How does Rust handle HTTP request timeouts and retries when scraping?

In Rust, handling HTTP request timeouts and retries when scraping can be achieved by using libraries such as reqwest for making HTTP requests and tokio for asynchronous runtime, which is required by reqwest. To handle timeouts and retries, you would typically use the timeout functionality provided by tokio in combination with a retry strategy that you can implement manually or by using a crate like retry or backoff.

Below is an example of how you can handle HTTP request timeouts and implement retries in Rust using the reqwest and tokio crates:

use reqwest::Error;
use std::time::Duration;
use tokio::time::sleep;

#[tokio::main]
async fn main() -> Result<(), Error> {
    let client = reqwest::Client::new();
    let url = "http://example.com";

    let max_retries = 3;
    let mut attempts = 0;

    loop {
        let response_result = tokio::time::timeout(
            Duration::from_secs(5), // Set the timeout for each request
            client.get(url).send()
        ).await;

        match response_result {
            Ok(Ok(response)) if response.status().is_success() => {
                // Handle successful response
                println!("Response: {:?}", response.text().await?);
                break;
            },
            Ok(Err(e)) => {
                // Handle request error (excluding timeout)
                eprintln!("Request error: {}", e);
            },
            Err(_) => {
                // Handle timeout
                eprintln!("Request timed out");
            }
        }

        if attempts >= max_retries {
            // If we've reached the maximum number of retries, return an error
            return Err(reqwest::Error::from(
                std::io::Error::new(std::io::ErrorKind::TimedOut, "Reached maximum retries"),
            ));
        }

        // Exponential backoff (e.g., wait 2s, then 4s, then 8s)
        sleep(Duration::from_secs(1 << attempts)).await;
        attempts += 1;
    }

    Ok(())
}

In this example, we're using a loop to attempt the HTTP request up to max_retries times. We use tokio::time::timeout to set a timeout for each attempt. If the request times out or fails for another reason, we print an error message, wait for a backoff period using sleep, increment our attempt counter, and retry.

The backoff strategy implemented here is a simple exponential backoff, which doubles the wait time after each failed attempt. You can also use a crate like backoff to handle more sophisticated backoff strategies.

Please note that you need to add the reqwest and tokio crates to your Cargo.toml file to use them in your project:

[dependencies]
reqwest = "0.11"
tokio = { version = "1", features = ["full"] }

Make sure you're using the appropriate versions of these crates, as the API might change in future releases.