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@pif
Created October 23, 2016 22:28
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//////////// Exercise Web Crawler / Golang
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)
}
var cache = make(map[string]bool)
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher, res chan string) {
defer close(res)
// TODO: Fetch URLs in parallel.
// TODO: Don't fetch the same URL twice.
// This implementation doesn't do either:
if depth <= 0 {
return
}
if cache[url] {
fmt.Println("skipping...\t", url)
return
} else {
cache[url] = true
}
_, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
return
}
res <- url
subs := make([]chan string, len(urls))
for i, u := range urls {
subs[i] = make(chan string)
go Crawl(u, depth-1, fetcher, subs[i])
}
for i, _ := range subs {
for v := range subs[i] {
res <- v
}
}
return
}
func main() {
res := make(chan string)
go Crawl("http://golang.org/", 4, fetcher, res)
for v := range res {
fmt.Println("MAIN: ", 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/",
},
},
}
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