How do I handle redirects when scraping with Kanna?

Kanna is a Swift library for parsing HTML and XML, often used in iOS development. It doesn't handle network requests or redirects directly; instead, it processes the HTML content that you provide to it. To handle redirects while scraping web content in an iOS app, you would typically use a combination of networking APIs like URLSession to manage the requests and handle redirects, and then parse the received HTML content with Kanna.

Here's a step-by-step guide on how to handle redirects when scraping with Kanna:

Step 1: Make a Network Request

Use URLSession to make a network request. URLSession automatically follows HTTP redirects by default, but you can customize this behavior by implementing the URLSessionTaskDelegate protocol.

import Foundation

let url = URL(string: "http://example.com")!
let session = URLSession(configuration: .default, delegate: self, delegateQueue: nil)

let task = session.dataTask(with: url) { (data, response, error) in
    // Handle the response here
}
task.resume()

Step 2: Implement URLSessionTaskDelegate (Optional)

If you need to customize how redirects are handled, implement the URLSessionTaskDelegate protocol's urlSession(_:task:willPerformHTTPRedirection:newRequest:completionHandler:) method.

extension YourClass: URLSessionTaskDelegate {
    func urlSession(_ session: URLSession, task: URLSessionTask, willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest, completionHandler: @escaping (URLRequest?) -> Void) {

        // You can modify the newRequest here if needed before following the redirect
        // For example, to stop following redirects, you could call completionHandler(nil)

        completionHandler(request) // Follow the redirect
    }
}

Step 3: Parse the HTML with Kanna

Once you have received the data from the final URL after all redirects, use Kanna to parse the HTML.

import Kanna

// Function to be called once the data has been received
func parseHTML(data: Data) {
    do {
        let doc = try HTML(html: data, encoding: .utf8)
        // Now you can use Kanna to scrape the needed information from the HTML
    } catch {
        print("Error parsing HTML: \(error)")
    }
}

Full Example

Here's a full example of making a request, handling redirects, and parsing HTML with Kanna:

import Foundation
import Kanna

class Scraper: NSObject, URLSessionTaskDelegate {

    let session: URLSession

    override init() {
        session = URLSession(configuration: .default, delegate: self, delegateQueue: nil)
        super.init()
    }

    func scrape(url: URL) {
        let task = session.dataTask(with: url) { [weak self] (data, response, error) in
            guard let data = data, error == nil else {
                print("Network request failed: \(String(describing: error))")
                return
            }
            self?.parseHTML(data: data)
        }
        task.resume()
    }

    func parseHTML(data: Data) {
        do {
            let doc = try HTML(html: data, encoding: .utf8)
            // Use Kanna to extract data from the HTML document
            for link in doc.xpath("//a | //link") {
                if let href = link["href"] {
                    print(href)
                }
            }
        } catch {
            print("Error parsing HTML: \(error)")
        }
    }

    // URLSessionTaskDelegate method to handle redirects
    func urlSession(_ session: URLSession, task: URLSessionTask, willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest, completionHandler: @escaping (URLRequest?) -> Void) {
        completionHandler(request) // Follow the redirect
    }
}

// Usage
let scraper = Scraper()
scraper.scrape(url: URL(string: "http://example.com")!)

In this example, Scraper is a class that conforms to the URLSessionTaskDelegate protocol and can handle network requests, including redirects. After receiving the final data, it uses Kanna to parse the HTML content. You can customize the parseHTML method to suit your scraping needs.