How do I handle pagination while scraping websites in Go?

Handling pagination while scraping websites in Go involves iterating over the pages you want to scrape and making requests to each page's URL. You'll typically identify the pattern in the URL that changes from one page to the next or locate the 'next page' link dynamically from the page content.

Here's a general approach to handle pagination in Go using the popular colly package, which simplifies web scraping tasks. You can install colly using the following command:

go get -u github.com/gocolly/colly/v2

Below is an example in Go to illustrate how you might handle pagination:

package main

import (
    "fmt"
    "log"
    "strconv"

    "github.com/gocolly/colly/v2"
)

func main() {
    // Instantiate the collector
    c := colly.NewCollector(
        colly.AllowedDomains("example.com"), // Replace with the domain you are scraping
    )

    // On every a element which has href attribute call callback
    c.OnHTML("a[href]", func(e *colly.HTMLElement) {
        link := e.Attr("href")

        // Check if the href attribute might point to the next page
        // This is a naive check and should be adjusted according to the website structure
        if e.Text == "Next" || e.Text == "More" {
            err := e.Request.Visit(link)
            if err != nil {
                log.Fatal(err)
            }
        }
    })

    // Callback for when a visited page is loaded
    c.OnResponse(func(r *colly.Response) {
        fmt.Println("Visited", r.Request.URL)
    })

    // Callback for when an error occurs
    c.OnError(func(r *colly.Response, err error) {
        log.Println("Error:", err, r.Request.URL)
    })

    // Start scraping on page 1
    // You might want to construct this URL based on specific patterns observed in pagination
    startURL := "http://example.com/page/1"
    err := c.Visit(startURL)
    if err != nil {
        log.Fatal(err)
    }
}

The key part of this code is how we handle links with OnHTML callback. Here, we look for an "a" element with href attribute, which usually represents a link, and check if the link text corresponds to a label that might indicate the next page (such as "Next" or "More"). This is a simplified example, and the actual logic might need to be more complex, depending on the website's structure.

In some cases, the URL pattern for pagination might be predictable (e.g., http://example.com/page/1, http://example.com/page/2, etc.). If so, you could use a loop to iterate through the page numbers:

for i := 1; i <= totalPages; i++ {
    pageURL := fmt.Sprintf("http://example.com/page/%d", i)
    err := c.Visit(pageURL)
    if err != nil {
        log.Fatal(err)
    }
}

Remember to respect the website's robots.txt file and terms of service when scraping, and consider the ethical implications and legality of your actions. It's also a good practice to configure your scraper to not put too much load on the website's server by setting rate limits and delays.