多线程链接检查器
- 任务

多线程链接检查器

运用掌握的新知识创建一个多线程链接检查工具。应先从网页入手，并检查网页上的链接是否有效。该工具应以递归方式检查同一网域中的其他网页，并且一直执行此操作，直到所有网页都通过验证。

For this, you will need an HTTP client such as reqwest. You will also need a way to find links, we can use scraper. Finally, we’ll need some way of handling errors, we will use thiserror.

Create a new Cargo project and reqwest it as a dependency with:

cargo new link-checker
cd link-checker
cargo add --features blocking,rustls-tls reqwest
cargo add scraper
cargo add thiserror

如果 cargo add 操作失败并显示 error: no such subcommand，请手动修改 Cargo.toml 文件。添加下面列出的依赖项。

cargo add 调用会将 Cargo.toml 文件更新为如下所示：

[package]
name = "link-checker"
version = "0.1.0"
edition = "2021"
publish = false
[dependencies]
reqwest = { version = "0.11.12", features = ["blocking", "rustls-tls"] }
scraper = "0.13.0"
thiserror = "1.0.37"

您现在可以下载初始页了。请尝试使用一个小网站，例如 https://www.google.org/。

您的 src/main.rs 文件应如下所示：

use reqwest::blocking::Client;
use reqwest::Url;
use scraper::{Html, Selector};
use thiserror::Error;
#[derive(Error, Debug)]
enum Error {
    #[error("request error: {0}")]
    ReqwestError(#[from] reqwest::Error),
    #[error("bad http response: {0}")]
    BadResponse(String),
}
#[derive(Debug)]
struct CrawlCommand {
    url: Url,
    extract_links: bool,
}
fn visit_page(client: &Client, command: &CrawlCommand) -> Result<Vec<Url>, Error> {
    println!("Checking {:#}", command.url);
    let response = client.get(command.url.clone()).send()?;
    if !response.status().is_success() {
        return Err(Error::BadResponse(response.status().to_string()));
    }
    let mut link_urls = Vec::new();
    if !command.extract_links {
        return Ok(link_urls);
    }
    let base_url = response.url().to_owned();
    let body_text = response.text()?;
    let document = Html::parse_document(&body_text);
    let selector = Selector::parse("a").unwrap();
    let href_values = document
        .select(&selector)
        .filter_map(|element| element.value().attr("href"));
    for href in href_values {
        match base_url.join(href) {
            Ok(link_url) => {
                link_urls.push(link_url);
            }
            Err(err) => {
                println!("On {base_url:#}: ignored unparsable {href:?}: {err}");
            }
        }
    }
    Ok(link_urls)
}
fn main() {
    let client = Client::new();
    let start_url = Url::parse("https://www.google.org").unwrap();
    let crawl_command = CrawlCommand{ url: start_url, extract_links: true };
    match visit_page(&client, &crawl_command) {
        Ok(links) => println!("Links: {links:#?}"),
        Err(err) => println!("Could not extract links: {err:#}"),
    }
}

使用以下命令运行 src/main.rs 中的代码

cargo run

任务

通过线程并行检查链接：将要检查的网址发送到某个通道，然后使用多个线程并行检查这些网址。
您可以对此进行扩展，以递归方式从 www.google.org 网域的所有网页中提取链接。设置网页上限（例如 100 个），以免被网站屏蔽。

62.2. 多线程链接检查器

多线程链接检查器

任务