pkg/": &fakeResult{
		"Packages",
		[]string{
			"https://golang.org/",
			"https://golang.org/cmd/",
			"https://golang.org/pkg/fmt/",
			"https://golang.org/pkg/os/",
		},
	},
	"https://golang.org/pkg/fmt/": &fakeResult{
		"Package fmt",
		[]string{
			"https://golang.org/",
			"https://golang.org/pkg/",
		},
	},
	"https://golang.org/pkg/os/": &fakeResult{
		"Package os",
		[]string{
			"https://golang.org/",
			"https://golang.org/pkg/",
		},
	},
}