How can I handle pagination with Scraper (Rust)?

Handling pagination with Scraper, which is a Rust crate for HTML parsing and querying (similar to Python's Beautiful Soup), involves programmatically navigating through multiple pages of a website, extracting data from each page, and following the links to the next page until all desired pages have been processed.

To implement pagination, you typically need to:

1. Identify the URL pattern or the "Next" link that allows you to move from one page to another.
2. Fetch each page's content using HTTP requests.
3. Parse the HTML content to extract data and the link to the next page.
4. Loop through this process until you reach the last page.

Here's a basic example in Rust using the Scraper crate and reqwest for performing HTTP requests. This example demonstrates how you might handle pagination where the pages are in a simple numeric sequence (e.g., page=1, page=2, etc.):

extern crate reqwest;
extern crate scraper;

use scraper::{Html, Selector};
use std::error::Error;

fn main() -> Result<(), Box<dyn Error>> {
    // Define the base URL and selector for pagination.
    let base_url = "http://example.com/items?page=";
    let page_selector = Selector::parse(".pagination .next").unwrap();

    // Start from the first page.
    let mut current_page = 1;

    loop {
        // Construct the URL for the current page.
        let url = format!("{}{}", base_url, current_page);
        println!("Fetching page: {}", url);

        // Perform the HTTP GET request.
        let resp = reqwest::blocking::get(&url)?;
        assert!(resp.status().is_success());

        // Parse the response body as HTML.
        let body = resp.text()?;
        let document = Html::parse_document(&body);

        // TODO: Extract data from the current page.
        // ...

        // Try to find the 'Next' page link and update `current_page`.
        if let Some(next_page_element) = document.select(&page_selector).next() {
            // Extract the next page number from the 'href' attribute or text content.
            // This will depend on how the 'Next' link is structured in the HTML.
            // You may need to parse the 'href' attribute value to extract the page number.

            // For example, if the 'Next' button contains the page number as text:
            let next_page_number = next_page_element.text().next().unwrap().trim().parse::<u32>().unwrap();

            // Update `current_page` if the next page is greater than the current page.
            // This check prevents infinite loops if the 'Next' link always appears.
            if next_page_number > current_page {
                current_page = next_page_number;
            } else {
                break;
            }
        } else {
            // No 'Next' link found; we've reached the last page.
            break;
        }
    }

    Ok(())
}

Please note the following:

• This example uses reqwest::blocking for simplicity, but you might want to consider using async requests in a real-world application.
• The TODO comment is where you would extract data from the current page. You would define selectors based on the HTML structure of the pages you're scraping.
• The example assumes that the 'Next' link contains the page number. Depending on the website, you might find the 'Next' link in the form of a relative URL, an absolute URL, or just a button with JavaScript actions. You'll need to adjust the code to suit the specific case you're dealing with.
• Error handling is simplified in this example. You should handle potential errors appropriately in a real-world application.
• Websites may have terms of service that forbid or restrict web scraping. Always check the website's terms of service and use ethical scraping practices.

Remember that web pagination structures can vary widely from site to site. You may need to tailor the logic to handle different URL patterns, find "Next" buttons with dynamic JavaScript actions, or extract page numbers from the URL query parameters.