Golang with Colly: Use Random Fake User-Agents When Scraping

Website scraping often leads to blocks due to the use of standard or inappropriate user-agents. This article demonstrates a simple method to mitigate this by using randomized fake user-agents within your Go Colly scrapers.

Understanding Fake User-Agents

User-agents are strings identifying the client making a web request. They convey information about the application, operating system (Windows, macOS, Linux), and browser (Chrome, Firefox, Safari). Websites use this information for various purposes, including security and analytics.

A typical user-agent string might look like this (Chrome on Android):

<code>'User-Agent': 'Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Mobile Safari/537.36'</code>

Go Colly's default user-agent:

<code>"User-Agent": "colly - https://www.php.cn/link/953bd83cb0b9c9f9dc4b3ba0bfc1b236",</code>

easily identifies your scraper, increasing the risk of being blocked. Therefore, employing a custom, randomized user-agent is crucial.

Implementing a Fake User-Agent with Go Colly

Modifying request headers to include a custom user-agent is achieved using the OnRequest() callback. This ensures each request uses a different user-agent string.

<code class="language-go">package main

import (
    "bytes"
    "log"
    "github.com/gocolly/colly"
)

func main() {
    c := colly.NewCollector(colly.AllowURLRevisit())

    c.OnRequest(func(r *colly.Request) {
        r.Headers.Set("User-Agent", "Mozilla/5.0 (iPad; CPU OS 12_2 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Mobile/15E148")
    })

    c.OnResponse(func(r *colly.Response) {
        log.Printf("%s\n", bytes.Replace(r.Body, []byte("\n"), nil, -1))
    })

    for i := 0; i < 5; i++ {
        c.Visit("httpbin.org/headers")
    }
}</code>

This sets a single user-agent for all requests. For more robust scraping, use a randomized approach.

Rotating Through Random User-Agents

The github.com/lib4u/fake-useragent package simplifies random user-agent selection.

<code class="language-go">package main

import (
    "bytes"
    "fmt"
    "log"
    "github.com/gocolly/colly"
    uaFake "github.com/lib4u/fake-useragent"
)

func main() {
    ua, err := uaFake.New()
    if err != nil {
        fmt.Println(err)
    }
    c := colly.NewCollector(colly.AllowURLRevisit())

    c.OnRequest(func(r *colly.Request) {
        r.Headers.Set("User-Agent", ua.Filter().GetRandom())
    })

    c.OnResponse(func(r *colly.Response) {
        log.Printf("%s\n", bytes.Replace(r.Body, []byte("\n"), nil, -1))
    })

    for i := 0; i < 5; i++ {
        c.Visit("httpbin.org/headers")
    }
}</code>

This code snippet retrieves a random user-agent for each request.

Using Specific Fake User-Agents

github.com/lib4u/fake-useragent provides filtering options. For example, to use a random desktop Chrome user-agent:

<code class="language-go">r.Headers.Set("User-Agent", ua.Filter().Chrome().Platform(uaFake.Desktop).Get())</code>

Remember to always respect a website's robots.txt and terms of service when scraping. Using random user-agents is one technique among many for responsible web scraping; consider using proxies and other header management strategies as well.

References:

• github.com/lib4u/fake-useragent
• github.com/gocolly/colly

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