Can I extend Colly's functionality with plugins?

Yes, you can extend Colly's functionality with plugins. Colly is a popular Golang library used for web scraping, and it provides a basic structure to which you can add extra functionality according to your needs. This can be achieved by implementing Colly's Collector interface methods or by registering callbacks for various events that Colly emits.

In Colly, plugins are essentially pieces of middleware that can process the requests or responses in some way. You can create a plugin by writing a function that takes a *colly.Collector as an argument and sets up the necessary callbacks or options.

Here's how you can create a simple plugin to log requests:

package main

import (
    "fmt"
    "log"

    "github.com/gocolly/colly"
)

// LogRequest is a simple logging plugin that prints out requests
func LogRequest(c *colly.Collector) {
    c.OnRequest(func(r *colly.Request) {
        log.Println("Visiting", r.URL.String())
    })
}

func main() {
    // Create a new collector
    c := colly.NewCollector()

    // Apply the LogRequest plugin
    LogRequest(c)

    // Start scraping
    c.OnHTML("a[href]", func(e *colly.HTMLElement) {
        link := e.Attr("href")
        fmt.Printf("Link found: %q -> %s\n", e.Text, link)
        // Visit link found on page
        // Only those links are visited which are in AllowedDomains
        c.Visit(e.Request.AbsoluteURL(link))
    })

    // Define the main page to scrape
    c.Visit("http://httpbin.org/")
}

In this example, LogRequest is a plugin that hooks into the OnRequest event and logs every request URL. You can apply this plugin to any colly.Collector by simply calling LogRequest(c) where c is your collector.

It's also possible to create more complex plugins that handle errors, responses, or manipulate the data before it's processed by your main scraping logic. Here's an example of a plugin that sets a custom User-Agent header for every request:

// SetUserAgent is a plugin to set a custom User-Agent for all requests
func SetUserAgent(c *colly.Collector, userAgent string) {
    c.OnRequest(func(r *colly.Request) {
        r.Headers.Set("User-Agent", userAgent)
    })
}

func main() {
    c := colly.NewCollector()
    SetUserAgent(c, "MyCustomUserAgent/1.0")

    // ... rest of your code ...
}

Create as many plugins as you need to keep your code organized and reusable. Each plugin should have a clear purpose and operate independently of others. This will help you build a modular and maintainable web scraping solution using Colly.