How do I avoid getting IP banned while scraping with Go?

When web scraping, it's important to respect the terms of service of the website you are scraping and to ensure you are not violating any laws. However, even with legitimate intentions, aggressive scraping can lead to your IP address being banned. To avoid getting IP banned while scraping with Go or any other programming language, consider the following tips:

1. Respect robots.txt: This file located at the root of a website (e.g., http://example.com/robots.txt) specifies the scraping rules for that site. Make sure your scraper abides by these rules.

2. User-Agent Rotation: Websites often check the User-Agent string to identify the client making the request. By rotating different user-agent strings, your requests appear to come from different browsers or devices.

3. Request Throttling: Limit the rate of your requests to avoid overwhelming the server. You can implement a delay between requests to mimic human browsing behavior.

4. Use Proxies: By using a pool of proxy servers, you can distribute your requests over multiple IP addresses, reducing the chance of any single IP being banned.

5. Referrer Header: Some websites check the Referrer header to see if the request is coming from a legitimate page within their site. You can set this header to a reasonable value to avoid detection.

6. Handle Errors Gracefully: If you encounter a 429 (Too Many Requests) or a 403 (Forbidden) HTTP response code, your scraper should back off for a while before trying again.

7. Session Management: If the site requires login, make sure you manage sessions and cookies properly. Re-login if your session expires, but do so judiciously to avoid detection.

Here's a simple example in Go incorporating some of these tips:

package main

import (
    "fmt"
    "io/ioutil"
    "net/http"
    "time"
    "math/rand"
)

var userAgents = []string{
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3",
    "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.0.3 Safari/605.1.15",
    // Add more user agents here
}

func getRandomUserAgent() string {
    return userAgents[rand.Intn(len(userAgents))]
}

func scrape(url string) {
    client := &http.Client{}
    req, _ := http.NewRequest("GET", url, nil)

    // Rotate user agent
    req.Header.Set("User-Agent", getRandomUserAgent())

    // Set a referrer
    req.Header.Set("Referrer", "http://www.google.com")

    resp, err := client.Do(req)
    if err != nil {
        fmt.Printf("Error fetching: %v\n", err)
        return
    }
    defer resp.Body.Close()

    if resp.StatusCode == http.StatusOK {
        bodyBytes, err := ioutil.ReadAll(resp.Body)
        if err != nil {
            fmt.Printf("Error reading response body: %v\n", err)
            return
        }
        bodyString := string(bodyBytes)
        fmt.Println(bodyString)
    } else {
        fmt.Printf("Server returned status code: %d\n", resp.StatusCode)
        // Implement backoff strategy here
    }

    // Wait a bit before making the next request
    delay := time.Duration(rand.Intn(5)+1) * time.Second
    time.Sleep(delay)
}

func main() {
    // Seed random number generator
    rand.Seed(time.Now().UnixNano())

    urls := []string{
        "http://example.com/page1",
        "http://example.com/page2",
        // Add more URLs here
    }

    for _, url := range urls {
        scrape(url)
    }
}

In this example, we're rotating the User-Agent header and setting a Referrer. We also implement a delay between requests to throttle our scraping speed. If you needed to use proxies, you could configure the http.Transport of the http.Client to use a proxy by setting its Proxy field.

Remember to comply with the website's terms of use and legal requirements when scraping, and always scrape responsibly.