How to use Go language for web crawler development?

With the development of the Internet, information has exploded, and web crawlers, as a means of automatically obtaining network data, have become increasingly important in this information age.

Among them, Go language, as a lightweight and efficient programming language, also has considerable use value in web crawler development. Next, we will introduce in detail how to use Go language for web crawler development.

1. Advantages of Go language

Compared with other programming languages, Go language has the following advantages:

• Excellent performance: The original intention of Go language is to Process a large number of network tasks efficiently and concurrently. Its concurrency and memory management capabilities are stronger than most programming languages.
• Simple syntax: The syntax of Go language is relatively simple and easy to understand, and the learning threshold is relatively low.
• High reliability: Go language is widely used by Internet companies. After a long period of verification and use, its stability and reliability have been proven.
• Cross-platform: Go language provides a rich standard library and tools, can run across platforms, and supports many operating systems.

Based on the above advantages, Go language has become one of the important languages ​​​​for web crawler development.

2. Selection of crawler tools and libraries

Before developing web crawlers, you need to understand some common crawler tools and libraries.

1. Crawler framework

The crawler framework is an encapsulated crawler tool that provides a simple interface and some extensibility, making it easier to write crawlers. Common crawler frameworks include:

• PuerkitoBio/goquery: Go library for processing HTML and XML documents.
• Colly: A flexible web crawler framework that supports asynchronous requests and distributed crawling.
• Gocolly/colly: An extended and improved version based on Colly 1.0.
• Gocrawl: A simple and easy-to-use web crawler framework that supports depth first and breadth first.
• Teleport: A multi-threaded crawler framework that supports both URL-based crawlers and parent node-based crawlers.

2. HTTP client

The HTTP library provided by Go language is very simple and easy to use. Common HTTP client libraries are:

• Go's own net/http client
• unrolled/utl
• PuekitoBio/goquery
• Google's json

The following is Go The built-in net/http client is used as an example to explain in detail

3. Case analysis

1. Capture web content and store the results

package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
)

func main() {
    resp, err := http.Get("https://www.baidu.com")
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(string(body))
}

The above code is The simplest crawler code implementation, which captures the HTML content of Baidu's homepage and outputs the results to the terminal.

2. Regular expression analysis of web page content

package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
    "regexp"
)

func main() {
    resp, err := http.Get("https://www.baidu.com")
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }

    re := regexp.MustCompile(`href="(.*?)"`)
    result := re.FindAllStringSubmatch(string(body), -1)

    for _, v := range result {
        fmt.Println(v[1])
    }
}

The above code implements the extraction of all link addresses in the HTML content of Baidu homepage and outputs it to the terminal.

3. Concurrent crawling of web pages

package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
)

func fetch(url string, ch chan<- string) {
    resp, err := http.Get(url)
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }

    ch <- fmt.Sprintf("%s %d", url, len(body))
}

func main() {
    urls := []string{
        "https://www.baidu.com",
        "https://www.sina.com",
        "https://www.qq.com",
    }

    ch := make(chan string)
    for _, url := range urls {
        go fetch(url, ch)
    }

    for range urls {
        fmt.Println(<-ch)
    }
}

The above code realizes concurrent crawling of multiple websites. Use the go keyword to start multiple goroutines at the same time, and use channel Communicate to get results for each website.

4. Summary

This article introduces how to use Go language for web crawler development. First, we briefly introduced the advantages of the Go language and selected crawler tools and libraries. Subsequently, we gave a detailed explanation through simple crawler code implementation and case analysis, and implemented web content crawling, regular expression parsing and concurrent crawling. If you are interested in crawler development using Go language, this article will provide you with some basics and references.

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