golang - Go tour - exercise solution - webcrawler

webcrawler.go

package main

import (
  "fmt"
)

type Fetcher interface {
  Fetch(url string) (body string, urls []string, err error)
}

func Crawl(url string, fetcher Fetcher, ch chan string, visited chan string) {

  body, urls, err := fetcher.Fetch(url)

  if err != nil {
    fmt.Println(err)
    visited <- url
    return
  }
  
  fmt.Printf("found: %s %q\n", url, body)
  
  for _, u := range urls {
    ch <- u
  }
  
  visited <- url
  return

}

func main() {
  sitemap := make(map[string]int)
  ch := make(chan string)
  visited := make(chan string)

  go Crawl("http://golang.org/", fetcher, ch, visited)

  for {
    select {
    case u := <-ch:
      if _, ok := sitemap[u]; !ok {
        sitemap[u] = 0
        go Crawl(u, fetcher, ch, visited)
      }
    case v := <-visited:
      sitemap[v] = 1
    default:
      done := 1

      if len(sitemap) == 0 {
        done = 0
      }

      for _, v := range sitemap {
        if v == 0 {
          done = 0
        }
      }

      if done == 1 {
        return
      }
    }
  }
}

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)
}

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/",
    },
  },
}