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@nakabonne

GoでWebクローラー作ってみた

キーワードを入力すると、そのワードでオーガニック検索した際の1ページ目のページURLを取得できるコマンドラインツールを作りました。
詳しくは下記のリポジトリを見て下さい。

参考

http://blog.kechako.com/entry/2016/03/09/225345
大変参考になりました。

コード全貌

main.go
package main

import (
    "flag"
    "log"
    "net/http"
    "net/url"
    "strings"

    "github.com/PuerkitoBio/goquery"
)

func Crawl(url string, depth int, m *message) {
    defer func() { m.quit <- 0 }()

    // WebページからURLを取得
    urls, err := Fetch(url)

    // 結果送信
    m.res <- &respons{
        url: url,
        err: err,
    }

    if err == nil {
        for _, url := range urls {
            // 新しいリクエスト送信
            m.req <- &request{
                url:   url,
                depth: depth - 1,
            }
        }
    }
}

func Fetch(u string) (urls []string, err error) {
    baseUrl, err := url.Parse(u)
    if err != nil {
        return
    }

    resp, err := http.Get(baseUrl.String())
    if err != nil {
        return
    }
    defer resp.Body.Close()

    // 取得したhtmlを文字列で確認したい時はこれ
    //body, err := ioutil.ReadAll(resp.Body)
    //buf := bytes.NewBuffer(body)
    //html := buf.String()
    //fmt.Println(html)
    // ---------------

    doc, err := goquery.NewDocumentFromReader(resp.Body)
    if err != nil {
        return
    }

    urls = make([]string, 0)
    doc.Find(".r").Each(func(_ int, srg *goquery.Selection) {
        srg.Find("a").Each(func(_ int, s *goquery.Selection) {
            href, exists := s.Attr("href")
            if exists {
                reqUrl, err := baseUrl.Parse(href)
                if err == nil {
                    urls = append(urls, reqUrl.String())
                }
            }
        })
    })

    return
}

func main() {
    var word = flag.String("w", " ", "検索ワードを入力して下さい")
    flag.Parse()
    log.Println("検索ワード:", *word)
    *word = strings.Replace(*word, " ", "+", -1)
    firstURL := "https://www.google.co.jp/search?rlz=1C5CHFA_enJP693JP693&q=" + string(*word)
    log.Println("検索URL:", firstURL)
    m := newMessage()
    go m.execute()
    m.req <- &request{
        url:   firstURL,
        depth: 2,
    }

    if err := http.ListenAndServe(":8080", nil); err != nil {
        log.Fatal("ListenAndSearver:", err)
    }
}

message.go
package main

import (
    "fmt"
    "log"
    "os"
)

type message struct {
    res  chan *respons
    req  chan *request
    quit chan int
}
type respons struct {
    url string
    err interface{}
}
type request struct {
    url   string
    depth int
}

func newMessage() *message {
    return &message{
        res:  make(chan *respons),
        req:  make(chan *request),
        quit: make(chan int),
    }
}

func (m *message) execute() {
    // ワーカーの数
    wc := 0
    urlMap := make(map[string]bool, 100)
    done := false
    for !done {
        select {
        case res := <-m.res:
            if res.err == nil {
                fmt.Printf("%s\n", res.url)
            } else {
                fmt.Fprintf(os.Stderr, "Error %s\n%v\n", res.url, res.err)
            }
        case req := <-m.req:
            if req.depth == 0 {
                break
            }

            if urlMap[req.url] {
                // 取得済み
                break
            }
            urlMap[req.url] = true

            wc++
            go Crawl(req.url, req.depth, m)
        case <-m.quit:
            wc--
            if wc == 0 {
                done = true
            }
        }
    }
    log.Println("スクレイピング完了")
    os.Exit(0)
}

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15
Help us understand the problem. What are the problem?