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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)
}
type unprocessed struct {
depth int
url[] string
}
func getPage(url string, depth int, r chan unprocessed){
body, urls, err := fetcher.Fetch(url)
fmt.Printf("found: %s %q\n", url, body)
if err != nil {
fmt.Println(err)
}
r <- unprocessed{ depth - 1, urls }
}
func Crawl(url string, depth int, fetcher Fetcher) {
//setup channel for inputs to be processed
up := make(chan unprocessed, 0)
//kick off processing and count how many pages are left to process
go getPage(url, depth, up)
outstanding := 1
visited := make(map[string]bool)
for outstanding > 0 {
//pop a visit from the channel
next := <-up
outstanding--
//if were too deep, skip it
if next.depth <= 0 {
continue
}
//loop over all urls to visit from that page
for _, link := range next.url {
//check we havent visited them before
if visited[link] {
continue
}
//all good to visit them
outstanding++
visited[link] = true
go getPage(link, depth, up)
}
}
}
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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