How to stop crawler in golang

With the development of the Internet, crawler technology has gradually become one of the important tools for obtaining network information. People can use crawler technology to obtain large amounts of data from websites to make more accurate analyzes and predictions. However, crawlers also face many difficulties and limitations. Especially in Golang programming, stopping crawlers is still a common problem.

Golang is a relatively new programming language, and its emergence has attracted widespread attention. Compared with other languages, Go language has the advantages of efficiency, simplicity, concurrency, etc., so it has been widely used in network programming, system programming, cloud computing and other fields. However, when using Golang in crawler programming, we also need to pay attention to some issues.

Generally speaking, the writing of crawlers involves two basic operations, namely requesting web pages and parsing web pages. Golang's standard library provides two packages, "net/http" and "goquery", which are used to send requests and parse HTML documents respectively. We can use these tools to implement a complete crawler program. The code is as follows:

package main

import (
    "fmt"
    "github.com/PuerkitoBio/goquery"
    "net/http"
)

func main() {
    // Step 1: 发送请求
    url := "https://www.example.com"
    req, _ := http.NewRequest("GET", url, nil)
    req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3")
    client := &http.Client{}
    resp, _ := client.Do(req)
    defer resp.Body.Close()

    // Step 2: 解析网页
    doc, _ := goquery.NewDocumentFromReader(resp.Body)
    doc.Find("a").Each(func(i int, s *goquery.Selection) {
        href, _ := s.Attr("href")
        fmt.Println(href)
    })
}

In this code, we first use the "net/http" package to send HTTP requests, and then use the "goquery" package Parse the HTML document to obtain all links in the target web page. At this point, we may need to consider how to stop the execution of the crawler program.

A common approach is to set a counter and stop the crawler when it reaches a certain value. In the Go language, you can use the "select" statement and "chan" type variables to implement the timer function. The specific operation is as follows:

package main

import (
    "fmt"
    "github.com/PuerkitoBio/goquery"
    "net/http"
    "time"
)

func main() {
    url := "https://www.example.com"
    req, _ := http.NewRequest("GET", url, nil)
    req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3")

    client := &http.Client{}
    resp, _ := client.Do(req)
    defer resp.Body.Close()

    doc, _ := goquery.NewDocumentFromReader(resp.Body)

    done := make(chan int)
    go func() {
        doc.Find("a").Each(func(i int, s *goquery.Selection) {
            href, _ := s.Attr("href")
            fmt.Println(href)
            if i == 10 { //停止条件
                done <- 1
            }
        })
    }()

    select {
    case <-done:
        fmt.Println("Done!")
    case <-time.After(time.Second * 10):
        fmt.Println("Time out!")
    }
}

In this example, we use the "chan" type variable "done" to communicate. When the counter reaches a specific value, a message is sent to the main process through the "done" variable to stop The operation of the crawler program. At the same time, we also set a 10-second timer. If the crawling task cannot be completed within 10 seconds, the program will automatically stop.

To summarize, in Golang programming, we can use the "net/http" and "goquery" packages in the standard library to send requests and parse HTML documents. At the same time, use the "select" statement and "chan " type variables to implement timer and communication functions. These tools can help us write efficient and stable crawler programs, stop program execution in time when necessary, and avoid unnecessary data waste and computing resource consumption.

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