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WebCrawler.go
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WebCrawler.go
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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 urlStorage struct {
urls map[string]int
mux sync.Mutex
}
var urlstorage urlStorage
// 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 Crawl(url string, depth int, fetcher Fetcher, wg *sync.WaitGroup) {
defer wg.Done() // 确保在函数结束时通知WaitGroup,当前goroutine的工作已完成
// TODO: 并行的抓取 URL。
// TODO: 不重复抓取页面。
// 下面并没有实现上面两种情况:
// fmt.Println("Handling: ", url)
if depth <= 0 {
return
}
urlstorage.mux.Lock()
_, found := urlstorage.urls[url]
if found {
urlstorage.mux.Unlock()
return
}
urlstorage.urls[url] = 0
urlstorage.mux.Unlock()
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("found: %s %q\n", url, body)
// fmt.Printf("found url num: %v\n", len(urls))
for _, u := range urls {
wg.Add(1)
go Crawl(u, depth-1, fetcher, wg)
// fmt.Printf("launch url: %s\n", u)
}
return
}
func main() {
urlstorage.urls = make(map[string]int)
var wg sync.WaitGroup
wg.Add(1)
Crawl("https://golang.org/", 4, fetcher, &wg)
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/",
},
},
}